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Full text of "A collection of instrumentation papers presented at the Marine Sciences Conference held September 11-15, 1961, at Woods Hole, Mass., sponsored by the Instrument Society of America and the American Society of Limnology and Oceanography; and, papers from the marine sciences sessions of the 1961 Instrument Society of America Symposia, held at Toronto and Los Angeles"

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WOODS HOLE 
'. .**" OCEANOGRAPHIC INSTITUTION 



LABORATORY 
BOOK COLLECTION 

FEB 2::. 1363 A^e/er^.cc ^ooo, 



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MARINE SCIENCES INSTRUMENTATION 

Volume 1 



^ In order that the scientific information herein 
might be disseminated to the public as rapidly 
as possible this publication has been produced 
by offset reproduction of material furnished by 
the authors. 



A publication of 
INSTRUMENT SOCIETY OF AMERICA 



MARINE SCIENCES INSTRUMENTATION 

Volume 1 

A Collection of Instrumentation Papers 

Presented at the Marine Sciences Conference 

Held September 11-15, 1961, at Woods Hole, Mass., 

Sponsored by the Instrument Society of America 

and the American Society of Limnology and Oceanography 

and 

^5 Papers from the Marine Sciences Sessions of the 1961 

^= Instrument Society of America Symposia Held at 

^~— Toronto and Los Angeles 

_ =0 

x^=S EDITORS 

^^^^= o 

m Roy D. Gaul 

'^^^ □ Agricultural and Mechanical College of Texas 

□ David D. Ketchum 

^^S a Woods Hole Oceanographic Institution 

— Jack T. Shaw 

— — Minneapolis-Honeywell Regulator Company 

James M. Snodgrass 

Scripps Institution of Oceanography 



Distributed by 

PLENUM PRESS 
NEW YORK 

4/ jlL 00 



Copyright © 1962 

INSTRUMENT SOCIETY of AMERICA 

Penn-Sheraton Hotel 

530 William Penn Place 

Pittsburgh 19, Pa. 



CONTENTS 

THE DESIGN AND INSTALLATION OF THE FIXED ACOUSTIC BUOY 

by Richard P. Oberlin 1 

THE QUIET PLATFORM, KEY TO SUCCESSFUL OCEANOGRAPHIC 
ACOUSTIC RESEARCH 

by A. Donn Cobb 6 

INSTRUMENTATION FOR THE MEASUREMENT OF HYDRODYNAMIC 
FLOW-NOISE 

by Chester L. Wakamo and Robert C. Fitzpatrick 8 

ACOUSTICAL NOISE MEASURING BUOY WITH DIGITAL DATA RE- 
CORDING 

by Dr. T. F. Hueter, D. M. Baker, and J. T. Shaw 21 

DEEP TRANSDUCER DESIGN 

by R. P. Delaney 25 

LOCATION OF UNDERWATER OR SURFACE SOUND SOURCES BY MEANS 
OF COMPUTER-LINKED GABLED-HYDROPHONE FIELDS 

by James H. Morrissey 28 

EFFECTS OF THE SPECTRAL COMPOSITION OF RANDOM THERMAL 
VARIATIONS ON PHASE AND AMPLITUDE FLUCTUATIONS OF A SOUND 
WAVE PROPAGATING IN THE SEA 

by Aimo Salenius 31 

A TELEMETERING THERMOMETER 

by Dr. Angelo J. Campanella 39 

A LONG-RANGE, OCEANOGRAPHIC TELEMETERING SYSTEM 

by Robert G. Walden and David H. Frantz, Jr 50 

A DATA ACQUISITION AND REDUCTION SYSTEM FOROCEANOGRAPH- 
IC MEASUREMENTS 

by David D. Ketchum and Raymond G. Stevens 55 

THE PROBLEMS OF RELIABLE LONG-RANGE TRANSMISSION OF RE- 
MOTE OCEANOGRAPHIC MEASUREMENTS 

by C. McLoon 61 

A DATA PROCESSING AND DISPLAY INSTRUMENT FOR OCEANO- 
GRAPHIC RESEARCH 

by Joseph T. Laing 65 

TIMING CONTROL METHODS AVAILABLE FOR SELF-CONTAINED 
RECORDING SYSTEMS 

by Alexander L. M. Dingee, Jr., and A. Fred Feyling 77 



A CONCEPT FOR A REMOTELY INTERROGATED SYNOPTIC OCEANO- 
GRAPHIC DATA SAMPLING BUOY 

vy Richard A. Zlotky 80 

DATA RECORDING DEVICE FOR UNDERWATER INSTRUMENTATION 

by Jay W. Harford and Earl D. Van Reenan 88 

PROGRESS REPORT ON TRANSIT 

by R. B. Kershner 91 

INFLUENCE OF A HIGH HYDROSTATIC PRESSURE ENVIRONMENT ON 
ELECTRONIC COMPONENTS 

by Chester L. Buchanan and Matthew Plato 119 

INTERNAL WAVES AND THEIR MEASUREMENT 

by E. C. LaFond 137 

QUANTITATIVE MULTIPLE OPENING-AND-CLOSING PLANKTON SAM- 
PLERS 

by Dr. Allan W. H. Be 156 

LONG-RANGE OUTLOOK FOR OCEANOGRAPHIC TELEMETERING 

by James M. Snodgrass 163 

THE SVTP INSTRUMENT AND SOME APPLICATIONS TO OCEANO- 
GRAPHY 

by J. R. Lovett 168 

THE WORLD'S LONGEST SALT BRIDGE 

by Dr. Paul C. Mangelsdorf, Jr 173 

AN INSTRUMENT FOR THE DIRECT MEASUREMENT OF THE SPEED 
OF SOUND IN THE OCEAN 

by F.J. Suellentrop, A. E. Brown, and Eric Rule 186 

AN ACOUSTIC OCEAN-CURRENT METER 

by F.J. Suellentrop, A. E. Brown, and Eric Rule 190 

A DOPPLER-SHIFT OCEAN-CURRENT METER 

by J. D. Chalupnik and P. S. Green 194 

HIGH-ACCURACY, SELF-CALIBRATING ACOUSTIC LOW METERS 

by R. A. Lester 200 

CURRENT MEASUREMENTS FROM MOORED BUOYS 

by William S. Richardson 205 

DEEP CURRENT MEASUREMENTS NEAR BERMUDA 

by Raymond F. McAllister 210 

SEA STATE-EFFECTS AND PROBLEMS 

by Lee M. Hunt 223 

THE BATHYPAGE 

by Dr. A. A. Mills 239 

AN EXTERNAL CORE-RETAINER 

by Dr. A. A. Mills 244 



SOME NEW MECHANICAL DEVICES FOR OCEANOGRAPHIC RESEARCH 

by Shale J. Niskin 24ti 

USE OF THE PRECISION GRAPHIC RECORDER (PGR) IN OCEANOG- 
RAPHY 

by S. T. Knott 251 

INVERTED ECHO SOUNDER 

by Willard Dow and Stephen L. Stillman 263 

A BOTTOM STRIP MAP CAMERA 

by Dr. Angelo J. Campanella 273 

SOME RECENT ADVANCES IN UNDERWATER CAMERA EQUIPMENT 

by Harold E. Edgerton and Samuel O. Raymond 279 

A COMPLETE SONAR THUMPER SEISMIC SYSTEM 

by Earl D. Van Reenan 283 

THERMOELECTRIC POWER FOR OCEANOGRAPHIC RESEARCH 

by Melvin Barmat 289 

APPLICATION OF MODERN REMOTE HANDLING TECHNIQUES TO 
OCEANOGRAPHY 

by John W. Clark 294 

PORPOISE - OCEANOGRAPHIC RESEARCH VEHICLE 

by W. L. Cannon 305 

SCUBA AS A TOOL FOR SCIENTISTS 

by Eugene K. Parker 310 

EQUIPMENT FOR OBSERVATION OF THE NATURAL ELECTROMAG- 
NETIC BACKGROUND IN THE FREQUENCY RANGE 0.01-30 CYCLES 
PER SECOND 

by W.N. English, D.J. Evans, J. E. Lokken, J. A. Shand, and 

C. S. Wright 321 

OXYGEN AND CARBON DIOXIDE INSTRUMENTATION 

by John W. Kanwisher 334 

AN ANALYSIS OF A CLASS OF PATTERN RECOGNITION NETWORKS 

by Laveen Kanal 340 

AN ADAPTIVE CORRELATOR FOR UNDERWATER MEASUREMENTS 

by Dr. Alfred A. Wolf and J. H. Dietz 347 



THE DESIGN AND INSTALLATION OF THE FIXED ACOUSTIC BUOY 

by RICHARD P. OBERLIN 

Project Engineer, Fixed Acoustic Buoy 

The Martin Company, Baltimore, Maryland 



ABSTRACT 



The Fixed Acoustic Buoy is a deep sea instru- 
mentation device which measures acoustic data 
at a depth of 14,000 feet. It is controlled and 
powered from shore via a cable and has numer- 
ous modes of operation. Signal processing is 
accomplished in the deep sea unit to allow use of 
a single coaxial cable. The paper describes the 
electronic system design and the techniques used 
to protect the components from the high ambient 
pressure while still allowing electrical intercon- 
nections. The installation technique and prob- 
lems encountered are also discussed. 



INTRODUCTION 



System design of deep ocean acoustic equip- 
ment is impaired by lack of data at the desired 
depths. The Fixed Acoustic Buoy (FAB) is a 
system which was designed for the Navy to obtain 
some of this missing data. The data itself and 
the types of tests involved are classified and will 
therefore not be discussed in this paper. 

The great significance of FAB, as far as 
oceanographic instrumentation is concerned, is 
that it is a radical design departure from normal 
practice. In FAB almost all of the signal proc- 
essing is accomplished electronically in the deep 
sea portion. This results in a considerable cost 
saving because it allows use of a single coaxial 
cable with medium bandwidth requirements 
instead of 21 pair medium bandwidth cable or 
one high bandwidth coaxial cable with 21 channel 
multiplexing. The suitability of this approach 
has been considerably strengthened with the 
successful implantment of the system during 
December 1960 in 14,000 feet of water south of 
Bermuda. System operation and data collection 
has continued since that time in a satisfactory 
manner. 



SYSTEM DESCRIPTION 



The system consists of a bottom unit, a co- 
axial cable and shore equipment. The bottom 
unit is shown in Figure 1. It consists of a 21 
element vertically steerable acoustic array, a 



buoyancy tank to hold the array vertical, a pres- 
sure tight sphere housing the electronics and 
beamforming networks, a battery, a tilt indicator 
and an anchor. 

The cable consists of about 27 miles of coaxial 
cable which is similar in construction and char- 
acteristics to the A. T. & T. Trans-Atlantic tele- 
phone cable linking the United States and Europe. 
Slightly over one mile of this cable is double 
armored and magnetically shielded. The remain- 
der is single armored with no magnetic shielding. 

The shore equipment consists of the control 
circuitry, data recording equipment and power 
supplies required to manually operate the system. 
The shore equipment is located on a Texas Tower 
type structure called "Argus Island" . 

Five normal control functions are available to 
the shore operator, as shown in Figure 1. These 
are steer forward (a command for the deep unit 
to acoustically look at the next higher angle), re- 
set (a command to return to the lowest angle), 
steer feedback instrumentation on and off, tilt- 
pitch instrumentation on and off, and tilt-roll 
instrumentation on and off. The commands are 
initiated by sending the appropriate frequency (in 
the range of 10 to 12 KC) down the cable to the 
sea unit. An additional function ("fail safe") is 
commanded by a reversal of the power supply 
voltage to the deep unit. This causes a large 
portion of the circuitry to be bypassed in case of 
a failure. 

Fifteen different modes of acoustic data col- 
lection can be commanded via the steer channel. 
Thirteen of these are narrow listening beams at 
various vertical angles from 0° to 90°. The last 
two are omnidirectional listening modes. In 
"fail safe" operation, only the 0° beam is avail- 
able. The acoustic data is acquired in the range 
of 400 cps to 5 KC. 

The instrumentation functions answer back 
with FM signals in the range of 6 to 8 KC. Steer 
feedback tells which particular step the beam is 
on and the tilt channels give the tilt of the array 
from vertical in. two mutually perpendicular axes. 

The block diagram of the system is shown in 
Figure 2. As can be seen, the DC power and 



FIXED ACOUSTIC BUOr 



GASOLINE 
TANK 



MILLER SWIVEL 



BATHRY CASE 
CONCRETE ANCHOR 



CAME ID 
SHOtK 




21 ELEMENT ARRAY 

niT INDICATOR 
CASE 

NON-TWIST CHAIN 

jrf'APPROX 



ELECISONK SPHERE 



FAB 
CHARACTERISTICS 

STEER VERTICAL MAX 

POSITION ANGLE (DEG) FRE9UENa(ICC)l 



I 
Z 3 

3 6 

4 9 

5 1Z 

6 15 

7 18 

8 21 

9 24 

10 33 

II 44 

12 59 

13 90 

14 OMNI 

15 OMNI 
SYSTEM BANDWIDTH 400 CPS TO SKC 

CONTROL CHANNELS | INSTRUMENTATUM | 
STEER I0.5KC 
RESET II, 5KC 

STEER FEEDBACK 10.0 KC 

TILT -PITCH ll.OKC 

TILT-ROLL 12.0KC 



5 
S 
5 

5 
4.9 
4.8 
4.6 
4.3 
4,0 
3.7 
3.4 
3.1 
2,5 
S 
5 



CHANNELS 

6-iKC 
S-GKC 
S-6KC 



FIXED ACOUSTIC BUOV SYSTEM 

U DEEP EQUIPMENT -\' 



HYDROPHONES 

PREAMPLIFIERS 



-CABLE LINK tU- 



. SHORE EQUIPMENT - 



TO ALL CIRCUITS 
EXCEPT STEPPING 
SWITCH CIRCUITS 



TO STEPPING COMMANDS 

SWITCH CIRCUITS laOkc STEER-FDBK 

1 t M V "l-^k' STEER 

T ^_^__ _^J^" ILOkc TILT PITCH 

REGUIATOR REGUIATOR ~*BAn 



U. Skc RESET 
12.0kc TILT-ROLL 



CABLE DRIVER 




■SEWSOff 



FJgute 2 



command functions are put in from the shore end. 
These pass through the necessary cable driving 
circuits and then the cable itself. At the deep 
end, the various commands are sorted out 
according to frequency and polarity. These 
cause the deep unit to go to the desired configu- 
ration. Instrumentation and acoustic data are 
mixed together and amplified by a pair of cable 
driver amplifiers (for redundancy). These sig- 
nals are separated at the shore end of the cable 
by the appropriate filters and then recorded in 
analog form on magnetic tape. The data is then 
sent back and reduced using existing reduction 
facilities at Martin-Baltimore. The deep elec- 
tronics are entirely powered from shore except 
for the stepping switches themselves. These 
operate from a ni-cad battery which is charged 
from the shore supply. 

The deep sea electronics circuitry contains 
over 200 transistors most of which are protected 
from the 6000 psi ambient pressure by a large 
steel sphere. The hydrophone preamplifiers 
are protected by being placed in a small steel 
chamber located inside each hydrophone. The 
tilt indicators and the battery are similarly pro- 
tected by individual steel cylindrical chambers. 

The various components are thus protected 
but necessarily must be electrically connected 
together. This means reliable electrical feed- 
throughs are required which must be able to 
withstand a pressure differential of at least 6000 
psi. The design used is shown in Figure 3. 
This design is an adaptation of that used on 
Piccard's Bathyscaphe and in fact was suggested 
by Mr. Jacques Piccard who was used as a con- 
sultant on the mechanical problems. 

The operation of the feedthrough is as follows: 
The high pressure differential forces the araldite 
(an epoxy) into the tapered hole thus effectively 
sealing the hole. The Bathyceri (a wax like sub- 
stance) is forced into the voids between the aral- 
dite and the polyethylene wires and prevents 
water from causing electrical faults between 
adjacent wires. The PR701 (a sticky putty like 
substance) is used to prevent water from getting 
into the feedthrough when the pressure level is 
too low to ensure sealing due to the above ac- 
tions. Feedthroughs throughout the FAB equip- 
ment are of this design. 

The hydrophone, of necessity, must with- 
stand direct exposure to the 6000 psi pressure 
and this involves some tricky problems also. 
These problems are dealt with in more detail 
in the subsequent paper by Mr. Delaney. 



INSTALLATION 

The installation procedure is shown in 
Figure 4. A two ship operation was necessary 
utilizing a cable laying ship and a smaller aux- 
iliary ship. 



The first step of the installation was to bring 
one end of the shore end cable to Argus Island. 
This was accomplished by use of a work boat in 
conjunction with the cable layer. The cable was 
firmly attached to one of the tower legs by the 
work boat and personnel on the tower. The cable 
ship then laid the 1+ miles of shore cable and 
attached a marker buoy to the end of the cable. 
At this point, the cable ship went to the desired 
implantment location but due to a failure of the 
polyethylene covered array harness in the FAB 
array the operation was postponed while the 
harness was reworked at the factory. 

The array harness had failed at the molded 
splice joint due to improper annealing of the 
molded polyethylene. A second harness was con- 
structed and properly annealed. This was used 
to replace the original harness. 

Prior to the second implantment attempt, the 
completed deep sea unit was lowered into the 
water over the cable layer bow while dockside in 
Bermuda. Final checkout was completed and 
the deep sea unit was attached to the front of the 
bow sheaves. 

The cable layer took it's position as shown 
in Figure 2 and three miles of nylon line were 
paid out to the auxiliary ship. The nylon line 
was attached to the top of the buoyancy tank 
through a corrosive link and the tank was attached 
to the array by 240 feet of grapnel rope. The 
gasoline filled tank was allowed to slide in the 
water from a skid attached to the side of the 
cable layer. 

The corrosive link was not designed to take 
any lateral force but inadvertently was subjected 
to considerable lateral forces during the release 
of the buoyancy tank. Due to this, two links 
were broken during the installation. A three 
foot piece of steel rope was inserted between the 
top of the tank and the link and proved to be a 
satisfactory universal joint preventing any further 
link failures. 

The tank was towed away from the cable ship 
by ship No. 2 and the deep unit was lowered by 
it's coaxial cable to the bottom of the sea, 
14,000 feet down. At this point, the cable layer 
laid the rest of the cable toward Argus Island, 
picked up the marker buoy and the end of the 
shore cable and spliced the two ends of the cable 
together. 

The shore equipment had been installed on 
the cable ship to operate and monitor the deep 
equipment during checkout and installation. The 
installation was completed, except for the re- 
moval of the nylon line, with the transfer of the 
shore equipment to Argus Island and subsequent 
connection with the cable. 

The nylon line was used during the operation 
to prevent fouling of the gasoline tank and the 
coaxial cable. It was also to be used to retrieve 
the deep unit in case of failure during the three 



HIGH ?nssvn iiicnKM feedthrough 




ARALDITE 



BAT I CERA 



PR701M 



POLYETHYlfNE 
COVERED WIRES 






FAB IMPLANTMENT 



ARGUS ISLAND 




Figure 4 



days following Implantment. The corrosive link 
was supposed to release the nylon after four 
days but either never completely released or the 
line became entangled. The nylon line was then 
weighted and allowed to sink. The array went 
from 20° tilt to less than three degrees during 
this operation as the line sank and the hydrody- 
namic drag forces were reduced. 

The unit was accepted with a demonstration 
of it's performance and data collection was 
started. 



CONCLUSIONS 

A fairly complex electronic-acoustic device 
can be successfully designed and installed in a 
deep ocean environment. 



THE QUIET PLATFORM, KEY TO SUCCESSFUL OCEANOGRAPHIC 
ACOUSTIC RESEARCH 

by A. DONN COBB, Electronic Engineer 
U.S. Navy Underwater Sound Laboratory 
Fort Trumbull, New London, Connecticut 



ABSTRACT 



This paper discusses the surface vessel as a plat- 
form from which to conduct acoustic research. It 
points out the main problems attendant to such a plat- 
form and discusses techniques for control and for 
elimination of many types of acoustic self-noise. An 
attempt is made in this paper to bring cause and effect 
together in the light of available corrective measures to 
provide a foundation for valid measurements of acous- 
tic data. 

*^ + **t + + + + 

In any electroacoustic investigation which is predi- 
cated on the detection of low-level signals especially 
when they have a broad spectral distribution, the 
signal-to-noise ratio is of great importance. This is 
particularly true in acoustic survey work such as the 
mapping of a muddy bottom or the recording of sounds 
of biological origin. A quiet platform is essential to 
this type of work; when a ship is used for the surveys, 
every effort should be made to keep interfering noise 
at a minimum. 

NOISE SOURCES 

It is the intent of this paper to describe a method 
of determining the principal noise sources of a vessel 
and to suggest remedial action. Let us first consider 
the types of noise that may be encountered. Assuming 
the presence of a signal of some finite level, the inter- 
fering noise may be divided into three broad types. 
These are: 

1. Electrical noise. 

2. Sea state noise. 

3. Self-noise of the carrying vessel. 

For the purpose of this article it will be assumed 
(1) that electrical noise can be controlled, and (2) that 
sea-state noise can be kept at a predetermined level 
by the selection of the time and place for the conduct 
of the experiment. We are then left with the self-noise 
of the vessel, which will be the subject of this article. 

The acoustic self-noise of a vessel dead in the 
water is usually composed of noises generated by main 
propulsion machinery, auxiliary machinery, ventilating 
system, etc. , and when under way, by all these plus 
the hydrodynamic flow noise of water. 



To determine the charateristics of the machinery 
noises, a comprehensive machinery noise survey should 
be conducted. To this end a calibrated broad-band, 
onmi-directional hydrophone should be installed at, or 
as near as is feasible to, the location of the research 
transducer. A word of caution seems in order here: 
inasmuch as the machinery noise to be measured is 
generated to a large extent as structural vibration and 
then transferred to the water surroimding the ship's 
hull, a suitable vibration isolation mounting for the 
hydrophone must be provided in order to prevent direct 
vibrational excitation. The simple expedient of sus- 
pending the hydrophone with shock cord is often very 
effective; where more permanence is desired, a 
mounting consisting of several flanges alternately of 
brass and rubber can be used. 

EQUIPMENT 

Since accurate analysis equipment is generally too 
large to take to sea, it is usually necessary to record 
data on magnetic tape for later analysis in the labora- 
tory. An idealized system for such recording would 
include all battery-operated equipment, with a pre- 
amplifier between the hydrophone and the tape recorder. 

A word here about the preamplifier will help 
anyone interested in conducting this type of survey. 
Typical acoustic noise, when plotted as a curve of 
amplitude versus frequency, displays about a 6-db-per- 
octave negative slope. If we consider the 10 octaves 
of frequency between 20 cycles and 20 kilocycles as 
the observational band, we find that our tape recorder 
must be able to accept a dynamic range of amplitude of 
60 db. Even the most ambitious sellers of tape record- 
ing equipment do not claim this capability. If, however, 
6-db-per-octave pre-emphasis is added to the preampli- 
fier, it becomes apparent that theoretically all portions 
of the spectrum from 20 cycles to 20 kc will have the 
same amplitude; consequently, very unsophisticated 
recording equipment will suffice. In practice, the 
noise to be observed is not precisely random, and the 
deviation from the mean noise level may cause as 
much as ±10 db of signal amplitude difference through 
this system. This 20-db dynamic range is well within 
the capabilities of most tape-recording equipment. 



Some provision should also be made for a low- 
level calibrate signal at the input of the preamplifier. 
Before commencement of the noise survey, a suitable 
number of discrete calibration frequencies should be 
recorded on the tape to provide a means of deter- 
mining the recording system gain throughout the spec- 
trum of interest. These levels, along with the cali- 
bration of the hydrophone, will provide means for 
reducing the recorded noise data to equivalent plane- 
wave sound pressure in the water. 

RECORDING 

Once the equipment is set up and properly checked 
out, the vessel should proceed to deep water, i.e. , 
more than 100 fathoms, where Sea State 2 or less 
prevails. On arrival, the vessel should stop and 
secure all machinery. A sample of this noise field 
should be recorded; this is the base line or quietest 
condition attainable. Then each item of machinery 
should be operated individually, insofar as possible, 
with samples recorded under each condition. If the 
basic acoustic research to be conducted will require 
the vessel to be under way, a noise-versus-speed 
observation should be made by recording data at one- 
or two-knot intervals throughout the speed range 
desired. 



noise reduction especially at high speeds. Generally 
speaking, the achievement of a quiet platform requires 
some or all of the previously mentioned devices. 

If a truly quiet platform is to be achieved, it may 
be necessary to repeat the sea test several times 
after various remedial measures have been taken. 

CONCLUSION 

In conclusion, it should again be emphasized that 
the end result of good interference-free data more than 
justifies the effort required to achieve a quiet working 
platform. 



CORRECTIVE ACTION 

If the analysis of the sea-test data indicates that 
the vessel is too noisy (as it probably will), there are 
several potential "fixes" available: 

1. Quite often relocation of the research trans- 
ducer away from known high-intensity noise sources 
can be effective. 

2. Isolation mounting of machinery observed to be 
noisy may solve the problem. There are many fine 
isolation mountings available. 

3. If the machinery to be isolated is too large or 
for some other reason cannot be isolated, a visco- 
elastic damping material applied to the machine and/or 
the hull in the vicinity of the acoustic research trans- 
ducer may effectively dissipate this energy. 

4. If the research to be conducted does not require 
the research transducer to see in all directions, 
baffles can be arranged in the desired blind spots as 
well as above the transducer. 



In the preparation of the research transducer for 
the under-way portion of any research project, care 
should be exercised to provide a suitably vibration 
damped and isolated streamlined enclosure. Any 
smoothing of hull discontinuities ahead of the research 
transducer location should assist in hydrodynamic 



INSTRUMENTATION FOR THE MEASUREMENT OF HYDRODYNAMIC 
FLOW-NOISE 

by CHESTER L. WAKAMO, Associate Research Engineer, 
and ROBERT C. FITZPATRICK, Researcli Associate 
Institute of Science and Technology, The University of Michigan, 
Ann Arlx)r, Michigan 



ABSTRACT 



An experimental study of the generation of 
acoustic energy by fluid turbulence near an ex- 
tended solid boundary was performed. For this 
study, a free-falling self-contained missile was 
conceived. Parameters affecting the design of 
the vehicle were stability, velocity, recovery of 
the vehicle, skin vibration or "Self noise" fac- 
tor, and the effects of acceleration and decel- 
eration on equipment performance. An inboard 
magnetic tape data recording system stores the 
acoustic signals for subsequent analysis. De- 
tailed information on the depth-measurement cir- 
cuitry, automatic recovery mechanism, calibration 
procedure and check-out for a typical launching 
and recovery are presented. 



IHTRODUCTIOM 

The study of acoustics is primarily con- 
cerned with the generation, transmission, and re- 
ception of energy in the form of pressure and 
velocity fluctuations. One particular aspect of 
this study is the process of generation of acous- 
tic energy by fluid turbulence near an extended 
solid boundary. Effects of boundary-layer tur- 
bulence are of special importance in high speed 
aircraft and missiles^ torpedos, submarines, and 
surface ships. 

To measure the acoustic noise generated by 
boundary-layer turbulence the use of a missile 
type vehicle moving through water was considered. 
It was decided that a free-falling finless body 
with a self-contained electronic system to re- 
cord noise data was the best approach. Such a 
missile was designed, fabricated, and tested. 
The electronic system consisted of hydrophone 
transducers, a suitable magnetic-tape recorder, 
batteries for power, a pressure transducer to 
determine pressure and depth, and pressiore-op- 
erated control switches. The vehicle was re- 
leased from a launching rack suspended just be- 
low the surface of the water. It would fall 



freely, with no ropes or cables attached, to a 
depth of no more than 500 ft. At some control- 
lable predetermined distance its descent was 
checked when the pressure-controlled switches 
caused the release of drag fins at the sides of 
the missile. As the deceleration produced by 
the drag fins occurred, switches shut off the 
recording system and released a bouyant tail sec- 
tion from the main body; this section rose to the 
surface, pulling with it a nylon recovery line 
which was unreeled from a spool secured to the 
main body. Figure 1 shows the missile in its 
launching frame. 

Preliminary tests were conducted at Orchard 
Lake, Michigan, a semi-private lake ^t-O miles 
northeast from Ann Arbor, chosen for its depth 
and relatively low background noise. A launch- 
ing platform was moored in 110 ft of water, per- 
mitting about 5 sec of flow-noise data from each 
drop of the missile. Provision was made to re- 
cord the depth during the missile descent by 
utilizing a pressure transducer and associated 
electronics. The depth record was later used to 
calculate the velocity. 



VEHICLE DESCRIPTIOM 

Parameters affecting the design of the 
vehicle were stability, velocity, recovery of 
vehicle, skin vibration or "self-noise" factor, 
and the effects of acceleration and deceleration 
on equipment performance. 

The vehicle consisted of 3 sections: a 
cast-aluminum nose, an extruded, tubular, alu- 
minum midsection, and a cast-aluminum tail 
(Fig. 2 and 5). 

The nose section was an ellipsoid of re- 
volution with the radius ratio a/b = 1.3, and 
dimensions of 7 in. and IO-3/I+ in. A 100- lb 
lead ballast plug was bolted into the nose dur- 



/ 



I 

FIG. 1 MISSILE IN LAUNCHING 
FRAME 




FIG. 2 MIDSECTION OF MISSILE, NOSE OFF 



With access fo electronics and drag fins open 



Rim A 
old Down 




FIG. 3 TAIL SECTION OF MISSILE 




TIME (seci 

FIG. 4. DESIGN AND VELOCITY CHARACTERISTICS OF HYDRODYNAMIC-FLOW -NOISE 

MISSILE 



10 



ing the test drops. Hie nose was screwed into 
the midsection using an "0 Ring" seal to make the 

connection watertight. 



tially inserted into itstracked supporting frame 
in the missile. 



The midsection or main body of the vehicle 
(Fig. 2) was an extruded aluminum tuhe IO-jA in. 
In diameter, KQ in. long, with 3/8 in. walls. 
The forward two thirds of the midsection made up 
a watertight compartment containing the recorder 
and all the accessory electronics and components 
of the data system. Two flush-mounted hydro- 
phones were located on opposite sides of the mid- 
section at its midpoint. On the rear of the 
hulkhead terminating the watertight section was 
fixed the recovery mechanism and holddown clamps 
for securing the tail section. Four rectangular 
doors or "drag fins" were mounted flush with the 
outside surface in the afterend of the midsec- 
tion. These were opened (to decelerate the mis- 
sile) by the recovery and tail-locking assembly 
to be described. 

The tail section of the missile (Fig. 5) 
was a cast-aluminum ellipsoid of revolution with 
the ratio a/b = k. It was 10-3/'+ in, in diam- 
eter and 2I-I/2 in. long. This section was a 
sealed bouyant body which, when released from 
the forward bodies, rose to the surface trailing 
a nylon recovery line secured to the midsection. 
The tail was clamped tightly in place on the 
afterend of the midsection by means of four tog- 
gles which were looked and released by action of 
the release-recovery mechanism. Figure 2 shows 
the completed missile. Figure h shows the the- 
oretically predicted performance characteristics 
of the missile. 

Model studies indicated that the vehicle as 
designed, with a fineness ratio of 7»15 and with 
its mass distribution, would be stable through 
its maximum test velocity. 

The data-recording system and accessory 
components were mounted on a shock- and vibra- 
tion-isolated assembly in the midsection. The 
equipment was integrated into a rigid frame 
which in turn was slid into tracks on a struc- 
ture secured to the watertight after bulkhead by 
Barrymount shock mounts. When the missile was 
in the vertical or drop attitude, the equipment 
was suspended on the Barrymounts and was held 
rigidly in the tracked structure by four wing 
nuts on threaded steel rods. The suspended 
structure was isolated from the shell of the 
missile by suitable rubber pads. The equipment 
rack was easily removable for access to the re- 
corder and electronics for calibration and 
changing the tape supply prior to test drops. 
Figure 5 is a view of the electronics rack par- 



PRTOCIPLES OF OPERATION 

Data Recording System 

The recorder was a special modification of 
the Stancil-Hbffman standard Model m8 Minitape 
Recorder. This recorder used l/h in. tape and 
operated at I5 in. /sec. The two record-track 
widths were 0.100 in., separated by 0.062 in. 
The recording heads were shielded to reduce 
crosstalk. The recorder motor was driven at 
3600 rpm; speed control was obtained by using 
a centrifugal governor which varied the shunt- 
field current to keep the speed constant. A 12- 
volt Sonotone sintered-plate nickel-cadmium bat- 
tery supplied power to both the motor system and 
the amplifier system of the recorder. 

Each of the two channels of the recorder's 
electronic system consisted of a preamplifier. 
Model AC23, and a record amplifier. Model AR23. 
A jack was provided by which the output of a 
single full-track playback head could be mon- 
itored. This output provided a signal to an ex- 
ternal playback amplifier during the checkout 
and calibration procedure described below. 

The two transistorized AC23 amplifiers had 
gains of approximately 85 db and input impedances 
designed for 1000 ohms. Each had a push-piill 
stage, using four RCA 2H105 transistors, trans- 
former coupled to a Texas Instrument 2N185 tran- 
sistor. The automatic gain control employed in 
the AC23's of the original M8 model was discon- 
nected for preliminary tests. 

The two Model AR23 recording amplifiers fed 
audio signals mixed with a 60-kc bias from the 
AC23's to the recording heads. The input to the 
AR23 was approximately dbm at less than 1000 
ohms impedance. The output impedance of the 
amplifier fed a recording head of approximately 
3.5 lull. The 60-kc bias appearing across the 
head was 7-5 volts. 

Wow and flutter for the recorder was found 
to be 1^ rms, using the standard test. The 
signal-to-noise ratio, measured at Ij-OO cps, was 
determined to be 3I db. The signal level for 
this test was chosen to be the 3^ distortion 
point (including nonlinear distortion, hum, tape 
noise) . The cross-tali ratio between the re- 
cord tracks was measured to be 55 db, 

Channel 1 of the recorder was used to re- 



11 



cord the audio information from one of the hull- 
mounted hydrophones. The second hydrophone, 
mounted diametrically opposite the first on the 
cylindrical midsection, was connected to the in- 
put of channel 2 on the tape recorder. A fre- 
quency-modulated signal containing depth informa- 
tion and operating with a carrier frequency of 
15.5 kc was also recorded on channel 2. This 
depth information originated in a pressure trans- 
ducer and associated circuitry. 



transducer. Type h'Jl'^2, produced hy G. M. Gian- 
nini and Company. The modulator utilized varicap 
capacitors in parallel with the tuned circuit of 
the modulator oscillator. Voltage from the 
pressure potentiometer, amplified by 20 db to 
put it within the varicap 's linear range, was 
inserted across the varicap capacitors. The 
varicap capacitance was proportional to the volt- 
age across it, hence the tuning of the modulator 
was proportional to the 200-cps oscillator's 
input amplitude. 



Depth Measurement Circuitry 

Channel 2 was specially adapted by appro- 
priate filtering to record flow-noise data in 
the region below 6 kc and to record depth and 
time information in the region above 10 kc, using 
a frequency-modulated 13.5-l5;c carrier. A func- 
tional diagram of the depth-measurement circuit 
is shown in Fig. 6. 

From the recorded pressure and time informa- 
tion the depth and velocity of the missile was 
determined for any time during the missile's fall. 
The carrier frequency of 13 -5 kc was modulated by 
a 200-cps voltage the amplitude of which was de- 
creased linearly with water pressure by means of 
the pressure potentiometer (Fig. 6). The 200-cps 
frequency which modulated the 15-5-l^c carrier 
was used as a time reference by demodulating the 
tape information and counting the number of cy- 
cles during any desired data period. The ampli- 
tude of the 200-cps voltage from the pressure 
potentiometer determined the frequency deviation 
of the FM carrier. Upon demodulation, the 200- 
cps amplitude was proportional to pressure and 
therefore to depth. Velocity and acceleration 
were calculated from depth and time data. 

The 200-cps oscillator, the 20-db amplifier, 
the l^t-db amplifier, and the varicap modulator 
were designed and built by this laboratory. De- 
tailed schematics of each of these units are 
shown in Figs. 7-10- 

The most critical unit in the depth- informa- 
tion system was the 200-cps oscillator. The 
frequency of this oscillator had to be an ac- 
curate 200-cps. The final design showed an ac- 
curacy of 1^ in laboratory tests. For accurate 
depth information it was necessary that the 
amplitude of the oscillator remain stable from 
the time of the field calibration (described 
later in this section) to the end of the drop. 
Small changes in oscillator amplitude from day 
to day were of no concern. 

The pressure potentiometer was a commercial 



Deviations in linearity of the pressure 
transducer and the varicap characteristics were 
not sources of error because of the field cal- 
ibration procedure used. Daring this calibra- 
tion a separate potentiometer which accurately 
simulated the pressure potentiometer was in- 
serted in its place. The potentiometer was hand 
set to simulate various pressure levels, and the 
corresponding 200-cps signal amplitudes were re- 
corded on the tape. The simulating potentio- 
meter accurately duplicated the pressure trans- 
ducer in resistance variation. Precision re- 
sistor steps were used, and the duplication was 
accurate to ± 1^. 

The high- and low-pass filters used in 
channel 2 recording were United Transformer 
Company Type HML 12000 and LML 6OOO. An at- 
tenuator pad was connected to the 600-ohm im- 
pedance level of the llj— db output amplifier. 
This amplifier raised the combined signal level 
up to the necessary dbm record level. 



Automatic Recovery Mechanism 

The recovery- system mechanism consisted of 
the equipment shown in Fig. ULj this was mounted 
in the afterend of the cylindrical midsection of 
the vehicle (Fig. 12) and in the tall section 
(Fig. 3) . When the tail section was mounted in 
place, the heads of four toggle clamps, one of 
which is A (Fig. 11), bore against the top in- 
side of rim A (Fig. 3) of the bouyant tail sec- 
tion, thereby holding the tail tight against the 
midsection (Fig. 12). In the locked-down at- 
titude the levers of the toggle clamps were then 
horizontal and held down, bearing against the 
bottom of disk C. Disk C is an integral part of 
locking unit 0, which is moved downward against 
spring F during loading. The tail was thus held 
securely in place against the midsection by 
means of the four toggle clamps. The locking 
unit (Fig. 11) was in turn held down by tog- 
gle clamp D, the head of which bore against the 
bottom of slot E of the locking unit 0. This 
required that spring F, sliding with the locking 



12 




FIG. 5 RECORDER AND ELECTRONICS MOUNTING, BACK 



Hydrophone 

1 







Hydrophonel 



O 



85 -db 
Amplifier 



AC23 

1 



Recording 
Amplifier 



AR23 
1 



Channel 1 



AC23 
2 




Recorder - M8 - X2 



Recording 

Head 

1 



filter 
ta=6 kc 



pT.^^S^ 



20 -db 
Amplifier 






Varicap 
Modulator 


12 


_ 




V 


Carrier 
f := 13.5 kc 



High 
Pass 



AR23 
2 



Recording 

Head 

2 



200 

MAAAH 



filter 
f ,:10 kc 



200 

— MAAi — ' 

6-db 

Matching 

Pad 



14 -db 
Amplifier 



Pressure 
Transducer 



FIG. 6. DIAGRAM OF DEPTH-DATA CIRCUITRY 



13 



0.11 ut 




0.1 (if 

11 2N185 



LevelJ-HI O 

<i-26v Adjuster"? To 5Ki2 

Pressure 
Transducer 



FIG. 7. 200-CPS OSCILLATOR AND GROUNDED COLLECTOR STAGE 



0.1 (if 

X— II V^AA/W 

200'i/Signal lOK 
from Depth iA 

o 
Potentiometer [-. 



4.7K t 

I — VWVV — WMr 

lOK 



2.0 pf 



4.7 megB 

vwv — I 




lOK 10 vt 

c-sMAA/^ — ^ — Ih- 



0.001 



•26 V 



FIG. 8. 200-CPS FM MODULATOR AMPLIFIER, -20 DB 



I 



i® 



To 

13.5 kc 

Oscillator 



Data Signal goO 



Low - Pass 
Filter 



200 

AAAAA^ 1 



200 10 /if 

— vvw 



I© 

13.5 ko 
FM - Modulated 

Signal from 
High - Pass Filter 



10 vt igK 

_|| v^AAA/v- 




FIG. 9. DATA- AND DEPTH-SIGNAL AMPLIFIER, -14 DB 



14 



0.001 /if 



10 ^t 




FIG. 10. 13.5-KC OSCILLATOR AND GROUNDED COLLECTOR STAGE 



Disk C 



Explosive Motor 



Support Rod H 



Locking Unit O 




oted Door 
Mount M 



Nylon Recovery Line 



FIG. 11. RECOVERY MECHANISM 



15 



Toggle ^-^-^^^^^^^^ ^T*^ f 



Push Rod L 



Toggle D 




FIG. 12 RECOVERY MECHANISM IN PLACE. Drag fins open, one removed 



Explosion 
Motor 



Meletron-4141 



Pressure 
S^vitch 



1 35 psi 
80 ft 

2 43 psi 
100 ft 



H 



N.C, 



N.O. N.C 



V . V 



N.O. 



6 V 

' ' ' t" 

k 



Nickel - Cadmium —12 v to _ 

Recorder Battery Recorder 



External j 

Switch 



I ^ 00000/ — ' 

I Coil A 




Coil B 



25 vt 



I N.C, 



FIG. 13. RECOVERY CIRCUITRY 



16 



unit along steel pipe G, be compressed complete- 
ly. Spring F was compressed by hydraulic ally 
loading a long, thin, slotted steel rod whicli 
fitted over support rod H In the locking unit 
and passed up through the center fluid pressure 
equalizing tube through the tail. When spring 
F was completely depressed, toggle D was closed 
manually through one of the door ports. "Load- 
ing" the tail was done in the launching frame 
with the missile in the launch attitude. 

In Fig. 12, the drag fins are open and one 
is removed. Toggle clamp D, the key element in 
the tail-locking assembly, was released when the 
explosion motor, mounted as shown, received a 
d-c electrical impulse from a pressure switch. 
On release of toggle D the spring quickly ex- 
panded, pushing up the locking unit which re- 
leased the four toggle clamps and imparting Ein 
initial thrust to the tall section. 



explosion motor when the missile reached a pre- 
determined depth, thus initiating the tail- 
releasing sequence, 

(b) It shut off the recorder at another 
predetermined depth to keep the recorder from 
loading the nickel-cadmium battery during the 
time of missile recovery. 

Figure 13 is a complete schematic of the 
recovery circuitry. The main controlling circuit 
element was a Meletron Model ^t-ll+l pressure switch. 
Switch Ho. 1 of the pressure switch was set at 
55 psi or 80 ft. When the missile reached a 
depth of 80 ft, the normally open contact closed 
and the explosion motor was set off. Water pres- 
sure reached the switch through a hydraulic hose 
from the water- filled afterend of the cylindrical 
midsection of the missile, which acted as an 
accumulator. 



The locking unit also controlled the doors 
or drag fins. At the time of "loading" three of 
the doors which were secured to their mounts 
were locked into place. The fourth was fixed 
in place after loading and locking toggle D. 
The doors were closed by push rods K, forced 
outward by the inclined surface I, acting against 
their inside upper edge. Each door was fast- 
ened by two bolts to a mount M which revolved 
vertically around a pin. The force exerted on 
the door by the push rods above the revolving 
mounts kept the bottom of the doors locked flush 
with the surface of the missile by simple lever 
action. The push rods were forced outward by 
Incline I as the spring and locking unit were 
forced down under load. In the locked position 
the push rods were pressed between the straight 
area J and their contact points at the tops of 
their respective doors. Upon release of the 
spring F, push-rod force was released from the 
doors, or fins, and they were snapped open by 
the action of spring N (Fig. 12) against their 
bottom inside edge. The fin opening angle was 
restricted (Fig. 12). The position of the 
closed doors was kept to close tolerance and 
was critical because of the outside surface had 
to be flush, and the doors tightly held. Any 
door rattle or protrusion of the door edges 
above the missile surface during fall would dis- 
tort the hydrodynamic-flow-nolse data. 



Recovery Circuitry 

The recovery circuitry served two func- 



tions : 



(a) It applied a 6-volt signal across the 



A few seconds prior to each drop of the mis- 
sile, the recorder was turned on by the external 
switch (Fig. 13) . This energized the normally 
open relay, and closed and mechanically latched 
it. Through this switch, 12 volts was fed to 
recorder. When the missile reached 100 ft the 
normally open contact of Switch No. 2 closed, 
shutting off the recorder. A second coil was 
used to keep the recorder off during the re- 
covery of the missile as it was returned to lower 
pressure. Coil B is energized long enough to 
throw the normally closed contacts open and latch 
the relay mechanically in the open position. 
This terminated the 12-volt recorder supply. By 
cutting off the current to the coil, the drain 
of current from the 12-volt battery was stopped. 
The 25-n f condenser prolonged the current pulse 
through self-cutting coil B. 



Checkout and Calibration Procedures 

A calibration and circuit test unit (Fig. 
ih) was designed and built for use in the field. 
This unit included a VU meter, the AP23 play- 
back amplifier, a pressure-transducer simulator 
consisting of a potentiometer with precision re- 
sistor steps, two inputs to the recorder ampli- 
fiers bypassing the hydrophone inputs, control 
switches, and a 27-pin Jones plug connector. 
During the checkout the Jones plug from the 
checkout unit was inserted into the missile elec- 
tronic system in place of a similar Jones-plug 
dummy connector through which the circuits were 
connected during normal operation. 

The calibration-test unit provided means to 
determine: 



17 




o 
z 
< 

5 



z 
o 

< 

00 

-J 

< 

u 

o 

z 
< 



O 
u 

UJ 

X 

u 

I 



18 



(1) The voltage of the 12-volt nickel-cad- 
rniiun battery under load. 

(2) The voltage of the 26-volt depth-cir- 
cuit hattery. 

(3) The frequency and voltage level of the 
200-cps oscillator in the depth circuit. 

(h) The presence and level of the 13.5-kc 
carrier in the depth circuit. 

(5) The operating condition of the recorder 
and its four amplifiers. 

Test-unit information was obtained visually 
from the VU meter. A four-position selector 
switch and a visually monitored VU meter permit- 
ted reading the 12-volt, 200-cps and playback 
signal levels. The 12-volt, 26-volt, and 200-cps 
levels were put directly on the VU-meter termi- 
nals through an appropriate series resistance so 
that the meter read in decibels above or below 
the design level. 

With the VU- input selection switch in the 
"playback" position, the AP23 playback-amplifier 
output was monitored. The VU meter which indi- 
cated the recorded signal of all the channel 
signals combined or of channel 1, channel 2 
audio, or channel 2 FM alone was recorded. The 
desired signal was selected by properly setting 
a four-position "record monitoring" switch which 
controlled the B+ voltages to the amplifiers in 
channel 1, channel 2, and the depth circuit. 
This arrangement provided a separate visual in- 
dication of the recording of any signal on chan- 
nel 1 or channel 2 audio inputs or of the re- 
cording of depth-circuit signals. 

A "remove 200 cycles" button made it pos- 
sible to record the unmodulated 13.5-kc carrier 
signal on "channel 2 M" and obtain a visual in- 
dication of the "clear" carrier recorded level 
on the VU meter. 

The hydrophone inputs were bypassed and had 
no connection to the electronic system during 
checkout. Prior to launching, the continuity of 
the complete system, from the hydrophones to the 
tape, was tested. 

The calibration precedure performed two im- 
portant functions. First, reference- signal lev- 
els at 1000 cps and 8OOO cps were recorded on 
the tape by means of an oscillator wand and the 
proper attenuation pad. Second, a calibration 
of the depth-measuring circuit was made by feed- 
ing channel 2 FM of the tape a calibrating signal. 



The insertion of the checkout unit Into the 
electronic system replaced the pressure-trans- 
ducer potentiometer by the checkout unit's pres- 
sure-transducer-simulator potentiometer made up 
of precision resistors accurate to ± O.5 ohm. 
The simulator passed signal levels corresponding 
to actual pressures of 0, I5, 30, 37.5 and k^ psl 
used to modulate the 13.5-kc carrier. Each of 
the resulting FM signals was recorded during the 
checkout procedure by setting the record-monitor 
switch to "channel 2 FM, " the VU-meter monitor 
switch to "playback," turning on the recorder, 
and setting the simulator to various pressure 
levels by hand. 

The record-level calibration signals with 
which to compare hydrodynainic-flow-noise data 
were recorded during the checkout procedure by 
Inserting the oscillator wand (a small battery- 
powered oscillator for field use) connected to 
an attenuation pad into the channel 1 and channel 
2 checkout-unit inputs. The wand and pad fed to 
the recorder amplifiers reference signals of -75 
db on a 1-volt reference at 1000 and 8OOO cps. 
Only the lOOO-cps signal was recorded for channel 
2 audio because of the 6000-cps cut-off of the 
audio portion of this channel. By comparing the 
hydrodynamic-flow-noise level to these signal 
levels on the tape, an accurate value of the 
hydrodynamic-flow-noise level was obtained. 



Launching and Recovery Procedure 

Preceding the actual drop, the missile mid- 
section was mounted horizontally in the launch- 
ing frame (Fig. 2) and the electronics partially 
inserted by sliding the electronics rack along 
the tracks mounted inside the missile midsection. 
The checkout procedure and calibration already 
described were then performed, the installation 
of the electronics rack was completed, and the 
missile was rotated to a vertical attitude In the 
launching frame. The missile nose section was 
threaded onto the midsection and the tail mounted 
and locked by means of a hydraulic Jack located 
at the top of the launch frame. The Jack loaded 
the release spring by forcing down a long steel 
rod which slides down the middle of the tail and 
fits over the support rod mentioned previously. 
The missile completely assembled, was held in the 
launch frame as shown in Fig. 1. The launch 
frame and missile assembly were lowered through 
the center of the launching platform by means of 
a winch and steel cable until the upper end of 
the launch frame was Just below the surface of 
the water. 

The missile was released on opening the 



19 



doors ty whlcli it was held at the base of the 
launch frame. 

After the drop, the tail section was re- 
covered and the recovery line secured to a winch. 
The missile was then pulled back up into its 
launching frame. The doors holding the missile 
were then shut and made safe by the Insertion of 
a pin in the toggle clamp. The entire launch 
frame and missile were then lifted to the deck 
level, secured, and readied for the next drop. 



CONCLUSIOHS 

The results of tests conducted by the Acous- 
tics and Seismics Laboratory indicated that the 
experimental approach using a free-falling vehicle 
was sound and that this type of instrument could 
be valuable in acquiring information to increase 
the present knowledge of the physics of hydro- 
dynamic-flow noise. 

This work was supported by the DTMB and a 
contract administered by the Office of Naval 
Research. 



20 



ACOUSTICAL NOISE MEASURING BUOY WITH DIGITAL DATA RECORDING 



by DR. T. F. HUETER, D. M. BAKER, and J. T. SHAW 
Minneapolis-Honeywell Regulator Company 
Ordnance Division, Seattle Development Laboratory 
Seattle, Washington 



ABSTRACT 



An ambient noise measuring system is being 
developed for use in a deep-water moored buoy . 
The acoustic spectrum between 50 and UOO cps is 
measured at four discrete frequencies and 
sampled at regular intervals . The analog signal 
is converted to a binary digital code and photo- 
graphically recorded for later processing. 

A qualitative measurement of sea state is 
meide during each measurement cycle, permitting 
a correlation between wave height and ambient 
noise to be accomplished. 

Auxiliary devices are provided which effect 
buoy recovery upon reception of a coded acoustic 
command signal. The buoy is designed for 
operation at depths to 1000 feet with a dura- 
tion on station of three months. Solid-state 
devices are used where possible to keep power 
consumption to a relatively low value. 

INTRODUCTIOH 

Generally, the variations in the ambient 
noise spectra at frequencies above 500 cps 
can be identified with one of several sources 
which happen to predominate at a given time 
and location. Examples of these sources are 
marine life, precipitation, ship traffic and 
man-made noise, seismic sources, and the wind- 
generated agitation of the sea surface itself. 
The well-known Knudsen curves demonstrate the 
dependence of acoustic noise levels on sea 
state over the range of frequencies for which 
the curves have been calculated. 

In the case of frequencies below 500 cps, 
however, investigations have shown that the 
dependency of noise levels upon surface con- 
ditions decreases as the frequency is lowered 
and that below 100 cps the variations may be 
independent of that source. 

The development of a remotely operated 
buoy system for the measurement of ambient 
noise in the ocean could be expected to provide 
a useful tool in fxirthering the investigation 
of mechanisms involved in the low- frequency 
acoustic phenomena. The use of a submerged 
buoy system for such a purpose offers several 
important advantages as a "listening platform" 
from which to make low- level measurements. A 
submerged buoy can be an inherently quiet plat- 
form, free of unnatural disturbances and noise 



produced by extraneous sources. The mooring 
problem is simplified and the probability of buoy 
loss reduced due to the absence of strain on the 
anchoring system created by storms and high sea 
states. A degree of freedom from possible 
damage to the system from encounters with sur- 
face traffic is also realized. 

Electrical power derived from storage bat- 
teries or other low voltage dc power sources 
results in an electrically quiet environment in 
which to operate low- level, high- gain amplifier 
circuitry. The absence of interfering electro- 
static and magnetic fields associated with 
systems operating from high voltage ac power 
sources or with systems which employ long lengths 
of electrical cable is a distinct advantage in 
reducing extraneous electrical noise. This re- 
sults in better signal-to-noise ratios and in- 
creased dynamic ranges in measurement circuitry. 

The Office of Naval Research has sponsored 
the development of such a buoy by the Minneapolis- 
Honeywell Regulator Company. The buoy system to 
be described is intended for use in the open 
ocean for the measurement and recording of 
ambient noise levels at specific frequencies in 
the range between 50 and UOO cps. 

ACOUSTIC MEASUREMENr BUOY SYSTEM 

The acoustic measurement buoy is designed 
for continuous remote operation for periods up 
to three months. Simultaineous measurements of 
wave height and the acoustic spectrum level in 
discrete bands at center frequencies of 50, 
100, 200, and UOO cps are made at predetermined 
intein/-als and photographically recorded on 35- 
mm film. The acoustic levels are recorded in 
digital form by use of a 6-bit binary coding 
system. 

The acoustic measurement buoy is composed 
of seven basic subsystems: (l) buoy hull and 
mooring system, (2) timing and programming 
system, (3) acoustic measurement system, (h) 
wave- height measurement system, (5) data con- 
version and recording system, (6) recovery 
system, and (7) the electrical power system. 



21 



The basic buoy hull is a cylindrical alumi- 
num tube (Alloy b063-T5) approximately l6 inches 
in diameter by 7 feet long with a one-half inch 
wall thickness. The pressure capability of the 
hull design allows for a 1000- foot submergence. 
A net positive buoyance of approximately 150 
pounds is obtained including all internal com- 
ponents. Calculations made for assumed con- 
ditions of buoy attitude, mooring line length, 
and wire diameters indicate reduced drag and, 
consequently, the least heeling angle is ob- 
tained with the buoy moored in a horizontal 
position. Minimum hee3j.ng angle is desired to 
obtain satisfactory operation of the wave- 
height sensor which in the existing design has 
a depth limitation of 80 feet. Provision is 
made for the attachment of buoyance adjustment 
tanks and fairings at nose and tail. 

The noise hydrophone mount is attached to 
the underside of the main hull with provisions 
for suspending the hydrophone at desired depths 
below the hull as required. The wave-height 
measuring transducer is mounted on top of the 
hull with provisions for buoying the transducer 
above the main hull if desired. 

A taut-wire mooring system is used which 
employs a concrete block anchor and anchor 
line attachment bridle at the buoy end. An 
explosive anchor release is incorporated in the 
anchor line at the buoy end which effects buoy 
release and return to the surface under control 
of the recovery system. 

Access to the buoy interior is gained 
through an "0" ring sealed end cap held in 
place by a flanged coupling. Electrical con- 
nections from the buoy interior to the hydro- 
phone and wave-height sensor are made by means 
of Marsh Marine bulkhead fittings in the end 
cap. 

The measurement circuitry, data recording 
system, and electrical power supply are con- 
tained as a modular assembly which can be re- 
moved from the buoy hull in one piece. This 
arrangement permits simplified bench testing 
and servicing procedures. The equipment com- 
ponents are mounted on coaxially aligned 
stacked circular decks and the complete assembly 
is held in place within the hull by means of 
integral guide rails . 

TIMIMG AM) COHTROL SYSTEM 

An electrically wound spring- driven clock 
(Massey Dickenson) provides the basic measure- 
ment sampling interval and control of buoy 
operation by means of the programmer. The 
accuracy of the clock is ±10 seconds per day. 
The programmer provides for the sequential 
application of voltages to the measuring systems 



and the operation of the photo-data recording 
system through a series of motor-driven cam- 
operated switches. Adjustable contacts on the 
main clock trigger the programmer into a measure- 
ment cycle once each sampling interval. 

During a measurement cycle, power is first 
applied to a thermal delay relay by the clock 
which allows a 20- second warmup period for the 
noise-measuring amplifiers. In series and 
simultaneously with the end of the warmup period 
a 60- second solid-state delay relay is actuated. 
During the delay period, the acoustic integra- 
tions are performed. Closure of the 60-second 
solid-state delay relay at the end of its cycle 
actuates the programmer which performs all sub- 
sequent functions, including channel selection, 
comparison for each channel, sea-state sensing, 
and frame shift of the cajnera. At the end of 
the program, the system is returned to its 
initial standby state. 

The programmer also controls a predetermining 
counter. The counter reading is recorded on 
each film frame along with the acoustic noise 
and wave- height data. When the predetermined 
timing interval has been reached, the counter 
contacts energize the acoustic command recovery 
system, thereby initiating the recovery cycle 
at the end of the buoy operational period. 

ACOUSTIC MEASUREMEMT SYSTEM 

The acoustic measurement system consists 
essentially of the hydrophone and associated pre- 
amplifier, the bandpass filter and matching 
amplifiers and the rectifier/integrator circuits. 
All amplifier and integrator circuits are tran- 
sistorized with the exception of the input stage 
of the hydrophone preamplifier. 

The measurement technique involves amplifi- 
cation and selective filtering of the acoustic 
signal. The output of each filter is rectified 
and integrated to produce one minute averages of 
the sound pressure in four, l/3 octave bands at 
50, 100, 200, and it^OO cps. 

The hydrophone signal is first amplified 
and shaped by a passive filter with bandpass 
from 30 to 600 cps. This filter serves to 
eliminate frequencies outside the band of in- 
terest and reduce the possibility of amplifier 
overloading. The bandpass filter output is 
then applied to four, l/3 octave band filters 
connected in parallel through impedance matching 
amplifiers. The output of each l/3 octave 
filter is matched to identical rectifier/ 
integrator circuits through variable gain linear 
power amplifiers. The averaged spectrum level 
output of the Integrator circuits is stored in 
low- loss tantalum capacitors (General Electric 
Type 29F107'*). 



22 



The hydrophone is an omai directional barium- 
titanate unit with a sensitivity of -85 db 
reference to one volt per microbar. When ter- 
minated in a 20-megohm load, the response is 
essentially flat between 10 cps and 2 kc . 

The hydrophone signal is amplified in a 
hybrid preamplifier stage which provides a 
voltage gain of 280. A vacuum tube is employed 
in the input stage in order to achieve the 
necessary high input impedance and low equiva- 
lent noise input. A Sylvania 590'+ subminiature 
triode with a 2'+- volt filament and plate supply 
eliminates the need for a special vacuum tube 
plate supply. This tube is powered directly 
from the transistor amplifier supply. The 
equivalent noise input of the preamplifier re- 
ferred to the input grid over a 600- cycle 
bandpass is less than one-half microvolt. 

The voltage gain from the hydrophone pre- 
an^jlifier input to the rectifier/integrator 
circuit is approximately 100,000, and the dy- 
namic range of the voltage amplifier and filter 
channels up to the rectifier/integrator input 
is 95 db. The rectifier/integrator circuit has 
a useable dynamic range of kO db with correc- 
tions for nonlinear operation and is linear 
over a 30- db range. 

WAVE- HEIGHT NEAgUREMEMT 

A q\ia3J.tative measurement of wave height 
is accon^ilished by means of a small transis- 
torized depth sounder operating at I98 kc . 
The transducer is mounted in a small buoy which 
can be either fastened directly to or floated 
upward above the main buoy hull. The trans- 
ducer beam is directed upward and uses the 
underside of the air-water interface as the 
reflecting surface. The rotating neon lamp 
wave-height indication is converted to a linear 
display providing a measurement of the wave- 
height in one-foot increments. The wave-height 
data is displayed in the data photo matrix 
along with the acoustic digital display and 
main counter reading. The wave- height recording 
extends for a period of 15 seconds during each 
measurement cycle. 

DATA CONVERSIOH AMD PHOTO- RECORDING SYSTEM 

The analog- to- digital conversion of the 
acoustic level measurements is recorded on 
35-nim film in digital fonn. The digital en- 
coding is accomplished by a 12-baiik, 52-polnt 
stepping switch and a matrix of neon lamps . 
The lamp matrix ccnsists of four rows of eight 
lamps. Six lamps in each row are used in a 
six-bit gray code. The seventh lamp is used 
to provide a parity check, and the eighth 
lamp provides for channel identification. 



Seven banks on the stepping switch are used 
to provide the grounding pattern for the binary 
code on the lamp matrix corresponding to the 
switch wiper arm position as it steps through 
the 52 levels. One bank contains a precision 
resistor divider network providing one db step 
changes in the voltage level picked off by the 
wiper. Therefore, the voltage picked off the 
divider network at any switch level is repre- 
sented simultaneously by the binarj digital 
code established in the neon lamp matrix through 
the grounding pattern. 

The voltage picked off the precision resistor 
divider network In the stepping switch is com- 
pared to the voltage stored in the integrator 
capacitor. As the stepping switch operates, 
the divider voltage eventually equals or slightly 
exceeds the capacitor voltage at some particular 
switch level. At the balance or crossover point, 
the voltage comparator circuit discharges a 
capacitor through the neon lamp matrix. The 
binary code corresponding to the integrator 
capacitor voltage is exposed on the film by the 
flash of the appropriate lamps . 

The programmer selects and applies each 
integrator output sequentially to the voltage 
comparator and the corresponding row in the 
digital matrix. Each film frame, therefore, 
contains the digitized spectrum level from each 
of the four bandpass filters. 

RECOVERY SYSTEM 

Buoy recovery will be effected In three 
phases. Assuming the general situation in 
which the buoy is moored in the open ocean, the 
first phase In recovery is essentiallj- a navi- 
gation problem in which the recovery ship must 
return to the general area where the buoy is 
moored. The first stage Is accomplished by use 
of ordinary navigational methods ( LORAN, DF 
bearings, celestial navigation, radar fix, 
soundings, etc.), employing whichever methods 
are best suited to the particular conditions at 
hand. The second phase in recovery results in 
release of the buoy and its return to the sur- 
face in a free- floating condition accomplished 
by an acoiistic interrogation from the recoverj' 
ship. The third recovery phase required 
localization of the buoy on the surface and sub- 
sequent retrieval by the ship. 

Each phase in the recovery procedure requires 
the solution of particular interrelated pro- 
blems in order to achieve reliable operation. 
The navigational accuracy requirements are 
determined primarily by the acoustic interroga- 
tion ranges which can be achieved and secon- 
darily by the localization ajid visual sighting 
aids employed when the buoy is on the surface. 



23 



The buoy contains two separate and electri- 
cally independent anchor release circuits pro- 
viding three modes of actuation. In normal 
operation, the main buoy clock/programmer actu- 
ates the acoustic command receiver circuits at 
the end of the timed measurement period. The 
acoustic command receiver circuit is energized 
for a period of approximately three days during 
which time reception of the correct acoustic 
code will fire the anchor release. The enable 
period is designed to be adjustable and can be 
set anywhere between 9 and 99 hours in incre- 
ments of 10 hours. If the proper acoustic code 
has not been received at the end of the enable 
period, the main buoy programmer will fire the 
anchor release. 



PCMEB SUPPLY 

Electrical power is supplied by a Yardney 
silver- cadmium battery assembled from 22 YS-40 
units in a series connection. This combination 
supplies 960 watt-hours of electrical energy 
which is sufficient to make 1600 measurement 
cycles leaving a 20-percent battery charge in 
reserve. 



An additional separate timer powered from 
its own battery pack will also fire the re- 
lease mechanism through completely independent 
circuits, providing backup to the acoxistic 
command receiver circuit in the event of a 
failure in the main battery or electrical con- 
trol system. The secondary timer will be set 
to fire after runout of the acoustic enable 
period has occurred. 

The acoustic command receiver function pro- 
vides two valuable features in the recovery 
system. In normal operation, the recovery 
ship is not required to be in a precise posi- 
tion at a precise time to insure that the buoy 
will surface relatively close at hand. There- 
fore, an allowance is made for the routing 
emergencies and delays which continually arise 
such as equipment breakdown or inclement 
weather conditions . Secondly, the relatively 
short acoustic command range provides a higher 
probability that the buoy will surface within 
visual sighting range. The backup circuit pro- 
vides for eventual buoy release and return to 
the surface in case of a failure in another 
part of the recovery system. 

The acoustic command receiver responds to 
a pair of accurately timed signals provided 
by small explosive charges (No. 6 blasting 
caps). This system was chosen because of the 
simplicity and inexpensiveness of the signal 
generator requirements . The recovery ship 
does not need a specialized transmitting trans- 
ducer and associated electronics. 

Provision Is also made against actuation 
of the release mechanism by random background 
and/or ship noises. Decoder circuit, therefore, 
is incorporated in the receiver design to dis- 
criminate against background noise, reducing 
the probability of false triggering. 



24 



DEEP TRANSDUCER DESIGN 

by R. P. DELANEY 
The Martin Company 
Baltimore, Maryland 



ABSTRACT 

The problem of design of deep sea (10^ 000 ft) 
transducers is a severe one particularly from 
the point of view of maintaining good efficiency 
without conventional pressure release materials. 

The design of the MBP-1 Transducer met 
this problem by pressure equalization. This 
projector has been operated at 10,000 ft deep 
with 50% efficiency at 2700 cps. Similar trans- 
ducers designed for lower frequencies have 
displayed similar performance. Design data 
and performance of these transducers are 
discussed. 



INTRODUCTION 

The title of my paper is somewhat mis- 
leading in that I intend to confine my remarks 
to a particular type of transducer, namely, 
configurations based on ceramic cylinders. 
Since 1958 The Martin Company has designed, 
built, and tested a number of projectors and 
hydrophones suitable for employment at great 
depth (below 5000 ft). I have selected 4 of the 
more successful configurations to describe 
today and I shall try to point out how and why 
they work in order to assist others in avoiding 
pitfalls attending this field. 

When faced with a new environment and new 
design problem, it is a common approach to 
take a familiar design suitable for another 
environment and seek to adapt or modify it for 
the new environment. This tendency probably 
accounts for our use of ceramic cylinders when 
faced with the problem of designing hydrophones 
and projectors for deep use, because for near 
surface applied ceramic cylinders are a very 
common transducer type. Operated in the 
fundamental circumferential mode as pro- 
jectors, the outside surface of the cylinder is 
commonly exposed to the medium by means of 
a rubber boot while the inside wall is pressure 
relieved with air or one of the common pressure 
release materials, celltite rubber or corprene. 
They are a simple design acoustically and 
mechanically and a very effective one. Hydro- 
phones of this design exhibit desirable broad 
band characteristics below resonance and 
projectors when using the stave construction 
methods of Mr. Green of NEL show excellent 
efficiencies. However, this rather pleasant 
situation is upset when the static pressure of 
the deep ocean environment is introduced. On 
a theoretical basis the wall thickness of 
ceramic cylinders can be increased to the part 
where an air backed hydrophone becomes 



possible. We have never been able to build an 
air backed unit which survives long periods under 
pressure. We have had units last 6 weeks at 
9000 psi only to implode. We therefore turned 
our attention toward the development of con- 
figurations which are pressure equalized using 
oil or water at ambient pressure on the back or 
inside of the cylinder to reduce the stress levels 
in the ceramic, and using one means or another 
to prevent the loss of sensitivity (about 15 db) 
which occurs when the inside is acoustically 
short circuited. 



HYDROPHONE DESIGNS 

I should now like to describe two hydrophone 
configurations which we have successfully tested 
and used. I would first like to acknowledge a 
debt of gratitude we owe to the Hudson Labora- 
tories who first developed the equalization method 
described below and who were most generous in 
their advice and assistance. Mr. Oberlin has 
discussed the Fixed Acoustic Buoy installed and 
the first hydrophone I shall describe was designed 
for the FAB. The active element is a PZT-5 
cylinder 2 in. tall by 1. 5 in. OD and 0. 25 in. 
wall thickness. The inside of the cylinder is 
pressure equalized with castor oil which is 
connected to a reservoir outside the cylinder via 
a small orifice in the rigid end caps. Mr. Ted 
Madison of General Electric gave a paper in the 
Fall of 1960 at the Under Water Acoustic Sympo- 
sium on the theory of operation of such a device. 
It is based on Helmholtz Resonator theory where 
the orifice is transparent at frequencies below 
the resonance frequency of the orifice --chamber 
combination, so that the inside and outside are 
in static equilibrium; while at frequencies above 
resonance the orifice is opaque and the acoustic 
pressure will not be transmitted. In such a 
transducer the main design problems are to make 
the cylinder large enough for the desired sen- 
sitively, design the orifice and chamber to push 
the Helmholtz Resonance below the band of 
interest and yet have the cylinder small enough 
so that its lowest length resonance considering 
the mass loading of the end cap is above the 
upper end of the desired frequency band. I 
mention the length resonance because the mass 
loading effect of the end caps will often reduce 
the length resonance below the fundamental 
circumferential mode resonance. Slide 1 gives 
an idea of the FAB hydrophone configuration. 
Slide 2 is the receiving response of the FAB 
hydrophone. 



25 



FAB HYDROPHONE CONFIGURATION 



CAVITY FILLED 
WITH 200 FLUID 
DOW SILICONE 
OIL 



5-7/8 



L£AD 
ZIRCONATE ■ 
CYLINDER 



ARALDITE 



LOWER END CAP ' 




PREAMPLIFIER 



CASTER OIL RESERVOIR 

ORFICE 

CAVITY FILLED WITH 
CASTER OIL 



PHENOLIC 
SPACER 



PREAMP CAVITY (15 PS lA) 



6000 psi 




V 



ASSEMBLY STAGES-FIXED ACOUSTIC BUOY HYDROPHONE 



26 



The FAB hydrophone is sufficient to its task 
and showed no change in sensitivity with pres- 
sure to 9000 psi and has since performed effec- 
tively over the last 9 months. However, its 
sensitivity was not all one would wish and its 
upper frequency limit was too low for many 
applications. We therefore embarked on a 
hydrophone development program utilizing the 
same basic equalization system but seeking 
ways to increase the sensitivity and to drive 
down the Helmholtz Resonance and to increase 
the basic cylinder resonances. The design of 
one of the resulting hydrophones is shown in 
slide 3 and whose response is shown in slide 4. 
As can be seen, this hydrophone is quite an 
improvement on the FAB unit. The use of a 
very small orifice and a smaller cavity reduced 
the frequency of the Helnaholtz Resonance. The 
sensitivity of the unit was increased while the 
cylinder size was reduced by decreasing the 
wall thickness. The upper resonance was raised 
by use of a shorter cylinder and aluminum end 
caps. We also feel we get some increase in 
sensitivity by the end caps acoustically coupling 
to the cylinder ends. 



PROJECTOR DESIGNS 

The projectors I shall discuss are of the 
pressure equalized segmented cylinder type. 
The MBP-1 represents the first real experience 
with the design of an acoustic projector for a 
very high pressure ambient. Projector design 
is in general a more difficult problem than 
hydrophone design because of the necessity for 
good efficiency. This is especially true in the 
case of deep transducer design where the back 
radiation is a problem. In the case of the 
MBP-1 our approach was to take a transducer 
mechanism which is basically efficient (namely 
the large cylinder made up of staves polarized 
and energized in the circumferential direction) 
and accept the losses which the lack of pres- 
sure release on the inside of the cylinder 
causes. This was done because of the need 
for this transducer to series of experiments 
we carried out with the Naval Research Labora- 
tory under the direction of Mr. Benhannan. 
The cylinder was 20 in. OD, 9 in. high with a 
1 in. wall thickness; the inside was filled with 
castor oil, the top and bottom plates of the 
cavity were 1/4 in. steel. The unit is shown 
in slides 5 and 6. The response of this unit 
is shown in slide 7. The efficiency of this 
unit, about 6 0%, indicates that the back wave 
and the lack of pressure release causes us no 
significant problem. The calibration of this 
unit at 1000 psi shows no change from shallow 
water measurements and, at sea measure- 
ments at depths up to 12, 000 ft showed no 
change in response within the accuracy of 
measurement. One of the MBP-1 units has 
been operated for more than 150 hours at 
depths exceeding 10, 000 ft. At the end of this 
series of tests the unit was recalibrated and 
shows no sign of deterioration either acoustical 
or mechanical. We feel that the attainment of 



such high efficiency in a unit of such simple and 
reliable design whose performance is independent 
of depth is a significant step forward in trans- 
ducer design. 

The MBP-2 is an improved version of the 
proven techniques of the MBP-1 and is shown 
in slides 8 and 9. It was designed and built by 
The Martin Company under contract to the 
Bell Telephone Laboratories. As can be seen 
from the slide, it uses two rather short rings 
4 in. high 0.4 in. thick and 20 in. in diameter. 
These rings are contained in separate water- 
tight housings. The thinness of the rings has 
two main effects on the performance. It lowers 
the mechanical Q and decreases the resonance 
frequency since the mass loading effect of the 
medium is a more significant part of the 
vibrating system mass. These effects can be 
seen in slide 10. Even though the circumference 
is the same as that of the MBP-1 the frequency 
has dropped to 1900 cps and the mechanical Q 
is only two. The efficiency has dropped to 35% 
because of the power loading at the lower 
frequency. Stacking more than two rings should 
improve the loading and therefore, the efficiency 
appreciably. A single ring by itself has an 
efficiency of only 20%. Slide 11 shows the 
efficiency of the MBP-2 as a function of fre- 
quency. The smooth response and low Q shown 
in slide 10 lead to a transducer which has a 
useful efficiency over a broad frequency band 
making it of real value as a general purpose 
sound projector. This is especially true when 
one considers that they can be stacked in the 
vertical to get higher efficiency, better power 
handling and some directivity. The calibration 
of this unit has been checked at 1000 psi with 
no change in characteristics and it is expected 
that it will be as insensitive to depth as was the 
MBP-1. 



CONCLUSIONS 

We have reviewed the design of a number 
of transducers which are suitable for operation 
at great depth. Two of these have operated at 
depth for appreciable time. The design of 
transducers for this environment presents 
problems new to the transducer designer none 
of these problems.however, are insuperable. 
By the application of known transducer theory 
and by careful testing under pressure, we feel 
that the problem deep transducer design can 
be placed on as firm a foundation as present 
day shallow transducer design. We have con- 
fined our remarks to a cylindrical ceramic type 
but there are several other configurations under 
development which fit other needs and appli- 
cations. 



27 



LOCATION OF UNDERWATER OR SURFACE SOUND SOURCES BY 
MEANS OF COMPUTER- LINKED CABLED- HYDROPHONE FIELDS 

by JAMES H. MORRISSEY, Engineering Specialist 
Philco Corporation 
Philadelphia, Pennsylvania 



ABSTRACT 



A method Is described whereby 
the position (xyz) of a sound source 
already detected by multi-otatic 
sonar field of hydrophones may be 
determined, from observed time delays, 
by means of a data processing algo- 
rithm involving pre-eolution of two 
redundant systems of linear simulta- 
neous equations. Geometrically this 
algorithm, now designated MULCAP 
(MUlti-etation Linear CArteslan Po- 
sitioning)^, may be interpreted as 
sound-source location by means of 
intersecting planes. The direction 
cosines of these planes are deter- 
mined only by the hydrophone-field 
configuration; they are independent 
of the position of the sound source 
and of its velocity. 



INTRODUCTION 



During pre-proposal effort on 
undersea surveillance systems, there 
was developed, early in i960 by the 
Advanced Systems Group of the Commu- 
nications and Weapon Systems Division 
of Philco Corporation, the new geom- 
etry-oriented data-processing technique 
since designated MULCAP. Although 
this new data-processing technique is 
believed to have potential applica- 
bility to many systems, radar and 
sonar, existing or proposed, involving 
acquisition or tracking of trans- 
mitting or reflecting vehicles, its 
first implementation with realistic 
Input data has occurred in connection 
with a proposed precision underwater 
tracking system. An error analysis 
of MULCAP, with particular emphasis 
on errors attributable to refraction 
effects peculiar to the ocean medium, 
is now being carried out by Philco 
Corporation under contract with the 
Naval Underwater Ordnance Station, 



at Newport, Rhode Island. 

The vehicle located by MULCAP 
methodology is assumed to be a source 
of sound in either of two senses: 
(1) it may carry a transmitter, by 
design or by necessity; (2) it may 
reflect a transmitted signal. In the 
former case the inputs are the differ- 
ences in arrival time among the n 
fixed receiving stationsChydrophones) . 
In the latter case, where the n 
stations are assumed to consist of p 
transmitters and q receivers, the 
inputs are the pq possible transmitter- 
to-vehlcle-to-recelver propagation 
intervals. The first case is desig- 
nated the "passive* mode; the second 
case, the "active" mode. 

Before the advent of MULCAP, 
systems appropriate to Its passive 
mode were known as "hyperbolic systems* 
because the mathematical routine 
whereby the transmitter was located 
involved the simultaneous solution of 
quadratic equations representing hyper- 
bolas or hyperbololds, respectively, 
for plane or space applications. 
Systems appropriate to its active mode 
("pinging", for example) were known, 
before its advent, as "elliptic 
systems" because the mathematical 
routine for determining position 
coordinates of the reflecting vehicle 
consisted of the simultaneous solution 
of quadratic equations representing 
ellipses or ellipsoids, respectively, 
for plane or space applications. 

MULCAP makes it possible to 
eliminate completely from the multi- 
station vehicle-location routine the 
simultaneous solution of quadratic 
equations. In situations where the 
hydrophone configuration effectively 
spans the surveillance space, MULCAP 
locates the vehicle by a completely 
linear process. I.e., by a series of 
matrlx-by-vector multiplications. On 
the other hand, in those situations 
where physical or economic factors 
prevent effective spanning of the 
surveillance space, MULCAP' s linear 



Superior numbers refer to similarly numbered references at the end of this paper. 



28 



procesB yields, by Itself, the pro- 
jection of the sound source's location 
on whatever sub-space Is effectively 
spanned. For example, If the hydro- 
phones constituting the "front end" 
of a sonar surveillance system must, 
for reasons of economy, be mounted 
on a flat portion of the ocean bottom, 
then MULCAP yields by Itself merely 
the projection on that bottom of the 
sound source's location. In this 
case, however, a supplementary routine 
Involving n square-root operations Is 
employed to obtain the necessary 
depth (z) coordinate from the already- 
known (xy) coordinates; the supple- 
mentary routine does not Involve the 
simultaneous solution of quadratic 
equations. MULCAP abolishes the 
latter process from all multi-static 
location systems; In so doing it opens 
the way to much more rapid computation 
of vehicle location. It also elimi- 
nates entirely the need for rejection 
of false roots of quadratic equations. 

By virtue of the greater speed 
of a MULCAP system (resulting from 
its exclusive use of linear equations), 
and of the related convenience and 
ease with which such a system can be 
established, augmented, and calibrated, 
data from many hydrophones can be 
processed almost as easily as that 
from a minimum number. Precision of 
vehicle location is directly dependent 
on the number of hydrophones in the 
field. Thus any desired accuracy can, 
in principle, be obtained, provided 
the economics of the situation permit, 
merely by increasing the number of 
hydrophones to a suitable value. 
Five non-co-planar hydrophones con- 
stitute a useful minimum for three- 
space applications; four non-co-llnear 
hydrophones constitute a useful mini- 
mum for planar applications. MULCAP 
is, however, a location system based 
In a fundamental sense on the exploi- 
tation of redundancy; minimal config- 
urations are, therefore, not to be 
encouraged. Because of the impor- 
tance of redundancy to optimum util- 
ization of MULCAP, the principle of 
least squares plays a central role 
therein; ten or more linear equations 
(equations of planes) must be utilized 
in order to determine three Cartesian 
spatial coordinates; six or more 
linear equations (equations of lines) 
must be utilized in order to determine 
two Cartesian planar coordinates. 



GEOMETRIC INTEEiPRETATION 



The "families" of planes or lines 
(more generally, of linear loci) which 
are utilized in this method of sound- 
source location are, each of them, 
associated with a distinct transducer- 
hydrophone or hydrophone-hydrophone 
pair, depending on whether the active 
mode or the passive mode is under 
discussion. If a field of p trans- 
ducers and q hydrophones is utilized 
to locate a reflecting vehicle, there 
are pq families of planes. Similarly 
if a field of n hydrophones only is 
used to locate a transmitting vehicle, 
there are ^n(n - 1) families of planes. 
Each member of a family of lines, or 
planes, is parallel to every other 
member of the same family; thus each 
member has the same set of direction 
cosines as every other member, that 
set determined by a line Joining the 
two members of a pair of field elements. 
A vehicle, transmitting or reflecting, 
in the surveillance space, is located 
by the common Intersection of a set 
of planes, a "locating cluster", 
consisting of one plane from each of 
the families. 

Only in a completely noise-free 
situation will the intersection of the 
planes, or lines, in the locating 
cluster be "clean", i.e., only then 
will all these planes pass through a 
single point. A residual sum-of- 
squares measure of the departure of 
the planes in the cluster from a 
unique common intersection provides a 
measure of the precision of vehicle 
location. In a noise-free situation, 
this measure is zero. 

A crucial step in the series of 
arithmetic operations which consti- 
tutes 14ULCAP, is the computation of 
the critical, or true, value of "mean 
range" (the sum, divided by n, of the 
n ranges from the vehicle to the n 
hydrophones) . This quantity may be 
thought of as a variable parameter; 
its critical value is that value which 
minimizes the residual sum-of-squares 
value referred to above. 



ALGEBRAIC FORMULATION 



Since, in the development of a 
satisfactory precision undervrater 
tracking system, toward which this 
presentation of MULCAP is oriented, 
vehicle acquisition is not a major 



29 



problem, the presentation of the 
acqulBltion-loop portion of MULCAP 
will be omitted. Furthermore, for 
the sake of brevity, only >fULCAP'3 
passive mode will herein be presented 
In detail. 

Let there be known an n x 1 
vector dQ whose n elements are the n 
ranges to the vehicle from the n 
hydrophones each diminished by their 
common mean. Let the squares of these 
n elements constitute the n elements 
of bo. Matrices bg and do contain 
the information derivable from tirae- 
of-arrlval data of the sort assumed 
for passive-mode MULCAP. The initial 
lack of knowledge of the vehicle's 
true n ranges is reflected in the 
inltiai, quite arbitrary, assumption 
that their mean value is zero. 

Let N be an n X 3 matrix whose 
elements are the doubles, In (xyz) 
order, of the n hydrophone coordinates. 
Let the 3 x m matrix M denote the 
conditional inverse of ZN, where Z is 
a systeTiatic differencing matrix of 
order m x n, where m <s gnCn - 1) . 
Let the n elements of the n x 1 matrix 
r denote the n distances, squared, 
from the origin to each of the n 
hydrophones. 

It is assumed that the field 
characteristic n x n matrix F defined 
as follows: 

(1) F = z'^z - zTzn{n'^z'^zn)-1n'^z'^z, 

Is stored in the computer. 

The mean range pQ to the vehicle 
is computed by means of the formula: 
T. 



(2) /=>■ 



= do'F(r - bp) 
2do'^Fdo 



Let the 3x1 matrix pp be com- 
puted by means of the formula: 

(3) Po = M2(r _ bo) . 

Pc,a 3 X 1 matrix whose three 
elements are respectively the best 
estimates available of the Cartesian 
coordinates of the position of the 
sound source, is, finally, computed 
as follows: 

C^) Pc = Po - (2/>c)MZdo . 



CONCLUSION 

When the locations of underwater 
sound sources near the surface are 
computed utilizing a MULCAP routine 
based upon equations (1), (2), (3), 
and (4) above, from simulated data 



obtained with a velocity profile 
representing the real-ocean medium at 
depths of 6000 feet and with bottom- 
mounted hydrophones with base lines 
up to 10,000 feet, in hexagonal con- 
figuration, the precisions attained 
are better than one part in 10 . 



REFERENCE 



1. Korrissey, J. H., MULCAP, Philco 
Tech Rep Division Bulletin , Vol. 11, 
No. 2, March-Aoril, I96I • 



30 



EFFECTS OF THE SPECTRAL COMPOSITION OF RANDOM 
THERMAL VARIATIONS ON PHASE AND AMPLITUDE 
FLUCTUATIONS OF A SOUND WAVE PROPAGATING IN THE SEA 

by AIMO SALENIUS 
Sperry Gyroscope Company 
Great Neck, New York 



ABSTRACT. 

Equations are derived for the spectral densities of 
the phase and amplitude fluctuations, as well as the mean 
square fluctuation of the wave front normal direction in 
terms of the spectral density of the index of refraction 
variations for the wave of a harmonic point source in a 
slightly random medium whose mean index of refraction 
is constant. Since in the sea the spectral density of the 
refractive index fluctuations is, for all practical purposes, 
determined as a multiple of the spectral density of the 
thermal variations, the equations permit the study of the 
effects of the spectral composition of the random thermal 
variations over various space wavelengths in order to 
determine the sampling distances required to obtain rel- 
evant statistics of the thermal variations. 

I. INTRODUCTION. 

The phase and amplitude fluctuations of a sound 
wave propagating in the sea have considerable effects 
on reducing the quality of performance of sonars. The 
phase fluctuations contribute to bearing errors while the 
amplitude fluctuations create difficulties in detection and 
signal processing. It is well known that a major portion 
of these fluctuations are caused by the random thermal 
structure of the sea which causes the speed of sound to 
vary randomly from point to point in the medium. 

In the following analysis we shall assume that the 
mean temperature is known throughout the medium and 
that the fluctuations about the mean are stationary to the 
second order. Furthermore, in order to make the problem 
tractable we shall also assume the random field of the 
temperature variations to be homogeneous and isotropic. 
A better characterization of the temperature variations 
would be to consider them axisymmetric about the depth 
axis, however, the additional complexities would not 
significantly contribute to the qualitative aspects of the 
results. 

One may consider the thermal variations as con- 
sisting of a continuous distribution of periodic variations 
of random amplitudes over various space wavelengths, or 
component sizes. The average power of the fluctuations 
can be represented by means of a continuous distribution 
of power density over the various size components. This 
is achieved mathematically by the Fourier transform of 



the autocorrelation function of the temperature variations. 
The resulting power density spectrum will be simply re- 
ferred to as the spectrum of the thermal variations. For 
small variations of temperature, neglecting the effects of 
the extremely small variations in salinity, the power den- 
sity spectrum of the index of refraction variations is de- 
termined as a multiple of the power density spectrum of 
the thermal variations. Thus, when we refer to the spec- 
trum of the index of refraction variations we are also re- 
ferring to the spectrum of the thermal variations. 

We shall be concerned particularly with the effects 
on the phase and amplitude fluctuations of the manner in 
which the power of the thermal variations is distributed 
among its various size components. Knowing the effects 
of the thermal fluctuations of various size components, 
it will be possible to plan experiments for gathering the 
statistics of the temperature variations such that they 
will be useful in the study of sonar performance. In par- 
ticular, it will be possible to determine the smallest sam- 
pling distances required to secure adequate statistics. 

Since target bearings obtained by correlation sonars 
are determined by measuring the orientation of the wave- 
front, we shall also investigate the effects of the spectrum 
of the thermal variations on the mean square fluctuation 
of the direction of the normal to the wave front in order 
to get a measure of sonar bearing accuracies. 

In most sonar applications the sound source is 
considered as a point source and the sound field is very 
nearly spherical. For this reason we shall study the case 
of a harmonic point source in a medium whose mean index 
of refraction is a constant. Furthermore, since correla- 
tion sonars are concerned primarily with the correlation 
of signals along a base line transverse to the direction of 
wave propagation, we shall concern ourselves with the 
spectra of the transverse phase and amplitude fluctuations. 

Tatarski^ has analyzed the problem of the mean 
square fluctuation of phase and amplitude at a point in 
the field of a point source in a random medium whose 
mean structure is constant. The results herein are ob- 
tained by a modification and extension of the approach 
used by Tatarski in order to determine as well the trans- 
verse phase and amplitude spectra, and the mean square 
fluctuation of the wave front normal direction. 



31 



II. PHASE AND AMPLITUDE FLUCTUATION SPECTAA . 

We shall assume the vave length of the 
soond to be very much less than the dimensions 
of the smallest size component of the thermal 
rariations. We shall also assume that the 
source is located at the origin of the co- 
ordinate system. Folio-wing Tatarski ve maj 
express the fluctuations of the phase and the 
logarithmic amplitude ( hereinafter simply 
termed the amplitude fluctuation) at th« plane 
X o L bj means of the stochastic Foarier- 
Stieltjes integrals} 



Sj(L,y,z) - S - S^ 



JI 



i(K2y+K3z) 



dsCKg.Kg.L) (1) 



and 

B(L,7,z) - log(A/A„) 



+eo 



i(K27+K3Z^ 



daCK^.KgjL) (2) 



with random complex amplitudes ds and da. 

In particular, the correlations of the 
phase and amplitude fluctuations at the points 
(L,r/2,0) and (L,-r/2,0) using (1) and (2) are 
given Iryt- 



Bg(r)- Sj(L,r/2,0)Sf(L,-r/2,0) 



II 



i(K2+Kp(r/2) 



ds(K2,K3,L)ds»(K',K^,L) 
(3) 



and 



R^(r)- B(L,r/2,0)B«(L,-r/2,0) 



+Q0 



i(K +K')(r/2) 

e " da(K2,K3,L)da«(K«,K«,L) 

(4) 

where the star (*) denotes the complex 
conjugate. . 

Using equation (9.17) in Tatarski and 
its analog for the correlation of the ampli- 
tudes of the random phases, we get 

* -oo o O 1 

P [^"2^ '^'' I ll 

^n[-'^.K-2|J 
cosFm^^l!!!] co.Kii:^" 

■'"L 2kx^ J "-[ 2kxf . 



X F„ 



X exp[iiK2(l + xg/xj)] 



(6) 



where F„ denotes the two dimensional spectral 



density of the index of refraction fluctuations 
and k denotes the wave number of the sound. We 
observe that the correlation functions are sym- 
metric abount the origin in the pleine x « L. 
Using polar coordinates and employing the simpli- 
fying approximations used by Tatarski, equation 
(S) may be reduced to 

■hOO 



V""^- 4rrV f dltK^„(K) 



a^(r) 



where (^i^(K) is the three dimensional spectrum 
of the index of refraction variations. 
If we let X « (L£:')/k in the inner 
integral of (6) and interchange the order of 
integrations we get 

+00 



Rs(r). 



4rr^k 



^/ 



K dK J-(KL) 



*eo o 



'^ I^r^^'''^ Zl^b'^'^^M'^ ^'^ 



where K and K* have been interchanged. 
Now, since 

4-00 



h^''K 2rf f J (Kr) 



Fs(k) 

F^(K) 



KdK 



(8) 



where Fe(K) and F.(k) are the two dimensional 
spectra of the phase and amplitude fluctuations, 
then comparing (8) with (7) we have 



^S^'^). 



2T»'k 



Fj^(K) 



*0O ^2 

K (9) 



Defining 



K 



f zrriL 2-n- 

^ "VxT 



as the process wave number , and writing 



and 



K*- K 



we may express (9) finally as 
o +i 



Fg(n) an-k-L 
F^(n)" ■ 



J|J^(n.* n) "%[nn.1»'] 



dn* 



(10) 



Given the three dimensional spectrum of 
the index of refraction variations, equation 
(10) may be used to determine the spectra of 
the transverse phase and amplitude fluctuations. 
If the results are inserted in equation (8) 
we may also obtain the correlation functions 
of the transverse phase and amplitude fluctua- 
tions. 



32 



Ill, MEAM SQUARE FLUCTUATION OF TH£ WAVE FBONT 
MOBMAJ DIRECTION (BEABIMG FLUCTUATION)! 
If ve consider the phase at tvo points 
(L,r/2,0) and (L,-r/2,0) where r«L then the 
angle ^ made by the normal to the intersection 
of the " wave front at (L,0,0) and the plane 
z = and the x axis is given approximately by 

S,(L,r/2,0) - S,(L,-r/2,0) 
•.« -i ^ (11) 

Similarly, the angle made in the plane y » 
is given approximately by 

Sj(L,0,r/2) - Sj(L,0,-r/2) 



^« Tk 



(12) 



If the angles fr and (^ are small, then the 
angle ^ between the ^normal to the wave front 
at(L,0,0) and the i axis is given by the 
relationship 



»^» *y + »Z • 



(13) 



Squaring (11) and (12), substituting in 
(13), averaging the sum and noting that 



[Sj (L, r/2,0)]^ ■ [s^(L,-r/2,0)]' 



[Sj(L,0,it/2)]^ - [Sj(L,0,-r/2)]' 



and 



Sj(L,r/2,0)Sf(L,-if/2,0) . 



Sj(L,0,r/2)Sj(L,0,-r/2) 



(I3) becomes 



S-^^|^[s,(L,r/2,0)]^- 

Sj(L,r/2,0)Sf(L,-r/2,0)l. (14) 



If r is very small, then 



4 



(15) 



[Sj(L,r/2,0)] « [sj(L,0,0)]2 _ ^^^^^ 
whence (14) becomes 

As r-^O (15) becomes an equality or 

Using equation (6), we may write (16) as 



X fiw Ml 



e o 



X co« 



Carrying out the limiting o^ration we get 



» 



2 47> 



•LK3^,(K)/xWrii^]dx. 
o (18) 



Evaluating the inner integral and making the 
substitution n m e/K where K is defined 
above, (18) becomes 



■¥(», 



,2 TT IK, 



o 

+ Moos R7rn^C(n)+8iDri»'n^]s(n) 

^U«8[i7rn^]s(n)-sin[j»rn2]c(n)|| 

X n^ ^jj(n) n do (19) 

where C(n) and S(n) are the Fresnel integrals. 



IV. EFFECTS OF THE COMPOSITION OF THE INDEX 
oFIcthACTION SPECTRUM (THERMAL SPECTRUM) . 
From the theory of isotropie-turbnlent 
scalar fields the thermal spectrum, or the 
index of refraction spectrum, can be repre- 
sented approximately by a Yon Karman type 
interpolation formula, or 

2 sRVe) 

'^^^"^"'^ e7^^3/2)p(^/3)^3J^^(^^J2/^2■|(^l/«) 

> t n>n. , 

where n. is the wave number of the smallest size 
component of the refractive index fluctuation* 
in terms of the process wave number and^^ia the 
Ems fluctuation af the indt^x of refraction 
variations. Fig. 1 shows the plot of the spectrum. 

Although the spectrum of the thermal 
variations in the sea may not correspond exactly 
to that of an Isotropie-turbnlent scalar field, 
the use of the above approximation should result 
in reasonably good qualitative relationships 
between the thermal spectrum and the spectra 
of the phase and amplitude fluctuations, especi- 
ally over the small size components. In any 
event, should the spectrum be considerably 



33 



<^N(n) = M 



'2r(|/3)K3 r| + (J^^)2lll'« 



4,f,M 




FIG. I -SPECTRUM OF THERMAL VARIATIONS 
APPROXIMATED BY VON KARMAN 
INTERPOLATION FORMULA 




FIRST MAX OF f^(n, n') 
2n ') FIRST MIN OF f^. (n,n') 



FIG. 2 -PLOT OF FIRST MAXIMUM OF U (n,n' 
FIRST MINIMUM OF fj (n,n ) 
AND TERMINAL POINT OF THE 
SPECTRUM FUNCTION (^N (n) 



34 



different fron the assumed approximation, the 
Analysis herein presented can be similarly 
applied to any other spectrum. 

We shall examine the two cases: 



Case I 1 


K,<Kp or 


Dj < 1, and 


l>i8e lit 


Kp>K, or 


1 < n^. 


Writing 




, 2 
1 cos r_ 

n .2 1" 
sin 



fnn'W J 



then from equation (10) the spectra of the 
phase and amplitude fluctuations may be 
written 



FgCn) 
F^(n) 



2rrkhf^Ju'+n) 's<°'"'^ dn'.(2l) 
J Vn.n.) 



For each value of n the integral in (21) deter- 
mines the contribution to the power density 
spectra F„(n) and F.(n) of the power density 
from the various ware numbers of ^„(n). It is 
observed that as n increases the function 
^y,(a'+ n) is shifted to the left on the n' axis. 
Also, as n increases the period of the functions 
f„(n,n*) and f,(n,n*) increase with respect to n*. 

The first minimum of f„(n,n') 6ind the first 
maximum of f (n,n') for a given n occur when 
n'= l/(2n), 'Srhile the spectral function (^^.(n'+n) 
will terminate at n'~ n.- n. If both of these 
points are plotted against n for case I and 
case II the results would appear as shown in 
Fig. 2. 

From the figure we see that for case I 
the first minimum of f„(n,n') and the first 
maximum of f.(n,n') on the n' axis will occur 
'at higher vaTues of n' than at which the 
spectral function ^ (n'+ n) terminates. 
Fig. 3 illustrates the relationships that 
exist between ^„(n'-t- n) and the functions 
f (n,n') and f (n,n') for case I. For these 
relationships we note that 



fs(»"">* f 



and 



f^(n,n')2: 



,.2 



TT 



8 



For the integrand involving f_(n,n') the 
maximura will fall near the origin or at low 
values of n'. For small n the contributions 
will come from the large size components of ^„ 
For large n the contributions will come from 
the smaller components of )^^, however, their 
effects will be considerably less since ^„(n'+n) 
is less in value and f„(n,n') falls off as 
n ^. 

Since ^j,(n«+ n) is nearly constant at 
the origin and increasingly decays until the 
rate is proportional to the -11/3 power of 
n' over the larger values of n'<n.- n, the 
integrand in (2l) involving f.(n» i' ) »ill 
have a maxinnim on the n' axis oetween the 



middle to large values of n'<n - n for 
.small values of n and at small values of 
n' for large values of n. Thus, the chief 
contributions will occur from the middle 
to small size components of ^jj. 

For case II we see from Fig. 2 that the 
first minimum of f (n,n') and the first max- 
imum of f (n,n') will generally occur at 
values of^n* much smaller than the value 
n - n at which the spectral function )J„(n*-fn) 
terminates as shown in Fig. 4. For both inte- 
grands the maximum for most values of n will 
occur over the large size components of the 
spectrum (^ , especially for the integrand 
in the formula for the phase spectmm which 
has its maximum at n*a 0. For the integrand 
involving the function f (n,n') the maximum 
will tend to lie over the range of large to 
middle size components of ^^. The effects 
of the small size components as n increases 
is reduced by the fact that the average 
values of f (n,n') and f (n,n') fall of as n . 
It can be shown by examples that the max- 
imuffl contributions to the amplitude fluctu- 
ation spectrum will come from components of 
)» whose dimensions are of orderVXL . 



"N 



We shall now examine the effects of the 



spectrum ^„(n) on the mean square fluctuation 
of the wave front normal direction. Defining 
the term in the curled brackets of the inte- 
grand of equation (19) as fQ(n) 'o aaj write 
equation (19) as 

"^ - iir^lX* yt^(n) n^ )^^(n) ndn. (22) 

o 
Pig. 5 shows the relationships between the 

spectral function f^»(u) and the function f^(n) 
for case I. We observe that in this case 
f (n)^5; 8/3. Since ^jj(n) decays as n to the 
-T1/3 power over the higher wave numbers, the 
integrand of (22) will be a maximum over the 
largest size components of the spectrum ^ , 
However, comparing this with case I for 
the phase fluctuations we observe that the 
contributions from the smaller size components 
of )> are more significant for the wave front 
normal fluctuations because of the presence of 
the additional term n^. 

Fig. 6 shows the relationships between 
f.(n) and ^„(n) for case II. Except in the 

vicinity of very low wave numbers, the function 
'«(") *^ 4/3. Thus, the maximum contribution to 
the mean square fluctuation of the wave front 
normal direction will come from the large size 
components of |l„. 



V. CONCLUSIONS . 

1. The small components of the thermal variations 
principally affect the spectmm of the amplitude 
fluctuations when the smallest comp one nt of th« 
thermal variations is greater thanVXL. The 
manner in which the small componentrs affect the 



35 



-fj(n,n')= fj cos^ Cnn'TTD 




FIG. 3-CASE h nj-ri, RELATIONSHIPS 
BETWEEN (I),^(n'i-n) AND THE 
FUNCTIONS yn,n') AND fg(n,n'). 




FIG. 4- CASE II' n|>li RELATIONSHIPS 
BETWEEN .^N^n'+n) AND THE 
FUNCTIONS fftCn.n') AND fgCn-n") 



36 



ln)--|- 



J4 I 



C0S(^^C(n)4•SIN(^^S(n) 



COS(^')S(n)-S:N(^)C(n) 




FIG. 5 -CASE I: n,<l ; RELATIONSHIP 
BETWEEN *N(n) AND tg (n) 



COS(^^)C{n) + SIN(^)S(n) 



-K COS(-^)S(n)-SIN(- 




FIG 6- CASEi:n,>l; RELATIONSHIP BETWEEN 
<^,^ (n) AND fe(n) 



37 



spectrum of the amplitude fluctuations depends 
strongly on the decay rate of the thermal vari- 
ation spectrum over the small components, or 
high space wave numbers. 

2. When the smallest component of the thermal 
variations is less thanVXL ( as is generally 
the case in sonar ), the n t he components whose 
dimensions are of order'VAL have the greatest 
effect on the spectrjim of the amplitude fluctu- 
ations. As an example, at a range of 4000 yards 
at 20 kc. the thermal variations of dimensions 
of the order of 18 yards have the greatest 
effect on the amplitude fluctuations. This 
implies that in order to gather the statistics 
of the thermal variations which most affect the 
(usplitnde fluctuations the temperatures must 

be sampled over distances less than 18 yards. 

3. The spectrum of the phase fluctuations is 
principally affected by the large size components 
of the thermal variations, while the mean square 
fluctuation of the wave front normal direction 

is principally affected by the large to middle 
size components. 

4. Should the form of the spectrtui of the 
thermal variations differ considerably from 
the one used in the analysis, represented 

by the Von Karman interpolation formula, the 
conclusions reached above may differ consider- 
ably, especially for the amplitude fluctuations 
which are most sensitive to the form of the 
thermal variation spectrum. Thus, measurements 
are needed to establish the form of the thermal 
variation spectnun, which requires making 
measurements over small as well as large 
distances. 

6. In order to overcome the effects of phase 
and amplitude fluctuations, statistical pro- 
cessing of sonar signals seems in order. If 
the random thermal structure changes rapidly 
in time then a good statistical sample of 
target bearings can be obtained which when 
processed will reduce the errors due to 
the fluctuations. This implies that all the 
component sizes in the thermal variations 
change rapidly in time. It is more likely, 
however, that the larger components will 
vary more slowly in time than the smaller 
components. Under this condition, it becomes 
necessary that the statistics of the thermal 
variations in time also be investigated in 
order to establish the effectiveness of 
statistically processing the fluctuating 
sonar data. 



REFERENCES . 

1. Tatarski, V.I., "Wave Propagation In A 
Turbulent Medium", McGraw-Hill Book Co., Inc. 
New York, 1961. 

2. Hinze, J.O., "Turbulence, An Introduction 
to Its Mechanism and Theory", McGraw-Hill 
Book Co., Inc., New Tork, 1969, Chapter 3. 



38 



A TELEMETERING THERMOMETER 

by DR. ANGELO J. CAMPANELLA, Senior Physicist 

HRB-Singer, Inc. 

State College, Pennsylvania 



ABSTRACT 

A temperature transducer for temperature 
measurement at depth for a radio telemetering 
link from a drift buoy has been developed. The 
nominal design depth is 200 meters for the 
transducer. It has an accuracy of 0. 1 C or 
better depending on radio link quality. The 
system is operational and has been tested at 
shallow depths, approximately 4 meters, by the 
Woods Hole Oceanographic Institute. 



INTRODUCTION 



1 



Radio drift buoys currently in use provide 
a means for tracing the motion of surface waters 
in the open sea. No information concerning the 
identity of the water in which the buoy rests at 
the moment of observation is available other than 
that accumulated from past sampling. In drift 
experiments it is important to know whether the 
buoy has remained with the water mass in which 
it was deposited or conversely to know some 
parameter of the water immediately under it. 
Surface temperature is relatively meaningless 
due to environmental influences. The tempera- 
ture at a depth of 200 meters is suitable for the 
purposes of identification since it lies below the 
daily, and most seasonal, influences. A length 
of multi-conductor cable that is suitable for 
suspension at this depth is well-logging cable. 
The temperature can be measured to 1°C or 
better depending upon the radio link signal-to- 
noise ratio. The unit has been laboratory 
calibrated from 0° to 30°C and is repeatable to 
within . 03°C. The response time for a temper- 
ature excursion from room temperature to 0°C 
is about one minute for 2% full scale accuracy 
and about one hour for the remainder, all within 
calibration accuracy. The longer lag is due to 
the temperature coefficient of the Mylar ca- 
pacitors in the Wien Bridge. The response 
time can be reduced to a few seconds by simple 
design improvements. 



COMPONENT DESCRIPTION 

BUOY 

The drift buoy developed by Franz, Walden, 
and Ketchem is shown in Figures 1 and 2. 
Figure 3 is a block diagram of this system. In 
its quiescent state the receiver is tuned to a 
radio frequency of 2398 KC. When a radio 
signal modulated by the proper audio tone is 
picked up by the antenna, one of two resonant 



reed relays is actuated, depending on the par- 
ticular tone, and a sequence of events then 
occurs. If the first relay is actuated, the call 
sign of the buoy is transmitted in international 
morse code in A-1 emission(CW), followed by a 
long dash. If the second relay is actuated by the 
proper tone, either a long dash, or some special 
signal is transmitted. 

For the telemetering thermometer application 
this buoy was used in a slightly modified form 
which included the attachment of a temperature 
transducer. The mode of transmission was 
changed to F-1 (frequency shift keying). The 
mark-space rate of shifting was made to depend 
on the temperature at the depth of the transducer. 
FSK modulation is used due to its FM-like noise 
rejection and good anti-fade qualities. 

To effect F-1 modulation of the transmitted 
signal, several components were added to the 
crystal oscillator circuit. See Figure 4. A 300 
picofarad capacitor was placed between the 
2398 KC crystal and ground. The final R. F. stage 
is allowed to run continually, and the diode across 
the capacitor self biases itself to a high im- 
pedance. When the keying contacts close, the 
diode CR2 no longer can bias itself and conse- 
quently shorts the 300 picofarad capacitor. The 
carrier frequency is then shifted 140 cps lower 
in frequency. Crystal diode CR3 and the . 001 
capacitor isolate the circuits from the keying 
leads, and hence remote keying is possible. To 
produce conductance switching, a transistor can 
adequately replace the relay in this operation. 



TRANSDUCER SUSPENSION 

Short length of BT wire is used for suspension 
of the pressure case for shallow water so that no 
mechanical support is required from the con- 
ducting cables. See Figure 2. No difficulty is 
anticipated for the 200 meter suspension es- 
pecially since it comprises not a mooring but 
merely a suspension for the pressure case plus 
whatever weight is needed to maintain a suitably 
vertical wire angle in the presence of current 
shear. Extra flotation may be required at the 
surface buoy to support this. 

Electrical leads were brought through the 
heavy top plate by water-tight connection and a 
joint made with a Joy 3-prong connector. A 3- 
conductor cable ran down to the temperature 
transducer and terminated in a Joy single contact 
pressure connector. Although a sea return or 
suspension cable could have been used as one lead. 



39 




Fig. 1 - Buoy with Temperature Transducer 



•■—ANTENNA 



3 CONDUCTOR JOY PLUG 



DRIFT BUOY- 



f 



-FLEXIBLE CORD 



|4',APPR0X, 



^ 



BT WIRE-» 



PRESSURE CASE- 



& 



[•—FENDER 



THERMISTORS IN 
END CAP 



Fig Z - Buoy - Temperature Transducer System 



40 



24 -volt 
Battery 



High 
Voltage 



Keying 
Unit 



Trans- 
nnitter 



Relay 
Unit 



Whip 
Antenna 



Antenna 
Relay 



-Power 



-AAAr- 



Current 

Limiting 

Resistor 



Mode 
No. 1 
Reed 



Mode 
No. 2 
Reed 



Signal 



Receiver 



Receiver 
Battery 



o 



Temper- 
ature 
Sensor 



Fig. 3 - Buoy Block Diagram 
41 




PI 

o 

nl 
o 



O 



o 
pq 



Q 



60 

•r-f 



u 

m 

C 
oi 

H 



W 
r- 

•* 



42 



it was chosen not to do so to ensure good reliable 
contacts. The signal circuit impedance is about 
500 ohm.s so that small conductance cable leaks 
will not adversely affect performance. 



TEMPERATURE TRANSDUCER 

The transducer pressure case contains 
thermistors imbedded in the lower end cap. 
See Figures 5, 6, and 7. The transistorized 
electronic oscillator and the Zener voltage 
regulator diode are attached to the upper end 
cap. The buoy's 24v batteries are used to 
power the temperature transducer through a 
dropping resistor. In the event that a short 
circuit occurs in the cable, only about 0. 1 
amps will flow through the resistor. This is 
small compared to the current consumed by 
the rest of the transmitter. 

The transducer oscillator is a Wien Bridge 
type well known for its amplitude and frequency 
stability. This bridge is shown in Figure 8. 

The active thermistors Rl and R2 in the 
right hand arms are the frequency determining 
resistors along with capacitors CI and CZ. The 
frequency of oscillation is determ'ned by the 
relation 



1 



f = 



(1) 



Ztt/Ri Ri Ci Ci 

The thermistors Rl and R2 are located in the 
lower end cap. The capacitances CI and C2 are 
the Mylar dielectric type chosen for a degree of 
temperature stability. They are attached to the 
back of the circuit board. Their temperature 
coefficient is such that their capacity at 0°C is 
2% less than that at room temperature. This is 
better than paper capacitors but not as good as 
the polyethylene type which has a nearly zero 
temperature coefficient. With the latter units, 
the response time for good accuracy can be 
reduced to that time required for the thermistors 
to come to equilibrium with their surroundings. 
In the drift buoy application the transducer will 
remain continuously in its environment and 
hence it is acceptable to calibrate the entire 
unit in a constant temperature bath. 

A square wave is generated by a squaring 
amplifier. It is fed by the divided outputs of the 
push-pull oscillator. The square wave is fed 
through an emitter follower for additional 
isolation and low impedance. The signal output 
is a square wave from to +13 volts for a 
positive supply and to -13 for a negative 
supply. The frequency of this square wave 
ranges from about 2 to 1 cps or from 100 to 
500 millisfeconds per cycle. The latter time 
period expression is commonly used in this 
report. The transmitter keying relay can run 
at the highest repetition rate encountered and is 
used unmodified. Conductance switching can be 
used if higher rates are ever required. The 
buoy transmitter keying is achieved by opening 
the internal keying circuit and allowing the 



temperature transducer output signal to do the 
keying. See Figure 4. 



CALIBRATION DATA 

Figure 9 is a reproduction of the calibration 
curve from which the integer temperature read- 
ings were made. A table was prepared which 
gave interpolation values to 0.1 °C. Further 
interpolation to 0.01°C could be made with the 
listing of proportional parts. The raw data is 
good to + . 01 °C, the manual curve fit to perhaps 
+ . 03°C. For accurate calibration to within 
. 03'-'C a least-square-curve fit should be made 
with the raw data. 



RECEIVING STATION ASHORE 

The buoy transmits on a frequency of 2398 KC 
with a power output of approximately 20 watts. 
The radiated power is on the order of 2 watts due 
to antenna inefficiency. A downward shift of the 
R.F. carrier frequency of 140 cps occurs when 
the keying contacts close. 

The receiving station is shown schematically 
in Figure 10. The carrier is converted to an 
audio tone by operating the receiver in the BFO- 
ON position. The carrier shift of 140 cps down- 
ward produces an audio tone shift of 140 cps 
downward when the BFO frequency is below the 
carrier frequency and 140 cps upward when the BFO 
frequency is above the carrier frequency. See 
Figure 1 1 . 

In the case of temperature measurement it is 
inconsequential whether the BFO is set above or 
below the carrier since the datum comprises the 
total time period for one complete cycle of freq- 
uency shift. To convert the FSK audio signal 
into a signal suitable for triggering a timing cir- 
cuit, the signal is fed through a standard IRIG 
subcarrier discriminator centered at 1700 cps. 
This discriminator as a linear output over a 
+ 7. 5% range. The discriminator response 
limits the bandwidth to that frequency occupied by 
its "S" curve. A narrow pass frequency occurs 
for lower center frequency units. The 960 cps 
center frequency (IRIG Channel No. 4) has a pass 
band of slightly more than 144 cps. The reason 
for choosing a low oscillator frequency is so that 
a very narrow shift hence a narrow discriminator 
response can be used and still have a high modu- 
lation index. The narrow shift allows a narrow 
band pass, off the shelf, discriminator to be used 
to advantage. Keying of the transmitter is 
simplified to merely "pulling" the crystal R.F. 
oscillator with series capacitance. Also the FSK 
mode of transmission has good antifade qualities. 
This is not to say that a wider shift, or extremely 
wide shift, say 6 KC, couldn't be used to ad- 
vantage, to allow frequency diversity reception 
techniques. This requires some special filters, 
keyers, etc. and comprises a new field of develop- 
ment effort. 



43 




Fig. 5 - Pressure Case 



44 




Fig. 6 - Electronic Circuitry 



45 



Z Noiii Dr. 
Tap For ^-tC: 
^ ■ Ddtp 



/'I Drill J Tip Depth, 
Than f Drill, | Tip Depth ^ 

2 Hold 



Torn To . Hi 




/ — 



Orill To Clear 6-J2 
rcuJS - 6 Holts 




Drill and Top §-/t 



3toc(-: /'Auminun, P/ats 



S/T'Cori oi7 
T'/ie.riniStor 



Therrii s tor Mount Octojl 



Fig. 7 - Lower End Cap 



2V RMS 
SI NE WAVE 



I//)*, MYLAR 




BASE OF 05 



C2 

Z^Jf, MYLAR 



VOLTAGE STABILITY ARMS 



TEMPERATURE SENSITIVE ARMS 



Fig. 8 - Wien Bridge 



46 



5000 




30 32 



Fig. 9 - Calibration Curve 



47 



ANTENNA 



V 



RADIO 
RECEIVER 
COLLI N S 
51 J 4 



F, SK 

auDio 



TONE 



AUDIO 
AMPLIFIER 



I RIG 
SUBCAR RIER 

Dl SCRIMIN ATOR 
1700 CPSl 7.5% 



2,5 TO 

10 CPS 



SQUARE 
WAVE 



LOW - PASS 
FILTER 
14 CPS 

CUT - OFF 



ELECTRONIC 

COUNTER 
"10 PERIOD 
AVERAGE " 
HP. 



Fig. 10 - Receiver Station Block Diagram 



RECEIVER SET 
FREQUENCY 
2,398.0 KC 



2396.3 KC 



MARKER TRANSNfllTTER 
FREQUENCY FOR B FO 
ZERO BEAT 



1700 CPS- 



I400CPS-^ 



H 



2396 



T 
2397 
/ 



'm, 



140 
'CPS 



\ 



RECEIVER 1400 CPS 
MECHANICAL FILTER 
RESPONSE 



2399 
\ 



1 

2400 



FREQUENCY KC 

KEYED CARRIER UNKEYED CARRIER 

Fig. 11 - Spectral Presentation of Receiver Adjustment 



48 



The discriminator output is a square wave 
whose period is to be measured. It is first 
filtered by an output filter of high cutoff any- 
where from 14 to 80 cps. It is suitable to 
trigger an electronic counter set in its period 
position or the 10-period average position. The 
latter was used in initial calibration measure- 
ments and may suit the data acquisition as well. 
The average over 10 periods could be adversely 
affected by static noise bursts under poor signal 
conditions when the buoy is a long distance away. 
In this case several 10-period measurements 
should be made and those widely different from 
a median are disregarded. Single period 
measurement between static crashes provides a 
second alternative. 



CONCLUSION 

The temperature transducer attachment to 
the buoy, elementary telemetering link, and 
calibration are completed. Tests at a depth of 
14 feet have been carried out. A test at a depth 
of 100 meters is included in a paper by Walden 
and Franz^ of this conference. 



BIBLIOGRAPHY 

1. "A Radio Telemetering System for Ocean- 
ography, " Franz, Ketchum, and Walden, 
W.H.O. l#58-29. May 1958. 

Z. "Long Range Oceanographic Telennetering 
System," Walden, R. G. , and Franz, D. H. 
Jr. ASLO and ISA Marine Sciences 
Conference, Woods Hole, Massachusetts. 
September 11-15, 1961. 



ACKNOWLEDGMENT 

The facilities of the Woods Hole Oceano- 
graphic Institution were used for the con- 
struction of the unit. Mr. Neil Brown is 
responsible for the basic stable oscillator cir- 
cuit. The author's work represented by this 
report was accomplished during a stay at the 
Woods Hole Oceanographic Institution arranged 
by mutual agreement with HRB-Singer, Inc. 



49 



A LONG-RANGE, OCEANOGRAPHIC TELEMETERING SYSTEM 

by ROBERT G. WALDEN 

Woods Hole Oceanographic Institution 

Woods Hole, Massachusetts 

and DAVID H. FRANTZ, Jr., President 

Ocean Research Equipment Company 

Vineyard Haven, Massachusetts 



ABSTRACT 



A low cost transponding buoy for medium 
frequency, long-range ocean telemetry has been 
developed at the Woods Hole Oceanographic 
Institution, and further refined commercially. 
Its use as a drift buoy has been previously 
described; more recently a series of propaga- 
tion tests at 2.4 mc. and 7 mc. has been con- 
ducted out to a 1400 mile range, and tempera- 
ture measurements have been transmitted on a 
regular schedule. The buoy, and associated 
receiving and recording equipment are des- 
cribed, as well as the necessary buoy con- 
trol circuitry for certain typical problems 
in physical oceanography. 



INTRODUCTION 

Almost ten years ago, Henry Storamel 
then of the Woods Hole Oceanographic Insti- 
tution, designed an experiment to study the 
movement of water in the Sargasso Sea near 
the region of Bermuda, and more specifically 
to establish the effect of a given wind on 
the water column to a considerable depth as 
a function of time. The primary tool used 
in this study was a set of radio drift buoys 
designed and built by Hodgson, Parson, Walden 
and Stommel, primarily out of sheet steel, 
plywood, surplus stepping relays and a few 
vacuum tubes, automobile clocks, and, as I 
recall, a rattrap. The rattrap was a vital 
part of a scuttling device which was to sink 
the buoy after a month, to prevent its re- 
maining a menace to navigation. We could 
never bring ourselves to arm the rattrap, 
even though the useful life was considerably 
less than a month. The buoy transmitted on 
schedule a series of tone modulated signals 
representing the output of a number of trans- 
ducers, which included two current meters to 
measure current velocity relative to the buoy 
itself at the surface and at depth, the mo- 
tion of the buoy being determined by daily 
fixes. We obtained the fixes by getting 
bearings with a portable radio direction 
finder mounted on a jeep. Since Bermuda is 
about one sixth the size of Martha's Vineyard, 
the accuracy of the fixes deteriorated 
rapidly with distance from the island. Addi- 
tional transducers on the buoy were an 
anemometer, a compass, and later, thermistors. 



The experiment was a success; enough 
of the buoys survived long enough to give a 
valuable insight into the behavior of the 
water mass influenced by wind and of the 
general drift around Bermuda. It also sug- 
gested a host of ways in which similar ex- 
periments could be conducted in the future, 
using radio telemetering buoys. 

If this story were to be presented in 
the classic format, the description of this 
early, crude buoy design would be followed 
by one of more recent developments which 
have enabled us to perform much more sophis- 
ticated experiments working with greater 
quantities of data. We could describe the 
greater reliability of modern oceanographic 
telemetry systems, their greater range and 
longer life. Unfortunately, I am aware of 
no automatic oceanographic data gathering 
system involving more than one or two buoys 
which has produced any more real scientific, 
unclassified data via a radio telemetering 
link than the one operated by Stommel in the 
winter of 1953-4. Nor am I able to explain 
why this is so. It is certainly within the 
state of the art that there be such systems 
in successful operation since by now, most 
components of such a system have- had consider- 
able sea experience. Apparently it has been 
rare until now that the financing, the engi- 
neering talents, and the scientific interest 
have all occurred at the same time. The 
major program coming closest to it is 
Richardson's buoy line to Bermuda, and to 
date this has involved recording rather than 
telemetering techniques, and for very adequate 
reasons. 



THEORY OF OPERATION 

The vast extent of oceanic areas has 
required a re-evaluation of our past tele- 
metry schemes. Frequencies in the two to 
three megacycles range are inadequate for 
distances of over a few hundred miles. Trans- 
missions and coding systems such as FM/AM 
quickly become useless due to the signal to 
noise ratios involved. 



50 



We are presently using a completely trans- 
istorized buoy operating on 6970 kiloycles for 
our long range oceanographic telemetry. This 
buoy, manufactured by Concord Control, Inc. of 
Boston, is some thirteen feet long and eight 
inches in diameter. The bottom plate is two 
feet in diameter made of bronze, and acts both 
as a ground and as a vertical motion damper. 
The case is fiberglass or polyvinyl chloride. 
The electronics are built in modules which plug 
into a rack frame four feet long attached to 
the top plate. Figure 1 shows this rack. The 
top plate contains the antenna base insulator, 
tuning meter and necessary tuning and loading 
controls. The batteries, located in the bot- 
tom portion of the case, are LeClanche cells 
packaged in an eight inch cylinder three feet 
long. The receiver is a more or less standard 
crystal controlled super-heterodyne whose out- 
put drives two resonant reed relays. These 
relays, through special delay circuitry ener- 
gize command function relays. Three interroga- 
tion command functions are thus possible, one 
or the other resonant reed relays or both 
simultaneously. Once interrogated, a timer is 
activated which causes the transmitter either 
to send out its call sign or a data transmis- 
sion, depending upon the function chosen. The 
transmitter supplies 30 watts of power to a 
center-loaded marine type whip antenna. We 
have been using frequency-shift keying with a 
nominal shift of 240 cycles in our experiments. 

1 would like to discuss a recent experi- 
ment which was designed to determine the 
feasibility of 1) the modest power output 
2) the 7 mc. frequency chosen, and 3) the FSK 
mode of operation. Accordingly a tract of 
land in Waquoit, Massachusetts (twelve miles 
from Woods Hole) was leased, and a beam anten- 
na for 6970 kc. erected. A communication van 
housing receiving equipment, discriminators, 
and a tape recorder, was installed at the base 
of the antenna as shown in Figure 2. This 
receiving site proved excellent from a noise 
standpoint. The beam constructed was a three 
element array with parasitically excited re- 
flector and director. Subsequent field pattern 
tests run with the aid of our Helio Courier 
aircraft acting as a signal source, established 
the major lobe at lAO degrees true, the direc- 
tion desired for our tests. The front to back 
ratio was better than 15 db, and the horizon- 
tal beam width about 80 degrees. A Concord 
buoy, like the one just described, was taken 
to sea and put in the water at intervals. 
Measurements of signal strength and readabil- 
ity were then made at Waquoit. Because of the 
small number of transmissions, we are unable 
to present reliable statistics, but we can 
make certain generalizations of the results. 
The buoy was put overboard and allowed to 
drift away from the ship about a thousand feet 
and interrogated from the ship. A typical 
picture of the buoy in the water is shown. 



It was put over at different times of day and 
at ranges between 200 and 140U miles from 
Waquoit. At least 50'/, of the transmissions 
were received at each range at Waquoit well 
enough to retrieve data regardless of time of 
day. Obviously this modest percentage is 
greatly weighted by the fact that some of the 
tests were run at the most adverse times of 
day, as far as propagation was concerned. At 
optimum time of day, the percentage was better, 
and by providing some sort of redundancy, we 
feel that we can have a reliable link. We 
believe that low power, high frequency FSK 
transmissions can be practically utilized 
for oceanographic telemetry, assuming that 
the optimum time of day be utilized, and that 
interrogation techniques be used. The inter- 
rogation technique allows repeat of transmis- 
sions to allow data redundancy during periods 
of high noise or interference. The data rate 
was 10 bits per second during these tests; 
however we anticipate rates of up to 100 bits 
per second. 



CONCLUSIONS 

The serial observation of oceanographical 
data from buoys located at certain remote 
sensitive areas of the ocean can in many in- 
stances supply the oceanographer with informa- 
tion not otherwise obtained. A monitor of this 
sort might provide a warning of some specific 
change, or it might indicate a trend whose 
correlation with other data ashore proves 
valuable. 

What of the immediate future as far as 
telemetry systems are concerned? We feel that 
regardless of the admittedly higher data hand- 
ling capabilities of the VHF bands, the line 
of sight limitation imposes too heavy a burden 
on auxiliary equipment to make it an immediate 
solution to the long range telemetry problem. 
If and when there are hundreds of buoys in the 
water, satellite relaying or data collection by 
high-flying aircraft may be worthwhile, and in 
fact necessary because of problems of frequency 
allocation, but if we were to start now to 
design a system of more modest extent for use 
in a given ocean area, there is no doubt in our 
minds that the high frequency bands will be 
utilized. 

For example, Richardson's buoy line 
between here and Bermuda is presently recording 
at about ten buoy stations, and as far as we 
know, it is the only area now being monitored 
by a whole system of buoys for scientific pur- 
poses. Presumably it is well worthwhile to 
maintain this line more or less indefinitely, 
and as soon as the telemetry can be as reliable 
as the recording apparatus, and the platforms 
can maintain themselves reliably for six months 
or more, it will undoubtedly be more desirable 



51 



Figure 1 



52 




Figure 2 




53 



to transmit the data to a shore station than 
to collect it by ship. When we consider how 
best to convert this line to telemeter data 
either on schedule or on demand to Waquoit, 
there can be little doubt that it will be done 
using the high frequency bands rather than the 
VHF bands. The number of units is too small 
to justify air cover and a satellite is out of 
the question. Even at several times the pres- 
ent sampling rate and several times the pres- 
ent number of buoys, an HF link is quite feas- 
ible, and we can use existing equipment which 
has already proven at least its capability of 
functioning at sea. 

At this point we must emphasize that we 
are attempting to describe a system which will 
be a tool useful and readily acceptable to the 
practicing oceanographer. I have made no men- 
tion of transducers, or of the transducer to 
surface link, or of the storage method. The 
design of the system must in no way dictate 
what the oceanographer should measure or how 
accurately he measures it, subject to the real 
technical limitations imposed by the state of 
the art. It is complicated enough and expen- 
sive enough to require a degree of standardi- 
zation of components, but it must be adaptable 
to a wide variety of measurements by the 
choice of specific transducers. 



ACKNOWLEDGMENT 

The work discussed in this paper was 
made possible by support from the Office of 
Naval Research, Department of the Navy, under 
Contract Nonr 2196(00). 



54 



A DATA ACQUISITION AND REDUCTION SYSTEM 
FOR OCEANOGRAPHIC MEASUREMENTS 

by DAVID D. KETCHUM and RAYMOND G. STEVENS 
Woods Hole Oceanographic Institution 
Woods Hole, Massachusetts 



.^STRACT 



A system for recording and reducing 
oceanographic daca in many tirae-dependenC 
variables is described. The system permits 
recording up to twelve simultaneous data 
channels with a nominal frequency response 
from DC to 10 cycles. Transducer outputs 
are converted to FM-analog form using stan- 
dard telemetry techniques and components. 
The data multiplex is recorded on magnetic 
tape with or without an intervening tele- 
metering linl;. 

The tape recorded data is played back 
into an analog to digital data reduction 
system, which samples the individual chan- 
nels, converting the analog data into digital 
format suitable for entry into an electronic 
digital computer. 

The use of a standardized tape format 
and modular components in field data acqui- 
sition units assures a highly flexible 
system applicable to a wide variety of 
oceanographic and marine meteorological 
problems. 



INTRODUCTION 

One unusual feature of oceanographic 
science is the fact that the basic phenomena 
which we strive to understand are charac- 
terized by variables which are both time 
and space dependent. 

Most of the early work, and much of the 
present work, in oceanography consists of a 
spatial sampling of oceanographic parameters 
wherein observations are made from ships 
covering the wide expanse and depth of ocean. 
In many cases the time dependence of such 
data must be ignored since it cannot be 
observed. The so-called "classical" oceanog- 
raphy which has so carefully traced the 
spatial distribution of water masses and 
their chemical and thermal content falls 
into this category. However, since we know 
that the ocean is dynamic, always in motion, 
always influenced by spatial and time varying 
solar radiation, atmospheric winds and pre- 
cipitation it would seem essential to ob- 
serve the time variable characteristics of 



the ocean as well as its spatial variability 
if we are to gain an understanding of its 
dynamic processes. 

Until very recently oceanographers 
have not had the technological or financial 
resources at their disposal to carry out 
extensive time dependent observations. 
However, some recent technological advances 
make possible the design of compact fast 
response transducers for the measurement 
of many physical and chemical variables. 
Another important technological advance 
is in the area of information transmission, 
storage and retrieval which provides the 
link between field observations and the 
digital computer, thus forming a unified 
system for observation and analysis of 
time varying data. 

The remainder of this paper is devoted 
to a description of one system which per- 
forms the function of information trans- 
mission, storage and retrieval. It should 
be pointed out before entering into the 
technical discussion that there are many 
S'lbtle but important differences between 
serial time dependent observations and 
the broad scale spatial observations in 
oceanography. For example, time serial 
observations tend to accumulate vast 
quantities of data which must be handled 
by rather elaborate statistical techniques - 
thus the requirement for a digital computer 
and automatic data reduction systems. 
Furthermore it is absolutely essential 
that the dynamic characteristics of the 
entire data acquisition and reduction 
system be considered in addition to the 
more usual consideration of accuracy of 
the measuring system. In fact accuracy 
and dynamic response are inextricably 
linked when measuring time dependent 
variables . 



FUNCTIONAL DESCRIPTION 

In recognition of the need for a 
system capable of recording several simul- 
taneous channels of continuous time-depen- 
dent data with frequency components ranging 



Woods Hole Oceanographic Institution 
Contribution No. 1227 



55 



up to the order of 10 cps , a system has slowly 
been developed at Woods Hole. An early effort 
by Fanner on this line was used for the 
measurement of ocean waves, where a record of 
heights and instantaneous slopes at fixed 
points on the sea surface was desired. Ini- 
tial experiments where these variables were 
measured and directly recorded on a multi- 
channel galvanometer recorder soon revealed 
the necessity for a more sophisticated 
approach. 

First, the need for remote measurements 
beyond the reach of a conveniently handled 
cable link was recognized. Second, the task 
of manually reducing the data from a contin- 
uous strip-chart recording was soon found to 
be far too tedious to be practical or economi- 
cal. Further, the requirements of the various 
analyses applied to the data were of such a 
nature that automatic digital computing tech- 
niques were mandatory. Thus at an early stage 
in the wave measurement program the need for a 
telemetry and data processing system, whose 
final output would be sampled data in a format 
suitable for entry into a digital computer, 
was recognized. 

As the system evolved and it became 
evident that it could usefully be applied to 
a wide variety of problems in oceanography 
and meteorology, the following desirable 
characteristics were specified: 

1) Flexibility: The input to the system 
should be compatible with a wide variety 
of transducers. 

2) Analog storage: The data should be 
stored in analog form with minimum 
degradation, and the storage medium 
should be chosen to allow fast, automatic 
sampling and digitization for ultimate 
entry into a computer. 

Functionally, the system may be repre- 
sented by the block diagram shown in 
Figure 1 . It is divided into two major 
parts, which perform the functions first of 
data acquisition and storage, and second of 
playback and processing. The data acquisi- 
tion and storage function is performed as 
follows. 



link. The data multiplex, after passing 
through the transmission link, is stored 
in analog form. Note that at this point the 
raw data is still in existence, degraded only 
by the distortion and noise inherent in the 
system. The analog storage medium is of a 
permanent nature so that the raw data can be 
stored Indefinitely, if desired. 

An inspect function is shown, which 
allows the investigator to observe the pro- 
gress of his experiment and determine the 
proper operation of the system. The position 
of this function is shown at the input of 
the modulators, but it may actually be located 
anywhere between the transducer outputs and 
the output of the transmission link. 

Processing begins with playing back the 
raw, multiplexed data. The individual chan- 
nels are separated out by the demultiplexers 
and demodulated. The result of these opera- 
tions is a set of voltages directly propor- 
tional to the transducer outputs. 

At this point the data may be displayed 
for inspection, for example on a graphic 
recorder, to allow the experimenter to exam- 
ine and edit his data for further analysis. 
It is now necessary to prepare the data for 
entry into the computer. The several chan- 
nels are scanned in sequence by the commu- 
tator, and the sampled voltages are converted 
into binary coded numbers, which are entered 
into the computer. 



TECHNICAL DESCRIPTION 

In choosing the techniques and components 
to realize the various functions saown in 
Figure 1 every attempt was made to utilize 
standard hardware and well-developed methods 
wherever possible. At an early stage it 
became apparent that the needs of the aircraft 
and missile industry had fostered the devel- 
opment of standard telemetry systems which 
could be adapted to the needs of our science. 
Accordingly we were able to draw heavily upon 
the accumulated experience of specialists in 
this field and find "off the shelf" components 
produced by several companies specializing in 
the techniques of data transmission. 



The electrical outputs of the trans- 
ducers (usually voltages which are analogs 
of the physical quantities being measured) 
are processed by signal conditioners to bring 
them to level and form suitable for operating 
the modulators. The modulators further 
operate on the transducer signals in such a 
way that they may be transmitted and stored 
with minimum degradation. A second function 
of the modulators is to multiplex the sever- 
al signals for transmission over a single 



The method chosen was a well-proven 
technique of frequency-division multiplexing 
wherein the signal from each transducer fre- 
quency modulates an audio oscillator over a 
rather narrow range. A separate center fre- 
quency is assigned to each oscillator and 
sent over the transmission link. It is gener- 
ally most convenient, where a radio link is 
necessary, to use FM transmission. In this 
case the technique is referred to as FM-FM 
telemetry, signifying that both the subcarriers 



56 







CALI- 
BRATION 






TRANSDUCERS 










SIGNAL 

CONDITIONERS MODUL ATORS 








tv 


















k 










\ 




\ 










■ 


k 








N^ MULTI- 














\ PLEXED 
























\^ DATS 


TRANS- 
MISSION 
LINK 


H. 


ANALOG 
STORAGE 






1 

1 1 










^ 


? 






' 


1 






+ 








/ 


«IULTIPLE> 










1 








/ DE 


ERS DEMODULATORS 








1 1 
! 1 




/ 






1 


■ 




C 


M 
M 

U 
T 
A 
T 

fl 






1 














/ 
















!r^ 










. 




_y 














ANALOG TO DIGITAL 












" 












CONVERTER 




1 






' 


i 










PLAY 












■ 






DIGITAL OUTPUT 
















* 




^T 




TO COMPUTER 








' 




1 


1 




1 




+ 








REFERENCE 






• 


tin 




1 ; ; 














INSPECT 






1 




1 










EXCITATION 


1 






- 




PRO- 
GRAMMER 














































^^^ 










NSPECT 


FIGURE 1 



TRANSDUCERS 



VOLTAGE 
CONTROLLED 
OSCILLATORS 



CHANNEL 1 




V V 



MAGNETIC 

TAPE 
RECORDER 



FIGURE 2 



TRANSDUCER 

EXCITATION 





BAND PASS 
FILTERS 


FM 
DISCRIMINATORS 




OUTPUT 

FILTERS 




SAMPLING 






* 


CHANNEL 
1 
















SW 


TCH 

) ANALOG TO DIGITAL 


















Q <i 










- 


\ 




















































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TAPE 
PLAYBAO 




CHANNEL 

2 












































i 


. 










J 


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CHANNEL 
12 


. 














PROGRAM- 
MER 






* 








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r 1 


' 1 


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i 


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GALVA- 
NOMETER 
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TAF 












>E S( 


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ITOR 




















FIG 



DIGITAL OUTPUT 
TO COMPUTER 



57 



and the RF carrier are frequency modulated. 
At the receiving terminal the subcarrier 
multiplex is recovered from the RF carrier 
by means of a conventional FM receiver and 
directly recorded on magnetic tape. 

The advantages of the FM-FM technique 
are several: 

1) The use of frequency-division multi- 
plexing makes possible the simultaneous 
recording of several continuous time-depen- 
dent variables without introducing, the sam- 
pling errors encountered in time-division 
schemes. 

2) Frequency modulation of the sub- 
carriers not only carries with it the well- 
known advantages of signal to noise ratio 
improvement in the transmission link, but 
also overcomes the problem of intolerably 
large amplitude fluctuations caused by lack 
of uniformity in the magnetic tape. 

3) FM subcarriers allow the recording 
of DC levels on magnetic tape. 

A limitation of the FM-FM system is 
imposed by its large bandwidth, which re- 
quires the use of a very high frequency 
carrier. Although there is a valuable re- 
duction in atmospheric noise in this part 
of the radio frequency spectrum, the trans- 
mission distance is limited by the line of 
sight. It is, however, possible to employ 
the FM-AM technique, where the frequency- 
modulated subcarriers amplitude modulate a 
carrier at a lower frequency suitable for 
trans-horizon communication. The bandwidth 
allowable at these frequencies severely 
limits the number of channels, and trans- 
mitter power must be increased to offset 
the increase in atmospheric noise. 

Figure 2 shows the actual components 
of a typical data acquisition system, repre- 
senting merely one of several variations 
which are compatible with the data reduction 
equipment. In this case the transducers are 
AC excited bridges, and it is required that 
the sense of the bridge unbalance be known. 
The bridge output voltages are therefore fed 
to differential amplifiers in order to bring 
them to a level suitable for operating 
phase-sensitive demodulators. The outputs 
of the demodulators are DC voltages propor- 
tional to the AC transducer outputs. Their 
polarity is determined by the phase of the 
amplified transducer signals with respect to 
the reference voltage, which is derived from 
the transducer excitation source. The DC 
output voltages from the demodulators vary 
the frequency of voltage-controlled sub- 
carrier oscillators, and the frequency 



multiplex modulates an FM transmitter operating 
in the VHF telemetry band. An FM receiver at 
the receiving terminal recovers the frequency 
multiplex, which is recorded on a single track 
of magnetic tape. 

There are many cases where the telemetry 
link is not necessary, and it is merely desired 
to record the data in a compact form at the 
site of the experiment. Here, of course, the 
mixed output from the subcarrier oscillators 
is directly recorded on the magnetic tape. 
The individual components shown in the data 
acquisition system are all either available 
commercially as standard transistorized plug- 
in units or as designs developed at WHOI. 
Thus data acquisition units for field use may 
easily be designed using the modular concept 
with a minimum of circuit development. Both 
voltage-controlled and resistance-controlled 
oscillators are available for a wide range 
of sensitivities. Where DC excited trans- 
ducers are used, the amplifiers and demodu- 
lators are, in most cases, unnecessary. For 
AC systems a specially developed differential 
amplifier-demodulator combination is now 
available commercially. The inspect function 
would probably be omitted in remote, unattended 
installations, but a monitoring arrangement 
then becomes desirable at the output of the 
FM receiver or cable link. Calibration sig- 
nals are inserted in the usual manner at the 
input to the system by substituting standard- 
ized signals for the transducer output. 

In the recording process a certain 
amount of variation in the transport speed 
of the tape is always present. Tape speed 
variation frequency modulates the recorded 
signal, and in an FM system results in noise. 
A well-known method is used to overcome this 
difficulty. In addition to the data multi- 
plex a signal from a frequency-stabilized 
oscillator operating at a different frequency 
from any of the subcarriers is recorded on 
the tape. During play-back the deviations 
in the frequency of this signal are detected 
and used to compensate for variations in the 
data signals caused by tape speed variation. 

The playback and processing system 
known as ADDReSOR, (Analog to Digital Data 
Reduction System for Oceanographic Research) 
has recently been put into operation at the 
Woods Hole Oceanographic Institution, sup- 
planting earlier apparatus of more limited 
scope. Figure 3 shows a much simplified 
block diagram of the device which was manu- 
factured by Tele-Dynamics Division of American 
Bosch Arma to WHOI specifications. A total 
of twelve channels may be accommodated. De- 
multiplexing and demodulation are accomplished 
by standard subcarrier discriminators, each 
of which contains in one unit an appropriate 
band-pass filter for selecting the desired 
subcarrier, an FM discriminator, and a low- 



58 



pass filter in the output for removing subcarri- 
er ripple from the recovered data signal . One 
more discriminator is used to detect variations 
in the frequency of the reference signal. The 
output of this unit is applied to the other 
discriminators in such a way that it corrects 
the effects of tape speed variation. The in- 
spect function may be provided by connecting a 
multi-channel recording galvanometer to the 
outputs of the discriminators. 

The function of the Programmer-Digitizer 
is to sample analogue voltages and convert them 
into a binary digital format suitable for 
direct entry into the Recomp II computer. 
This may be done simultaneously with, or 
independently from the graphic presentation. 

The Programmer-Digitizer has 12 input 
connections on a patch panel to receive up to 
12 analog voltages. The number of input con- 
nections used in a given case is called the 
GROUP SIZE and may be any number from 1 to 12. 
A dial marked GROUP SIZE SELECTOR is set to 
correspond with the number of input connections 
in use. 

An internal switching device scans all 
of the active input voltages in sequence and 
transmits the voltage to an analog-digital 
converter. The frequency with which the 
switching device scans the entire GROUP of 
voltages is called the GROUP SA>IPLING RATE 
and is adjustable by dial settings from 1 to 
100 times per second. Since the patch panel 
permits plugging the same voltage into any or 
all twelve inputs it is possible to sample 
a single voltage 1200 times per second, two 
voltages 600 times per second, 12 voltages 
100 times per second and so on. It should be 
noted, however, that the sampling speed of 
the Programmer-Digitizer may exceed the abil- 
ity of the computer to receive digitized in- 
formation. If need arises, and as opportunity 
is presented, the computer capabilities will 
be suitably improved. 

Since the computer memory has a finite 
capacity it is necessary to provide a means 
of limiting the number of samples which will 
be stored. A panel control marked TOTAL is 
set to the total number of samples per chan- 
nel desired. The computer capacity is in 
excess of 12,000 DATA WORDS so that for a 
GROUP SIZE of 12 the maximum permissible 
TOTAL setting would be something over 1000. 
For a GROUP SIZE of 2 the TOTAL setting could 
be over 6000 and so on. 

Manual controls are provided to allow 
the programmer to be advanced manually through 
the samplirg sequence, during calibration and 
test procedures, and to permit sampling rates 
to be controlled by accessory apparatus. 



A visual binary display of the buffer 
contents is provided on the panel. 

The sampling sequence is as follows: 

1) Upon receipt of a signal from the 
computer the analog tape playback is energized. 

2) The channel selector switch steps 
to input number 1 and samples the voltage at 
that input. In order to achieve accuracy 
when sampling rapidly varying data the time 
duration of the sample, called the aperture 
time, is limited to 1 microsecond. 

3) The sampled voltage is converted into 
a 10 bit binary number and read directly into 
the computer. The actual timing sequence of 
this operation depends upon the input capabil- 
ity of tiie computer. 

4) The channel selector switch is then 
stepped CO input number 2 and the above opera- 
tion repeated. Stepping continues through 
successive inputs until the number of inputs 
specified by the GROUP SIZE selector have been 
sampled. The channel selector switch is then 
returned to its off position. At this point 

a timing device is actuated causing the chan- 
nel selector to wait an interval of time before 
recycling through the various inputs. The 
time delay is determined by the setting of 
the GROUP SAtlPLE RATE dials. 

5) After completion of each group 
sampling the programmer advances the group 
counter by one count and compares the 
.counter with the setting of the TOTAL dials. 
When the two numbers agree the programmer 
generates a termination sequence to the com- 
puter which stops data filling and may cause 
the computer to start executing an internal 
program. 

The present computer used with the 
ADDReSOR is an Autonetics Recomp II which 
requires 7.5 ms to enter and store each 
DATA WORD. Thus a total of 90 ros is required 
to scan all 12 channels, or in other words 
a phase lag of nearly 180° would occur 
between 10 cps data on channel 1 and channel 
12. Furthermore, this relatively slow input 
rate limits the system to 11 samples per 
second per channel when using all 12 channels, 
22 samples per second per channel for 6 
channels and so on. This restriction means 
that no more than 5 cps intelligence frequency 
can be recovered when using all twelve channels, 
10 cps intelligence frequency can be recovered 
when using 6 channels, etc. Present plans call 
for incorporating a faster computer into the 
data processing system in the near future so 
that these restrictions will be removed. 



59 



The data entered into the computer froiti 
ADDReSOR consists of 10 binary bit words. This 
would imply an accuracy of 0.17o if taken at 
face value. However, FM subcarrier system 
accuracy is probably no better than + 1% so 
that some of the binary bits are extraneous and 
should be ignored in the computations. 

A few general purpose programs have been 
developed for use with the ADDReSOR. First, 
a control program is used to enter and evalu- 
ate the calibration signals and enter the data 
samples. This program reads into the computer 
100 samples of the field calibration signals, 
computes the mean and variance of these sig- 
nals and the calibration constants for each 
variable. The operator may inspect these 
results before proceeding with further compu- 
tations. Up to 12,000 data samples may then 
be entered and the means and variances of 
each variable may then be computed if desired. 

A second program consists of an unpack 
and punch routine which multiplies each 
variable by its appropriate calibration factor 
and punches the calibrated data in either 10 
bit binary format or in teletype format. The 
punched tape may be used for reentry into 
RECOMP II or for entry into other computers. 

Using a computer as a medium for tempo- 
rary storage of the digitized data has cer- 
tain advantages. First of all, it is not 
feasible to use either a tape punch or a 
magnetic tape transport directly on the out- 
put of ADDReSOR since the sampling rate may 
be too high for mechanical punches and too 
variable for magnetic tape transports without 
some means of temporary storage. Secondly, 
a small or medium size computer is probably 
the most economic means for temporary data 
storage, particularly since it may be used 
for a wide variety of other computing problems. 
Thirdly, elementary calculations such as means 
and variances, running means, calibration, 
etc. may be performed before punching the 
data onto tape. 



Restrictions on the frequency response 
can be improved by using a faster computer 
and by replacing the output low pass filters 
on certain subcarrier discriminators. It is 
possible also that the total number of data 
samples may be increased by using a high speed 
computer. For the moment, however, there is 
a vast area of oceanographic research which 
can be accomplished within these restrictions. 



ACKNOWLEDGMENTS 

The authors wish to acknowledge the 
invaluable assistance of Mr. Raymond A. Stahl 
of Tele-Dynamics Division of Arr,erican Bosch 
Arma Corporation who designed and supervised 
construction of the ADDReSOR, the personnel 
of Geodyne Corporation who developed the 
special purpose amplifier, and Mr. Leonard 
Shodin of the WHOI staff who designed and 
constructed much of the data acquisition 
system. The developments reported in this 
paper were made possible by the Office of 
Naval Research Contracts Nonr 2196 (00) 
Nonr 3351 (00). 



REFERENCES 

1. Farmer, H. G. and Ketchum, D. D. (1960). 
An Instrumentation System for Wave 
Measurements, Recording and Analysis. 
Proc. 7th Conf. Coastal Eng. Council 
Wave Res., Univ. of Calif. Berkeley 

2, Proceedings of the Conference on Automatic 
Data Handling for Oceanographic Observa- 
tions (1959). Ref. No. 60-10. Woods Hole 
Oceanographic Institution, Woods Hole, 
Mass. (Unpublished manuscript). 



CONCLUSIONS 

We have described here a completely 
integrated data acquisition and reduction 
system which has the following general 
characteristics at the present time: 

1. 12 channels of continuous data 
storage 

2. Frequency response for 12 channels 

~ 5 cps 
6 channels or less ~ 10 cps 

3. Accuracy overall is presumed to be 
better than + 2% 

4. Total data samples 12,000 + 



60 



THE PROBLEMS OF RELIABLE LONG-RANGE TRANSMISSION 
OF REMOTE OCEANOGRAPHIC MEASUREMENTS 

by C. McLOON, Member Technical Staff 
Hughes Aircraft Company 
Los Angeles, California 



PRECIS 

Data telemetry transmission falls 
basically into two categories: line-of-sight and 
beyond-line-of- sight. When the transition to long 
range is made, entirely new telemetry techniques 
are required. This paper describes the problems 
involved with long range telemetry, together with 
some state-of-the-art solutions. 



INTRODUCTION 

With the advent of mass oceanographic 
measurements brought about by the emphasis the 
Government is placing on oceanography, tech- 
niques must change to handle the increased volume 
of data. One of the principal changes will be in 
the manner in which measurements are taken. 
The trend will be toward full automatic electronic 
systems wherever possible. This, then, will 
mean an expansion in the field of data telemetry. 

Because of the "remote nature" of the 
oceans, remote measurements will be required. 
For year-round data collection automatic telem- 
etry systems will be used. At the field location 
this will entail an automatic examination of the 
sensor, coding of the information, and trans- 
mission of this coded information. At the receiv- 
ing station these data will be received, detected, 
decoded, and presented or stored in some manner. 
These techniques are not new to the telemetry and 
communication industries but, considering the 
ranges involved, the application to oceanography 
is unique. The problems involved in the long 
range transmission of these measurements are 
discussed below. 



texts, published articles, and papers on the sub- 
ject, it would seem reasonable to guess that about 
99 percent of them make reference to radio 
telemetry application in one of the fields of 
science listed above. 

The work in the above areas has advanced 
the field of telemetry using techniques such as 
AM-FM, PPM, PAM, and PDM, to name but a 
few. For reasons to be explained later, these 
systems are limited to use in line-of-sight VHF 
and UHF systems and certain scatter systems, 
but are not usable in HF systems. Beyond-line- 
of- sight telemetry has somewhat lost its associa- 
tion with the telemetry industry and is now termed 
data transmission systems. Unfortunately, this 
field has not received the attention given to line- 
of-sight telemetry and therefore is open for 
improvement. In general, there are presently 
three means of propagation that are used to one 
degree or another for beyond-Iine-of-sight radio 
telemetry: high frequency radio, ionospheric 
scatter, and tropospheric scatter. Each of these 
methods has certain disadvantages such as the 
extreme multipath problems^ experienced in HF 
radio, a degree of multipath^ in the scatter sys- 
tems, and high power requirements of the scatter 
systems. 

It will be assumed that for remote 
oceanographic measurements an unmanned buoy 
of small size is to be used. Therefore, large 
power sources are out of the question from a 
physical standpoint, thereby eliminating scatter 
systems. This paper will detail the HF radio 
technique which is judged to show the greatest 
promise. 



TELEMETRY SYSTEMS 

Radio telemetry appears to have had its 
inception^ about 1930 by telemetering data from 
weather balloons in Germany. Since that day, 
the word telemetry has become practically synon- 
ymous with aircraft data, missile data, and space 
data whereas, in reality, the word is synonymous 
with data transmission. In reading telemetry 



HF TELEMETRY PROBLEMS 

Long range operation in the HF spectrum 
depends wholly on the ionosphere. The ionosphere 
functions to reflect radio waves of certain fre- 
quencies. Characteristics affecting the use of the 
ionosphere are: time of day (or night), season, 
II -year cycle sunspot activity, frequency, and 
geographical location. Unexplained anomalies 



Superior numbers refer to similarly numbered references at the end of this paper. 



61 



exist which occasionally cause what are apparent 
holes or areas of absorption in the ionosphere 
where radio waves are not reflected. Ordinarily, 
during daylight hours, the ionosphere consists of 
three layers of ionization capable of reflecting 
radio waves. This is best illustrated in Figure 1. 
The signal frompoint A to point B traverses three 
different paths simultaneously but, due to the dif- 
ferences in path lengths, do not arrive at point B 
simultaneously. This is another characteristic 
of the ionosphere called multipath propagation. 

When reliable signals are requiredthat 
are not distorted in amplitude, frequency, or time, 
HF systems cannot be tolerated. It was stated 
earlier that the pulse modulation techniques used 
in VHF and UHF systems were not usable in HF 
systems and only to a degree in scatter systems. 
This limitation results from the effects of multi- 
path. 



HF TECHNIQUES 

Perhaps the oldest use to which the HF 
spectrum has been applied for pulse propagation 
is radio-telegraph. Here data are transmitted in 
the form of short or long pulses called dots and 
dashes. The alternate signal paths caused by 
multipath ordinarily do not cause differential 
delays of more than 2 to 3 ms although, in some 
cases, delays of up to 14 ms have been measured. 
Three-ms delay is negligible at normal telegraph 
speeds and therefore causes no trouble. However, 
attempts to speed up a conventional radio-tele- 
graph transmission beyond, say, 300 wpm, 
become unsuccessful because delayed, or multi- 
path, components of one signal element start to 
overlap the first arriving components of the suc- 
ceeding signal element. Preceding the arrival of 
those pulse components over longer transmission 
paths, the first arrived pulse will have an am- 
plitude determined solely by ionospheric con- 
ditions, transmitted power, antennas, frequency, 
and like factors. The succeeding train of received 
pulses resulting from the one transmitted pulse 
and arriving via different propagation paths, will 
be of such phases and amplitudes as to increase or 
decrease the amplitude of the first arrived pulse 
and to distort its waveform. In the simple case 
of the two paths providing equal signal strengths, 
the resultant received signal may vary from zero 
to twice the amplitude of either in the overlapping 
area, depending upon the relative r-f phase. This 
point is best shown by using an illustration. 
Figure 2 shows a series of transmitted pulses with 
the assumed position of a single multipath com- 
ponent. If the r-f of the multipath pulse is in- 
phase with the first arrival or primary pulse, 
both amplitude and width distortion will occur. 
If out-of-phase distortion occurs for a nonsyn- 
chronous system, the number of pulses have been 
multiplied. Figure 3 shows actual photographs of 
a transmittedpulse and the corresponding received 
pulse train with the many multipath pulses. 

Another old HF pulse system is FSK 
radio-teletype. This system uses two carrier 



frequencies separated conventionally by about 
800 cps. When one carrier is on it is called a 
teletype mark, the other carrier being called a 
teletype space. The two channels are never keyed 
simultaneously. The pulses, at normal speeds of 
60 or 100 wpm, are somewhat distorted by multi- 
path components but usually do not cause garbling; 
however, greatly increased speeds are not reliably 
attainable. 

Several other pulse systems exist which 
are used in the HF spectrum. For these the same 
argument holds that the pulse repetition frequency 
must be limited to retain intelligence. Any of 
these systems may be used quite successfully for 
slow speed data systems. They should be con- 
sidered seriously if they will handle the data rate 
desired. 



STATE-OF-THE-ART 

The communications industry has been 
faced with this multipath problem for years in 
their digital systems for data, printed-message 
communications, and speech. The solution to the 
problem lies inkeeping the pulse width sufficiently 
narrow to allow the primary pulse to completely 
arrive before its multipath components and to 
space these primary pulses out in time so as to 
allow all the multipath components of one pulse 
to arrive before the second pulse. If it is 
assumed that a 3-ms gap between pulses will 
allow for the arrival of all important strength 
multipath components and a 1-ms pulse is trans- 
mitted, the data rate becomes 250 pps. 

The problems of multipath have been 
overcome successfully in several systems built 
for the U. S. Government. These systems utilize 
a modulation technique called Quantized Frequency 
Modulation. ^ Many tests have proved that these 
systems will continue to perform satisfactorily 
when the more conventional systems fail. This 
technique enables the data rate to be increased 
and, at the same time, provides multipath protec- 
tion. Quantized Frequency Modulation (QFM) is a 
frequency shifting technique applicable to digital 
transmission systems in which the transmitter 
carrier frequency is caused to change cyclically 
with time in quantized increments. By means of 
discrete frequency changes in the receiving sys- 
tem, in synchronism with those in the transmitter, 
the receiving system is made responsive to the 
QFM channels in use at any instant in time, and 
ignores the other channels. Alternatively, the 
receiver may have a bank of filters, one for each 
QFM channel and, by means of sampling tech- 
niques, achieve the same results. In both cases, 
signals propagated to the receiver over paths that 
have transmission time delays that differ from 
that of the prime path, arrive at the receiver at 
a time such that they are not normally effective 
in the receiver's digital decision process. In 
this manner, the deleterious effects of multipath 
are greatly diminished. A similar technique, 
termed Quantized Phase Modulation (QPM), 
contains the intelligence in the r-f phase as 



62 



opposed to the dual symbol type intelligence of 
QFM. (A dual symbol systen-i is one where the 
binary intelligence is contained in a pulse on 
either of two channels, such as FSK teletype. ) 

Table 1 shows the modulation modes of 
the Air Force AN/URC-33 equipment. 

TABLE 1 
AN/URC-23 Modulation Modes 







Number of 


Band- 


Data Rates 




qfm/qpm 


width 


(bits/second) 


Modulation 


Channels 


(kc) 


1000 


QFM-DCAM 


8 


7 


2000 


QFM-DCAM 


16 


14 


1000 


QPM-PM-2ct) 


4 


4 


2000 


QPM-PM-2<t> 


8 


7 


4000 


QPM-PM-2<t> 


16 


14 


4000 


QPM-PM-44> 


8 


7 


8000 


QPM-PM-44> 


16 


14 



The above table illustrates several of the 
modulation schemes possible with QFM and OPM 
but does not include any of the redundant inodes of 
operation. (A redundant system is one where the 
same binary bit of intelligence is representedon 
two or more channels, thus giving repetition. ) To 
illustrate the modulation technique in more detail, 
a dual channel system with a redundancy factor of 
four will be described. 

Figure 4 shows a typical transmitter 
output as viewed at the antenna. The signal con- 
sists of a series of cosine-squared shaped pulses 
but not all at the same radio frequency and each 
group of four representing one binary digit. The 
separate received waveforms are shown with a 
small amount of multipath which exists inthe 
receiver system through detection and integration, 
but has no effect on the converted digital output. 
This form of redundancy serves to improve 
reliability in the presence of interference. 

There are many possible configurations 
of QFM and QPM. Categorically, a particular 
system cannot be recommended for oceanographic 
use until such parameters as data rate, reliability, 
bandwidth allocation, and geographical locations 
are determined. In addition, several other 
problems enter into the system. If continuous 
24-hour data are required and interim storage at 
the source is impossible, operating frequency 
becomes a problem. Usually, the optimum fre- 
quency for daytime use will not even be usable at 
nighttime and vice versa, therefore, multiple fre- 
quencies will be required for continuous duty. 
Power, of course, will be a never-ceasing problem 
for an unmanned buoy but will not be treated here. 



The final problem, but not inthe technical 
area, is one of getting a frequency allocation in 
the HF band. A recent letter from the FCC to the 
author indicates that there are presently no alloca- 
tions for oceanographic data use, nor is the Com- 
mission anticipating the allocation of any for such 
work. This will not interfere with data collection 
by Government organizations because their cur- 
rent allocations may be used as they see fit in 
most cases; but the private institution will suffer 
unless their sponsoring agency grants an alloca- 
tion. However, experimental licenses and alloca- 
tions may be obtained and, although good only for 
a limited period of time, may be adequate to com- 
plete a specific program. 



FUTURE TECHNIQUES 

It has been suggested that in the future 
data may be collected in remote locations and 
telemetered to shore via a satellite system. 
This is probably very practical and feasible, but 
is still many years in the future considering the 
other more pressing requirements of communica- 
tion satellites. 

A possible new field of communications 
exists where the earth strata found just under the 
deep oceanfloor may propagate transmitted energy 
to a receiver site. If so, oceanographic equipment 
may be placed on or near the ocean floor, thus 
eliminating the need for surface equipment, except 
for a subsurface buoy for maintenance purposes. 
This would eliminate the surface equipment which 
is always subject to pilferage and ship damage. 
Investigation of these techniques is now in 
progress. 



REFERENCES 

1) Nichols and Ranch, Radio Telemetry, 
edition. 



2nd 



2) J. D. Lambert, "High Frequency Multipath 
Analysis bythe Short F>ulse— Long Pulse Method, " 
IRE Convention Record , Part 1, pp 294 to 299, 
1957 Wescon. 

3) J. H. Chisholm, et al, "Investigation of 
Angular Scattering and Multipath Properties of 
Tropospheric Propagation of Short Radio Waves 
Beyond the Horizon, " Proc. IRE, Vol. 43, 
pp 1317 to 1335, October 1955. 

4) George A. Scheer, "New System Defeats 
Multipath Effect, " Electronic Industries, May 
I960. 

5) J. M. Snodgrass, "Problems of the Oceanog- 
rapher in the Space Age," Proc. of the 
National Telemetering Conference, p 12-9, 
TWT. 



63 





TRANSMITTED PULSE 




FIGURE 1. MULTIPLE SIGNAL PATHS VIA THE IONOSPHERE. 



RECEIVED PULSE 
FIGURE 3. PHOTOGRAPH OF MULTIPATH COMPONENTS. 




TRANSMITTED R-F 



-0000000000000000000000000000- 



.NSMITTER OUTPUT 




TRANSMITTED R-F WITH MULTIPiTH COMPONENTS 




r\r 




RECEIVED R-f WITH MULTiPflTM IN PHASE 



RECEIVED H-F WITH MULTiPATh OUT OF PHASE 



-O 0)^~o — 

-o o— o— 

—o o-o- 

— o c^-o- 



-o- 



— o 



— o— o— o- 



RECEIVED WAVEFORMS AFTER SEPARATION 



-Oy-O-O — 

-O — o — o — 




ITEGRATEO DATA 



^ r 



CONVERTED DIGITAL DATA 



FIGURE 2. EFFECTS OF MULTIPATH. 



FIGURE 4. DUAL SYMBOL REDUNDANT SYSTEM WAVEFORMS. 



64 



A DATA PROCESSING AND DISPLAY INSTRUMENT 
FOR OCEANOGRAPHIC RESEARCH 

by JOSEPH T. LAING, Section Manager, Ocean Survey Systems 
Westinghouse Electric Corporation, Ordnance Department 
Baltimore, Maryland 



ABSTRACT 

A data processing and display instrument 
consisting of a high-speed digital computer and 
precision X-Y plotter is described. Originally 
developed by Westinghouse for navigational 
purposes, the instrument is suitable for similar 
use in oceanographic survey work as well as real- 
time processing and plotting of such oceano- 
graphic research data as temperature, depth, 
sound velocity, water currents, and similar pa- 
rameters. By means of a universal input-output 
system and the capacity for general purpose 
programming, the instrument can be easily adapted 
to a wide range of oceanographic problems at sea 
and in the laboratory. Pictures are shown 
depicting the type of equipment currently 
available, and modifications for several specific 
applications are discussed. 



INTRODUCTION 

The expanding effort on the national scene of 
oceanographic research and world-wide surveys is 
presenting the scientific community with greater 
challenges than ever before in the collection and 
analysis of oceanic data. No less challenge is 
presented to industry in supporting the scien- 
tific community through mechanization of instru- 
mentation systems which are truly responsive to 
the oceanographic problems at hand. There is 
perhaps no greater challenge in this area than 
the processing and reduction of the vast quanti- 
ties of data emanating from oceanographic 
research and survey programs. In this paper I 
will describe one general- purpose instrument 
designed for shipboard processing and recording 
of certain types of data, and I will attempt to 
show its application to a wide range of oceano- 
graphic data processing problems. 



GENERAL DESCRIPTION OF OPERATION 

The instrument is essentially a digital 
computer and X-Y plotter integrated into one 
package. It was originally designed and built 
for the U.S. Navy Bureau of Ships as part of a 
military defense system. The nature of its 
mission here required that it be versatile in 
its adaptability to various modesof operation 
related to the original problem. The same 



versatility also permits the solution of problems 
of a somewhat different nature. 

In its principal mode of operation the 
instrument accepts analog data in the form of 
ranges or bearings from navigational control 
stations, computes the precise geographical 
position of the ship, and plots this position on 
a nautical chart. In addition, the position 
data are transmitted digitally to other output 
devices. Fig. 1 is a block diagram of the 
instrument. In the main computer- plotter console, 
a bank of analog- to-digital converters converts 
the voltages from various sensors into binary 
form for entry into the computer. Sensor voltages 
are, in the case shown, cabled to the console from 
the navigational control system (such as Shoran, 
Loran C, or OMEGA) and entered into the computer 
by this route. The computer, having been 
previously instructed by insertion of an appropri- 
ate program, performs the computations necessary 
to determine the geographic position of the ship. 
Upon command from the computer, this position is 
plotted on the chart and simultaneously trans- 
mitted to remote output devices which include a 
Friden Flexowriter and remote digital displays. 
Note that in the case of the plotter the position 
data must be converted to analog voltages for 
driving the plotter servo system. Full digital 
accuracy is, of course, preserved in the data 
printed out on the Flexowriter and displayed 
elsewhere. 

The steering aid shown is actually a by- 
product of the position computation, in that it 
permits the comparison of the computed position 
with a desired position based on some preselected 
course of the ship. An appropriate error signal, 
proportional to distance off course or preferably 
distance plus angle, may be displayed at the helm 
as an aid in following survey lines. 

Other sensor data may be brought in as desired. 
The plotting of some position other than ship 
position, as, for example, that of a remote 
sensor in communication with the ship, may require 
a correction for ship's heading. In another case, 
on-station plots of temperature versus depth for 
synoptic surveys may be desired and may be 
cabled in along with other parametric data. In 
yet another case, ship's course and speed may 
be brought in to operate the instrument as a 
dead- reckoning tracer. 



65 




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In all cases the computer program is the key 
to the use of the instrument. The computer may 
by considered a general purpose machine to the 
extent that the desired functions fall within its 
storage and arithmetic capacities, which I will 
discuss later on. Programs which have been 
previously written, coded, and prepared on 
punched paper tape are loaded through the tape 
reader on the Flexowriter. In this way a change 
from one mode of operation to another may be 
achieved with convenience and minimum down time. 



DESCRIPTION OF EQUIPMENT 

Fig. 2 shows the main computer-plotter console 
with the plotter cover in the raised position. 
Thisunit is 51 inches long, 46 inches wide, and 
44 inches high. It weighs approximately 1600 
pounds. The X-Y plotter was built by Electronic 
Associates, Inc., to our specifications and, for 
installation, is separable from the base cabinet 
containing the digital computer and input-output 
units. The base cabinet is modular and can be 
further subdivided to facilitate installation or 
removal of the equipment. The master control 
panel shown governs operational mode selection, 
insertion of operational constants germane to the 
task being performed, and various other control 
functions affecting the computer and plotter. 
One of the operational constants mentioned would 
be, in a typical case, the geographical coordi- 
nates of the navigational control stations. 
Another would be the chart scale factor, etc. 

Fig. 3 shows the Friden Flexowriter used with 
the instrument. In a typical case the machine 
prints out positional and other parametric data 
required by the program and simultaneously 
punches the same data on coded paper tape. The 
punched tape data may be used for further data 
processing at a central facility as well as for 
recreating the plotted data on the same or 
similar instrument at another time. 



INPUT ANALOG -TO- DIGITAL CONVERTERS 

As mentioned previously, data enters the 
console as analog voltages which are converted 
internally to binary form. 400 cps. synchros 
have been standardized on for transmission of 
shaft positional data to the console. A bank 
of several shaft position-to-digital converters 
is provided to accept this information and con- 
vert it into 10-bit binary numbers. Relays are 
used to switch the limited number of converters 
among the many data sources necessitated by the 
various operating modes, thus attaining a 
measure of input flexibility while maintaining 
economy of equipment. 

Fig. 4 is a schematic diagram of one analog- 
to-digital converter presently used. It is a 
simple servo follower in which the voltage from 
the 400 cps. synchro transmitter at the data 



source feeds the stator of the control trans- 
former in the converter unit. The amplitude of 
the voltage across the rotor will be proportional 
to its angular displacement from the null 
position and the phase of the voltage will 
indicate the direction of the displacement. The 
error voltage is amplified by the transistor 
servo amplifier .which then drives a servo motor 
coupled through a gear train to a lO-bit code 
wheel and to the control transformer rotor. 
With the servo nulled, the digital number 
generated by the code wheel corresponds to the 
angular position of the remote synchro trans- 
mitter. A photograph of one of the servo 
follower units is shown in Fig. 5. These units 
are manufactured by the Datex Corporation. 

Other means of data entry can be provided in 
those cases where digital data are already 
available or where voltage- to-digital conversion 
is required. 



DIGITAL COMPUTER 

The digital computer contained in this 
instrument is a general purpose transistor 
computer designed for shipboard applications. 
The program is stored in a magnetic drum memory. 
Physically, the computer is subdivided into 
printed card chassis, as shown in Fig. 6, which 
are mounted on the cabinet doors and hinged on 
one side to provide access to the chassis 
wiring at the back. Each chassis contains 
approximately one hundred printed solid-state 
logic cards of standard Westinghouse design. 
They contain accessible test points for trouble 
shooting and are easily removed and replaced. 
The computer contains five such chassis, 
including input-output units, in addition to 
other subassemblies containing power supplies 
and memory circuits in the interior of the 
cabinet „ 

Although the design of the computer is an 
interesting subject in itself, a detailed 
discussion of it would not be appropriate or 
possible here. Needless to say, it is, in terms 
of physical and technological complexity, the 
principal item in the instrument. The philosophy 
of its design was founded on the requirement 
for a computing facility combining rapid 
arithmetic computation in real time, precision, 
reasonable storage capacity, and physical com- 
pactness. A summary of the important computer 
characteristics should be of interest and will 
be listed. 

Summary of Computer Characteristics 

Input-Output Unit: 

Up to 32 programmed inputs of 23 bits each 
(parallel transfer) 

Up to 512 outputs of 23 bits each (parallel 
transfer) 



67 




FIGURE 2 COMPUTER -PLOTTER CONSOLE 



68 



Control Panel 



Keyboard 




Tape Punch 



Punch Indicator 
Light 



Tape Reader 



Writing Machine 



FIGURE 3 FRIDEN FLEXOWRITER 



^A[/i6Arioi[J Aid 

I 1 




1 15 V 
400 CPS 



FIGURE 4 INPUT SERVO SYSTEM SCHEMATIC DIAGRAM 



69 




FIGURE 5 INPUT SERVO FOLLOWER UNIT 




FIGURE 6 DIGITAL COMPUTER SUBASSEMBLY 



70 



Memory Unit: 

4032 words of command storage 
1008 words of constant storage 
404 words of data storage 

5 fast access registers of 2, 3, 5, 7, and 
9 words 

Arithmetic and Control Unit: 

Modified 5-address command structure 
6 arithmetic commands: 



Add 

Subtract 
Multiply 
Divide 
Square root 



165 microseconds 
155 microseconds 
165 microseconds 
2000 microseconds 
2000 microseconds 



3 transmit commands 

5 conditional transfer commands 

Number representation: binary, fixed point, 
fractional 

Instruction and data word length: 23 bits + 
sign 

Clock rate: 300 KC 

The above characteristics of the computer, 
combined with suitable programming, endow the 
instrument with the capacity to compute 
geographic positions to a net accuracy of about 
one part in 18,000, which is considerably better 
than the accuracy of any navigational control 
system in existence today. However, the basic 
computer itself is about ten times more accurate 
than this, allowing some margin for future 
accommodation of more accurate navigation 
systems through reprogramming and reorganization 
of input circuits. Similar considerations apply 
for other types of data to be processed. 



the feedback potentiometer and to the printer 
carriage in a conventional servo loop. The servo 
is nulled and the printer carriage correctly 
positioned when the feedback voltage equals the in- 
put voltage. A similar servo is used to position 
the plotter arm on which the printer carriage 
moves. All converter and plotter circuits are 
solid-state. 

The symbol printer, shown in Fig. 8, contains 
a stamping mechanism, ribbon supply, a cross-hair 
for visual alignment, and symbol selector logic 
governing the selection of any of twelve different 
symbols. In normally automatic operation, 
plotting is performed upon command of the computer 
when plotter arm and printer carriage are sensed 
to be correctly positioned. Symbol selection 
is also normally governed by programmed 
instructions in the computer, which transmits 
the commands in accordance with the binary coding 
arrangement shown in Fig. 9. The symbols shown 
are located around the periphery of a small disc 
which also contains the conductive coding pattern. 
The symbols are selected by matching the 4-bit 
word associated with each symbol with the 
corresponding word sent by the computer. 

In automatic operation, data points relatively 
close together may be plotted as fast as once per 
second. Points separated by distances up to the 
maximum dimension of the plotting area may require 
two or three seconds. Points may also be plotted 
manually from the master control panel through 
appropriate controls for setting in data and 
energizing the symbol printer. 



OCEANOGRAPHIC USES 



DIGITAL-TO-ANALOG CONVERTER AND PLOTTER 

The digital-to-analog converter converts 
binary- coded-decimal data from the computer to 
highly accurate D.C. voltages to drive the 
plotter. This conversion process takes place 
with an accuracy of about one part in 10,000. 
The servo drives in the plotter and the plotting 
mechanism itself reduce the overall plotting 
accuracy to about one part in 1,000, which on the 
30-inch plotting surface is 0.03 inch. The 
plotting accuracy is thus far less than the 
inherent digital accuracy of the instrument, but 
this is of little consequence since the digital 
data are printed and punched in code on the 
Flexowriter for whatever use one wishes to make 
of them. 

A simplified schematic diagram of the plotter 
servo system is shown in Fig. 7. The analog 
voltage from the operational amplifier in the 
digital-to-analog converter is added in series 
with the voltage across a feedback potentiometer 
which is energized from a constant voltage 
source. The resultant error voltage is chopped 
and amplified to drive a servo motor coupled to 



With this brief description of the instrument 
itself in mind, I would like to direct your 
attention to two possible uses of this instrument 
in oceanographic work. They are both elementary 
examples and both make use of the position 
computation mode I have described. 

In the first case, assuming the availability 
of an adequate fathometer, one has the means at 
hand to generate a bottom contour map in real 
time during a survey. As shown in Fig. 10, the 
computer can be instructed by its internal 
program to recognize preselected contour intervals 
and to plot them accordingly with chosen symbols. 
It is assumed here that corrections in either 
positional or bathymetric data can be made either 
at the source or transmitted separately to the 
computer for inclusion in the data processing. 
As fathometers and navigation systems improve, 
the resulting increase in the volume of meaning- 
ful data collected will furnish great incentive 
for this type of instrumentation. 

In the second case, shown in Fig. 11, the 
printer is modified to select numbers instead of 
abstract symbols. The result is simply a depth 
plot similar to a hydrographic smooth sheet and 



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Ribbon 
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Ribbon 



FIGURE 8 SYMBOL PRINTER 



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FIGURE 9 SYMBOL PRIHTER CODE 



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any contouring would be performed manually. 
Parameters other than depth could be similarly 
plotted in this mode. 



CONCLUSION 

In conclusion, I have described a digital 
data processing and display instrument of rather 
broad capabilities as an example, if you will, of 
the tools which modern-day technology is making 
available to scientists working in oceanography. 
I have attempted to relate certain character- 
istics of the instrument, such as precision, 
real-time reduction, flexibility, and functional 
completeness, to similar requirements which 
seem to me to be pertinent to the oceanographer ' s 
task. And finally, I have shown two elementary 
examples, and there are many more, of how such 
an instrument could be put to work in a very 
practical sense, relieving the scientist of much 
of the burden of his own data reduction. 



ACKNOWLEDGMENT 

I would like to acknowledge the efforts of the 
many people whose individual skills and hard 
work are represented collectively by this 
instrument; in particular, the contribution of 
D. M. Scott of the Westinghouse Electronics 
Division, under whose supervision the digital 
computer was designed and built. 



76 



TIMING CONTROL METHODS AVAILABLE 
FOR SELF-CONTAINED RECORDING SYSTEMS 

by ALEXANDER L. M. DINGEE, Jr., and A. FRED FEYLING 
Geodyne Corporation 
Waltham, Massachusetts 



ABSTRACT 

Tiniing methods are important in data col- 
lection. There are a large variety of direct 
current powered timing devices which might be 
used in self-contained data recording or trans- 
mitting devices. This paper discusses accuracy, 
price and some of the significant aspects of 
various timing devices which can be used in 
oceanographic and limnological equipment. 



1 part in 10 to 1 part in 5. For practical pur- 
poses we eliminated atomic resonance for we felt 
that most oceanographers would not want to pay 
between +10,000 and $100,000 for accuracies of 
one-ten millionth of a second per day. 



Discussio:: of td-iers 



INTRODUCTION 

In recording oceanographic and limnological 
data, the time axis is often as important as the 
variables being recorded. Recording or con- 
trolling with respect to time can be difficult 
without 60 cycle A. C. power available. For ex- 
ample, in self-contained recording or telemetry 
buoys, using lapse-time techniques to store or 
transmit information, the simple closure of a 
switch on cycle presents significant problems 
which can easily be solved in the laboratory 
with a $1.95 clock motor. 

Oceanographers are not the only group faced 
with this problem. Lincoln Laboratories, at 
K.I.T. , received an ionospheric sounder to 
measure the time it takes a radar pulse to travel 
to the ionosphere and return. These units were 
used throughout the world for the International 
Geophysical Year. The equipment also required 
a switch closure once every fifteen minutes to 
control a film advance mechanism. Two large 
crates were delivered to Lincoln Laboratory. The 
first contained a six-foot rack of sophisticated 
space-age electronics for measurinf; the radar re- 
flectance time. This was the ionospheric sounder 
unit. The second crate, larger than the first, 
contained the time standard for the film re- 
corder, complete with proper cams and micro 
switches. It stood over 6' tall in the original 
beautiful mahogony case. This timing unit, sup- 
plied by a well-known space-age company, was a 
good, reliable grandfather's clock. 

In this study of small, self-contained D. C. 
powered timing sources capable of low frequency 
switching, cycles of one minute to twelve hours 
were covered. Other considerations were: tem- 
perature ran?e, dependability, size, weight, 
power consumption and ease of maintenance and ad- 
justment. Repeatability, accuracy ran from 



Points to be considered with electronic 
timers are the effect of volta~e variation, tem- 
perature variation, moisture and aging of parts. 
Generally electronic timers operate at high fre- 
quencies and require preset counting circuits to 
trigger Evritches. The contact closure is usually 
controlled magnetically or by solid-state relay. 
Types of timers are as follows: 

Crystal Co ntrolled Ofipillator. A crystal 
which can operate at frequencies as low as 1 kilo- 
cycle can easily obtain accuracy of ±1/10 of a 
second per day. The use of counting circuits is 
necessary to count down to the desired number of 
pulses per hour. Due to this counting the price 
of such a unit v/il]. run from approximately $500 
to $£,000. 

Tuninj: Fork Oscillator . This is much the same 
as a crystal oscillator except that a tuning fork 
is used for the frequency source. Such a unit may 
operate as low as 5C cycles per second. The 
accuracy is ilO seconds per day. The counting 
circuit is simplified because the base frequency 
is lower. Cost of such a unit would be $350 to 
$1,600. 

L. G. Resonant Circuit . Proper combination of 
inductance and capacitance will give a circuit 
which will oscillate at a given frequency. Ac- 
curacy can be better than ±1 minute per day. An 
L. C. circuit can be made to operate as low as 
5 or 10 cycles per second. A counting circuit 
for switch closure is still required. The approx- 
imate price would be $200 to $500- 

Relaxation Oscillator using resistive and 
capacitive or inductive circuitry. An example is 
the charging of a capacitor with s battery to a 
given voltage level at which point a neon bulb, or 
other detector, triggers and discharges the capa- 
citor. The cycle time is limited by the size and 
leakage from the capacitor. It is fairly easy to 



77 



make such circuits with cycle times of several 
minutes. These can be extended with care to 

1 hour. Accuracy of il'* minutes per day can be 
obtained. Such a unit might draw anywhere from 

2 to 5 watts maximum power. The price would run 
between $100 and $200, 

Reed Controlled Count Down , A more in- 
expensive version of the tuning fork method is to 
use a vibrating reed which directly makes an 
electrical contact. This circuit closure then 
would be counted down the same as the tuning fork 
frequency. Estimated accuracy on such a unit is 
i? minutes per day. Life would be dependent upon 
contacts and might be as much as 2,000 hours. 
The estimated price would run $100 to $200. 



MECHANICAL TIMERS 

Possible trouble points in mechanical timers 
are: position sensitivity, temperature compensa- 
tion, variation of rate with battery voltage, 
life of brushes, life of the rate controlling 
mechanism, power consximption , resistance to shock, 
low torque, generation of electrical interference 
and lubrication, bearing quality and lubrication. 

D, C, motors are used widely as timers, Un- 
governed D. C„ motors as a rule cannot be counted 
on for accuracies of better than ±2 hours per day 
because of battery life. Also, if the temperature 
in the winding increases, the resistance drop in- 
creases and, therefore, speed vrill drop. Prices 
on D. C. motors can range anywhere from thirty 
cents to many hundreds of dollars. 

Governed D.C, Motors , (a) Centrifical Speed 
Control. Centrifically operated contacts mounted 
on the motor shaft will break motor power con- 
tacts or switch in dropping resistors as the de- 
sired speed is exceeded. Approximate accuracy 
is tl'* minutes per day. This motor would draw 
.03 to .06 watts and give 4 ounce inches torque 
at 1 R,P,M. The life will be around 1,000 hours. 
The price can be as low as $17. To construct a 
timing device from a D.C. motor, one must add 
cost for cam, switch, bracket and housing; 
(b) Reed Contact Control. The motor receives 
part of its power through contacts mounted on a 
reed which vibrate at a given frequency. The 
reed passes current to the motor shaft in pulses. 
If pickup on the shaft is not in phase with the 
reed pulse, pulse duration to the motor is 
shortened or lengthened, depending on whether the 
motor is lagging or leading the control speed; 
thus, the length of time that power is applied to 
the motor per pulse is varied as a speed control. 
This method can hold accuracies of ±7 minutes per 
day. If it is adjusted closely and voltage 
fluctuations are not too great, accuracies ap- 
proaching ±3 minutes per day may be obtained. 
The unit is position sensitive, however. Life 
figures on this unit are incomplete. Life may 



approximate 3>C00 hours, but there is some ques- 
tion of contact failure. Power input is l/2 to 
2 watts. The price of the motor itself is $45» 
The switching assembly would be extra; (c) Chrono- 
metric Contact Control. This unit functions ap- 
proximately the same as the reed contact control 
except that the frequency standard is chronometric 
rather than reed. It is capable of holding 
i8 minutes per day in a temperature range -10° 
to lOQOF. Speed can be held to i2 minutes per day 
in narrow temperature ranges. The current re- 
quired by this unit is 250 micro amperes at 
1.5 volts. Points to check in this unit are; 
ability to withstand shook, contact life and 
position sensitivity. Life is estimated to be in 
the order of years. The approximate price is $100 
for the motor without the cam-switch assembly. 
There is another unit available which has higher 
current drains but has better resistance to shook 
and more torque output. Price of this unit is 
$75. Life is guaranteed for 1,200 hours. 

Clock Movements . These are used the same as 
the D.C. motor, i.e., to rotate a cam against a 
micro switch at uniform rate, (a) Impulse Type. 
The balance wheel is given an impulse every cycle. 
This type of movement generally has few or no 
jewelled bearings. The estimated price is $10 to 
$12, not including timing assembly; (b) Solenoid 
or Motor-Winding Type. In this unit a spring is 
wound by a solenoid or motor once every few 
minutes. The average power input of this type is 
approximately 1 milliwatt. Torque output of such 
units covers a wide range — a representative figure 
might be k grams centimeters torque at 1 revolu- 
tion per hour. As the movements operate from 
spring power, voltage fluctuations do not affect 
them. The units should be checked for jewelled 
bearings, shock mounting of pivot shaft and 
proper temperature compensation. Accuracies can 
be expected of ±10 seconds per day with a life of 
1 to 5 years. This type of movement will cost 
from $12 to $30 with no provision for timing 
assembly; (c) Spring-Wound Movement, In these 
units a heavy-duty clock movement is driven by a 
hand-wound spring. The torque output is sufficiat 
to be used as a circular chart drive. Thirty-one 
day movements can be obtained. Accuracy is es- 
timated at ±10 minutes per day. Price of such a 
unit without the timing assembly— $12.50. 

Thermal Timers . A bi-metallic strip is de- 
flected by an electric heater, making or breaking 
a contact. Reset tiine is determined by how 
quickly the unit cools off. The cycle depends 
upon voltage and ambient temperature. Accuracy of 
about ±2 hours per day. Price $.50. 

Restricted Flow of Mass . A series of timers 
depend upon an orifice restrictlnf mass flow at a 
gi\^en rate. An example would be air compressed by 
a solenoid-driven piston and released slowly 
through an orifice. These units provide reliable 
operation with an accuracy of ±2 to j hours per 
day but are limited to maximum intervals of 



78 



20 minutes. Averare power consumption is 6 watts. 
The price will range from $.50 to $150. The 
price of the above air device is $30. 



COKCLUSIOM 

To solve our switching problems, we used the 
grandfather clock technique. We selected a 
solenoid-wound chronometric movement for our base 
timing source because it offered acceptable ac- 
curacy of ilO seconds per day at a reasonable 
cost. Also involved in our consideration were 
low power consumption, independence from voltage 
fluctuations, long life, small size, simplicity, 
dependability and flexibility in selection of 
cycles ranging from 1 minute to 12 hours by 
changing cams. We adjust these sequence timers 
on a crystal oscillator time standard recorder 
and ship the recording slip with the unit. The 
timers have been produced for over a year and 
have proven their ability to retain reliability 
and accuracy after the rough handling and 
droppage involved in placing an instrument pack- 
age in the ocean. 

Grandfather's old clock is still good. 



79 



A CONCEPT FOR A REMOTELY INTERROGATED 
SYNOPTIC OCEANOGRAPHIC DATA SAMPLING BUOY 



by RICHARD A. ZLOTKY, Project Engineer 
Chance Vought Corporation 
Dallas, Texas 



ABSTRACT 



A concept is proposed for a remotely inter- 
rogated synoptic oceanographic data sampling 
buoy system. It is an anchored system capable 
of sampling oceanographic data from the ocean 
surface to a depth of approximately U^OOO feet. 
An electro-mechanical system that converts 
ocean wave energy into electrical power is dis- 
cussed. It is this power generator that makes 
the proposed long life buoy concept feasible. 



INTRODUCTION 

Chance Vought Corporation, in its effort 
to develop more effective ASW systems, realizes 
the necessity for more knowledge about the 
ocean environment than is presently available. 
Synoptic conditions in the sea must be known 
before ASW prediction systems become success- 
ful, and before ASW acoustic techniques 
become reliable. As a result of this need, 
Chance Vought Corporation has examined the 
feasibility of providing a long life buoy to 
be deployed in large areas of the ocean. The 
proposed concept can sample and store data, 
and can be interrogated by an airplane, ship 
or shore station. 



CYCLE DESCRIPTION 

The cycle description is shown in Figure 2. 
The first phase consists of a three hour period 
for charging the batteries in both the equip- 
ment buoy and bobbing buoy. The main batteries 
are charged by the MECH-CON-SEA power generator 
and the bobbing buoy batteries are charged by 
the main batteries. In the second phase, the 
buoyancy of the bobbing buoy is changed from 
plus 5 Ih. to minus 5 lb. During this 6 minute 
period the electronic equipment is given suf- 
ficient time to warm-up. During the third 
phase the bobbing buoy descends to a depth of 
U,000 ft. while data is being sampled and re- 
corded. The descent velocity is approximately 
k ft. per second which precludes instrument 
sensing lag time if data is sampled approxi- 
mately once per second. The buoyancy change 
from minus 5 Ih- to plus 5 lb. takes place dur- 
ing the 6 minute fourth phase and the buoy makes 
the l6 minute ascent back to the equipment buoy. 
The data recorded during the bobbing buoy des- 
cent and ascent is transferred to the equipment 
buoy whereby the bobbing buoy tape recorder is 
erased. All data is stored by the equipment 
buoy tape recorder until it is interrogated. 
Upon a successful data transmission, the equip- 
ment buoy tape recorder is given an erase com- 
mand. 



GENERAL ARRANGEMENT 



The general arrangement of the buoy system 
is shown in Figure 1 . The Company name for 
the buoy is TELME which stands for TELe metered 
Medium Environment. The buoy consists of a 
power generator system called MECH-CON-SEA 
which stands for MECH anical CONversion of SEA 
power, an equipment buoy, a bobbing buoy and a 
taut line anchoring system. The equipment buoy 
houses the main batteries, power generator, 
recording equipment, transmitter and receiver. 
The bobbing buoy houses a small battery supply, 
buoyancy cycle control system sensors, and tape 
recorder. The equipment buoy is located ap- 
proximately 50 ft. below the sea surface and 
the bobbing buoy rides the anchor cable from a 
depth of 50 ft. to approximately U,000 ft. 



MECH-CON-SEA POWER GENERATOR 

The MECH-CON-SEa power generator operates on 
the principle of obtaining maximum relative 
motion between the float and cable reel shown in 
Figure 3- Maximum relative motion is obtained 
by utilizing the taut wire plus a large trapped 
water mass in the lower compartment of the 
equipment buoy. The trapped water mass minimizes 
the tendency of the equipment buoy to rise along 
with the float. Energy is put into the power 
accumulator spring on the float upstroke only. 
The cable is rewound by the reel rewind spring 
as the float falls . The stored energy in the 
power accumulator spring is released through a 
gear box, A.C. generator, and a rectifier and 
regulator . 



80 



GENERAL ARRANGEMENT 



FLOAT (MECH -CON- SEA POWER) 
SOFT 



ANTENNA 



POWER CABLE £ BELLOWS SEAL 



L 



4000 FT 



CABLE WINCH 
BOBBING BUOY -UP POSITIOI 



BATTERIES 

CYCLE CONTSOL SYSTEM 

SENSORS 

TAPE RECORDER 




EQUIPMENT BUOY 



MAIN BATTERIES 
POWER GENERATOR 
RECORDING EOUIPMEMT 
TRANSMITTER 
RECEIVER 



ANCHOR CABLE 



BOBBING BUOY DOWN POSITION 




FIG. I 



e/ti^e ^iSSt?^/f^ai^ 



STANDBY BUOYANCY DESCEND BUOYANCY ASCEND 
CHANGE CHANGE 




CHA.RGE WAIN 

BATTERIES i 

BOBBING BUOY 

BATTERIES 



CHANGE FRO^^ 

+ 5 LB TO -5 LB 

WARN\ UP 

ELECTRONIC 

EQUIPMENT 



16/VMN. 

DESCEND AT 
4 FT/S - SAfAPLE 
DATA ONCE PER 
SECOND K RECORD 
TEWP- PRESSURE- 
TURBIPITY- CURRENTS 
SPEED OF SOUND, c/c 



BUOYANCY 
CHANGE FROM, 
-S LB TO +5 LB 



F(6 2 



16 MIN. 

ASCEND AT 
4 FT/S - SAMPLE 
DATA ONCE PER 
SECOND i RECORD 

15 MIN. 
TRANSFER. DATA 
TO EQUIP BUOY 



81 



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FLOAT 





STABILIZING ROP 

CABLE 

TEFLON BELLOWS 

SEAL 

-CABLE REEL 

-SEALED 
COMPARTMENT 
IN EQUIPMENT 
BUOY 



CABLE TO 
ANCHOR 



MECHANISM SCHEMATIC 



MAIN 
BATTERIES 



CABLE REEL 

RATCHET CLUTCHES 

li 




RECTIFIER 4 REGULATOR- 
SOLID STATE ELECTRICAL 
COMPONENTS 



A.C. GENERATOR 
GEAR BOX 

PQVWER ACCUMULATOR SPRING 



REEL REWIND SPRING 



FIG. 3 



£0^/A^£A^^iy!P/^ 



SEALED 
COMPARTMENT 



CABLE WINCH 



WATER MASS 
COMPARTMENT 
(NO SEALS) 



BOBBING BUOY 
UP POSITION 



CABLE TO ANCHOR 




CABLE REEL # 
GENERATOR 



- VENT 



WORM GEARS 
(IRREVERSABLE) 

GEAR SHAFT 
SHAFT LOCK CAP 



GEAR SHAFT 
MOTOR DRIVE 
(PLUG IN) 

TRANSFORMER 



FIG. 4. 



82 



EQUIPMENT BUOY 

A sketch of the equipment buoy is shown in 
Figure h. It consists of a sealed compartment 
for electronic equipment, MECH-CON-SEA mecha- 
nism, and a trapped water compartment . The 
bobbing buoy is shown in its up position as it 
is nested in the power transformer receptical . 
An inductance connection is used to transfer 
power from the equipment buoy to the bobbing 
buoy. The small winch shown in the sketch is 
used to winch the buoy down to the 50 ft . 
level . 



BOBBING BUOY 

The bobbing buoy cycling system is shown 
in Figure 5- The principle used is to take 
in water for negative buoyancy and to expel 
it for positive buoyancy. This is done with 
hydraulic accumulators. The timer provides a 
signal to the cycle control which starts the 
motor and hydraulic pump. In going from posi- 
tive to negative buoyancy, hydraulic oil is 
pumped from the accumulators into the air 
bottles until the liquid level sensor shuts 
off the motor. The average air pressure in 
the bottles is 1,000 psi so that the pump 
operates against a delta pressure of 1,000 psi 
both at the ocean surface and at the 4,000 ft. 
level. Pressure cut-off switches are provided 
in case the liquid level sensor fails to operate 
properly. The bobbing buoy configuration is 
shown in Figure 6. The buoy length is 72 in. 
and the maximum diameter is 20 in. A hollow 
tube used to guide the bobbing buoy down the 
cable extends lengthwise through the buoy. A 
rough and fine ballast adjustment is provided 
so that the buoy can be adjusted to neutral 
buoyancy in the water. A bilge pump is also 
provided to take care of any seepage of sea 
water into the buoy. 



ELECTRONIC EQUIPMENT 

A block diagram of the TELME buoy system 
electronic equipment is shown in Figure ?• 
The operation of the equipment is as follows. 
Timer #1 completes timing the period between 
cycles and opens the relay through which power 
is supplied from the battery to the static 
inverter. Power across the transformer is 
momentarily interrupted. Timer #2 is started 
by the power interruption and it provides a 
signal to energize switch unit #2. Switch 
unit #2 completes the circuit to start the 
electronic equipment in the bobbing buoy and 
it also sends a down signal to the buoyancy 
system. After the momentary Interruption of 
power across the transformer, the relay is 
deenergized and power flows normally to the 



bobbing buoy. Its battery is therefore fully 
charged as it starts the dive . At the end of 
the buoyancy change period, power to the trans- 
former is again interrupted. The bobbing buoy, 
now negatively buoyant but held in place by 
magnetic clutch action between the two trans- 
former cores, is released to dive. Timer #2 
times out the period necessary for the dive to 
4,000 ft. at which time it energizes the buoy- 
ancy system to go positive. Timer #2 times a 
30 minute period after the up signal is given. 
Normally the bobbing buoy will return to the 
equipment buoy within approximately 23 minutes. 
However, if something on the line prevents the 
return of the bobbing buoy, timer 7^2 will re- 
verse the buoyancy in 30 minutes. This proce- 
dure is repeated until the bobbing buoy battery 
is depleted or until it returns to the equip- 
ment buoy. The battery has sufficient capacity 
for three complete up and down cycles . When 
the bobbing buoy returns and the power trans- 
former is activated timer #1 starts timing a 
new cycle. Timer ffl energizes the recording 
system in the equipment buoy and timer ff2 
energizes the playback system in the bobbing 
buoy. Data is then transferred from the 
bobbing buoy to the equipment buoy. The re- 
ceiver in the equipment buoy operates continu- 
ously. When an interrogation signal is re- 
ceived, switch unit jfl Is energized from the 
receiver. The switch unit interrupts power to 
the timer and data acquisition system and 
energizes the data transmission system. An 
operator monitors the data received and after 
a satisfactory data reception he signals the 
buoy to erase the tape . 



SYSTEM POWER REQUIREMENTS 



The system power requirements are shown 
in Figure 8. Power requirements are broken 
down into the various parts of the h hour 
cycle. The total power required is 236 watt- 
hours. The power available from the MECH-CON- 
SEA power generator is shown in Figure 9- Wave 
data, height and period, are taken from sta- 
tistical sea state information from the Pacific 
Ocean. The average long time continuous power 
output of MECH-CON-SEA is 105 watts for a 40^ 
efficient system. Therefore on a long term 
basis, the power input to the system is 420 
watts for a h hour period whereby the power 
consumed is 236 watts. Size optimization of 
the MECH-CON-SEA power generator for the TELME 
buoy system has not yet been completed. Since 
ocean conditions are highly variable with 
reference to location, the main battery supply 
capacity is approximately 4,000 watt-hours. 
This is based on the assumption that three con- 
secutive days of calm periods may occur and 
4,000 watt -hours will permit 6 bobbing buoy 
cycles per day for the three days before the 
batteries are depleted. 



83 



^:^^/Ai? ^i^miftZ//Wf^/S!^/ff 



UP SIGNAL (on) 




-BUOY WALL 



-OIL RESERVOIR 

FIG. 5 



REEi 



^^ssm^^i^Of^ 



BATTERY 





CABLE 

GABLE TUBE i. 

ASSY BOLT 

BOLT HEAP 

POWER TRANSFORMER 

ELECTRONKi COMPARTMENT 



RECORDER 



TOTAL BUOY DISPLACEMENT=^IO LB 

A = HYDRAULIC ACCUMULATOR 

B = AIR BOTTLE 

C = CYCLE CONTROL 

M = PUMP MOTOR 

P = HYDRAULIC PUMP 

R = HYDRAULIC RESERVOIR 



CYCLE SYSTEM 
ELEC DISCONNECT 



BILSE PUMP 
ELEC DISCONNECT 
R 



TEMP SENSOR 




CYCLE S/S t BALLA5T COMPARTMENT 

BALUSr FINE ADJUSTMENT TANK 
BALLAST WEIGHTS 

BILGE COMPARTMENT 
BIL6E PUMP AND SWITCH 



ASSY NUT 



FIG 6 



84 




SHAFT POSITION 
CODER 

TEMP SERVO 
SENSOR AMP 



A/OTHER SENSORS 

r--^-| I 1 r--- 

I II II 



i-H I— I 
L__J L__J L__ 

I 1 I 1 I 

I I— I i— I 
I I I I I 

II I ' 



DEPTH SERVO SHAFT POSITION 
SENSOR AMP CODER 

BOBBING BUOY 



FI6. 7 



FLOAT 



^/^PBPf AC^p'se/efe^/^B^e/v?:^ 



OPERATION 




BUOYANCY 
CHANSE 


DESCENT 


BUOYANCE 
CHANGE 


ASCENT 


DATA 
TRANSFER 


STAND-ftY 


TIME 


MIN. 


6 


16 


6 


16 


16 




HRS. 


.10 


.27 


.10 


.27 


.27 


3.0 


EQUIPMENT 
BUOY 


WATTS 


59 


II 


8 


It 


105 


46 


WATT-HRJ 


5.9 


29 


.8 


2.9 


28 


138 


BOBBING 
BUOY 


WATTS 


216 


30 


203 


30 








WiTTHRS 


21.6 


8.1 


20.3 


8.1 









TDTAL EQUIPMENT BUOY POWER REQUIRED = 178.5 WATT-HOURS 

TOTAL BOBBING BUOY POWER REQUIRED = 58.1 WATT-HOURS 

TOTAL POWER REQUIRED FOR A 4 HR CYCLE 236.6 WATT-HOURS 

Fie e 



85 



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86 



SYSTEM LIFE AMD RELIABILITY 

Preliminary studies on the system life and 
reliability of the TELME buoy system indicate 
that a 6 month life, unattended, can be ex- 
pected with a probability of 10% - 80^ for 
completing the 6 month period satisfactorily. 
Components are off-the-shelf items with the 
exception of sensors. Total operating time 
of components are kept to a minimum by on -off 
utilization. Derated components can be used 
where weak links in the reliability chain 
exist . 



COHCLUSIOHS 

More knowledge about the ocean environment 
is not only a pressing task before the mili- 
tary, but a necessary requirement for under- 
standing and exploiting the sea . Synoptic 
surveillance of large areas of ocean neces- 
sitates the use of long life remote buoys. 
The economics of collecting oceanographic 
data over these large ocean areas suggests 
the use of aircraft as data collecting sources. 
The airplane, with its speed, altitude, and 
range capability coupled with long life buoys 
is an approach that seems worthy of develop- 
ment. Chance Vought Corporation has studied 
the feasibility of providing a long life buoy 
system. The results of the study are favor- 
able and hardware development is a logical next 
step. 



ACKNOWLEDGMENT 

The information presented in this paper 
resulted from the cooperative efforts of 
Mr. C. E. Lankford, Avionics Engineer, and 
Mr. R. A. Kelson, Electro Mechanical Engineer, 
both of Chance Vought Corporation. 



87 



DATA RECORDING DEVICE FOR UNDERWATER INSTRUMENTATION 

by JAY W. HARFORD, Engineer 

and EARL D. VAN REENAN, Senior Geophysicist 

Edgerton, Germeshausen&Grier, Inc. 

Boston, Massachusetts 



ABSTRACT 

Modified versions of a standard EG&G 
underwater camera are described with necessary 
circuitry to use as lapse-time data cameras. 
The standard camera can be modified to have one 
or two data chambers. The dual chamber data 
camera will take 4,000 data pictures sequentially 
in six pairs to handle up to 12 sensing instru- 
ments. The data camera can act as a versatile 
nucleus of an underwater instrument package for 
the recording of various oceanographic variables. 



I INTRODUCTION 

Recording of oceanographic variables 
in situ requires a reliable recording device 
which can record sequentially over extended 
periods of time while in an oceanographic envi- 
ronment. This paper describes a simple and com- 
patible data recording system which can serve as 
a nucleus instrument package for the read out of 
several measuring instruments. The basic re- 
corder consists of a data camera which is readily 
adaptable for many uses. This data camera can 
take data pictures from one end or both ends 
depending on the number of sensing elements used 
and type of meters required. 



II DESCRIPTION 

A. Single Ended Data Camera 

The basic single ended d 
a special modification of the EG&G 
Underwater Camera. The camera is 
high strength stainless steel hous 
withstand 20,000 psi. The read ou 
placed on the end cap. The data c 
capacity is 100 feet of 35 mm film 
loading spool. This gives 2,000 f 
with 15 millimeters per frame. Th 
a Wollensak Cine-Raptar 13 millime 



ata camera is 

Model 200 
contained in a 
ing designed to 
t meters are 
amera film 

on a daylight 
rames per roll 
e data lens is 
ter focal 



length, f2.5. The light source consists of an 
internal tungsten bulb. Automatic timing con- 
trol can be provided by a 6 volt d-c cam type 
timer which is available in various time 
intervals. 

B. Dual Ended Data Camera 

The dual ended data camera is an 
extension of the single ended data camera with 
data pictures taken at both ends. This provides 
greater meter area and more efficient utilization 
of film space. The dual ended data camera will 
take A, 000 data pictures per 100 foot roll. The 
camera lenses on either end of this camera are 
staggered to give a double row of data pictures. 
A maximum of 12 separate instruments can be 
sequentially recorded by this data camera. It is 
possible to use 2 or more meters with different 
ranges to reduce the problem of having the 
measuring instruments compatible with the read 
out. A clock, pressure gauge, and data card can 
be provided on one end of the camera if desired. 
The dual ended camera with a single meter is 
shown in Figure 1. 




Fig. 1 Data Camera Mechanism 



88 



Ill OPERATION 



The basic single ended or dual ended 
data cameras are highly versatile and can be 
applied with various electronic systems for 
sequential read out. This section describes a 
particular type of circuitry which allows up to 
12 separate sensors to be sequentially read out 
on meters. 

A. Circuitry 

The camera is driven by a d-c motor 
which serves two purposes: it advances the 
film and drives a 6-position selector switch 
which sequentially reads out the various instru- 
ments. 

For a 12-instrument sequential read 
out, a meter is placed at each end. The two ends 
of the data camera take pictures of the meters 
at either end simultaneously. At the same time, 
a small Indicator light at one end of the camera 
will indicate in the picture which instruments 
are being read out. For example, instruments 
No. 1 and 7 are read out with the No. 1 indicator 
light on, and instruments 2 and 8 correspond to 
the No. 2 indicator light, etc. Each time the 
film is advanced one frame, the selector switch 
is moved to a new position to read the next two 
instruments in sequence. The selector switch is 
mounted on top of the film advance socket 
mechanism as shown in Figure 1. A sample of the 
data picture is shown in Figure 2. 




Figure 2. 



Sample film strip from dual ended data 
camera. 



The camera is activated by momentarily 
grounding the power lead to the 6 volts d-c 
supply. Each time this occurs, three separate 
circuits operate on the camera: (See Figure 3) 

1) the data lamp capacitors (Cg) dis- 
charge through the incandescent bulb (B ) ex- 
posing the data chamber frame, 

2) the indicator light capacitors (Cc) 
discharge through the indicator bulbs in the end 
cap to show which instrument is being read out. 



CtQMTS 



ct^ 



POH£/i PLUS 




I I 



Fig. 3 Data Camera Circuit Diagram 
89 



discharges 



3) the motor starting capacitor (C_) 



When the timing motor cam returns S^ 
to position NO current is again fed to the indi- 
cator data lamp and motor starting capacitors. 
As capacitor Cy starts to charge up again, tran- 
sistor Q^ conducts, and current flows into the 
base of Q,. Operating current is supplied to the 
film driven motor M„ when transistor Q^ starts 
conducting. This current is transitory (lasting 
about 1 sec) and lasts until the voltage C-, rises 
to 6 volts. The film drive motor simultaneously 
drives cam switch S^ during this period into 
position NO which connects the film drive motor 
directly to the 6 volt current line. The film 
motor advances the film one frame. When cam S4 
moves back into position NC, power is removed 
from the motor. The film stops advancing, and 
the operating cycle is complete. Resistor Rj^j^ 
limits overtravel when current is removed from 
the motor by a dynamic braking action on the 
motor. 

B. Adaptability 

A terminal board at one end of the data 
camera facilitates wiring changes of the selector 



switch. The instrument outputs and selector 
switch leads are terminated at this board. The 
sensor instrument inputs are wired up patch panel 
fashion. The terminal board also allows place- 
ment of any meter shunts necessary to make each 
sensing instrument compatible with the read out 
meter. 



IV APPLICATIONS 

The data camera can be used for a wide 
variety of oceanographic data collecting appli- 
cations. It is very useful for lapse time data 
recording over extended periods of time up to 
several months. The data camera with associated 
sensing elements can be lowered to the sea floor 
and left for extended periods. For example, such 
things as temperature probes tor heat flow 
measurements can be recorded from a number of 
thermistors and bottom water temperatures can 
also be measured along with variables such as the 
current velocity and direction from current 
meters, salinity variation, and acoustical 
variables. Continuous hourly and daily variations 
of oceanic factors can be clearly and concisely 
recorded in this manner and analyzed when the 
entire unit is recovered and the film processed. 



90 



PROGRESS REPORT ON TRANSIT 

by R. B. KERSHNER 
The Johns Hopkins University 
Applied Physics Laboratory 
Silver Spring, Maryland 

"TRANSIT" is the code name for a program to develop 
and establish in being a system of near-earth satellites to provide 
a means for establishing locations (navigating) anywhere on the 
surface of the earth. The development phase is being carried out 
for the Bureau of Naval Weapons primarily by the Applied Physics 
Laboratory of The Johns Hopkins University with cooperative efforts 
by the Naval Weapons Laboratory at Dahlgren, Virginia, the Naval 
Ordnance Test Station at China Lake, and the Pacific Missile Range. 
The launching of the satellites is conducted by the Air Force 
Ballistic Missile Division. 

As a navigation system, TRANSIT will have the virtue 
of true global coverage, all weather operation, relative immunity 
to interference (either natural or man-made), unlimited traffic 
handling, frequent availability of fixes (every 100 minutes or 
of tener) , and very high accuracy. On the other hand, since posi- 
tion is available only intermittently and not continuously, for 
some purposes TRANSIT may not replace the various radio aids that 
do provide continuous position fixing in the areas where such aids 
are available. However, it should be noted that a relatively 
modest quality inertial system would suffice to provide continuous 
interpolation between TRANSIT fixes. 

The principle on which the design of the TRANSIT system 
is based is quite simple. Briefly stated, the entire system is 
based on the fact that a constant frequency radio transmission from 
an earth satellite is received by a ground station at the surface 
of the earth with an apparent variation of frequency. This variation 
in received frequency, the result of the well known Doppler effect, 
is an accurate measure of the rate of change of the slant range 



91 



between the transmitter and the receiver and hence is influenced 
both by the motion of the satellite in inertial space and by the 
motion of the receiving station as a point on a rotating earth. 
Because of the severe constraints imposed on the path of an earth 
satellite by Newton's laws and our reasonably complete knowledge 
of the forces acting, it is possible, simply from an accurate 
measurement of the Doppler shift at a ground station during the 
passage of a satellite within line-of-sight to do either of two 
things: (1) determine the orbit of the satellite if the position 
of the ground station is known, or (2) determine the location of 
the ground station if the orbit of the satellite is known. 

These two calculations are the basis of the TRANSIT 
system; the second calculation is performed by the navigator using 
a description of the orbit provided to him and a measurement of the 
Doppler shift which is made by his (navigating) equipment, the first 
calculation (or an elaboration of it) is used by the organization 
operating the system to determine the orbits for distribution to 
the users using Doppler measurements made at special ground stations 
at known locations. Of course the second calculation is vastly 
simpler than the first and can be done with much more accuracy since 
only two variables (latitude and longitude) are required to specify 
the location of a ground station while the specification of a satel- 
lite orbit requires that at least six parameters be determined. 
Fortunately, the first calculation usually need not be done since it 
is generally possible, for tracking the satellite, to acquire more 
information than the Doppler data for a single pass at a single 
ground station. In fact, the tracking of TRANSIT satellites is 
accomplished by the use of the Doppler data measured at a multi- 
plicity of ground stations and extending over a period of time (say 
12 hours) that includes a number of passes at each ground station. 
However, it is technically of interest that the multiplicity of 



92 



Doppler curves simply provides redundancy and a consequent increase 
in accuracy and that each Doppler curve, in principlej provides 
enough data to determine the orbit. 

To complete a description of the operation of the 
TRANSIT system, it is only necessary to add that the formidable 
communication problem of disseminating a description of the orbit 
to all potential users is solved by using the TRANSIT satellites 
as a special communication link for this purpose Specifically, 
after the orbit is determined on the ground a parametric descrip- 
tion of this orbit is transmitted to the satellite, recorded in a 
memory system contained in the satellite and subsequently broadcast 
at regular (2 minute) intervals. Thus the user receives a descrip- 
tion of the orbit of the satellite simultaneously with his measure- 
ment of the Doppler shift. By this means it is possible to improve 
the description of the orbit frequently; in fact, it is intended to 
insert a current or updated description every twelve hours. 

While the above description of the TRANSIT system sounds 
relatively simple, it can perhaps be imagined that there were a 
number of rather formidable technical difficulties to be overcome 
before a practical operating system could be designed in detail. 
It is the purpose of this article to indicate some of these problems 
and the progress that has been made toward their solution by the 
TRANSIT launchings to date. 

To the time of this writing there have been three TRANSIT 
satellites placed in orbit out of a total of five attempts. A few 
of the significant parameters of these three satellites are displayed 
in Fig. 1. It will be noticed that, although we have been moderately 
fortunate in getting satellites placed into orbit, we have been less 
fortunate in the orbits achieved. None of the three orbits has very 
closely approached the circularity that was desired and two of the 
three have had perigee at so low an altitude that atmospheric drag 
very seriously affected the calculation of the orbit. The last 



93 



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EQUENCY STABILITY: 
hanges with mean 
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RMS FREQUENCY N 
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94 



satellite, TRANSIT 3-B, had perigee so low that it had a life of 
only 36 days and it reentered the atmosphere and was consumed on 
March 30. There have also been a few equipment failures in the 
satellites themselves. A temperature sensitive switch, included 
in TRANSIT 1-B to protect the storage battery from overcharge, 
opened improperly and permanently on or about July 11, 1960, and 
the satellite ceased radiating due to loss of power. Thus TRANSIT 
1-B had a useful radiating life of 89 days. The same switch mal- 
functioned in TRANSIT 2-A . In this case a command by-pass of the 
switch had been incorporated and was actuated to prolong the life 
of the satellite. However, bypassing this switch removed the over- 
charge protection which was the reason for incorporating the switch 
and the storage battery was destroyed by overcharge during the 
period October 28 to November 14, 1960, while the satellite was in 
the sunlight at all times and correspondingly receiving maximum 
power from its solar cells. Since the loss of the storage battery 
the TRANSIT 2-A radiates only when it is in sunlight, receiving 
power directly from the solar cells. With this intermittent opera- 
tion the stability of the oscillators is, of course, not up to the 
level that obtained during the period of proper, full-time operation, 
TRANSIT 3-B operated fully throughout its short life. 

In spite of these various limitations, it has been 
possible, with the three satellites placed in orbit to date, to 
demonstrate rather remarkable progress toward overcoming the major 
technical obstacles that lay in the path of establishing an opera- 
tional system. In particular, there are no longer any questions 
about the feasibility of the operational concept and it is now 
possible to specify a detailed design with confidence that it will 
meet the requirements. 

In what follows, the various areas that were expected 
to provide technical difficulties will be discussed and the state 
of progress toward their solution will be described. 



95 



1 . stability of the Satellite Oscillator 

This was initially expected to be one of the difficult 
problems. The fact is that while the Doppler shift does determine 
the relative geometry of the satellite orbit and receiving station 
it requires a very accurate measure of the Doppler shift to obtain 
a good measure of this relative geometry. Although there is no 
simple relationship between an error in Doppler measurement and 
the corresponding position error, a crude rule-of-thumb relation- 
ship, usually valid within an order of magnitude, is given by the 
statement that an error of 1 cps in Doppler gives an error of 1 mile 
in position if the transmitter frequency is 100 mcps . Since, in the 
TRANSIT system, any variation in transmitted frequency during the 
time of a pass will be erroneously ascribed to the Doppler effect, 

Q 

it is clear that a frequency drift of only 1 part in 10 during the 
time of a pass can result in a serious error in position determina- 
tion. It is true that many oscillators with stability better by 

g 
orders of magnitude than 1 part in 10 had been built before the 

start of the TRANSIT program, but these were generally rather elab- 
orate devices including proportional heating ovens to control the 
crystal frequency and were not suitable for use in small and 
simple satellites. Actually, as can be seen from Fig. 1, the 
oscillator stability has not proved a very difficult problem. A 
rather elaborate temperature isolation of the crystal from external 
heat sources, taking advantage of the superb vacuum available in 
the operating environment, has kept the rate of change of frequency 
due to temperature change at the crystal within acceptable limits, 
and careful circuit design has minimized other sources of frequency 
change. Other techniques used include long burn-in of all crystals 
and selection of crystals on the basis of stability after this burn- 
in period. While techniques for still further improvement are under 
investigation, the presently achieved stabilities are good enough to 
meet the program objectives. 



96 



2 . Refraction by the Ionosphere 

The Doppler shift exhibited in the reception of a trans- 
mission from an earth satellite is not strictly proportional to the 
rate of change of the true slant range but rather is proportional to 
the rate of change of the transmission path length. If, as is 
normally the case, the satellite is above the ionosphere, then the 
transmission path is not the straight line joining the transmitter 
and receiver but instead is some lor.ger curved (or bent) path due 
to the refraction effect of the ionosphere. Hence, for a precision 
analysis of the Doppler shift, account must be taken of the effect 
of this ionospheric refraction on the Doppler. A rough model of the 
ionosphere indicates that the effect of ionospheric refraction on 
the Doppler shift should be inversely proportional to the square of 
the transmitter frequency. This suggests that refraction can be 
made negligible by going to a sufficiently high frequency. And, 
indeed, at microwave frequencies (and above) the ionosphere has a 
negligible effect on the received Doppler shift. Unfortunately the 
use of microwave frequencies would require either the use of large 
directional antennas for reception or of very high transmitter powers 
The first solution would be undesirable for many potential users of 
TRANSIT (e.g., submarines or aircraft) and the second is unavailable 
with small, easily launched satellites. Accordingly, it has been 
considered wise to restrict the TRANSIT frequencies to the range 
(hundreds of megacycles) where solid state amplifiers were usable. 
In this range, ionospheric refraction cannot be neglected with high 
accuracy. The technique used in TRANSIT is to transmit a pair of 
harmonically related (coherent) frequencies rather than a single 
frequency. From the Doppler shift obtained on each of these fre- 
quencies it is possible to obtain a measure of th/^ integrated 
electron density between the transmitter and tne receiver, and then 
to develop a good estimate of the Doppler shift that would have been 
measured in the absence of the ionosphere. It is this so-called 



97 



refraction corrected Doppler or vacuum Doppler that is actually 

used in the TRANSIT program for orbit determinations and precision 

navigation fixes. Actually, the generation of the vacuum Doppler 

from the individual Doppler shift at the two harmonically related 

1/ 
frequencies is accomplished by a relatively simple analog computer— 

2 
which would yield a precisely correct answer if the l/(freq.) 

refraction law were precisely correct. 

Results to date in the TRANSIT program indicate that 

at mid-latitudes or lower the refraction correction based on the 

2 
l/(freq.) assumption is sufficiently accurate to meet the TRANSIT 

program goals even in times of magnetic storm activity. However, 
there is need to explore further the refraction effect at high 
latitudes during heavy auroral activity to determine if this 
correction remains sufficiently accurate in these most severe con- 
ditions. Considerable effort in this area is planned for the next 
year . 

3 . Transmission of the Orbit Parameters 

In principle the transmission of the orbit parameters 
from the satellite poses a relatively easy communication problem 
and can be accomplished straightforwardly in a number of ways. 
Practically it is desirable to develop a means which poses the 
least increase in complexity or power on the part of the satellite 
equipment and the least special equipment for reception on the part 
of the navigator. To this end a system has been developed in which 
the orbit parameters are transmitted in binary notation (zeros and 
ones) coded as a phase modulation of the basic transmission which 
are used to generate the Doppler shift. A specific modulation (60° 
phase advance followed by a 60° phase retard) is used which does not 
interfere with the ability to measure the Doppler shift with preci- 
sion. The use of this approach avoids the need for an extra trans- 
mitter in the satellite or an extra receiver in the ground equipment 



1/ Weiffenbach, G.C., "Measurement of the Doppler Shift of Radio 
Transmissions from Satellites," Proceedings of the Institute 
of Radio Engineers, Vol. 48, No. 4, pp 750-754, April 1960 



98 



This system for the distribution of data by means of a satellite 
link was incorporated, for the first time, in the short-lived 
TRANSIT 3-B and operated perfectly throughout its life. 

4. Time Synchronization 

Since the time at which orbit parameters are trans- 
mitted is controlled by a satellite clock based on the same stable 
oscillator that controls the two basic frequencies, it is clear that 
the time of reception of orbit parameters can be used as a time 
signal by the ground equipment. This makes the TRANSIT system com- 
pletely self contained and independent of any other time source such 
as WWV. Actually, because of the short, well defined transmission 
path for the TRANSIT line-of -sight frequencies and the excellent 
knowledge of satellite position, the time signals available from 
TRANSIT will be more accurate than those available from WWV in most 
areas of the world. In fact, a precision of 100 microseconds should 
be readily available. A system has been developed for including along 
with the orbit parameter transmission a special word ("Barker" word) 
which serves the purposes of a start of message and time synchro- 
nization signal. This system also was successfully tested in 
TRANSIT 3-B. 

5. Thermal and Power Balances 

One technical problem that proved quite serious in the 
design of early satellites was to achieve the proper control of 
satellite temperature and input power under the varying conditions 
that occur in orbit. If one considers polar satellites, it is 
clear that when the orbital plane is roughly at right angles to 
the earth-sun line then the satellite will be exposed to sunlight 
throughout its orbit. At the other extreme, if the sun lies in 
the orbital plane the satellite will be in the earth's shadow for 
a considerable portion (about 40% for the satellites at altitudes 
intended for TRANSIT) of each orbit. Since for a polar satellite 
the orbital plane remains fixed in inertial space while the earth- 
sun line rotates in inertial space once a year, it is clear that 



99 



each of these conditions is reached at different times in the life 
of the satellite. Thus, there is considerable variation of the 
total amount of input thermal radiation and of the total power input 
from solar cells. Since the maximum electrical power and maximum 
thermal input occurs simultaneously, a serious battery temperature 
and overcharge condition is likely to occur in 100% sunlight orbits. 
This problem was responsible for the failures that eventually 
occurred in both TRANSIT 1-B and TRANSIT 2-A . Recently a very 
simple solution to this problem has been found by the proper choice 
of satellite configuration and limited attitude stabilization. 

Imagine a satellite in the shape of a drum with a 
magnet aligned with the symmetry axis of the drum. If proper damp- 
ing is provided and competing torques are kept low, such a satellite 
will be constrained by the magnetic torques to have its symmetry 
axis in the same plane as the earth's magnetic axis. Since the 
magnetic axis of the earth is approximately the rotation axis, the 
symmetry axis of the satellite will lie approximately in the orbital 
plane. It is then seen that during the 100% sunlight axis, when the 
orbital plane is at right angles to the earth-sun line, then the 
satellite's symmetry axis will also be approximately orthogonal to 
earth-sun line; in other words, the sun will illuminate the edge of 
the drum at all times and not the top and bottom. 

In the other extreme case, when the sun lies in the 
plane of the orbit, it is clear that the sun will illuminate the 
top and bottom of the drum-shaped satellite a reasonable percent 
of the time. It is clear that by making the top and bottom of the 
satellite large in area compared to the edge, it is possible to 
arrange that the effective received solar radiation at the satel- 
lite is just as great in the 60% sunlight case as it is in the 100% 
sunlight case. 

By the use of the design principle outlined above, a 
configuration has been developed for the operational TRANSIT satel- 
lite in which the total temperature extremes will vary by no more 



100 



than 10° and the total power input will remain constant within a 
few percent throughout the life of the satellite. 

6 . Tracking Accuracy 

When the TRANSIT program was first proposed, the most 
serious technical questions raised concerned the feasibility of 
tracking the satellites with sufficient accuracy. Obviously, to 
determine your position on earth by reference to the position of 
a satellite, it is necessary that the position of the satellite, 
at a given time, be known to higher accuracy than the accuracy 
with which your own position is to be determined. At the time 
the initial TRANSIT program proposal was being considered, typical 
satellite tracking or prediction errors ranged from 5 miles to as 
much as 50 miles. There was a wide spread belief among even well 
informed people that there were mysterious or at least unpredict- 
able forces of large magnitude acting on satellites which \\ould 
for years prevent orbit prediction with an accuracy of better than 
a number of miles. Fortunately, most of the difficulties of that 
period were a result of poor measurement rather than of a reflec- 
tion of basic unknowns. It is true that there were and still are, 
areas of ignorance concerning the precise formulation of the forces 
acting on a near earth satellite (for example, the proper descrip- 
tion of the earth's gravitational field is not too well known) but 
the effect of these uncertainties on the trajectory is one or two 
tenths of a mile rather than a number of miles. The fact that 
present knowledge of the forces acting on a satellite is sufficiently 
accurate to enable tracking and short term (12 hour) prediction of 
satellite position to an accuracy of a few tenths of a mile ha,s been 
shown conclusively by our tracking experience with TRANSIT 1-B and 
TRANSIT 2- A. 

One way to judge the accuracy with which orbit deter- 
minations are made is simply by observing the consistency of the 



101 



determination from one day to the next. In the TRANSIT program an 

orbit is determined for each day based solely on the data obtained 

on that day so that each determination is totally independent of 

all preceding data. Hence, the day-to-day consistency of orbit 

parameters is a very good indication of the precision of the system. 

The determination of orbit parameters through most of the radiating 

life of TRANSIT 1-B is given in Figs. 2 through 9. It will be seen 

that the first four or five points show a much larger scatter than 

the subsequent points (particularly in Figs. 7 and 9). This results 

from the fact that for this initial period the satellite was still 

spinning and the spin caused a modulation on reception that was 

interpreted by the ground equipment as a change in the Doppler 

2/ 
frequency. After this initial period the satellite was despun- 

and the data became much cleaner. It can be seen, particularly 

from Figs. 2 and 3 that, after the spinning period, the scatter of 

the day-to-day determinations of orbit parameters is generally well 

within one half of a kilometer or one quarter of a mile. 

The nature of the long term variation of the orbit 
parameters, particularly Figs. 2, 3, 4, and 5, is quite interesting. 
It is seen that both apogee and perigee exhibit a linear decrease 
with a sine wave oscillation superimposed. This oscillation has an 
amplitude of about 6 km and its period is the period of the preces- 
sion of perigee. Thus the sine wave terms in the formulae given 
for apogee and perigee are zero when perigee occurs at the equator 
and reaches its extreme values when perigee reaches the extremes 
of latitude. The linear decrease of apogee and perigee is due, of 
course, to drag. The effect of drag on apogee is five times as 
great as the effect on perigee. This is reasonable since most of 
the drag occurs as the satellites goes through perigee. This re- 
sults in a velocity decrease at perigee so that the satellite does 
not swing out quite as far at apogee the next time around. 



2/ Using the yo-yo technique. See "The TRANSIT Program", June 1960 
"■ Astronautics 



102 





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no 



The sine wave oscillation in the amplitude of apogee 
and perigee, in phase with the precession of perigee, clearly shows 
that the orbit behaves differently depending on whether perigee 
occurs in the northern or the southern hemisphere. This is a 
striking illustration of the existence of a north-south dissymmetry 
in the earth - the famous "pear-shaped" term in the expansion of 
the earth's gravitational field, first deduced by O'Keefe from 
Vanguard data. It is, of course, possible to confirm, quantita- 
tively the value of J„, the "pear-shaped" coefficient in the expan- 
sion of the gravitational field of the earth in spherical harmonics. 

In fact, from this data for TRANSIT 1~B together with similar data 

3/ 
for TRANSIT 2-A, R. R. Newton- has improved on the value for J„ 

and also obtained values for J^ and J , the next two odd-order 

coefficients beyond J_. 

Not all of the long term effects shown in Figs. 2 through 
9 are understood. For example, the very small but clearly signifi- 
cant increase in the inclination of the orbit through May and June 
has not been explained to date. 

The day-to-day consistency of the Kepler orbit elements 
is not the best way of judging the accuracy of the tracking and 
could indeed be misleading since there has been perforce some 
smoothing of data involved in the very act of describing the orbit 
by means of Kepler elements. Actually the true orbit, obtained by 
a numerical integration of the full equations of motion, departs 
from a Kepler ellipse (even with allowance for precession of perigee 
and the line of nodes) by one or two tenths of a mile. Obviously 
the "smoothness" of parameters which, at best, can only approxi- 
mately describe the orbit, cannot accurately indicate the precision 
of the system. 



3/ 

—R.R.Newton, "Odd Harmonics of the Earth's Gravitational Field" 

(to appear) 



111 



A somewhat better indication of the accuracy of TRANSIT 
tracking is obtained by a sort of closed-loop consistency calcula- 
tion. To accomplish this consistency check, the data for one 
particular pass at one station are held in reserve and the orbit 
is determined by the remaining passes during a particular time 
period. Then, using this orbit and the reserved single-pass data 
the location of the ground station is computed - just as would be 
done in a typical navigation fix. The result of this position 
determination is compared with the known ground station location 
and the assumption is made that the error in satellite position is 
no greater than this resulting error in station location (actually 
it should be appreciably less, on the average, since there would be 

some error in station location even with a perfectly known orbit). 

4/ 
Large numbers of these "closed-loop" calculations have been performed— 

based on data from TRANSIT 2-A , and the resulting sigma is well under 

one-quarter mile. 

It might be thought that the calculations described in 
the preceding paragraph are a direct test of the ability to perform 
navigation fixes by TRANSIT. Unfortunately this is not quite the 
case. For, in order to use TRANSIT for navigation in the practical 
operating system, it is necessary to base the calculation on an 
orbit determined previous to the time of the navigation fix (based 
on prior data). In other words, the practical use of TRANSIT for 
navigation always involves orbit extrapolation. This extrapolation 
process introduces a further error which obviously depends on the 
state of knowledge of the forces acting on the satellite and in 
particular on the knowledge of the gravitational field. Calcula- 
tions similar to those of the previous paragraph but where the data 
used for the position determination were obtained a day later than 
those used for the orbit determination (thus requiring a full day 
orbit extrapolation) indicate that the resulting error in position 
determination is now about one-half mile. Extending the orbit 



-^R.B.Kershner, "The TRANSIT System" Proceedings of the Institute 
of Radio Engineers, Sept. 1960 



112 



extrapolation further, for example to four days, increases the 
error to about three miles, with the error occurring mostly along 
the satellite track. 

All the above methods for estimating the error of 
tracking by TRANSIT techniques still leave a small uncertainty 
about the absolute precision since they are only self-consistency 
checks and it is possible to imagine some form of consistent bias 
that cancels out when you "close the loop." For example, all the 
consistency checks above could remain valid for a system that 
consistently tracks a phantom point five miles ahead of the real 
satellite on the same orbit. This would not matter for navigation 
but would introduce real trouble when one attempted to use the 
results to deduce geodetic consequences. Fortunately a completely 
independent check has been made possible by the availability of 
optical sighting data of reasonable precision reduced by Smith- 
sonian. The data for sightings of TRANSIT 1-B from optical sta- 
tions in the United States agree with TRANSIT determination of the 

5/ 
satellite position to about one-quarter mile— . Optical sightings 

elsewhere in the world disagree somewhat more (sometimes 1 to 
1-1/2 mile) because of uncertainties in the absolute location of 
these overseas sites relative to the center of the earth. 

It is seen that the precision of measurement now possible 
with TRANSIT techniques is quite good. However, both the determina- 
tion of orbit during a one day period and the ability to extrapolate 
the orbit for a day are presently limited (to a few tenths of a mile 
in each case) by inaccuracies in the present model of the force field 
(gravitational field, drag, etc.). On a world-wide basis there are 
further difficulties introduced by the unavailability of sufficiently 
accurate datum ties. To meet the ultimate program goals for TRANSIT 
thus requires considerable improvement in the present knowledge of 
these factors (roughly the shape and mass distribution of the earth) . 



5/ 

- W.H.Guier, "The Doppler Tracking of Project TRANSIT Satellites" 

Proceedings of the Institute of Radio Engineers, Sept. 1960. 



113 



This is the primary remaining development challenge of the TRANSIT 
program. Fortunately, the TRANSIT system itself provides one of 
the most powerful tools available for accomplishing these goals. 
Furthermore, considerable effort using both TRANSIT and other tech- 
niques is planned, or already under way, not only in the TRANSIT 
program, but by many other programs in the Army, Navy, Air Force 
and NASA. It is clear that the next year or two will see tremendous 
advances in these basic problems of geodesy. 

7. Other Problems 

While the discussion above covers the major technical 
aspects of the TRANSIT program, there have been, of course, a host 
of detailed technical or practical operational problems that 
required solution. Some of these solutions are sufficiently novel 
to merit comment. The problem of de-spinning satellites, alluded 
to above, is one such example. TRANSIT 1-B used the so-called yo- 
yo, devised independently by APL and JPL. Subsequently, it was 
found the same objective could be accomplished even more simply, 
without moving parts, by using magnetic damping in the earth's 
magnetic field. A combination of two phenomena, hysteresis loss 
and induced current loss, provides very effective despin.— 

A practical problem that has been solved quite effec- 
tively is that of making full use of the launch capabilities of 
the launch vehicles when these exceed the requirements of a specific 
payload. The solution adopted is to fire a multiplicity of payloads 
in a pick-a-back configuration (see Figs. 10 and 11). This technique 
has worked quite well . It is true there has been one failure to 
separate (TRANSIT 3-B) but this was caused by a simple programmer 
malfunction during the launch phase and not by any difficulties 
inherent in the multi-payload technique. 



a / 

— R.E .Fischell , "Magnetic Damping of the Angular Motions of Earth 
Satellites" American Rocket Society, 15th Annual Mtg. , Dec. 1960. 



114 




Figure 10 



115 




TRANSIT 3B SATELLITE 
WITH LOFTI 



FEB. 1961 



Figure 1 1 



116 



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117 



8 . Conclusion 

In conclusion, it may be stated that the TRANSIT program 
not only will provide a very useful practical application of earth 
satellites to the solution of a serious terrestrial problem (naviga- 
tion) but in the course of its development is making many important 
contributions to space technology and earth sciences. 



118 



INFLUENCE OF A HIGH HYDROSTATIC PRESSURE ENVIRONMENT 
ON ELECTRONIC COMPONENTS 

by CHESTER L. BUCHANAN, Branch Head - ^ 
and MATTHEW FLATO, Electronics Section Head 
Sonar Systems Branch, Sound Division 
U.S. Naval Research Laboratory 
Washington, D.C. 



ABSTRACT 



The rapidly expanding field of Oceano- 
graphic Instrumentation portends a large in- 
crease in the use of electronic instrumentation 
in various forms of deep ocean probes. One 
part of the oceanology program at USNRL is 
directed toward the development of such in- 
struments. 

Two approaches toward this development 
are available: The equipment can be sealed in 
rigid pressure-proof capsules with pressure- 
proof seals, or the equipment can be made of 
components which are inherently capable of 
operating satisfactorily under the environment- 
al pressure. The latter approach is attractive 
because of the probable savings in weight and 
cost. To this end, a serieg of commonly used 
electronic components have 'been tested in an 
oil bath under hydrostatic pressures up to 
10,000 psig. Components of each type tested 
have been found which will operate satisfactor- 
ily at all pressures up to 10, 000 psig. Diodes, 
transistors and even vacuum tubes have been 
found which operate at this high pressure. 
Entire circuits capable of operation under 
10,000 psig have been built from readily 
available components. 



INTRODUCTION 



than four miles submergence in the ocean. 
The initial phase of this study was exploratory; 
the objective was two-fold, to gain familiarity 
with techniques for testing components under 
high hydrostatic pressure and to determine the 
magnitude of the difficulties to be expected 
while operating equipment under such condi- 
tions. Initially several approaches are avail- 
able: the equipment can be constructed of com- 
ponents which are inherently capable of oper- 
ating satisfactorily under the environmental 
pressure, or the equipment can be encapsu- 
lated in plastic which fully protects the com- 
ponents. As an example of the results to be 
expected from the first mentioned approach, 
the "velocimeter", in which electronic circuit 
components weigh less than four ounces, re- 
quires a housing that weighs 25 pounds to pro- 
tect the components at a pressure of 10, 000 
psi. This high package to circuit weight ratio 
is typical of that to be expected from this 
practice. The probable saving in weight and 
cost, which can be expected from the latter 
two approaches, makes the further study of 
these techniques attractive. 

Several classes of electronic components 
have been tested in laboratory tanks (Figures 
1 and 2) which were designed to apply high 
hydrostatic pressure. 



It is a certainty that the rising tempo in 
Oceanographic Research will require an in- 
crease in the use of electronic instrumentation 
with various forms of deep sea probes. In- 
struments designed for deep submergence must 
be constructed to withstand the pressure expe- 
rienced at great depths. One part of the ocean- 
ographic instrumentation program at the U. S. 
Naval Research Laboratory is directed toward 
the development of packages for instruments 
whose electronic components are exposed to 
hydrostatic environments equivalent to more 



RESISTORS 

The first class of components tested was 
resistors. How the various types reacted 
under hydrostatic pressure may be compared 
in Figure 2. The resistance of those manu- 
factured by depositing either carbon film or 
tin oxide on glass rods was not changed by the 
application of pressure; the behavior of these 
two types of resistors strongly suggests their 
use in critical circuits. 



119 



The standard carbon composition resistors 
were found to change very radically with the 
application of pressure. Figure 3 summarizes 
the behavior of 100 to 10, 000,000-ohm resistors 
under the same hydrostatic pressure environ- 
ments (10,000 psig). Because of their marked 
sensitivity to pressure change, composition 
carbon resistors appeared attractive for use as 
pressure transducers. 



CAPACITORS 

A number of capacitors (molded mica, 
ceramic disk, glass, and paper) have undergone 
tests to 10,000 psig. All of these capacitors 
worked satisfactorily under the high pressure 
and suffered no damage. The molded mica and 
glass types showed no appreciable change in 
capacitance with varying pressure. Some ce- 
ramic types showed changes in capacitance of 
as much as two per cent but no effort was made 
to test all the types now available. Paper 
capacitors selected were mainly of the minia- 
ture types, in which size reduction had been 
accomplished by such methods as depositing 
the conductor directly on the dielectric. These 
miniature capacitors also are usually impreg- 
nated with wax and carefully treated to exclude 
all air bubbles. Surprisingly enough, these 
miniature types withstood the pressure and 
showed very little change in capacitance. 
Changes in the range of 1% were common with 
this type of capacitor. 

Capacitors sealed with air entrapped were 
not satisfactory for use under hydrostatic 
pressure; an example of such a capacitor is 
shown in Figure 5. Electrolytic capacitors 
frequently contain a considerable amount of 
void space and consequently collapse at a 
relatively low pressure. These units usually 
are operable at reduced voltages even after 
collapse. Some types of paper capacitors are 
inserted into a paper tube and sealed by pour- 
ing wax or plastic compound into the end of the 
tube. Such capacitors usually contain entrapped 
air and collapse at a relatively low pressure. 

There appears to be no problem at this 
time in selecting capacitors to meet the 
common electronic circuit requirements and 
to operate under hydrostatic pressures up to 
10,000 psig. 



MAGNETIC MATERIALS 

Measurements of various magnetic ma- 
terials were conducted by subjecting coils 
wound on various types of magnetic cores to 
hydrostatic pressures as high as 10,000 psig 
and measuring the inductance as the pressure 
was varied. The magnetic materials tested 
were some of those commonly used in elec- 
tronic circuits for instruments of various 
types. The materials tested were: 

1. Grain oriented silicon steel 

2. 75% nickel-iron 

3. 50% nickel-iron 

4. Powdered iron (high-frequency 
formulation) 

5. Powdered iron (low-frequency 
formulation) 

6. Powdered iron (medium frequency 
formulation) 

7. Molybdenom-nickel-iron dust core 

8. Ferrite core. 

The grain-oriented silicon core was of the 
split-rectangle type, while all other cores were 
torodial and approximately 1 inch in outside 
diameter. In all measurements the frequency 
was 1000 cps. 

The most dramatic change observed was 
in the 50% nickel-iron core of the grain-ori- 
ented square-loop type. This core nearly 
doubled in inductance at a very low pressure 
as shown in Figure 4. It is interesting to 

note that after the change occurred, further 
changes in pressure had very little effect on 
the inductance. Changes observed in the other 
types were less dramatic, but the grain-ori- 
ented silicon core was interesting in that it 
was the only type tested which exhibited a 
large decrease in inductance as the pressure 
increased. The total change observed was 
about 14% (negative), but the residual effect 
was a slight positive inductance change. The 
molybdenum-nickel-iron cores exhibited a 
change of about the same amount but in the 
opposite direction. 

Inductors using the powdered iron and the 
75% nickel-iron cores were found to exhibit 
inductance changes of less than 5% as the 
hydrostatic pressure was cycled between 
atmospheric pressure and 10, 000 psig, as 
shown in Figure 5. The inductors wound on 

the powdered iron cores sh^ ^ed an increase 
in inductance with increased pressure. The 



120 



percentage increase was proportional to the 
amount of iron in the core and inversely pro- 
portional to the frequency range in which the 
core was designed to be operated. The induct- 
ance of the coil wound on the 75 per cent 
nickel-iron core did not change significantly as 
the pressure was increased to 8000 psig. This 
coil also showed some permanent effects and a 
very small change in inductance as the pressure 
was increased from 8000 psig to 10, 000 psig. 

A "flux-gate" type magnetometer was 
tested under pressure with some rather pecul- 
iar results. It should be noted that whereas the 
toroidal cores for the previous test were 
essentially free from external magnetic effects, 
the "flux-gate" element was readily susceptible 
to external magnetic field changes. Tests with 
the "flux-gate" element in the tank showed that 
a considerable change occurred as the pressure 
was increased. Similar changes were noted 
with the "flux-gate" element taped to the out- 
side of the tank wall as the pressure was in- 
creased inside the tank. These results appear 
to indicate that considerable changes in the 
magnetic condition of the tank occur as the 
pressure in the tank is varied. 

GLASS TUBES AND ENVELOPES 

Various types of glass tubes and envelopes 
were subjected to high hydrostatic pressures, 
A type 6AL5 miniature tube (Figure 8) was 
tested and observed to fail by catastrophic 
implosion at about 2000 psig. Some subminia- 
ture types (Figure 9), however, were found to 
withstand the full 10,000 psig without mechani- 
cal or electrical failure. 



the tanlc, permitting observation of mechanical 
deformation of samples under pressure. A 
picture taken through the pressure window with 
illumination from these penlight bulbs is shown 
in Figure 11. Power to operate the bulbs is 
derived from a nickel-cadmium cell (Figure 
12), The vent of the cell was removed, and a 
rubber tube partially filled with electrolyte was 
installed for pressure equalization purposes. 
This cell was tested under a heavy-duty 
charge-discharge cycle both at psig and 
10, 000 psig with no significant difference in 
performance noted. While discussing the 
pressure tank, it should be mentioned that all 
the measurements are made with the tank 
filled with paraffin oil. Electrical leads are 
brought out the cover through pressure glands. 
Glass tubing of various diameters was tested 
by sealing both ends of short lengths of tubing 
and then subjecting the samples to high 
pressure. The seals consisted of surgical 
rubber tubing fitted over the glass tubing. 
The opposite ends of the rubber tubes were 
blocked with small solid cylinders of the same 
diameter as the glass tubes (see Figure 4). 
When the hydrostatic pressure increases, the 
rubber seals are squeezed tighter around the 
glass tube and the solid cylinder. Glass tubes 
with a wall thickness of 0. 039 in. and an out- 
side diameter of as great as 0. 355 in. 
successfully withstood 10,000 psig. It should 
be observed that glass has a compressive 
strength comparable to that of some steels. 

These results indicate that where the need 
arises sonne components in glass envelopes 
may be used in a high-pressure environment. 



Penlight bulbs, instrument bulbs, and 
small commercial neon bulbs were tested and 
a high percentage of these were found capable 
of withstanding the full 10, 000 psig without 
mechanical or electrical failure. Several 
dozens of the penlight bulbs were tested, and 
there were a few failures in each test group. 
Failure sometimes occurred by implosion and 
sometimes by oil leaks through the seal. Pen- 
light bulbs which did not fail were set aside for 
use in illuminating samples under test. 

The pressure vessel (Figure 1) used in 
these experiments has been fitted with an 
optical viewing port (Figure 10), a and b. 
Illumination from a number of penlight bulbs 
is directed on the object to be viewed within 



SEMICONDUCTORS 

Many semiconductor devices (diodes, 
tunnel diodes, rectifiers, and transistors) were 
tested under hydrostatic pressures to 10, 000 
psig. It is common practice to seal the active 
transistor element in a metal case filled with 
some inert material to prevent contamination 
of the transistor and subsequent change in 
characteristics, if not complete failure. 
Transistor cases are not constructed to with- 
stand the high pressure involved in this study, 
so most of the transistors failed the test, A 
few of the very small elements did withstand 
10,000 psig successfully, but most of the cases 
collapsed (Figure 14). Also, some early 
transistor types which were potted in an epoxy 



121 



resin were able to operate satisfactorily under 
hydrostatic pressures of 10, 000 psig. Most 
types of small transistors can be potted in 
plastic resins (either with their circuit, or 
separately) and made to withstand the high 
pressure. Several transistors of the type which 
failed because the case crushed were further 
tested after piercing the case with a sharp 
pointed tool and allowing it to fill with the 
paraffin oil in which it was submerged. In 
general, these transistors were able to per- 
form normally while under pressure, and for 
the short duration of the tests no contamination 
effects could have been expected. 

Several manufacturers are beginning to 
construct semiconductors with passivated sur- 
faces, so they can be immersed in fluids or 
potted in resins without fear of contamination. 
In addition, since they are very small, no case 
is needed. Several transistors and diodes of 
this type were tested and found to operate well 
under great hydrostatic pressure. One inter- 
esting type consisted of a silicon rectifier only 
0,04 in. in diameter and 0.019 in. thick. Its 
conduction characteristics are shown in Figure 
7. As can be seen, performance under high 
pressure was slightly improved over that under 
nornnal pressure. 

The results of these tests indicate that the 
semiconducting materials themselves are 
immune to the effects of pr.essure, at least for 
the short test periods used in this study. The 
passivated transistors now becoming available 
will serve very well under pressure. Where 
cased types must be used, it appears that 
standard potting compounds can provide 
sufficient protection to permit operation up 
to 10,000 psig for at least short time periods. 



POTTING AND PACKAGING 

Several tests were devised to measure the 
amount of protection afforded by potting methods 
and materials. One such test measured the 
degree in which the pressure was transmitted 
to the component under test. Since the resist- 
ance of composition carbon type resistors is 
nearly linear with pressure, resistors were 
used as sensors for these measurements. 
Comparison of resistance of resistors, before 
and after encapsulation, resulted in a relative 
measure of the pressure transmitted. It was 
found that with most plastics the pressure is 



transmitted directly to the resistor without any 
appreciable loss. To overcome this problem, 
epoxies of different types were molded over 
resistors, previously coated with a spongy type 
of silicont^ rubber. Figure 8 shows that the 
tv/o types of epoxies used over the silicone 
rubber had 'widely different capabilities in re- 
sisting transmission of pressure to the com- 
ponent. 

Components, such as transistors and 
capacitors which have internal cavities or 
voids, were found to be damaged when placed 
under pressure. A test was devised to deter- 
mine the thickness of potting material neces- 
sary to protect such components. Figure 9 
shows four very thin-walled, 1/Z-inch diam- 
eter, sealed aluminum tubes cast into a block. 
The four specimens were separated from the 
surface of the plastic block in increments of 
1/32 of an inch, starting with 1/32-inch. The 
two closest to the surface imploded at about 
2500 psig, while the other two successfully 
withstood the full 10,000 psig. This result 
illustrates the ability of the plastic casting to 
lend rigidity to embedded components and to 
prevent crushing. The end of the test block 
containing the two tubes which were not 
crushed in the original pressure test were 
placed in the small pressure tank illustrated 
in Figure 18 and were maintained continuously 
under high pressure to determine whether 
"cold flow" of the plastic material will eventu- 
ally permit collapse of the tubes. 

Several types of transistors and capaci- 
tors which, when unprotected, had failed under 
pressure have been potted and used success- 
fully in electronic circuits which were directly 
under the influence of hydrostatic pressure. 
Figure 19 is the electronic circuitry for a 
velocity meter which was operated satisfacto- 
rily in an oil bath for a period of forty hours 
at 10, 000 psig without failure. 

Another approach to this problem is the 
encapsulation of the entire circuit as a single 
unit. A complete three-stage transistor 
amplifier. Figure 20, was encapsulated in an 
epoxy-type resin and subjected to a hydro- 
static pressure of 10, 000 psig for several days. 
The thickness of the plastic over the components 
was less than 1/16-inch at some points. The 
circuit operated normally in spite of the fact 
that it contained many components which, in 
their original casing, would not have been 



122 



capable of operating under hydrostatic 
pressure. 

The use of fillers, such as small glass 
spheres, nnay permit construction of complete 
electronic circuits which will float. Figure Zl 
shows a 2B-gram test block, containing a 
"payload" of resistors weighing 5-grams, float- 
ing in fresh water. Illustrated in Figure 22 is 
an encapsulated circuit of the velocimeter, 
similar to that used in Figure 19. The entire 
unit can be constructed so that its specific 
gravity is at least 1. 1. The actual weight of 
the electronic circuit components in this instru- 
ment is only four ounces. By using the stand- 
ard technique of enclosing the electronic cir- 
cuits in a pressure-proof metal housing, the 
total instrument weight is increased by about 
25 pounds. The saving in weight and size 
which may be achieved by the development of 
instruments which can operate without 
pressure cases is obvious. 

To date, the results indicate that it is 
feasible to operate virtually every type of 
component required in electronic circuits under 
hydrostatic pressures up to 10, 000 psig, at 
least for short periods of time. It appears 
further that circuits can be constructed of 
lightweight materials and encapsulated in 
filled resins to obtain operating units which 
are lighter than water. Such techniques may 
well become mandatory in construction of 
complicated oceanographic or acoustic instru- 
mentation systems. 



123 



FIGURE CAPTIONS 

Fig. 1 Small pressure tank with electrical feed-through and optical viewing port closures 

Fig. 2 Large pressure tank (4 ft diameter, 8000 psi) showing screw plug and inner plug 

Fig. 3 Resistance as a function of pressure 

Fig. 4 Pressure sensitivity of carbon composition resistors 

Fig. 5 Typical failure of capacitor containing void spaces 

Fig. 6 Inductance changes in three types of cores under pressure 

Fig. 7 Inductance changes in five types of cores under pressure 

Fig. 8 Response of a type 6ALi5 vp.cuum tube to hydrostatic pressure (about 2000 psig) 

Fig. 9 Subminiature vacuum tubes subjected to 10,000 psig without mechanical or electrical 
failure 

Fig. 10 a. and b. Inside (a) and outside (b) views of optical port for observing objects under 
test in hydrostatic pressure tank 

Fig. 11 Transistor under test at 10, 000 psig as seen through optical viewing port 

Fig. 12 Nickel cadmium battery with pressure equalization 

Fig. 13 Glass tubing of various diameter was sealed as illustrated, then subjected to high 
hydrostatic pressures 

Fig. 14 Semiconductors subjected to hydrostatic pressure tests (10,000 psig, paraffin oil bath) 

Fig. 15 Conduction characteristics of a "passivated" diode under psig and 10,000 psig 

Fig. 16 Resistance of transmission of pressure to a component for two types of epoxies 

Fig. 17 Aluminum tube test block 

Fig. 18 Pressure tank for long-term test of electronic components 

124 



Figure Captions continued 

Fig. 19 Velocimeter circuit which operated in oil bath at 10,000 psig 



Fig. 20 Encapsulated amplifier 



Fig. 21 Floating test block with a total weight of 25 grams and with a "payload" (resistors) 
of 5 grams 



Fig. 22 Encapsulated velocimeter circuit 



125 



rJ" 




Figure 1 




<£,' dia, 8,000 psl 
Showins Screw Pl-ig 
»nd Isityr Plug 
February i960 



Figure 2 

126 



55 — 



50 



45 — 



^40 



35 



30 









RESISTANCE AS A 
FUNCTION OF PRESSURE 
Kfi VS PSIG 












• 


^^^-^ 








• 


^~^^"^^~"~---^ 


• 


RESISTORS 
1/2 WATT SIKfl 5% 


COMPOSITION CARBON 




o 


1 WATT 5IKn 5% 


COMPOSITION CARBON 




X 


2 WATT 5IKn 5% 


COMPOSITION CARBON 




A 

□ 


2 WATT SIKil 1% 
2 WATT 51KU 5% 


TIN OXIDE 
CARBON FILM 

1 1 1 


1 1 1 1 



1000 2000 3000 4000 5000 6000 

PRESSURE (PSIG) 
Figure 3 



7000 



8000 



9000 



10,000 



O 
O 
o 
o' 



2 



25 



20 



10 



PERCENT CHANGE IN RESISTANCE 
AT 10,000 PSIG VS RESISTANCE 
FOR CARBON COMPOSITION RESISTORS 



lOK 
RESISTANCE (OHMS) 
Figure 4 



lOOK 



IM 



lOM 



127 



200 



100 




B = I000 TURNS ON MOLYBDENUM-NICKEL- 1 RON DUST 

H = IOOO TURNS ON 50% NICKEL- IRON, GRAIN ORIENTED SQUARE LOOP 

M=GRAIN ORIENTED SILICON CORE 



6,000 



PRESSURE (P S IG) 
Figure 6 



128 



106- 



G- 1000 TURNS ON 75% NlCKEL-lRON CORE 
H-IOOO TURNS ON FERITE CORE 

I -1000 TURNS ON POWDERED IRON CORE, HIGH FREQUENCY FORMULATION 
J-IOOO TURNS ON POWDERED IRON CORE , MEDIUM FREQUENCY FORMULATION 
K-IOOO TURNS ON POWDERED IRON CORE, LOW FREQUENCY FORMULATION 



2 

2 3 104 



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O LiJ 



gj"^ 100 



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J \ L 



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2000 



4000 6000 

PRESSURE - (PSIG) 
Figure 7 



000 



6AL5 VACUUM TUBE 




BEFORE 
PRESSURE TEST 



AFTER 
FAILURE AT 2000 PSI 



INCHES 
12 3 

I ' ' ' I ' I ' I ' I ' I 

OCEANOLOGY SECTION 



129 



1 


SUBMINIATURE 


1 


« * 


SUBMINIATURE 


- -f 




*i 


BEFORE 


INCHES 

1 2 3 4 5 

1 . 1 , 1 , 1 . 1 . 1 . 1 . 1 . 1 . 1 1 1 1 1 


AFTER 

6 

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Figure 9 




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11 21 31 41 5 

INCHES 

Figure 10 (a) 



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Figure 10 (b) 




Figure 1 1 



131 




NitAcL CADMIUM BATTERY 
WITH PRESSURE EQUALIZATION 
CHARGE AND DISCHARGE 
OPERATIONS NORMAL 

TO 10.000 PS! ,^ 

Figure 12 



RUBBER 



GLASS (WALL THICKNESS ,039 IN.) 



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BRASS STUBS 



GLASS TUBES WHICH WITHSTOOD HYDROSTATIC PRESSURE OF 10,000 PSIG 



0.0 
.23 IN 
.27 IN. 
.35 IN. 



LENGTH 
2 13 IN. 
2.43IN 
2.50 IN. 



Figure 13 



132 



SEMICONDUCTORS UNDER HYDROSTATIC PRESSURE 
(10.000 PSI- PARAFFIN OIL BATH) 



DIODES 



POWER RECTIFIERS 



TRANSISTORS 



TRANSISTORS 
EPOXY POTTED 

TRANSISTORS 



BEFORE 



POWER TRANSISTOR 



INCHES 

I ■ Z 3 4 5 6 

1 - I - I ^ . . I . I . I . ^ . I . . , I . . . I 



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AFTER 



Figure 14 



PASSIVATED DIODE NO 2 
5/31/61 FWH 



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FORWARD VOLTS 

Figure 15 
133 



30 



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(2) lOOKil 1 W, IN DENSE EPOXY (COVERED WITH SILICON RUBBER) 
(3)100Kil IW, IN LIGHT EPOXY (COVERED WITH SILICON RUBBER) 




1000 2000 3000 



4000 5000 6000 
PRESSURE (PSIG) 



7000 8000 9000 10000 



• • ■ m M « . i [«l i - l l i H «iii "" « - ■ r > nn «i 




Figure t7 




134 




ll 21 5I 4I 



INCHES 



SONAR SYSTEMS BRANCH 



Figure 19 




ENCASED TRANSIFIER 
OPERATED NORMALLY 
FROM TO 10,000 PSK 

INCHES 
12 3 

I ' I ■ I ■ I ' I ' I ' I 

, OCEANOLOGY SECTION 

Figure 20 



135 




Figure 21 




Figure 22 

136 



INTERNAL WAVES AND THEIR MEASUREMENT 

by E. C. LaFOND, Head, Marine Environment Studies Branch 
U.S. Navy Electronics Center 
San Diego, California 



INTRODUCTION 



Internal waves are undulating swells occur- 
ring between subsurface water layers of varying 
density, even though the density change be 
slight. By contrast, in a homogeneous fluid 
only surfaces waves are possible, and the ampli- 
tude of their motion decreases with depth. In 
the ocean, vertical density gradients are 
virtually always present. Thus Internal waves 
are found in all oceans and probably most bays 
and lakes, and vary widely in amplitude, period, 
and depth. Although their amplitudes may exceed 
those of surface waves, internal waves are 
usually slower in speed. 

In a simple, two-layer density system, 
maximum amplitude exists at the boundary of the 
two layers and decreases linearly with distance 
above and below.-'- In a multiple -layer or 
continuous-density gradient system, as in the 
sea, the wave motions become much more complex. 
Under these conditions multiple wave patterns, 
having different characteristics, have been ob- 
served at different levels . 

CAUSE OF IMTERMAL WAVES 

The exact causes of specific internal 
waves have not yet been firmly established, but 
they are probably of varied origins. Experi- 
ments in the Norwegian fjords'^ showed that a 
slow-moving sailboat initiated internal waves 
at the shallow-layer boundary of nearly fresh 
water and higher-density sea water. The inter- 
nal waves, produced by the keel of the slow- 
moving ship, reduced its speed and created the 
phenomenon known as "dead water". 

Since internal waves are commonly found at 
water mass boundaries or "fronts," they are 
probably produced through direct displacement 
of one water mass by another. The front is 
characterized by a group of relatively large 
Internal waves followed by a change in the depth 
of the thermocline (fig. l) . Visual evidence 
of internal waves forming at water mass bound- 
aries has been shown in high-altitude photo- 
graphy3 of slick-type surface phenomena in 
Georgia Strait,* where such occurrences were 
attributed to large-scale discharge of water of 



varying density (fig. 2). Masses of fresh water 
created a tidal front, or zone of convergence 
and divergence, in which internal waves developed. 
Internal waves, coincident with tidal periods 
whether semidiurnal or diurnal, were commonly 
observed; thus, it was concluded, tidal forces 
must be instr-umental in generating them. ^5 

Certain internal waves may be created by 
two adjacent flows or by a flow impinging on a 
continental shelf or other obstruction. Experi- 
ments that showed internal waves to occur when 
a tidal stream flowed against a coastal bank 
have been conducted. It was further proven that 
obstacles in the path of an advancing wave give 
rise to internal waves. "i" The significant fact 
is that vertical oscillations in the thermal and 
density structure of sea, which are termed in- 
ternal waves, are apparently present in all 
oceans and at all depths. This indicates that 
their cause is likewise universal. 

MEASUREMENT EQUIPMENT AND TECHNIQUES 

Internal waves can be present only in water 
where a vertical density gradient exists. The 
vertical gradient may be caused either by tem- 
perature or salinity, or both. In fresh-water 
lakes, measurements of temperat\rre alone are 
sufficient to establish the existence of density 
gradients. In the sea, measurements are com- 
monly of temperature since they are easily ac- 
complished, and the temperature and salinity 
gradients usually coincide. In addition, the 
salinity gradients are normally small. 

On one occasion, however, internal waves 
were directly measured by their vertical oscil- 
lations of density. A large, buoyant container^ 
was floated on a given density boundary and its 
depth recorded. A drum, filled with glass balls, 
was guided vertically by a cable . A recording 
manometer on the drum successfully furnished a 
7-day record of the depth when it was weighted 
sufficiently to float on the maximum density 
gradient found in the southern Kattegat** in 
summer. 

Various instruments have been employed to 
measure vertical oscillation of temperature 



*The channel between Vancouver Island and **An arm of the North Sea 

southwest British Columbia. Denmark. 

"Superior numbers refer to similarly numbered references at the end of this paper. 



between Sweden and 



137 



(sometimes simultaneously with salinity). For 
long -period waves, reversing thermometers and 
water bottles were used. Repeated bathythermo- 
graph lowerings were made, and more recently 
the fast-responding thermistor beads have been 
utilized. 

THERMISTOR BEADS 

The most common method of measuring sea 
tenrperatures at the present time is with fast- 
responding thermistor beads. These come in 
various types; the most common is a sma]J., 
glass -encapsulated, high-thennal-resistant 
material with connecting leads. A current pas- 
sing through the beads is greatly influenced by 
temperature. Thus the temperature of the sea 
water is proportional to the electrical current. 

Since the beads are not precisely matched, 
resistance-wise, to each other, and temperature- 
resistance relations are not exactly linear, 
several schemes have been devised to increase 
accuracy by using compensating resistors in with 
the bead or by amplifying short stretches of the 
most linear part of the resistance-temperatiure 
curve. Another problem is their fragility and 
the watertight integrity between the glass beads 
and electrical connections (fig. 3) • 

One effective thermistor device to deter- 
mine sea temperatures and identify internal 
waves is the l6-channel temperature -sensing unit 
developed by the U. S. Navy Electronics Labora- 
tory (IIEL).5 It includes l6 thermistor beads 
cast in plastic and attached to electric leads. 
The leads and beads are part of a bridge circuit 
that feeds a recording-type potentiometer. The 
recorder prints numbered points consecutively 
from 1 to 16 on a power -driven strip chart, the 
location of each number indicating a particular 
temperature . In normal operation, a full cycle 
of 16 recordings requires approximately half a 
minute (fig. k) . The temperature at each depth 
is indicated on the chart to an accuracy of 
better than 0.02°F. 

The beads are suspended in one or more ver- 
tical series from a ship, anchored buoy, or 
fixed platform (fig. 5)- Temperature can thus 
be recorded at up to I6 depths for any desired 
period of time . However, to determine the 
character of internal waves, the depth of the 
isotherms must be scaled from the measured tem- 
peratiores at fixed depths. 

THERMISTOR CHAIU 

Strings of thermistor beads may be towed 
from a ship and their sensing elements scanned 
electronically. This procedure allows the iso- 
therms to be identified and printed directly-'-^ 
with reference to time or distance. 

MEL thermistor chain, from which are sus- 
pended the strings of thermistor beads, makes 
it possible to sense vertical sections of tem- 
perature structure from the surface down to 8OO 
feet when the ocean-going NEL research vessel 



USS MARYSVILLE cruises in waters of greater 
depth (fig. 6) . 

The thermistor chain, together with the 
drum on which it is wound, is large and rugged, 
weighing 37^500 pounds. The chain is composed 
of large, flat links about a foot long, 9 inches 
wide, and an inch thick. At its end is a 2300- 
pound, streamlined torpedo-shaped weight to 
hold it down. The weight and its connected 
chain are lowered from the stern as the oceano- 
graphic vessel proceeds through the water. 

About 80 pairs of insulated wires fit 
through grooves Inside the flat links . Every 
27 feet the wires connect with the thermistor 
beads, which sense the sea temperature. 

The upper ends of the electrical leads 
connect to a recorder located in the vessel's 
laboratory. Signals from the beads are scanned 
electronically every 10 seconds, and lines 
showing the depths of constant temperatures are 
printed on 19-inch-wide tape. This Is equiva- 
lent to taking a bathythermograph lowering 
every 100 feet if the ship proceeds at 6 knots. 
Recorded on the same tape are the depth of the 
weight (or maximum depth of observation) at the 
end of the chain and, in addition, the sea sur- 
face temperature (the uppermost bead in the 
chain) . This instrument thus gives essentially 
a two-dimensional picture of oceanic thermal 
structure and internal waves from the surface 
to 800 feet. 

ISOTHERM FOLLOWER 

Another device for directly measuring the 
temperature of internal waves is the isotherm 
follower-'--'-, which automatically traces isother- 
mal vertical oscillations with reference to 
time. This instrument is comprised of (l) a 
sea sensing unit; (2) an electric winch con- 
taining a cable to which the sea sensing unit 
is attached; (3) electronic components (servo- 
mechanism, amplifiers, power supply, controls, 
etc.); and (4) two recorders (depths and tem- 
perature) (fig. 7) • 

The sea sensing unit contains a thermistor 
bead balanced in a bridge circuit with a re- 
sistance corresponding to the desired isother- 
mal temperature. If the bridge becomes unbal- 
anced, a thyratron tube is fired. This 
activates a winch and causes it either to wind 
in or let out the sea unit, "locking it" onto 
the desired isotherm. The isotherm depth is 
continuously recorded on the ship by means of a 
pressure sensor in the sea unit. The net re- 
sult is a trace of the given Isotherm depth, 
effecti-ve to 6OO feet, with reference to time. 

The isotherm followers ha-ve been employed 
singly, or in triangular arrangements of three, 
to acquire the speed and direction of Internal 
wa-ves-'-^ by time of arrival and plase shlftslj. 
Virtually continuous operations throughout the 
summer months up to periods of one week have 
been successfully conducted from the NEL Oceano- 
graphlc Research Tower. Here they are suspended 
from the structure by IfO-foot booms (fig. 8). 



138 



TOWED ISOTHERM FOLLOWER 

A modification of the isotherm follower is 
a recently developed towed version. The prin- 
ciple is the same -- the follower seeks out a 
selected isotherm and traces it as the sea unit 
is towed from a ship. 

The sea unit is a torpedo-shaped device 
with fins (fig. 9) that are moved up or down by- 
its small motor which, like the winch, is 
directed by a signal from a thermistor bead in 
the nose of the sea unit. The instrument thus 
follows the isotherm up and down as its depth 
by pressure is recorded on the towing ship. 

The towed isothenn follower is generally 
used in shallow water (where the thermistor 
chain cannot be towed) to determine the nature 
of internal waves as they cross the continental 
shelf and eventually Impinge on the bottom. 

NATURE OF IMERMAL WAVES 

CHARACTEELSTICS 

Internal waves have been measured in 
all oceans and in several lakes throughout the 
world. Off southern California in summer, the 
vertical oscillations of the temperature struc- 
ture were measured by use of therailstor beads 
suspended vertically at a depth of 50 feet, 9 
later by isotherm followers at a depth of 60 
feetj-'-S by the HEL thermistor chain in the San 
Diego Trough, •'-^ and in the deep, open sea. In 
the next sections are described the character- 
istics of internal waves that were determined 
in these experiments. 

WA'/E HEIGHT 

The depth of a single isotherm in the 
thermocline was observed to fluctuate widely 
during one day in water only 60 feet deep. A 
day's record of smaller internal waves in the 
thermocline, as recorded by the isotherm fol- 
lower, is shown in figure 10. The short-period 
vertical oscillations are superimposed on the 
longer period tidal oscillations in the thermo- 
cline. Generally, the magnitude of the small 
vertical fluctuations was Inversely propor- 
tional to the gradients through which they pro- 
trnaded. Small fluctuations were nearly always 
present. 

Long periods of continuous isotherm 
or thermocline depth measurements have been re- 
corded. It was found that a frequency plot of 
thermocline depth for one 7-day series, 
recorded in summer off Mission Beach, Califor- 
nia, had a trimodal distribution. The central 
primary mode (l) around 32 feet was interpreted 
to be the depth of the seasonal thermocline. 
The others, (2) and (3), around l8 and Ulj- feet, 
were caused by Internal tide and amounted to 26 
feet at this time and place (fig. 11). 

During the periods of investigation, 
the maximum daily vertical migration of an iso- 
therm in the middle of the thermocline was 31 
feet. 



The frequency distribution of shallow 
Internal wave heights at this location for part 
of 12 days throughout the summer of 1958, and 7 
consecutive days in 1959, is shown in figure 12. 
Only waves higher than 2 feet were considered 
since the lower ones were probably only random 
fluctuations. It was found that 50 per cent of 
the internal waves were higher than 5.6 feet. 

In the San Diego Trough 20 miles from 
shore in 600 fathoms of water, the upper thermo- 
cline during a June period contained vertical 
oscillations that were no higher than those ob- 
served from the nearby MEL Oceanographic Research 
Tower. The median vertical change for changes 
greater than 1 foot was only k.6. This and 
other characteristics of the thermocline are 
shown in figure 13. 

During the same season, 200 miles from 
shore, the upper thermocline contained waves a 
little higher than those near shore. However, 
the vertical oscillations of constant tempera- 
ture were much higher at depths from 30O-800 
feet, their height being inversely related to 
the vertical temperature gradients. Here they 
were from 50 to 200 feet (fig. ih) . This in- 
verse relationship probably holds at greater 
depth where the vertical thermal and density 
gradients are even weaker. 

The tidal circulation described above 
also Influences long-period wave heights and 
wave periods (fig. I5). In the deep sea areas 
as well as on the continental shelf, internal 
waves of tidal period are commonly found-'-5. 
However, the relative phase of surface and in- 
ternal tide Is not consistent. 

WAVE FERIOD 

The frequency distribution for the 
duration of 1061 shallow-water in-fernal waves is 
shown in figure 15. Waves with periods of less 
than 2 minutes were excluded. Fifty per cent 
of all waves longer than 2 minutes had periods 
greater than 7.3 minutes. 

In deep water the internal-wave period 
is difficult to measure because of lack of suit- 
able platforms and adequate knowledge of the 
currents at different levels. An easier proced- 
ure is to measure the wave length or distance 
between crests with the towed chain. In the San 
Diego Trovigh, the upper thermocline oscillations 
greater than one foot occurred on the average of 
O.k mile apart, whereas in the deeper and more 
open areas, they occurred about 1 per mile at 
depths of about 5OO feet. 

SPEED 

In shallow water, the speed of internal 
waves was determined by measuring vertical os- 
cl3J.ations simultaneously in three locationsl6,12 
and deduced from the movement of their associated 
sea-surface slicks. 

Time-lapse films of surface slicks off 
southern California* showed that internal waves 

♦Mission Beach, La Jolla, and San Diego Bay 



139 



moved toward shore at speeds of 0.11 to 0.6 knot. 
Other measurements from anchored ships with range 
markers indicated an average speed of 0.3I knot. 
More recent measurements averaged with three 
isotherm followers were 0.29 knot in 60-foot- 
deep water (fig. I6) . 

The observed speed (c) agrees well 
with prior theoretical considerations when deal- 
ing with long internal waves as compared to their 
depth . -, 



g h h 
h + h' 



P - P 



r 



where h and h are the depth of a two-layer 
system having densities p and p, respectively. 
In 180 feet of water in the Atlantic 
Ocean, internal wave speed still agreed with 
established equations and gave speeds of about 
1.0 knot'^'^, thus it must be supposed that inter- 
nal waves in deep water, especia3_Ly deeper ones, 
must travel at considerably greater speeds . 

DIRECTIOH 

The shape of internal waves varied 
with shoreward movement and refraction as they 
moved into shallower areas . Their shape was 
also influenced by their proximity to the sur- 
face sea floor-'-". Wearly all internal waves 
proceeded from a west-to-southwest (mode T2.'4-°T) 
direction at the Mission Beach location (fig. 
17) . Efforts to obtain information on internal 
wave direction were ineffecti-ve in deep water. 
One such action involved towing of the HEL 
thermistor chain in different directions, but 
no clear-cut doppler effect could be established- 
It appeared from this experiment that deep-water 
internal waves are not in long parallel lines 
as they frequently are in shallow water. 

OTHER RELATED MOTIONS 

One approach to the study of internal 
wave motion in the sea is the assumption that 
they are progressive waves. In lakes and par- 
tially closed bodies of water, standing wa-ves 
are found. The nature of progressive waves 
between two liquids of different densities has 
already been analyze d.-'-^'^O ^g nature of this 
circulation as applied to the sea has been in- 
vestigated by direct and indirect means. For 
example, sea surface slicks, which often re- 
present visible evidence of internal waves belovj 
are seen as streaks or patches of relati-vely 
calm surface water surrounded by rippled water. 
The absence of wa-velets in a slick gives it a 
glassy appearance in contrast to the adjacent 
rippled water (fig. 18). These slicks ^^^2 
been studied in oceans, bays, and lakes. ' ' 
23,9 

The occurrence of visible slicks is 
contingent upon proper wind, lighting, suffi- 
cient organic matter on the water, and the 
nature of internal waves. The concentration of 
surface filjn depends on the interrelation of 
internal wave height and period. The average 
depth of the internal wave and its relation to 



water depth also influence the type of circula- 
tion and thus ha-ve a bearing on the formation of 
slicks. In 85 out of 105 cases, the slick was 
on the descending thermocline somewhere between 
the crest and the following trough (fig. I9) . 
This relationship is undoubtedly the result of 
convergent water circulation created by internal 
waves. The significant motion is therefore a 
surface convergence over the trailing slope of 
the internal wave . 

Direct measixrements of current asso- 
ciated with internal wa-ves were made at the NEL 
Ooeanographic Research Tower. By means of a 
closed-circuit tele-vision, obser-ving dye and 
motion streamers, and a current meter that dam- 
pens surface wave motion, the existence of con- 
vergence-type circulation associated with a 
slick was confirmed. The reverse circulation 
over shalJ.ow crests and over troughs was also 
established, thus substantially confirming in 
part the above circulation theory of a two-layer 
Internal -wave system in shallow water. 

SUMMARY AND COMCLUSIOMS 

Internal waves are now being measured by a 
number of instruments, including vertical 
strings of temperature sensors, which are sus- 
pended in one location, as with isotherm follow- 
ers, or towed, as with the KEIL thermistor chain. 
The vertical osclU-ations obser-ved in the 
thermal structure, commonly termed internal 
wa-ves, are present in the sea -vlrtuaJJ-y all the 
time. Their height, speed, direction, period, 
and other characteristics are found to vary 
widely with time, area, and depth. The larger 
wa-ves are associated with weaker gradients and 
thus ha-ve larger amplitudes in the deeper layers 
where temperature changes are smaU. Studies of 
their motion, spatial distribution, and cause 
are continuing. 

REFERENCES 

1. Fjeldstad, J. E., 1933, IMTERME WALLEW 
GEOFYSISKE Publikas joner. Vol. 10, Ho. 6, 
53 pp., 1933 Oslo. 

2. Ekman, V. W. , X90k, ON DEAD WATER, Sci. 
Results, Norwegian North Polar Exp. 1893-96, 
Vol. 5, No. 15, pp. 1-152. 

3. Shand, J. A., INTERNAL WAVES IN GEORGIA 
STRAIT, Trans. Amer. Geophys. Union, Vol. 
3I+, pp. 8I+9-856, 1953 

k. LaFond, E. C.and Poornachandra Rao, VERTICAL 
OSCILLATIONS OF TIDAL PERIODS IN THE TEM- 
PERATURE STRUCTURE OF THE SEA, Andhra Uni- 
■versity Memoirs in Oceanography, Vol. 1, 
pp. 109-116, 1954. 

5. Munk, W. H., 19iH, INTERMAL WAVES IN THE 
GULF OF CALIFORNIA, Jour, of Mar. Res., 
Vol. k, pp. 81-91. 

6. Zeilon, N., l.93h, EXPERIMENTS ON BOUNDARY 
TIDES, Goteborg Vetensksamh. Handl. Folj . 
5, Ser. B, Bd. 3, No. 10. 

7. Zeilon, N., 1913, ON THE SEICHES OF THE 
GULLMAR FJORD, S^renska Hydrogr-Biolog. Komm. 
skrifter 5 • 



140 



8. Kullenberg, B., 1935, INTERNAL WAVES IN THE Figure 
KA.TTEGAT, SYenska Hydro, Biolog. Koinm, 
Skrifier, Ny Serie Hydrografi, XII Figure 
(A.C.S.I.L, Translation #561). 

9. LaFond, E. C, SUCKS AND TEJIPERATURE Figure 
STRUCTURE IN THE SEA, U.S. Navy Electronics 
laboratory Report 937, 2 November 1959. 

10. Richardson, William S., 1958, ^ffiASUREMENT Figure 
OF THERMAL MIGROSTRUCTURE, W. H.O.I. Refer- Figure 
ence No, 58-11. 

11. LaFond, E.G., 1961, THE ISOTHERM FOLLOWER 
Jour, of Mar. Research, Vol. 19, No. 1, 
pp. 33-39, March, 1961. Figure 

12. Lee, O-.ven S., I96I, OBSERVATIONS ON Figure 
INTERNAL WAVES IN SHALKDW WATER, Limnology 
and Oceanography, Vol. 6, No. 3, July 1961. 

13. Lee, 0. S. and E. C. LaFond, I96I, ON Figure 11 
SHORT-PERIOD CHANGES IN ISOTHERM DEPTHS IN 
SHALLOW ..ATER OFF SAN DIEGO (In press). 

14. LaFond, E. C, 1961, TWO-DIMENSIONAL 
OCEANOGR.APHY, BUSHIPS Journal (In press). Figure 12 

15. UFond, E. C, THE USE OF BATHYTHEl:^:0(3l.y■lS 
TO MEASURE OCEM CURRENTS, Amer. Geoph. 
Union, Vol, 30, No. 2, pp. 231-237, Figure 
April 1949. 

16. Ufford, C. W., 1947, INTERNAL VJAVES Figure 
MEASURED AT THREE STATIONS, Trans. Amer. 
Geoph ys. Union 28, (l), pp. 87-95. Figure 

17. Gaul, Roy D., 1961, INTERNAL WAVE 0B3ERVA- Figure 
TIONS NEAR HUDSON CANYON, Jour, of Geoph. 
Research (In press). Figure 

18. LaFond, E. C, BOUNDARY EKFF.CTS ON THE Figure 
SHAPE OF INTERNAL WAVES, Indian Jour, of 
Meteorology and Geophysics, 12 April I96I. Figure 15 

19. Lamb, H., HYDRODYNAMICS, 6th Edition, p. 
372, Dover Pub. Co., New York, 1945. 

20. LaFond, E. C, I96I, THE TEMPERATURE Figure 
STRUCTURE OF THE UPPER LAYERS OF THE SEA 
Aim ITS VARIATION «TH TIME, Proc. of the 
3rd Symposium — Temperature, Its Measure Figure 
and Control in Science and Industry Instru- 
ment Society of America (In press). 

21. Dietz, R. 3. and E. C. LaFond, NATURAL 
SLICKS ON THE OCE.AN, Jour, of Mar, Res., Figure 18 - 
Vol. IX, No, 2, pp, 69-76, October 1950, 

22. Woodcock, A. H. and T. Wyman, 1946, CON- 
VECTIVE MOTION IN AIR OVER THE SEA, Ann. 
N.Y. Acad. Sci. 48, 749-776. Figure 19 - 

23. Forbes, A., 1945, PHOTOGR,\f'MEmi APPLIED 
TO AEROLOGY, Photogrammetric Eng, 2, 
181-192, 

FIGURES 



4 — Sixteen-channel temperature recording 
unit. 

5 - Internal ware measurements from an 
anchored ship, 

6 - U.S. Navy Electronics Laboratory's 
thermistor chain on USS MARYSVILLE 
(EPCER 857). 

7 - Isotherm follower assembly 

8 - Tnree isotherm followers in operation 
from booms suspended out from the U. 
S. Navy Electronics Laboratory oce.ano- 
graphic research tower, 

9 - Sea unit of towed isotherm follower, 

10 - Depth of isotherm measured with 
isotherm follower off Mission Beach, 
California (summer, 1961). 
Distribution of minute readings, 
over 7 consecutive days, of the 
dspth of an iso'.herm in the thenr.o- 
oline. 

Frequency distribution of internal 
wave heights over 2 feet (1958 and 
1959 data). 
• Operation area in San Diego Trough 

off Southern California. 
13B - Thermal structure of the sea as 

measured with the themistor chain. 
13c - Depth to the top of the thermocline, 
I3D - Maximum vertical temperature gra- 
dients in °C per fifty feet. 
13E - Roughness of the thermocline, 
14 - The nature of internal waves in 
deep ocean water. 

Frequency distribution of internal 
wave periods over 2 minutes (for 
1958 and 1959 data). 
Internal wave speed in 60-foot water 
from 674 observations using isotherm 
followers during the I96O summer. 
Internal wave direction in 60-foot 
water from 674 observations using 
three isotherm follower during the 
i960 summer. 

Sea surface slicks near the USNEL 
Oceanographic Research Tower, 
Slicks are surface evidence of in- 
ternal waves below. 
Relation between internal waves and 
sea surface slicks. Heavy bar at 
surface and vertical dashed lines 
represent the observed position of 
sea surface slicks with reference 
to thermal structure. 



13 A 



16 



17 



Figure 1 - Internal waves associated with a 
change in depth of a thermocline, 
(Waves are moving from right to left) 

Figure 2 - Sea surface appearance showing the 

probable formation of internal waves 
by tidal action between low-density 
discharge water and the Georgia 
Strait water (British Columbia 
Government Air Photo), 

Figure 3 - Thermistor beads and resistors 

mounted in plastic used for tempera- 
ture sensors. 



141 




!^30 



MO 



frSO 



^\ 


if \J^ 


u 
o 


w 

4 o 


o 


§ 


§ 


tn 
o 




SEA FLOOR 



§ 



10 MIN 



>?^/yy//y/y///v///vy/yy/^////^^^ 



'/ 



Figure 1 




I— 



09 

u 



CO 



CO CO 

— ^s 
E ™ 







143 




Figure 4 



144 



OBSERVATION 
SHIP 




Figure 5 








367 




'"igure 6 



145 




D 

recorders 



winch 



electonics 



Figure 7 



146 



r 



.« Si 





147 




4) 



148 



20 21 

26 MAY 61 



22 



23 



>»<w»r»K^^_^ .^..jiiliarh'-,^^^^ 



23 



24 



27 MAY 



LT 



50 FT. 



r^V^^ 




ISOTHERM 



HT DEPTH 



H 






14 



15 



16 



17 



'\yA^V^'''^''''^^Aw""^^'''^ 



17 



18 



19 



20 




Figure 10 



149 



0| 1 1 1 1 r 



X 

\- 

Q. 
U 
Q 



10 



20- 



30- 



40- 



50- 



60" 



< 



i 




r^ 



J L 



Figure 1 1 



D1 



J I I I I L 



12 3 4 5 6 7 8 9% 




150 



LONG 
BEACH 



'% 



I It 



SURFkCE 



C«TALIN« I. 



li 




OPEROTION 



SAN 
CLEMEKTE I. 



V. 



SAN 
DIEGO 






-~^l-/\ _^,.«.,-/v^~ 



14- ■ 

-13'- 






.■,s-'-* ■'^■^■^ 



-300 ft. 



B 



I 

1— - — I 




■UP 
DOWN 



I 2 




Figure 13 




151 



SURFACE : 

' ' i 



'■''^V^'"' 







■^^'^U'-' 






^/-,^.;^^^— ■ ^^^ 



■VS 



'v^^,\v^,,.., y^,^y/' S■^^'•'Vv'*^^ 



-e^^-'^'V/v^ 



--r'^^-*' 






-600ft. : - 



^^^.^^.-^s..-.^-^'^-^-^ 



BOO ft. 



Figure 14 



20 



10 



f^^ 


1 


1 

.•.•.'.•■•J 

.*.*.',•■'.•.' 
.'.■.■.■■• • • 
. . . 4. . . 
■.*.•.• J.*.*. 
*.•.•.*.■.•.*. 






1 1 1 

WAVE 
PERIOD 


"^•l* 


.•.•.'.I'.*.* 
.*.•.*.•■•.•." 
.*.•.*.•■•.•.' 
....... 




T| 




:•:• /.«5::::- 




[•.•.•.•.•.•.•irrrWn — i — th 


m 


■!•;• 



12 16 20min.24 

Figure 15 



152 



KNOTS 
0.1 0.2 0.3 0.4 0.5 0.6 0.1 0.8 0.9 1.0 

14 1 1 1 1 T I I I i r~ 



12 



10 



jtz. 



28.8 



U! 




± 



_L 



10 20 30 40 50 60 70 

FT./MIN. 

Figure 16 



80 90 100 no 120 




40 60 80 100 

DIRECTION (to) IN DEGREES 

Figure 17 



80 



153 




154 




Figure 19 



155 



QUANTITATIVE MULTIPLE OPENING- AND-CLOSING 
PLANKTON SAMPLERS 

by DR. ALLAN W. H. BE 
Lamont Geological Observatory 
(Columbia University) 
Palisades, New York 



Two quantitative opening-and-closing 
plankton eantpleTB are described for serial 
saiapling of zooplankton in the upper 1000 
meters of water. The Uiltiple PlanJrton Sampler 
(MPS) is designed for towing at three depth 
ranges (0-100 m; 100-250 m; and 250-500 m) in 
the upper 500 meters, and the Bathypelagic 
Sanpler (BPS) is intended for simultaneous 
towing in the more sparsely populated 500-1000 h 
depths. 



TKBORY OF OPERATION 



for: 
a. 



b. 



d. 



The two samplers were specifically designed 

filtering large volumes of water (10 mVoJin. 

or more) through horizontal and oblique 

towing; 

reliable opening-and-closing actions at the 

mouths of the nets, without fear of catch 

loss or contamination; 

obtaining a bathymetric series of plankton 

samples at accurately predetermined depth 

levels by means of a fool-proof release 

mechanism; and 

reducing ship's time operation by the use of 

multiple nets in single lowerings. 



It should be emphasized that the present 
samplers require towing at 2 to 4 knots with 
wire angles of 30° to 50°. Thus, they are 
primarily intended for deep bathymetric studies 
of zooplankton and are in a different category 
frcan the high-speed plankton saii5ilerslj2,3,4, 
which are towed mainly in the 0-100 m, near- 
surface zone. The ability of horizontal and 
oblique towing of the present saiaplers is 
considered an ir^jortant ijnprovement over the 
other nultiple plankton samplers requiring 
vertical hauls. ^>">''' 



^nt.-iT>lP Planktnn .'temnler 

The MFS is designed to take three saiqples 
and allows opening-and-closing actions of three 
separate plankton nets. Its operation depends 
upon the following ccaaponents: 

a. ^ m X i m square fiberglass frame containing 
three pivoting rods with a ccmnon axis of 
rotation in one comer. Three one-half 
meter nets are attached to the rods and to 
the comer opposite the ccnmon axis in such 
a manner that each net may be folded 
(closed) and/or opened by 90°-rotatlon 

of its corresponding pivoting rod (the 
rotational force upon the rods is provided 
by three elastic cords, attached to the 
frame's exterior and the outwardly extending 
ends of each pivoting rod); 

b. pressure-actuated, piston-type release mech- 
anism with three release levers; and 

c. three flowmeters. 

At the start of the tow all three rods are 
fastened by thin cables to each of the release 
levers, which in turn are held in cocked 
position by the piston stem of the release 
mechanism. The "shallow" net is open when 
lowered and ready to fish on the way down, while 
the other two nets are folded. 

At the first selected depth level (e.g. 
100 m), the piston stem will have travelled 
past and released the upper lever — thus 
triggering a 90°-rotation of the first rod and 
closing the first or "shallow" net while 
simultanlously opening the second net. At the 
end of the second depth Interval (e.g. 250 m), 
the second net is closed and the third net is 
opened simultanlously. The closing of the 
third net at 500 m depth concludes the MPS 
operation. 



"Superior numbers refer to similarly nvmbered references at the end of this paper." 



156 




157 




158 




159 




160 




161 



The Bathypelaglc Sampler (BPS) Is 
essentially a larger version of the UPS. It 
has a 1 B X 1 m square frame with a single, one- 
meter net and is made to sanple the 500-1000 m 
depth zone. Both the MPS and BPS have flow- 
meters that can record the amount of water 
filtered ty each net tew. 



The principle of the present samplers may 
be modified to suit the specific needs of other 
investigators, particularly with respect to 
size of frame opening, number of nets and depth 
ranges to be sampled. Larger frames and more 
nets, for instance, are recoomended for 
saa^ling the a'tyssopelagic realm. 



SEmmCES 

1. Hardy, A.C.(1926), "The herring in relation 
to its animate environment. Fart II: 
Report on trials with the plankton indica- 
tor", ll&ir. Fish. Invest., Ser. 2, ^(7): 
1-13. 

2. Gehrlnger, J.W.(1952), "An all-metal 
plankton sampler (Model Gulf III)". D.S. 
fish and fildl. Serv., Spec. Scl. Rep. 
Fish., No. 88: 7-12, 

3. Glover, R.S.(1953), "The Hardy plankton 
indicator and aanpler: a description of 
the various models in use". Bull. Ifer. 
Ecol., 4(26): 7-20. 

4. Ahlstrcm, E.H. (1958), "High-speed plankton 
saiopler". U.S. Fish and Wlldl. Serv., 
Fish. Bull., ^ (132): 187-214. 

5. Ibtoda, S. (1953), "New plankton samplers". 
Bull. F&c. Fish., Hokkaido Univ., 2 (3): 
181-86. 

6. Ibtoda, S.(1959), "Devices of simple 
plankton apparatus". Ifem. Faa. Fish., 
Hokkaido tiniv. Z (1/2): 7>94. 

7. Be, A.W.E. , & Ewlng, U., & Linton, L.W., 
(1959), "A quantitative nultiple opening 
and closing plankton wmnpler for vertical 
towing". J. du Cons. Int. Explor. Mar, 
25: 36-46. 



ACHCTLaqffitg 

The present saiiQ>lers were constructed by 
S.U. Barrlsan at the Laraont Geological 
Observatory and were successfully field 
tested on board the Observatoiy's research 
vessel VEU^ during July and August 1961. 
Financial support was given tcr the National 
Science Fioundatlon (NSF G-9557 and G-11593) 
and the Office of Naval Research (Ncnr 266 
(48)). 



162 



LONG-RANGE OUTLOOK FOR OCEANOGRAPHIC TELEMETERING 

by JAMES M. SNODGRASS, Head, Special Developments 
Scripps Institution of Oceanography 
University of California, San Diego 
LaJoUa, California 



ABSTRACT 

With expanding oceanographic re- 
search programs, communications promise 
to be a troublesome problem. Existing 
frequencies In the radio communications 
spectrum are almost completely absorbed 
by mllltaryj commercial and amateur In- 
terests. New means must be devised to 
communicate with research and survey 
ships. Circuits which will permit large 
amounts of data to be transmitted with 
high accuracy are needed. 

Data telemetering over vast ocean 
areas will require many new techniques 
since present practice in the missile and 
flight test field Is limited to line of 
sight. Conflicts with ocean missile 
ranges will need to be resolved, as well 
as devising suitable International 

♦Contribution from the Scripps Institu- 
tion of Oceanography, New Series, No. 000. 
This work was supported in part by funds 
from the Office of Naval Research, U.S. 
Navy. Reproduction in part or entirety 
is permitted for any purposes of the 
United States Government. 



agreements to permit long-range tele- 
metering and the establishment of un- 
attended deep-sea buoys and Instrument 
stations. 

Telemetering over ranges of several 
thousands of miles is necessary from un- 
manned floating Instrument stations. 
Proposed communications types of satel- 
lites offer promising possibilities. 



Communicat 
another, is in 
oceanographic 
ically-orlente 
fortunately, 1 
tively recent 
graphers have 
their needs. 
Involve truly 



ions, in one form or 
extricably linked with 
research and oceanograph- 
d research projects. Un- 
t is only within compara- 
time that the oceano- 
begun to become aware of 
The oceanographers ' needs 
world-wide requirements. 



Expanding oceanographic programs are 
planned which will require the use of in- 
strumented buoys and the transmission of 
Information by means of radio tele- 
metering both to ship and shore based 
stations. It appears to be almost im- 
possible to plan anything like a serious 



163 



program Involving the use of remote buoys 
or ocean stations, if we must count on 
presently available frequencies in the 
electromagnetic communications spectrum. 
The difficulties are complicated by the 
fact that available frequencies are al- 
ready largely allocated and are used al- 
most completely by the military, commer- 
cial and amateur interests. There do not 
appear to be any suitable frequencies for 
extensive reliable communications avail- 
able to the oceanographlcally-oriented 
research program. 

Anticipating the general problems of 
the oceanographer, the Office of Naval 
Research sponsored a study contract on 
oceanographic telemetry (Contract Nonr- 
3062(00)) with the Convair Division of 
the General Dynamics Corporation. The 
first phase of the study has been com- 
pleted, and an excellent report has been 
submitted to ONR. One of the purposes 
behind the study contract was to inves- 
tigate various factors Involved in tele- 
metering data from remote oceanographic 
instrument buoys to shore based facil- 
ities. The factors which must be con- 
sidered in this operation are tremen- 
dously involved and complicated. Some 
of the factors involve the behavior of 
specific radio frequencies in regard to 
radio propagation characteristics, such 
as skip distances, seasonal variations 
of noise with respect to latitude, solar 
induced radio propagation anomalies, 
power requirements, frequency bandwidths, 
etc. All of these variables have now 
been organized and collected together in 
the report submitted to ONR by Convair. 

It appears that long-range communi- 
cation may not be considered reliable 
using whatever frequencies may be avail- 
able between a shore based receiving 
station and remote buoy or ocean station. 
This is assuming that dependable communi- 
cation is required and that data be 
transmitted without objectionable error. 
It is quite true that one may obtain 
occasionally, and even for a limited 
period, transmission which might be con- 
sidered acceptable. The difficulty is, 
however, that such conditions cannot be 
counted upon if reliable transmission is 
required. It is therefore necessary to 
seek modifications of the system whereby 
reliable communications may be estab- 
lished. 

For somewhat over a decade Mr. E.F. 
Corwin, Mr. L.J. Allison and Mr. J.C. 
Appleby of the Meteorological Branch, 
Bureau of Naval Weapons,-^ and Mr. 
Hakkarinen of the Electronics Branch, 
National Bureau of Standards, have been 



carrying out highly significant work in 
the development of radio telemetering 
ocean buoys and instrument stations. It 
is interesting to note that, as time went 
on, each succeeding buoy design Involved 
the use of larger amounts of radiated RP 
power. Later designs tended to evolve 
around the "squirt" techniques and used 
radiated power levels as high as 5kw. 

The "squirt" system combined with 
knowledge gained in ionospheric research 
by the Canadian Defence Research Estab- 
lishment may well prove to be valuable. 
The substance of the method developed in- 
volves the use of an interrogation tech- 
nique between the shore based station and 
the remote buoy. In this technique the 
buoy would be equipped with a trans- 
ponder system which would be interrogated 
by means of short pulses on a short duty 
cycle transmitted repetitively by the 
shore based station. When the radio pro- 
pagation conditions are suitable, and the 
interrogation pulse is able to reach the 
buoy, the buoy transponder would send out 
a pulse to the shore station. The re- 
ceived pulse signifies that the communi- 
cations path is for the time being open 
between the two. stations. The shore 
based station then would send a coded 
request to the buoy to transmit its 
stored information. When this cycle is 
completed, the shore based station then 
seeks to interrogate another buoy, etc. 
This particular system is based upon the 
fact that when a given transmission 
channel becomes open between two stations 
it may be expected to remain open for a 
period of from four to five minutes. If 
suitable recording and memory systems are 
on board the buoy, it is quite practical 
to count on Interrogating the buoy at 
some time during a given 24-hour period. 
However, it is quite apparent that one 
cannot establish over a long period of 
time precisely when it will be possible 
to interrogate the buoy, and the memory 
system must take such variables Into 
account . 

There is an additional alternative to 
the above-outlined system, which is re- 
commended by the Canadian Defence Re- 
search group, and that is to have avail- 
able a selection of a wide range of radio 
frequencies for such a communication 
system and that the shore based inter- 
rogation system transmit an interrogation 
pulse in sequence through the different 
assigned frequency bands. This means, of 
course, that the remote buoy must have a 
somewhat more sophisticated receiving 
system, i.e., one which can listen simul- 
taneously on all of the expected fre- 
quency bands. However, if such a system 



164 



Is usedj the assurance of being able to 
effect communication with the remote 
station when desired Is tremendously Im- 
proved. This latter method Is the method 
which apparently receives the most favor- 
able recommendation by the Canadian 
group . 

It is quite possible If such a 
system as proposed were used that It 
would Involve substantial modifications 
In methods of licensing. This Is con- 
sidered to be beyond the scope of this 
discussion and will not be further con- 
sidered. 

Whether we like it or notj the re- 
search institutions find themselves in- 
volved in the problem of obtaining space 
in the electromagnetic communications 
spectrum. Since we have not been notably 
successful in the past in obtaining suit- 
able radio frequency assignments for re- 
search programs, it appears that we 
should turn our attention to methods of 
operation which will not be conflicting 
with existing operations. 

The problem of non-interference with 
existing services is an extremely sticky 
one. An installation for the collection 
of oceanographic Information now beingin- 
stalled in the Gulf of Mexico by Mr. Roy 
D. Gaul of the Department of Oceanography 
and Meteorology, A. & M. College of 
Texas, has encountered an entirely new 
series of headaches from the standpoint 
of the oceanographer. It so happened 
that the area in which it was planned to 
locate the telemetering system was phys- 
ically in an overlap area between Patrick 
Air Force Base Missile Range and Eglln 
Air Force Base Missile Range, and it ap- 
peared to be almost impossible to find a 
suitable means of using any radio fre- 
quencies which would be considered ac- 
ceptable by the Air Force. 

After considerable difficulty, Mr. 
Gaul has worked out a temporary arrange- 
ment for operation which meets with ap- 
proval of the Air Force representatives 
concerned. A significant point which his 
operations raise, however, is the problem 
faced in major buoy programs in both the 
Atlantic and the Pacific Oceans which un- 
doubtedly will run afoul the Atlantic 
Missile Range and the far more extensive 
Pacific Missile Range. We are already 
having problems in the San Diego area 
with respect to interference by trans- 
mitters in the San Diego area with the 
Pacific Missile Range operations. These 
are considered serious and they are by no 
means resolved at the present time. 



Looking first at techniques which 
would permit buoy operation, we have con- 
sidered the possibility of systems which 
would permit the use of relatively low- 
power transmitting systems in the buoys. 
Perhaps the most available method at 
present to begin to solve the buoy-shore 
communication problem, and evolve a 
method which could be put into effect 
with existing technical facilities, is 
the use of high flying aircraft to serve 
as an Interrogation platform for com- 
municating with floating buoys, etc. 
This would permit the use of relatively 
low-power radio transmitters in the buoys 
and a relatively simple information stor- 
age system. The high flying plane would 
transmit a suitable coded interrogation 
pulse which would insure the response of 
the desired buoy. Since the airplane 
would be carrying a suitable recording 
system, such as magnetic tape, the in- 
formation transmitted by the buoy could 
be recorded as desired. In this system 
it would be planned to have the data pro- 
cessed at the conclusion of the flight. 
Difficulties with this system are not to 
be minimized since it requires the avail- 
ability of suitable high flying long- 
range aircraft, as well as the necessary 
operating bases. However, it would be 
possible to car2ry out some fairly ex- 
tensive programs with existing bases and 
aircraft. It should also be pointed out 
that suitable radio frequency assignments 
must be made if communications of this 
type are to be carried out. Unquestion- 
ably, a suitable long-range aircraft for 
our purposes would be the U-2, which sat- 
isfies many of o\ir basic requirements. 
Wliether the plane would actually prove 
adequate for such operations, remains to 
be seen. 

Another and most promising system for 
long-term operation is to be found in the 
various types of communication satel- 
lites. For practical purposes we may 
discard the passive satellites of the 
ECHO type, since this involves very large 
high power and highly directive antenna 
systems which are quite impractical on 
buoys, and, for that matter, even on 
ships the size of oceanographic research 
vessels. The active satellites, however, 
would appear to be useful. The satel- 
lites which are planned on being pro- 
grammed for orbits between 5,000 and 
6,000 miles will undoubtedly require 
powers that are not readily available to 
small floating buoys and instrument 
stations. However, these satellites can 
be counted upon for communicating be- 
tween ships and shore bases using sta- 
bilized dish-type antennas. It would 



165 



thus be possible to transmit a very large 
amount of data with high reliability from 
ship-to-shore and vice versa using the 
satellite system. This would mean that 
it would be possible to send data directly 
ashore for data analysis as desired. The 
active satellites which are referred to 
for this type of data relaying operate in 
real time. Another type of satellite 
known as the COURIER type is perhaps the 
most adaptable lander the present basis of 
operation. The COURIER type of satel- 
lite does not retransmit radio signals in 
real time, but involves a memory system. 
The COURIER satellite is planned on being 
programmed to a much lower orbit, namely, 
the range from 300 to 400 miles. Since 
it is much lower, it will require a great 
deal less power to effect reliable com- 
munication between buoy and satellite. 
At present the COURIER type of satellite 
is designed to record Information re- 
ceived via radio and play it back on 
proper interrogation from the ground 
based station. It is considered prac- 
tical to program the COURIER type of sat- 
ellite to interrogate buoys as it passes 
over various portions of the ocean and 
then to playback the data obtained from 
the buoy when it passes over a suitable 
land based station. The land based sta- 
tion would be able to keep a longer con- 
tact with the satellite, since it would 
have a much superior antenna system than 
that possessed by the floating station. 

In view of the many difficulties 
which are found in the use of the con- 
ventional portions of the electromagnetic 
communications spectrum, perhaps we 
should search out other regions. 

A most significant problem presently 
exists with the proposed use of any of 
the satellites and this is the fact that 
there are now tremendous demands upon the 
electromagnetic communications spectrum 
that is expected to be available to the 
satellite systems, and unless the re- 
search groups interested in obtaining 
ocean data make a very strenuous effort 
to obtain proper frequency allocations, 
or time allocations, on the communica- 
tions types of satellites, it is quite 
probable that none will be available when 
needed at some future date. It is almost 
impossible to overemphasize the amount of 
pressure being brought to bear to obtain 
communications frequencies in the satel- 
lite programs. Since groups interested 
in collecting data from the ocean are not 
in any way represented on the committees 
and boards making such studies, it is im- 
perative that remedial steps be taken 
along this line as soon as possible. 



Since the oceanographers ' communi- 
cation problems extend well beyond the 
continental limits of the United States, 
it is apparent that international re- 
lationships are involved. This would be 
true whether high flying aircraft or sat- 
ellites are used in the solution of the 
communication problems. 

Unfortunately, the groups interested 
in various aspects of marine research in 
this country are not organized from the 
standpoint of representation to the FCC 
for frequency assignments. Also, there 
Is no voice from the oceanographers in 
the ICSU (International Co\incil of 
Scientific Unions), which through the 
CCIR (international Radio Consultative 
Committee), reports directly to the ITU, 
or International Telecommunications 
Union, for ultimate international fre- 
quency allocations. 

So much for the backgroimd. We have 
seen something of the problems confront- 
ing the oceanographer. We will now con- 
cern ourselves with the current status 
and what is being done. As of June 29, 
the National Academy of Sciences Com- 
mittee on Oceanography, acting for the 
oceanographic and meteorological com- 
munity, voted to initiate a formal study 
of the problem. The direct responsi- 
bility is placed with the Panel on New 
Devices which serves as a sub-committee. 

An engineering firm has been re- 
tained to assist in delimiting the en- 
gineering requirements from the inputs 
supplied by oceanographers and meteor- 
ologists. After the preliminary study 
is complete, the report wi]l be studied 
by the Panel on New Devices and plans 
developed to carry out the major program, 
which is the development of engineering 
requirements for the Justification of a 
new type of service in the field of radio 
communication. It will be necessary to 
work up a complete case which may then be 
ultimately presented to the FCC. 

The major engineering study will be 
worked up with the advice and assistance 
of the National Academy of Sciences Com- 
mittee on Radio Frequency Assignments 
for Science. This committee was formed 
initially to justify the radio frequency 
requirements of the radio astronomers, 
and will now be fulfilling a somewhat 
broader purpose. 

The National Academy of Sciences Com- 
mittee on Oceanography will undertake to 
check the input requirements from the 
standpoint of oceanographers and 



166 



meteorologists^ and the National Academy 
of Sciences Committee on Radio Frequency 
Assignments for Science will check and 
evaluate the engineering considerations. 

It should be apparent that the 
entire problem Is one of a rather complex 
sort and that its ultimate, satisfactory 
solution is of direct Interest to in- 
dustry. Since industry has a definite 
stake in the field of oceanography and 
meteorology, it is hoped that represent- 
atives of industry will be interested in 
assisting directly in formulating and re- 
commending possible systems which may 
assist in the solution of our communi- 
cations problem. 

The areas to be covered are essen- 
tially those of the oceans, so that in 
effect we require world-wide coverage. 
As an example of the numbers of unat- 
tended ocean instrument stations or buoys 
which may be required the figure of 100 
buoys for the northeast Pacific, i.e., 
the area east of l80° and north of the 
Equator may be used. It is felt that 
this is a somewhat conservative figure. 
This does not, however, include special 
buoys and Instrument stations for 
studying short-time projects, but rather 
represents the number which would be nec- 
essary for routine, relatively long-time 
programs. Integrated into this are also 
the requirements of the ship-to-shore 
communications, ship-to-ship, shlp-to- 
buoy, buoy-to-shlp, etc. It is quite 
probable that multiple solutions to the 
problem exist but major efforts will be 
centered toward determining what system, 
or systems, appear to be most suitable 
for the purpose. We earnestly solicit 
assistance from industry and research 
laboratories and will welcome serious 
recommendations and suggestions. 



REFERENCES 

1. "The Floating Automatic Weather 

Stations of the United States Navy, 
Weatherwlse , Vol. 12, No. 5, 
October 1959. 



167 



THE SVTP INSTRUMENT AND SOME APPLICATIONS TO OCEANOGRAPHY 

by J. R. LOVETT 

Oceanic Research Division 

Research Department 

U.S. Naval Ordnance Test Station 

China Lake, California 



ABSTRACT 



In the SVTP instrument, sound velocity is 
measured iDy a modified KBS "sing-around" veloci- 
meter, temperature by a Wien-bridge oscillator, 
and pressure by a Vibrotron. 

The sound- velocity section may exhibit shifts 
in calibration of about 2.25 m/sec unless 
adjusted correctly and then calibrations are 
stable within 0.15 m/sec. The temperature oscil- 
lator is accurate to +0.01°C for periods of sev- 
eral months . The Vibrotron has a short-term 
repeatability of 0.25fo of bandwidth. 

Eata processing systems consist of counters, 
discriminators driving X-Y plotters, and tape 
recorders with data later digitized or displayed 
on X-Y plots . 

Some applications in oceanography are in 
fathomfitry and internal vfave studies. 



DESCRIPTION OF THE INSTRUMENT 

A sound-velocity, temperature, and pressure 
(SVTP) instrument was built at the U. S. Naval 
Ordnance Ttest Station (NOTS) to give continuous, 
concurrent measurement and data transmission of 
these three oceanic parameters at any depth 
(Fig. 1). 

This completely transistorized instrument 
uses potted plug- in modules. The modules use 
the new welded-cordwood stacking construction 
for greatest reliability in the smallest space 
(Fig. 2). 

The sound-velocity section of the instrument 
is the velocimeter developed by Greenspan and 
Tschlegg of the National Bureau of Standards and 
modified to operate in IRIG telemetry band 8 
(3,000 cps center frequency). This is achieved 
by decreasing the free-running frequency and in- 
creasing the path length to 2U.7 cm. Care must 
be taken in setting the reflective path length, 
or the instrument may exhibit shifts in calibra- 
tion of about 2.25 m'sec due to the input trig- 
gering on a precursor of the 3-niegacycle pulse 
(Fig. 3)- ll^e connection between the amplifier 
and the triggering circuit is broken thus dis- 
abling the sing-around circuit. Leads are 
brought out to adjacent pins on the plug. Then 
the output of the amplifier is observed while 
the reflectors are adjusted so that the pulse 



has a good clean rise and there are no miiltiple 
reflections, '.ftien the desired waveform is ob- 
tained, the two pins are connected in order to 
trigger the blocking oscillator. There is a 
provision made to add negative feedback if the 
amplifier stages are oversensitive. The sound- 
velocity section is accurate to O.3O m/sec and 
has a repeatability of 0.15 m/sec. 

Temperature is measured by a thermistor- 
controlled Wien-bridge oscillator developed at 
NOTS. This oscillator works in the temperature 
range 0-30°C and in the frequency band 5,000- 
8,000 cps, thus giving a sensitivity of O.OIOC 
per cycle per second. By using aged thermistors, 
capacitors stable to less than 10 ppm/oc, and 
other techniques, the accuracy is +O.OIOC. Maxi- 
mum variation from a best straight line 5-20°C 
of -i-0.02°C is achieved by a 3-point match of the 
oscillator and thermistor curves. 

The Vibrotron is used for pressure measure- 
ments in the SVTP instrument; however, there is 
some uncertainty as to the future availability of 
this transducer. Pressure is sensed by deforma- 
tion of a diaphragm that in turn produces a 
change in tension, and, hence, in frequency 
(IRIG band 12) of a vibrating wire. A simple 
oscillator is used to sustain the forced vibra- 
tions. Repeatability, short term, is +0.25/^ 
linearity is within +3^ of a straight line 
between end points; and temperature sensitivity 
is less than +0.lfo of bandwidth per °C change of 
zero frequency. 

A summing cable-driving amplifier combines 
the sound-velocity, temperature, and pressure 
signals so that they may be transmitted as a 
mixed frequency signal over a single-conductor 
cable. Six thousand feet of semi -buoyant poly- 
ethelene covered cable with a breaking strength 
of 900 pounds has been used. IVhen in sea water 
it acts like a 50-ohra coaxial cable, and if 
driven with a matched amplifier, the voltage 
loss at 10 kilocycles is 2 db/l,000 ft. Iflien on 
the winch, capacitance of the cable is negligible 
while the inductance is about 3IO millihenries. 
At 10,000 cps, this inductance gives an impedance 
of about 20,000 ohms. Therefore, to avoid an 
intolerable voltage loss , a high input impedance 
amplifier must be used to drive the filters which 
separate the signals. 

Nickel-cadmium batteries are internally 



168 




FIG. 1. SVTP IristnL-nent. 




FIG. 2. Sound Velocity Oscillator Showing Welded-CordwocJd 

Construcxion. 



169 



PRESSURE 
PORT- 



OUTPUT 
TRANSDUCER- 




REFLECTOR 
TARGET 



FIG. 3. End Plate With Reflected Sound. 



1,495 M/SEC 




szoes'sa" n 

18" 2 9' 42" W 

21 MARCH ISei 



SUR 


♦ 


:ev 


1 
1,500 M/SEC 




- 











FIG. It. Sound Velocity vs. Depth, Outer 
Santa Barbara Channel. 



170 



■;=+ 



SURFACE 



'i*<>C 



ija'c 



.J.. 


y ' ^ 




i 


jT^ i 32'>99'52" N 

, ; f \ '■ ir9»2d'42" W 


I ! 




/ 50d METERS 2' '**'^<^" '5«l 






f 6PC 


' 



1,000 METERS 



FIG. 5' Temperature vs. Depth, Outer 
Santa Barbara Channel. 



1485 



Sound Velocity M/Sec 
1490 1495 



1500 



500 




Station Standard 

Time Study 

21 March 1961 



loeo 



FIG. 6. Sound Velocity vs. Depth, Outer Santa Barbara Channel. 
Time Study, 21 March I96I. 



171 



mounted, and are recharged through use of 
gravity-actuated mercury switches . 



DATA RECORDIMG AMD PROCESSING SYSTEMS 

Counters are always used for a visual check 
of the frequencies and for precise end-point 
measurements . 



U. S. Naval Ordnance Test Station. An 
Instrument for Continuous Deep-Sea Measure- 
ment of Velocity of Soxind, Temperature, and 
Pressure, by J. R. Lovett and S. H. Sessions. 
China Lake, California, NOTS, 9 May I961. 
(NAVWEPS Report 765O, NOTS TP 2673.) 



Three FM discriminators driving two X-Y plot- 
ters have been used for immediate visual display 
of the data (Fig. k and 5). Four- track tape 
recordings are also made with a precise 25-kc 
reference frequency recorded on one track. 
(Voice data may also be recorded on the same 
track.) The tapes are recorded at 15 ips and 
played back at 60 ips into the NODAC analog-to- 
digital converter. The IBM 709O computer can 
linearize the Vibrotron output and utilize the 
temperature data to compensate the sound- 
velocity data for path-length changes due to 
temperature. The data may be printed digitally 
with time information, or digital X-Y plots may 
be made . 



APPLICATIONS OF THE SVTP INSTRUMENT 

Two of the uses to which the SVTP instrument 
has been put by NOTS are given below. 

In fathometry, sound-velocity measurements 
to the bottom have yielded information for cor- 
recting a precision fathometer that assumes a 
sound speed of i*,800 fps . 

A study of the time variation in the distri- 
bution of sound velocity with depth at fixed 
stations has been made in the Outer Santa Barbara 
Channel. X-Y plots were made every 2 hours for 
36 hours down to the bottom of the basin, 
1,180 meters. Sound profiles obtained showed 
considerable activity in the water above the 
sill depth of 970 meters (Fig. 6). The observa- 
tions obtained suggest a tidal influence with a 
semi-diurnal periodicity. Previous observations 
in the Southern California waters indicate a 
high degree of variability due to internal waves. 
Present measurements made with the SVTP instru- 
ment are too widely spaced to detect the shorter 
periods of such internal waves . More rapid 
sampling is planned in future studies. 



BIBLIOGRAPHY 

a. Greenspan, Martin, and Carroll E. Tschiegg. 
"Sing- Around Ultrasonic Velocimeter for 
Liquids," REV SCI INSTRUMENT, Vol. 28, 

No. 11 (Nov. 1957), pp. 891-901. 

b. Tschiegg, C. E., and E. E. Hays. "Transis- 
torized Velocimeter for Measuring the Speed 
of Sound in the Sea," ACOUS SOC AM, J, 
Vol. 31, No. 7 (July 1959), pp. 1038-1039. 



172 



THE WORLD'S LONGEST SALT BRIDGE 

by DR. PAUL C. MANGELSDORF, Jr. 
Woods Hole Oceanographic Institution 
Woods Hole, Massachusetts 



ABSTRACT 

A variation of the Geomagnetic Electro- 
kinetograph has been developed in which the 
electrodes remain aboard ship immersed in sea 
water at constant composition and temperature. 
The electrical connection to the sea is made 
with lengths of polyethylene tubing filled with 
sea water. This arrangement greatly reduces 
the sensitivity of the system to gradients of 
salinity and temperature in the sea. It also 
permits a direct electrode zero by means of a 
sea water shunt between the two electrodes. 



INTRODUCTION 



It was Faraday, in 1832, who first pointed 
out that the motions of flowing water masses in 
the earth's magnetic field might be detected by 
the measurable EMFs which such motions ought to 
induce. Although Faraday was himself unable 
to verify the effect, his predictions were 
amply confirmed by later observers. Ultimately, 
in 1950, Von Arx reported the successful de- 
velopment of a practical instrument, which he 
named "Geomagnetic Electrokinetograph", for 
measuring the motionally induced potentials in 
the ocean. The theoretical interpretation of 
these potentials was also developed by Von Arx 
in the same paper; by Malkus and Stern , and by 
Longuet-Higgins, Stern, and Stommel . 

The biggest problem in measuring electro- 
magnetic potentials in the ocean arises from 
the fact that most measuring circuits are 
metallic and conduct electricity by means of 
free electrons. Sea water is an electrolyte 
solution which conducts by means of assorted 
ions, both positive and negative. Any me- 
tallic electrode inserted into the ocean as a 
probe can only function with the occurrence of 
one or more electrode reactions involving both 
ions and electrons. Such electrode reactions 
will be sensitive to temperature, to pressure, 
to ionic concentrations (i.e. salinity), to 
contcimination (z.b. oxygen tension). Moreover, 
if any of the participating reactions are at 
all irreversible, the electrode will be polar- 
Izable and its contact potential will change 
as current is passed. 

To overcome these difficulties, Von Arx 



used massive silver/silver chloride electrodes 
which are reasonably reversible to chloride ion 
in sea water (though they are probably poisoned 
somewhat by sulfate and bromide ions which are 
also present ). By taking great care to match 
each pair of electrodes as exactly as possible. 
Von Arx was able to minimize the differential 
responses to temperature, salinity, and oxygen 
tension which would cause spurious signals. But 
even the best electrode pairs displayed small, 
slow, residual drifts in contact potential, 
which could only be evaluated by interchanging 
the positions of the electrodes in the water. 
With towed electrodes, the simplest way to do 
this, though time-consuming, has been to reverse 
the ship's course. 

This system of towed silver/silver chloride 
electrodes has proven quite successful and has 
been widely used during the past decade for 
determining the horizontal potential gradients 
at the surface of the ocean. However, it is 
quite unsuitable for measuring vertical po- 
tential gradients. Two electrodes at different 
depths will automatically sense the corresponding 
differences in pressure, salinity, temperature, 
and oxygen tension, and will report these as 
large spurious potential differences. But, 
according to Malkus and Stern, the vertical po- 
tential distribution in the ocean would also be 
extremely valuable, if it could be measured, 
since it would yield directly the total east- 
west transport at the point of measurement. 



THE SALT BRIDGE PRINCIPLE 

After these difficulties had been drawn to 
our attention by Dr. Malkus, it occurred to us 
that there ought to be some advantage in moving 
the electrodes with their very sensitive 
metal/electrolyte junctions up out of the ocean 
entirely, and keeping them in a controlled en- 
vironment on shipboard. The electrical contacts 
with the ocean could then be made with columns 
of salt solution contained in insulating tubing 
of some sort. This is exactly the principle of 
the salt bridge - a familiar device frequently 
used by electrochemists to avoid dipping an 
electrode directly into a solution, if either 
the electrode or the solution would suffer 
thereby. 



Superior numbers refer to similarly numbered references at the end of this paper. 



173 



Any kind of electrolyte solution could, in 
principle, be used in such a salt bridge. How- 
ever, the boundary between two different 
electrolyte solutions has a contact potential, 
called a liquid junction potential , somewhat 
analogous to that between an electrode and a 
solution, though much less sensitive. While 
the traditional use of concentrated potassium 
chloride in laboratory salt bridges is supposed 
to minimize such liquid junction potentials, we 
preferred to eliminate them entirely, if we 
could, using sea water throughout. 



CHOICE OF TUBING 

The conductance of standard sea water is 
only .03-. 05 (ohm-cm.)" . The resistance of a 
long, thin column of sea water is large and in- 
creases with length. The electrical leakage 
path from such a column through the walls of an 
insulating tubing to sea water outside should 
be slight, but will increase with length. The 
net result, barring pronounced local leakages, 
will be that a sea-grounded DC signal fed into 
an infinite length of tubing filled with, and 
surrounded by, sea water - or any other con- 
ductor, for that matter - will damp out expo- 
nentially according to the formula 



Y=\^ 



(1) 



where S is the leakage conductance per unit 
length through the walls of the tubing, R is 
the resistance per unit length of the sea water 
column, X is the linear distance along the 
tubing. 

The damping length (SR) , thus defined, 
depends on the specific bulk resistivity p , 
the thickness T' , and the internal diameter U 
of the tubing, as well as on the specific 
conductivity cr of the sea water column ac- 
cording to the following approximate relation: 



(SR 



1 



(2) 



We have determined the damping lengths 
with sea water of a number of assorted samples 
of readily available tubing, with the results 
given in Table I. It is evident from the 
Table that polyethylene tubing is the most 
suitable for long distances. Since the poly- 
ethylene, at 2.7 cents/ft., was also the 
cheapest of the tubings we tested, and since 
it is quite inert chemically and very tough 
physically, the choice was not difficult. The 
polyethylene tubing as supplied by the manu- 
facturer (Crystal-X Corporation, Lenni Mills, 
Pa.), came in assorted lengths, some 500, 
1000, and 2000 lengths, but mostly 100 ft. 
lengths. We found that new and unused lengths 
of this tubing could be easily welded together 



by heating the ends over a gentle flame until 
they became transparent and sticky; and then 
joining them together with a little pressure 
causing them to flare out slightly. Quenching 
with cold water speeds the hardening. A well- 
formed joint of this kind does not appear to 
weaken the tubing either physically or electri- 
cally. 

Once the tubing has been exposed to sea 
water, however, these welds do not take very 
well, even when the two ends have been well 
cleaned in all the different ways we could think 
of. Some improvement can be had by sloshing the 
two ends in mineral oil before heating, but the 
joints are still likely to be bad and should be 
tested carefully before they are used. 

The 5/16" o.d. polyethylene tubing which we 
have used proved to be very well suited for 
towing. It is buoyant, even when filled with 
water, and snakes along very freely on the sea 
surface. The small diameter and smooth surface 
help keep the towing resistance very low. At 
10 knots in a moderate sea, a 200 meter length 
of tubing can be held with one hand without too 
much difficulty. 

The breaking strength of this tubing is 
about 200 lbs. 

To connect the polyethylene tubing to glass 
tubing, or to make temporary connections between 
two lengths of the polyethylene, we have used 
short lengths of snug- fitting {k," i.d.) tygon 
tubing as couplings. Because polyethylene, like 
most insulators, develops a markedly conducting 
surface film after sea water has dried on it, 
such connections tend to be very leaky electri- 
cally unless made with clean tubing. A liber- 
al application of mineral oil to all surfaces 
prior to making the connection seems to help a 
little. In any case, electrical leakage can be 
expected if the connection has borne the 20 lbs. 
pumping pressure for any length of time: some 
seepage evidently occurs. For this reason, the 
welded connections are decidedly preferable for 
connecting polyethylene pieces to one another. 
Glass-to-polyethylene connections should be 
kept well insulated in dry surroundings. 



CIRCUITRY REQUIREMENTS 

Sea water is not a very good conductor. A 
3/16" i.d. tubing filled with sea water offers 
about a megohm of resistance for every 100 meters 
of length. This high impedance of a long salt 
bridge is the biggest single drawback to the 
salt bridge technique at sea. While high im- 
pedance measurements and shipboard working 
conditions are not totally incompatible, neither 
are they very congenial. Most insulating 
surfaces seem to develop leakage resistances of 



174 



the order of 10 ohms or less when exposed to 
damp sea air. Such leakage paths are electro- 
lytic; when they connect two different metals, 
they form electrolytic cells with EMFs of the 
order of several tenths of a volt. If one of 
these leakage cells happens to discharge across 
a circuit element, such as a salt bridge, with 
a resistance of the order of 10° ohms, a spuri- 
ous signal of the order of several tenths of a 
millivolt may be developed in the circuit. If 
by some mischance, such a leakage path makes 
connections with the shipboard DC power supply, 
the situation can be many times worse. Clearly 
extraordinary precautions are called for. 

Fortunately the greater part of our 
circuitry problems have been solved for us ii. 
recent years by the electronics industry with 
the development of reliable high- impedance 
electrometers. We have found that the Keithly 
603 Electrometer Amplifier is very satisfactory 
in taking a few DC millivolts from a pair of 
high impedance salt bridges and converting 
this signal to a low impedance output of several 
volts. The Keithly performance seems to be 
quite immune to the damp salt air and power 
supply fluctuations of shipboard operation. 



which promises to give it greatest usefulness. 
By raising the water levels on both sides until 
they join at the Y, a low impedance sea water 
shunt can be established between the electrode 
compartments, permitting the electrode zero to 
be determined quickly and directly. By lowering 
the water level the shunt is broken and the 
measurements of sea voltages may be resumed. In 
this manner the unknown, and slowly drifting, 
contact potentials of the electrodes can be 
determined as often as may be needed during any 
set of measurements. In towing experiments, the 
burdensome procedure of reversing the ship's 
course can be dispensed with, although right- 
angle legs will still be necessary if both 
components of the surface potential gradient are 
to be determined. 



DETAILS OF CONSTRUCTION 

We have used the conventional G.E.K. 
silver/silver chloride electrodes developed by 
Dr. von Arx, several of which were kindly pro- 
vided for us by his assistant Mrs. Nellie 
Anderson. These are sealed into the pyrex 
electrode chambers with epoxy cement. 



THE ELECTRODE SYSTEM 

As the whole advantage of the salt bridge 
system arises from the thermal and chemical 
isolation of the electrodes, it follows that 
the actual electrode arrangement is very 
important. The system we have employed is 
shown in Figure I. 

The electrodes are sealed into pyrex 
electrode chambers immersed in an oil- filled 
thermos flask. Each electrode chamber connects 
to a 3-way stopcock, permitting it to connect 
down to the sea or up to an inverted-Y shunt, 
or to be cut off from the circuit entirely. 
The inverted Y leads up to a third 3-way stop- 
cock by means of which the sea water in the 
system may be admitted and manipulated. The 
temperature in the thermos flask is not regu- 
lated, but is allowed to drift in a gradual 
pursuit of the ambient room temperature. The 
fishhook shape of the electrode chambers is 
intended to protect the electrodes from sudden 
exposure to colder or saltier (i.e. denser) 
water that may make its way down from the 
stopcocks by convection. As long as no sudden 
changes occur at the electrodes, the long term 
drifts can be followed easily by means of the 
inverted-Y shunt. 



THE SEA WATER SHUNT 

This inverted-Y arrangement provides the 
one unique feature of the salt bridge system 



The 1-liter thermos flask filled with 
mineral oil is closed with a wooden lid satu- 
rated with oil and coated outside with paraffin. 
The flask is mounted in a wooden carrier which 
is also liberally smeared with paraffin. 

The A mm. standard taper pyrex stopcocks 
are used only as hydraulic switches; they do 
not provide effective electrical switching 
because their leakage resistance between 
branches is usually less than a megohm. They 
do protect the electrodes from the hydraulic 
pressure variations which occur when the lines 
are drained or filled. These stopcocks are 
wired to a sheet of paraffin-coated masonite 
mounted on the frame of the wooden carrier. 

All the glass-to-glass connections, as well 
as the glass-to-polyethylene connections are 
made with tygon couplings for flexibility and 
shock resistance. 

The tygon leaders in the branches of the Y 
are especially Important, since they provide 
the necessary high impedance when the Y is 
drained and the shunt broken. Most materials, 
Including glass and polyethylene, tend to form 
moist, juicy, highly conducting surface films 
when repeatedly exposed to sea water. Fortu- 
nately, tygon seems to be entirely immune to 
this. We have found that a tygon Y will drain 
quickly to something like 10 ohms after 
having been filled with sea water for 60 hours. 

Our high pressure sea water supply is pro- 
vided by a little centrifugal pump. Eastern 



175 



rrom turn 

Sea Water 
at XO P.S.I 



To "Vacuonn 



H- 



\o 



Thermos 

Flask 




^^. 



CP 



Uoodeh 
L-.<1 



Fioof?£ I 



176 



Industries, Inc., Model E- 1 with Monel fittings, 
which is mounted on the side of the carrier. 
This pump gives a no- flow pressure of about 
20 psi, which is adequate for moderate lengths 
of tubing. However, the filling time of a 
piece of tubing goes up as the square of the 
length; it took us an hour and forty minutes to 
pump through 1 kilometer of our polyethylene 
tubing. 

In our apparatus the "vacuum" indicated in 
Figure I is provided by the experimentalist. 
With a 12 or 15 foot drop to water level, the 
necessary suction may be too much for anyone 
who is not an experienced pipe smoker. Mechani- 
cal alternatives are available. 



BUBBLE TRAPS 



Bubbles in the line can be a serious 
problem. Even when they do not break the 
electrical continuity entirely, they can raise 
the impedance to a point where leakage voltages 
dominate the signal. Fortunately, no bubbles 
can arise or persist in tubing that is well 
submerged. Even quite long bubbles in a line 
filled on deck will disappear completely if 
the line is dropped 20 or 30 meters below the 
surface. Nor do bubbles seem to form or collect 
in floating lines being towed at the surface of 
the water. Most of the bubble trouble occurs 
in the lines on deck (or on shore) which carry 
a negative hydraulic head because of their 
height above sea level, and which may be 
exposed to the heat of the sun. The high 
permeability of polyethylene to atmospheric 
gases may also contribute to bubble formation. 

We have found it convenient to introduce 
glass bubble traps into the lines at points of 
greatest elevation. These permit quantities 
of gas to collect without breaking the circuit. 
A valve in each trap allows the gas to be with- 
drawn periodically. These traps also prevent 
accidental bubbles from being pumped into lines 
during the initial filling. Because these 
bubble traps require breaking into the poly- 
ethylene line, they are potential sources of 
leakage voltages and should be carefully insu- 
lated from accidental electrical contacts. 

It is useful to have an auxiliary 
electrode in each line so that one can test for 
continuity to the sea with an ohm-meter, with- 
out passing current through the operating 
electrodes. A platinum wire electrode sealed 
directly into a pyrex bubble trap, and plated 
with silver/silver chloride serves this 
purpose very nicely. 

With towed lines one has to worry about 
bubbles which may enter the open end of the 
line which is dragging at the surface. A 



narrow piece of torn bed-sheet, wrapped several 
times around the end of the line so as to form a 
sort of tubular wick two or three feet long 
dragging behind the line, is apparently enough 
to solve this problem. 



GROUNDING 

With the Keithly 603, the ground connection 
serves as a common input for both high impedance 
leads. Between the ship and the sea there may 
be large fluctuating potential differences due 
to corrosion, or electrical leakages. Even 
with the large in-phase rejection of the Keithly 
instrument, such a ground signal is unacceptable. 
To get around this, we isolate all of our 
electronics from the ship, except for AC power, 
and use a towed G.E.K. electrode for a single 
common ground directly to the sea. 

This arrangement produces considerable AC 
pickup, but the AC can easily be kept out of 
the electrometer by connecting the inputs to 
ground with by-pass capacitors. 



OPERATING PROCEDURE 



The salt bridges must first be filled with 
sea water. It is safer to start with a 
completely empty line; otherwise a small amount 
of water will tend to collect in the low spots 
in a line and one may discover that one has 
inadvertently created enough U- tube manometers 
connected in series to defeat the pump's best 
efforts. If the line is on a reel, the reel 
can be turned on its end; if the line is 
weighted to the bottom of a channel, and is 
looping gently from weight to weight, one has 
a nasty problem. 

After the lines are full the pump is 
turned off and disconnected, and air is admitted 
into the Y to drain the shunt. The lines are 
separately tested for continuity. The line 
resistances ought to be perfectly steady and 
proportional to the line lengths. Otherwise 
one looks for a bubble or a leak. 

If the lines are all right, the water levels 
are drawn back up in the Y to form the shunt, 
and the electrode zero is determined. The 
adjustable zero on the Keithly 603 permits one 
to make this initial electrode zero coincide 
with the zero on a chart recorder. Since the 
electrometer zero will drift slowly with time, 
even more than the electrode zero, it is also 
desirable to record the signal produced by 
shorting the electrometer inputs together. The 
difference between this signal and the electrode 
zero is due to the mismatch between the two 
electrodes. It will be small and will change 
slowly and steadily with time, unless the 



177 



electrodes have been mistreated in some way. 

When the zero has been determined the Y 
is drained, the electrode chambers are con- 
nected directly to the sea, and the recorder 
output should give true sea-voltages without 
correction. 

Excessive wave signal can be eliminated 
by crossing the inputs with a capacitor. One 
of the few advantages of the high impedance of 
the salt bridge circuit is the small amount of 
capacitance required to give a long time 
constant. 



and c 



If a salt bridge line is relatively dry 
lean, it will pick up an external electro- 
static charge when brushed or touched, which 
will show up as a sharp pip on the chart record. 
This is not usually objectionable. 



TH£ PROOF OF THE PUDDING 

Our first successful measurements using 
the salt bridge technique were made on a 
stationary line strung across the bottom of 
Woods Hole harbor from the home of Allyn Vine 
on Juniper Point to the dock on Mink Point, 
Nonamesset Island; a distance of 875 yards. The 
line itself was about 1000 yards in length, 
weighted with 10 lb. sash weights every 16 ft. 
(When we later took up the line we decided that 
one such weight every 100 feet would have been 
ample, except in shallow water.) We made a 
continuous recording, with several interruptions, 
from July 21 to August 9. 

On several occasions the signal was blocked 
by bubbles, which probably could have been 
prevented if we had used bubble traps. On 
another occasion the pump was inadvertently and 
disastrously connected to an electrode chamber 
instead of to the short line which was to be 
pumped free of bubbles. We had to close down 
for two days while we repaired the damage and 
modified the design to withstand future mis- 
takes of this sort. Twice the chart recorder 
ran out of ink. Otherwise the operation was 
nearly trouble-free. 

We were distressed, at first, by the large 
noise level in our signal. There were large 
fluctuations a millivolt or more in magnitude, 
which often continued for many minutes or even 
hours with no visible physical cause. Sometimes, 
especially in the early hours of the morning, 
the fluctuations were beautifully periodic with 
two or three minute cycles for a half an hour 
at a time. Sometimes there were no fluctu- 
ations at all. 

When we showed our records to Dr. von Arx, 
he immediately identified these disturbances as 
being due to earth currents associated with 



magnetic storms. In fact, his original paper 
on the G.E.K. warns of the possibility of such 
interference "in shoal waters near the land". 
When our noise level was compared with the 
magnetic noise level reported for each three- 
hour period by the Fredericksburg Magnetic 
Observatory of the U. S. Coast & Geodetic 
Survey, the agreement was overwhelming. 

The record reproduced in Figure II was 
chosen as being the quietest 12-hour tidal 
cycle which we obtained. It also happens to 
be the quietest such period in the magnetic 
records. While it is atypical in this respect, 
we believe it to be a fair reflection of the 
intrinsic precision of the instrument and the 
method. 

The pronounced disturbances occurring be- 
tween 1715 hrs. and 1830 hrs. on July 30 are 
recurrent with a 24-hour period, as can be 
seen by a comparison with the juxtaposed record 
of the corresponding period on the preceding 
day. They are caused by the ferryboats which 
operate out of Woods Hole to Nantucket and 
Martha's Vineyard. Like most large vessels, 
these steamers produce strong electrical fields 
in surrounding water due to bottom corrosion 
or electrical leaks. The sharp pulses corres- 
pond to ship passages across our line. The 
half-hour long prolonged 2-millivolt downward 
shift is due to the steamer Nantucket , as she 
stands at the wharf 250 yards away with her 
stern facing us, waiting for the Islander to 
leave the ferry slip. When the Islander leaves 
(sharp downward peak), the Nantucket is warped 
around into the slip and her signal vanishes. 
The later downward peak is the Nantucket 
crossing our lines going out. 

The R.V. Chain creates a similar electrical 
signal when she is in port, which is why we 
did not run our line from the Institution dock 
in the first place. The electrode zero which 
our instrument permits, is of small value when 
an unknown stationary signal of such origin 
exists in the water. 

To test our zero, we examined our measured 
voltages at the times of slack water in Woods 
Hole channel as predicted in Eldridge's tables. 
During our first week, while the Chain was at 
sea, these averaged to zero within a tenth of 
a millivolt. After the Chain returned, the 
average was off zero by a steady 2 millivolts. 
In order to get the true zero for the tidally- 
produced voltages, we were obliged to use these 
averages to correct for the non- tidal potential 
drop across the harbor. The true zero, thus 
estimated, has been drawn in as a heavy hori- 
zontal line in Figure II. 

In Figure II the full vertical scale is 
20 millivolts. Positive signals are due to 
water flowing westward through Woods Hole into 



178 



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t: 


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179 



Buzzards Bay; negative signals are due to water 
flowing eastward into Vineyard Sound. 

There is a pronounced disparity between 
the amounts of water flowing in the two di- 
rections. In this cycle, over two and a half 
times as much water passed through Woods Hole 
when the current was running eastward, as had 
passed through the other way during the pre- 
ceding westward flow. The inequality is 
frequently much worse than this, sometimes 
amounting to four times greater eastward flow 
than westward. Woods Hole passage acts as a 
half-wave rectifier! 

We were worried that this might be an 
artifact produced by a change in the flow 
geometry with the current direction. The G.E.K. 
output represents an integrated velocity average 
across the cross section, rather than an inte- 
grated flow. A shift in the current from a deep 
part of the channel will increase the G.E.K. 
signal. However, there seemed to be no reason 
to expect such an effect across the harbor where 
our measurements were made. Moreover, the same 
asymmetry shows up quite distinctly on the U. S. 
Coast & Geodetic Survey hourly tidal current 
charts for all stations in the passage between 
Buzzards Bay and Vineyard Sound, except the one 
in the most constricted part of the Hole. 

From the U. S. Coast & Geodetic Survey 
chart of Woods Hole, we estimate the average 
depth of the channel across our section to be 
26 feet at mean low water. From this we reckon 
that 1 millivolt on our chart is equivalent to 
a water flow of about 160 cubic meters a second, 

•5 

or 5.7 X 10-" cubic feet per second. Accordingfy, 
the maximum westward flow in Figure II is 
about 850 ra /sec; the maximum eastward flow is 
about 1600 m-^/sec. The total westward flow is 
about 11 x 10^ m3; the total eastward flow is 
about 27 X 10^ m^. 

Part of this discrepancy arises from the 
greater duration of the eastward flow; this 
phenomenon has been nicely explained by 
Redfield . The remainder of the difference is 
probably due to the rectifying action of a 
shallow sill on tidal oscillations. The tidal 
range in Buzzards Bay is about twice as great 
as in Vineyard Sound at Woods Hole, so that 
more water is pumped over the sill to the east- 
ward. 



VERTICAL SOUNDINGS 

We took the apparatus to sea aboard R. V; 
Atlantis and attempted vertical soundings in 
the Gulf Stream southeast of Nantucket. 

The first lowering was made north of the 
Stream at Atlantis Station 6156, in the 



vicinity of Richardson Buoy ' E" . We started 
with a 6000 foot length of tubing wound on a 
reel, but could not get an acceptable signal 
through this. A reel of tubing on deck with a 
negative internal hydrostatic head presents a 
standing invitation to bubble formation. We 
also found it quite cumbersome to have to discon- 
nect the line each time we needed to turn the 
reel. 

We next tried working with a free 250 meter 
length of tubing with much better results, as 
shown in Figure III. For this lowering the 
shorter reference line was weighted and dropped 
to a depth of 30 meters. The long sounding line 
was taped to the hydrographic wire, with the 
weighted end of the line dangling about 10 
meters below the lead weight on the wire, so as 
to avoid electrical pickup from the wire. On 
this occasion the line was taped to the wire 
every 20 meters, but we later found that 50 
meter intervals were not too long. As the line 
was brought in again, these tapes were cut. 
Instead of reeling the line in, we just let it 
float freely away from the ship in a big loop. 

The absence of any voltage gradient below 
100 meters in Figure III implies that the water 
there had no east-west motion relative to the 
ship: the ship and the water were moving to- 
gether, if at all. Since the loran log covering 
this period shows the ship to have moved east- 
ward only about one-fifth of a mile in 4 hours, 
there would appear to have been very little east- 
west current. 

The very pronounced signal near the surface 
in Figure III is, of course, due to the ship. 

A second lowering was made at Atlantis 
Station 6157 (38°15'N, 68°15'W) well inside the 
Gulf Stream. The results of this lowering are 
shown in Figure IV. The reference line in this 
case went to 15 meters, while the long line 
extended an equal amount below the hydro wire. 

At this station we were greatly troubled by 
a signal fluctuation amounting to several milli- 
volts with a period of five to ten minutes. It 
was very difficult to see what changes, if any, 
were produced as we raised and lowered the line 
to measure at different depths. Not until we 
had returned to Woods Hole did we discover that 
the gyrocompass record of the ship's heading 
showed similar fluctuations. These were re- 
portedly due to a practice of putting the rudder 
hard over when the ship was hove to on station: 
the ship headed up into the wind as she drifted 
forward and then fell away from the wind 
drifting backwards. These heading changes could 
probably have been avoided without too much 
difficulty, if they were indeed the source of 
the trouble. However, fluctuations in the wind 
force and in the resulting wind drift of the 



180 



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181 



ship would have had the same effect and could 
only have been overcome with some kind of sea 
anchor. 

Despite the scatter due to these fluctu- 
ations, the points in Figure IV show a distinct 
over-all trend, especially after the obser- 
vation nearest the surface has been corrected 
for the ship's bottom signal by reference to 
the curve in Figure III. If the profile is 
taken to be a straight line with a slope of 
about 1.5 millivolts per 100 meters, one ob- 
tains a uniform flow velocity relative to the 
ship of about 1.5 knots to eastward. There is 
some suggestion of a steeper voltage gradient 
at the lower depths, corresponding to an east- 
ward flow of 2 knots or more. These velocities 
will be somewhat low because meter wheel readiqgs 
were used instead of the true depths. 

It should be emphasized that it is only 
the east-west component of the flow velocity 
relative to the ship which is determined 
directly by vertical measurements of this sort. 
To obtain the true east-west flow velocity, 
one must add the eastward set of the ship as 
determined by loran, by horizontal G.E.K. 
measurements, or by carrying the vertical 
measurements to still water at great depths, as 
suggested by Malkus and Stern. 

At this station, the loran determinations 
gave a set to eastward of 1.7 knots corresponding 
to a true eastward flow velocity of about 3.2 
knots. Horizontal G.E.K. measurements made in 
the same vicinity several hours after the 
vertical measurements, indicated a set to east- 
ward of 1.4 knots. 

The vertically measured 1.5 knot flow 
velocity relative to the ship is due, of course, 
to the wind drift of the ship. Had there been 
no wind, so that the ship coasted with the Gulf 
Stream, no vertical potential gradient would 
have been observed on this shallow lowering. 
Approximately this situation arose the follow- 
ing day when the next lowering was attempted 
in the same general area. The estimated loran 
set was about 3.2 knots to eastward; the verti- 
cal voltage gradient, if any, was less than 
0.1 millivolt per 100 meters. 



Because 
lowerings we 
time, due to 
state on the 
measurements 
No really de 
now appears 
carried out 
difficulty. 

TOWING TESTS 



the results of these three 
re grossly misinterpreted at the 
the adverse effect of the sea 
Chief Scientist, the vertical 
were prematurely discontinued, 
ep soundings were attempted. It 
that deep soundings could be 
using the same procedures without 



customarily made with the G.E.K., we used a 
pair of lines taped together, one 200 meters 
long, the other 100 meters long. This gave a 
100 meter probe interval towed at 100 meters 
behind the ship. 

Though the polyethylene tubing is nowhere 
near as strong as the conventional G.E.K. line, 
it bore up quite well under sustained towing at 
10 knots. But it could not, we discovered, take 
the sudden strain of being brought up short 
after 100 meters or so had been let out all at 
once. This treatment snapped 100 meters off the 
long line of the towing pair during the first 
tests. As the failure occurred at a welded 
joint, it is possible that a single continuous 
line would not have failed. 

We had some difficulty in repairing this 
tubing successfully, since the repair weld was 
made perforce with tubing which had been exposed 
to sea water. These joints gave way or sprang 
leaks with great rapidity. We finally got a 
weld to hold together permanently by taping the 
line into a loop, so that the strain by-passed 
the joint. 

With this repaired line, we were able to 
make a continuous G.E.K. record from the Conti- 
nental Shelf Co Woods Hole harbor. The record 
was satisfactory in every respect. 

Figure V is an excerpt from that record 
showing the signals obtained on running a square. 
The pattern shows the expected symmetry around 
the electrode zero. 



SEA WATER THERMOCOUPLE 



For towing experiments of the type 



The sea water salt bridge is theoretically 
free of first order errors due to variations in 
pressure, temperature, or salinity. These are 
all supposed to be the same in both electrode 
chambers regardless of what may be happening in 
the sea. There is, however, a possibility of 
second order errors if the changes in one 
variable in going around the circuit do not 
coincide with the changes in another variable. 

If one constructs a sea water thermocouple 
with high salinity water as one element and low 
salinity water as the other, one can produce an 
EMF by heating one junction between the two 
while cooling the other junction. Part of this 
EMF will be due to the temperature coefficient 
of the liquid junction potential between the 
two; part will be due to a concentration de- 
pendence of the Thomson EMFs in the arms. 

We have constructed such sea water thermo- 
couples, and find that the EMF is about 0.2 
microvolts per degree per part- per- thousand 
salinity difference. 



182 

































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183 



On a conventional T/S diagram, such a 
therraocouple would appear as a rectangle paral- 
lel to the axes. The PAF is proportional to the 
area of the rectangle. The corresponding EMF 
in our sea water salt bridge circuit will be 
proportional to the net area, if any, enclosed 
by the T/S diagram of the circuit. 

From this it appears that the largest 
error to be expected in the open ocean would 
occur on a deep vertical measurement, if the 
long line carried water of surface salinity to 
great depths. This error would be about 10 
microvolts, which would be negligible. 

Strangely enough, the other two possible 
second order errors will be identically zero. 
The pressure and temperature will be the same 
inside a submerged tube as outside, so all 
cross effects between these two variables will 
cancel out. The pressure and salinity would 
seem a more likely pair. However, it is clear 
that if the salt consisted of a single thermo- 
dynamic component, say sodium chloride, the 
influence of both variables would be exercised 
through changes in the one thermodynamic chemi- 
cal potential, and no cross effects would be 
possible. Any cross effects arising from the 
presence of several components in the sea salt, 
would have to be considered as third order 
errors. 



OTHER USES 

Another potential use of the salt bridge 
technique at sea may be of interest to biologists. 
If two salt bridges are lowered together, and 
one of them is closed at the end by a membrane 
permeable to only one kind of ion, the signal 
produced will be a direct measure of the ratio 
of chemical "activities" of the ion inside and 
outside the membrane on the two sides of the 
membrane. Since the temperatures and pressures 
will be the same on both sides, and the salini- 
ties nearly the same, this ratio will vary 
essentially only as the concentration of the ion 
varies with depth. 

Suitable glass membranes for H , Na"*", iC*" 
and Ca"*" now exist. Moreover, any simple coated 
metallic electrode, such as the Ag/AgCl electrode, 
can be made thin with two Identical faces to 
serve the same purpose. Thus the possibility 
exists of making simple, direct, in situ measure- 
ments of individual ionic concentrations at depth. 



REFERENCES 



1. Michael Faraday, Phil. Trans. Roy. Soc. 1832 : 
Part I, 163. 

2. W. S. von Arx, Pap. Phys . Oceanogr. Meteor. 
11(3) (1950). 



OTHER CONSIDERATIONS 

We have received several suggestions that 
we avoid our bubble problems by continuous 
pumping of sea water through our lines. Even 
if this could be done without electrical 
leakages through a pump, we would expect 
undesirable electrokinetic potentials to be set 
up in the line by the water flow. 

Because of the traditional use of concen- 
trated KCl in laboratory salt bridges, we have 
also considered its use in our system. While 
it would greatly enhance the therraocouple effect, 
KCl solution might be desirable for horizontal 
measurements in rivers and estuaries where the 
local water is not suitable anyhow. It would 
be most undesirable for deep vertical measure- 
ments at sea: the added weight of the salt in 
a kilometer of tubing would create a prohibi- 
tive hydrostatic pressure difference on a 
vertical sounding. 

Similar, though less severe, hydrostatic 
pressure problems will arise if tubing filled 
with high salinity surface water is lowered to 
great depths. This can be prevented by an 
appropriate initial dilution of the water used 
to fill the tubing. 



3. K.V.R. Malkus and M. E. Stern, J. Mar. Res. 
11(2) . 97 (1952). 

4. M. S. Longuet-Higgins, M. E. Stern and H. 
Stommel, Pap. Phys. Oceangr. Meteor. 13(1) 
(1954). 

5. G. J. Janz, "Reference Electrodes", Academic 
Press, New York, 1950. Chapter 4, 220-222. 

6. A. C. Redfield, J. Mar. Res. 12(1) , 121 
(1953). 



ACKNOWLEDGMENT 



The author is especially indebted to Dr. 
Willem Malkus for first suggesting this investi- 
gation, to Dr. W. S. von Arx for indispensable 
advice, and to Dr. Vaughan T. Bowen for generous 
encouragement. He is also most grateful to the 
Allyn Vines for the use of their basement during 
the current measurements in Woods Hole. Finally, 
special mention must be made of Phil Ballard and 
Ellen Langenhelm, the other two-thirds of the 
"we" so often mentioned. 

This work was supported through a grant from 
the National Science Foundation. 

Contribution No. 1225 from the Woods Hole 
Oceanographic Institution. 



184 



TABLE I 



Tubing 

Green Vinyl Garden Hose 

Ortac (Goodyear), two layer, rubber. 
V i.d., 3/16" wall 

Nalgon Lab Hose 

k" i.d., 3/32" wall 

Gum Rubber Surgical Tubing 
3/16" i.d., 1/16" wall 

Car Heater Hose (Gates), three layer, rubber. 
5/8" i.d., 5/32" wall 

Black Rubber Lab Hose 

3/8" i.d., 1/8" wall 

White Rubber Lab Hose (A. H. Thomas) 
\'' i.d., 1/8" wall 

Polyethylene Tubing 

3/16" i.d., 1/16" wall 



Damping Length 
0.38 kilometers 

0.41 

1.0 

4.7 " 

8.7 
12.5 " 

12.6 
64 " 




Tif^i 



flG-ORS Y 



185 



AN INSTRUMENT FOR THE DIRECT MEASUREMENT 
OF THE SPEED OF SOUND IN THE OCEAN 

by F. J. SUELLENTROP, A. E. BROWN, and ERIC RULE 
Lockheed Missiles and Space Company 
Palo Alto, California 



ABSTRACT 

An instrument has been developed which 
operates on the same principle as the 
National Bureau of Standards velociraeter, 
but in irtiich a considerable reduction in 
size and circuit cwnplexity has been 
achieved. This reduction in size has been 
made possible by selecting electronic com- 
ponents which are insensitive to extreme 
pressures (up to 20,000 psi), so that the 
pressure housings of previous instruments 
have been eliminated. Results of cali- 
bration and stability tests on the instru- 
ment are given. 

INTRODUCTION 

The need for a simple and direct 
method of measuring the speed of sound in 
the ocean has recently been stressed in 
the literature.! At present, the speed 
of sound is usually derived indirectly ty 
considering the speed to be a function of 
the temperature, pressure and salinity in 
the ocean . Ifcowing or measuring the 
values of these parameters, the speed of 
sound is obtained using any one of a num- 
V|gj.2,3,U of empirically-derived formulae 
which contain up to six terms. This pro- 
cess involves considerable computation, 
and controversy exists as to which formula 
is most suitable.' 

Where the need exists to establish 
speed-of -sound profiles rapidly or to 
monitor continuously the speed of sound, 
the advantages of a direct-measuring in- 
strument are obvious. It should also be 
noted that direct measurement is to be 
preferred because the computational 
methods referred to above may not take 
account of all factors influencing the 
speed of sound. 



An instrument capable of measuring the 
speed of sound in fluids has been developed 
at the National Bureau of Standards" and has 
recently been adapted for use In the ocean. 7 
These devices use tlie well-ioiown "sing-around" 
principle in which the frequency of an oscil- 
lator is goveiTied by the transit time of a 
pulse of ultrasonic energy between two trans- 
ducers separated by a fixed distance in the 
liquid in which the speed-of -sound propagation 
is to be measured. 

The instrument described in the oresent 
paper, developed by Locl-iieed Missiles and 
Space Company, also makes use of the "sing- 
around" nrinciple but uses different circuitry 
(many fewer components) and a completely dif- 
ferent packaging philosophy (which results in 
a great reduction in size) than earlier in- 
struments. The improvement in packaging was 
made possible by a systematic study of the 
effect of extreme pressure on the character- 
istics of electronic circuit components such 
as transistors, resistors, inductors and cap- 
acitors. This study made possible the selec- 
tion for use in the velocimeter of components 
known to be stable over the pressure range 
- 20,000 psi. The electronic circuitry of 
the velocimeter can then be encapsulated in 
standard epoxy potting compound, when it is 
effectively exposed to the ambient pressure, 
instead of being contained in the bulky press- 
ure housings which have been sin undesirable 
feature of earlier instruments. 



PRINCIPLE OF OPERATION 

The principle of operation of the instru- 
ment and the functions of the major electronic 
circuits are shown in Fig. 1, The pulse gen- 
erator sends out a pulse to the piezoelectric 
transmitter, causing it to emit a 3-niegacycle 



Superior numbers refer to similarly numbered references at the end of this paper. 



186 



acoustic pulse into the liquid. After travers- 
ing the distance L at the speed of sound Cj the 
pulse is received at the piezoelectric receiver 
and converted into an electrical pulse. This 
pulse is then amplified and used to trigger the 
pulse generator, causing the pulses to sing 
around with a pulse repetition frequency being 
a function of the speed of sound. 

The relation between speed of sound in the 
liquid and output frequency of the instrument 
is not quite linear because of the finite time 
delay introduced by the electronic circuitry 
and piezoelectric transducers. Referring to 
Fig. 1, we have — 

Period of pulses = T + t 

where T is the transit time in the liquid and 
t is the delay time in the electronics. The 
expression for the pulse repetition frequency 
is then — 



1 



Since T = x;, where L is the path length and 
C is the speed of sound, we have ~ 



h^ 


c 


r 

1 


L 


!•¥ 



(1) 



tc 



The term "TT in equation (l) leads to nonlinear- 
ity in the relation between f and C and becomes 
less important as t becomes smaller with res- 
pect to T. Typical values for velocimeters 
constructed so far are C = 1500 m/sec, L = 0.1 
meters, and t = 0.6 microseconds so that the 
nonlinearity over small ranges in the speed of 
sound is small enough that the errors intro- 
duced by assuming a linear relation are within 
allowable limits. For example, if the speed 
of sound were to be measured over a range of 
2li90 to 1550 m/sec, the error introduced by 
assuming the linear relation is only +0.5 
meters per second. If, however, a larger range 
in the speed of sound is to be measured or the 
accuracy is to be improved, there are at least 
two methods of reducing the data. 

The first method is to construct a calibra- 
tion curve giving the relation between f and C, 
which is derived by measuring the output fre- 



quency of the instrument when immersed in dis- 
tilled water at different temperatures in which 
the speed of sound is known. ° Such a calibra- 
tion curve is shown in Fig. 2. 

The second method is to determine the values 
of L and t for each instrument such that the 
data can be reduced iising the relation — 



Lf 



tf 



For either of these methods to be valid un- 
der all oceanographic conditions it is necessary 
that the quantity t should not vaiy over the com- 
plete range of temperature and pressure encount- 
ered in the ocean, and quite elaborate test 
procedures are necessary to determine that this 
condition is fulfilled. The tests involve main- 
taining the transducers in a water bath in which 
temperature and pressure are constant while the 
electronic circuitry is subject to temperature 
and pressure changes over the range -5°C to UO°C 
and - 20,000 psi, respectively. Any change in 
output frequency is then undesirable and must be 
attributed to changes in the electronic circuit- 
ry. 

These tests have been carried out on the 
Lockheed velocineter. It was found that the 
change in time delay in the electronic circuitry 
over the temperature ranse of -5°C to U0°C af- 
fected the speed-of-sound readings by less than 
+0.2 m/sec. The change in time delay in the 
circuitry over the pressure range to 20,000 
psi affected the speed-of-sound readings by less 
than +0.1 m/sec. 

Another factor which may cause the time de- 
lay in the electronics to vary is variations in 
the voltage from the power supply. Tests on 
several of these instruments have shown that a 
change in voltage of +0.1 volt causes the speed- 
of-sound reading to change by less than +0.2 
m/sec . 



aSTRgMENT DESIGM 

The general form of the instrument is shown 
in Fig. 3. The transducers are located in the 
square end plates, which are made of Invar, 
as are the three rods which establish the trans- 
ducer separation and which serve to protect 
the transducers from accidental damage. Use 
of Invar ensures that changes in path length 
due to temperature differences in the ocean 
are negligible (less than one part in 25,000). 
The transrait-and-receive traisducers are 



187 



.-;s^;'^' 







FIG. I 



_l I l_ 



135 136 137 138 139 140 14.1 142 143 144 145 14 6 147 

OUTPUT FREQUENCY - f (KC) 



FIG. 2 



188 



polarized discs of piezoelectric ceramic backed 
with potting compound and operating in the 
thickness -re sonant mode at about 3 megacycles 
per second. The electronic circuitry has only 
five transistors (all type 2K393) and requires 
a Ij-volt power supply from which it draws less 
than 5 miliiampso A regulated power supply 
employing a rechargeable battery, which can be 
submerged with the velocimeter, has also been 
developed at LMoC. 



NOMENCLATURE 

C = speed of sound, meters per second 

f « pulse repetition frequency, pulses per 

second 
L = path length, meters 
t = time delay in electronic circuitry and 

transducers, seconds 
T = transit time in liquid, seconds 



ESFEiiENCES 

1. Thomas D. McGrath, Capt., USt! - UNDEBWAIEK 
ENGINESRING, 1, 3, p. 38 (i960). 

2. V. M. Albers, UND£3xWATER ACOUSTICS HANDBOOK 
(The Pennsylvania State University Press, 
University Park, Pennsylvania, I960). 

3. K. V. Mackenzie, J. AC0U3T, 30C. m. 32, 
100 (1960). 

)). Wayne D. VJilson, J. ACOuST. SOC. m. 32, 
6UI-6U4 (I960). 

5. F. £. Bellas, J. ACOUST. SOC. A.M. 33, 2h9 
(1961). 

6. H. Greenspan and C. S. Tschiegg, RiiV. SCI. 
INST. 28, 11, 897-901 (1957). 

7. C. li. Ts'chiegg and E. E. Hays, J. ACOUST. 
SOC. Ai-i. 31, 7, 1038-1039 (1959). 

8. M. Greenspan and C. E. Tschiegg, J. RE- 
SEARCH OF NATIONAL BUREAU OF STANDARDS 59, 
h, 2U9-25U (1957). 




FIG 3 



189 



AN ACOUSTIC OCEAN-CURRENT METER 



by F. J. SUELLENTROP, A. E. BROWN, and ERIC RULE 
Lockheed Missiles and Space Company 
Palo Alto, California 



ABSTRACT 

An ocean-current meter has been developed 
which is essentially two sing-around velocity- 
of-sound meters in which the directions of 
pulse transmission are opposite in sense. 
The instrument is oriented so that the direc- 
tion of acoustic pulse transmission is parallel 
to that of the flow to be measured, so that 
the time of pulse translation is greater in 
one velocimeter than in the other. The dif- 
ference in sing-around frequencies is then 
proportional to ocean-current velocity. 
Electronic circuitry is described by means of 
which a signal with frequency proportional to 
flow velocity is extracted. It is shovm that 
the current flow measurement is independent 
of variations in the velocity of sound. 



INTRODUCTION 



tivity-j on the one hand, and the need to avoid 
ambiguity, on the other, become contradictory 
in a wide -range instrunent. 

The instrument described in the present 
paper, being developed by Lockheed Missiles 
and Space Company, avoids the difficulties of 
the acoustic-tjfpe instruments described above. 
The instrument is basically simple and con- 
sists of two sing-around velocimeters arranged 
so that the transmission paths in the liquid 
are side-by-side and of equal length. The 
directions of pulse travel are opposite in the 
two velocimeters. One velocimeter measures 
the sum of the speed of sound and the speed of 
current flow while the other velocimeter meas- 
ures the difference between the two speeds. 
Therefore, by taking the difference of the 
sing-around frequencies of the velocimeters, 
we achieve a signal having a frequency propor- 
tional to current flow. 



The mechanical -impeller type of instrument 
most commonly used to measure ocean-current 
speeds is generally unsatisfactory because of 
bearing-friction problems and because inherent 
high-inertia leads to slow response to chang- 
ing rates of flow. Acoustic flowmeters which 
effectively measure the results of the veloc- 
ity of propagation of so'und ir a fluid and 
the velocity of the fluid with respect to a 
transmitting and receiving transducer have 
been described in the literature.-'- These in- 
struments are subject to error when used in 
a fluid in which the velocity of propagation 
can vary. In the case of a single-path in- 
strument the error in flow--vBlocity measure- 
ment is equal to the deviation in the veloc- 
ity of sound from the value pertaining when 
the instrument was calibrated, iiefinement of 
the instrument to a two-path type reduces 
this error to the extent that a given percent- 
age variation in the velocity of sound from 
calibration conditions will result in the 
same percentage error in flow m.easurement. 
The possible variation in the velocity of 
sound over tiie complete range of oceanographic 
conditions is about 12 per cent so that an un- 
acceptable error in flowmeter readings can be 
introduced in this way. A further objection 
to the type of acoustic flowm.eter usually 
described is that the technique involves a 
measurement of phase difference; therefore, 
the requirement of providing sufficient sensi- 



THiPRY OF OPERATION 

In the case of the ideal velocimeter, the 
output freqriency (f) is given by 



f =£ 



where C is the velocity of propagation and L 
is the separation between transmitter and re- 
ceiver. If one uses two velocimeters sending 
pulses in opposite directions and introduces 
a current flow (v), the two sing-around fre- 
quencies are 

P _ C + v 



and 



^2 = 



Then, by taking the difference of the sing- 
around frequencies, we obtain the frequency 



fl -f2 



2v 
L 



190 



which is proportional to current flow. In 
this ideal case, variations in the speed of 
sound do not affect the flow measurement. 

There is, however, a small but finite 
time delay in the electronic circuitry of 
each velocimeter which complicates the expres- 
sion for f^. The individual velocimeter out- 
put frequencies takinr- the time delay (t) into 
account are — 



i- 



C-v 
f = != 

^2 |+t^C::vO. 



c-v 



l-t(Czvl^. 



Typical values for the velocimeters used are 
(C ± v)— 1500 meters per second, L ■= 0.l5 
meter and t = 0.6 microseconds. The value of 
t(C ± v)/L^ .006 is small enough that the 
higher order terms in the expansions can be 
ignored. The expression for f^ is now — 



f - 2v 



2tC 

IT 



and the percentaj^e error in f caused by a 
change in C can be shown to be 0.012 times 
the percentage change in G (see Appendix A). 
This makes the error so small that it can be 
ignored. 

The foregoing discussion does not take 
into account differences in path length and 
delay times in the circuitry between the two 
velocimeters. The effect of having these dif- 
ferences is to limit the resolution of the 
instrument. These problems have been invest- 
igated at LI'ISC and it has been found in lab- 
oratory models that they limit the resolution 
to +0.1 foot per second. 



DESIGN 

In order to achieve the necessary sensi- 
tivity for a flowmeter of practical dimensions, 
some multiplication of the individual sing- 
around frequencies, before subtraction, is 
necessary. A flowmeter with the desired char- 
acteristics is shown in the block diagram of 
Fig. 1. The function of the balanced modu- 
lator is to take the sum and the difference 
of the frequencies of the two signals being 



injected into it. By using the low-pass and 
high-pass filters it is then possible to obtain 
signals prooortional to current speed and vel- 
ocity of sound, respectively. Such an instru- 
ment, in the forrn of an initial laboratory 
prototype, has been built at LMSC aid has been 
shown to function in the laboratory. The gen- 
eral form of this prototype is shown in i^^ig. 2. 



C+V 

L 


_C+v 

L 


1 t(cM ^,.. 


.IPPaiDIX A 


1+ t(C+v) 


Taking 



Taking the expression for the output fre- 
quency — 



2v 
L 



1 - 2tC 
L 



it is possible to find the chante in this fre- 
quency caused by a change in the speed of sound 
C — 



A f , 



Iivt 



A C 



The percentage error in f^ caused by a change 
A C in the speed of sound is then shown to be 



ZtAC 



X 100=1 



xlOO 



100 






For the values of C = 1500 m/sec, L = 0.1? 
meter and t = 0.6 microseconds, the value of 
2tC/L is found to be 0.012. Therefore, the per- 
centage error in f^ caused by a percentage 
change in the speed of sound A C/C x 100 is 
shown to be 0.012 times the percentage change 
in the speed of sound. 



N0>tENCLATURE 

C = speed of sound, meters per second 
f = frequency, cycles per second 
fc= outout frequency proportional to C, cycle 
per second 



191 



T -*- R 



R -^ T 



SING-AROUND 
CIRCUIT NO. I 



SING-AROUND 
CIRCUIT N0.2 



EJ -I-2 
CIRCUIT 




EJ -^ 2 
CIRCUIT 


■ 




' ' 


X5 

FILTER NO 1 




X5 

FILTER NO.I 


' 


' 




" 


AMPLIFIER 

ANDSCHMITT 

TRIGGER 




AMPLIFIER 

AND SCHMITT 

TRIGGER 


' 


r 




" 


X5 
FILTER NO. 2 




X5 
FILTER NO. 2 


1' 




\ 


> 


AMPLIFIER 




AMPLIFIER 




















BALANCED 
MODULATOR 


























L P FILTER 






FILTER 






^ HP 






' 


' 








' ' 







f. 



€ 



FIG. 



192 



fY= output frequencj^ proportional to v, cycle 
per second 

L = path length in liquid, meters 

t = time delay in electronic circuitr?/", sec- 
onds 

V = speed of current flow, meters '^er second 



1. H. p. Kalmus, "Electronic Flowmeter Sys- 
tem", R3V. SGI. INST., Vol. 25, Mo. 3, 
pp. 201-206, March 195L. 




FIG. 2 



193 



A DOPPLER-SHIFT OCEAN-CURRENT METER 

by J. D. CHALUPNIK and P. S. GREEN 
Lockheed Missiles and Space Company 
Palo Alto, California 



ABSTRACT 

An ocean-current meter utilizing the floppier 
effect has been developed and tested. With this 
device a collimated bean of ultrasonic energy 
is projected into the water and a volume rever- 
beration signal received. The meter detects 
the difference between the transmitted and re- 
ceived frequencies, this difference being pro- 
portional to the speed of the water past the 
meter. The device can be made to indicate sense 
as well as flow rate. 



INTaODDCTION 

Ocean-current meters commonly in use are 
mechanical devices using impellers turned by 
the dynamic pressure of the current, although 
other instruments which measure (1) dynamic 
pressure on static members, (2) electromotive 
force generated by the conducting liquid flow- 
ing in a magnetic field, (3) cooling effect of 
the current on hot wires, and (Ii) time required 
for a sound pulse to travel a specified dis- 
tance have been tried. ^* 

The impeller devices respond slowly to 
changing flows and operate over limited ranges 
of flow rates o They are large and do not give 
continuous readings. The instruments which 
measure dynamic pressures on static members 
are limited in operating range. Electro- 
magnetic current meters are limited in oper- 
ating range and are expensive. Hot-wir« 
anemometer-type devices are difficult to use 
and require frequent cleaning due to films 
forming on the wires. Ultrasonic current 
meters which have been reported prior to this 
meeting have been electronically conplicated 
and expensive. A paper being presented at 
this meeting by F. J. Suellentrop describes an 
improved version of this instrument which gives 
speed-of -sound information as well as flow rate . 

This paper describes a new instniment 
which makes use of the Doppler frequency shift 
to measure flow rates in ocean water and other 



liquidb cijntaining inhomogeneities. 



THEOriY 0? OPStAIIOM 

When a beam of liLtrasonic energy is pro- 
jected into an inhomogeneous liquid, it is 
scattered by irregularities in the liquid and 
some of the energy is returned in the direction 
of the transmitter. This returned signal is 
called volume reverberation. The volume re- 
verberation signal is found to shift in fre- 
quency due to the Doppler effect, provided 
there is net movement of the inhomogeneities 
along the axis of the beam. 2 If the scatterers 
are stationary with respect to the liquid, then 
the observed Doppler shift is proportional to 
the speed of the liquid relative to the meter. 
The D<^pler-shift ocean-current meter is a 
continuous-tone sonar device which detects the 
volume reverberation signal with a receiving 
transducer located adjacent to a transmitting 
transducer, then detects any shift in frequency 
between the transmitted and received signals. 
It is assumed that the vast majority of the 
CCTitributing scatterers axe nearly neutrally 
buoyant and move with the water. 

The application of the Doppler-shift prin- 
ciple to measuring currents in the ocean ap- 
peared to be fecisible, provided enough scat- 
terers were present in the water. Since ilay- 
leigh scattering increases with the fourth 
power of frequency, only high frequencies were 
investigated, 2.5 and 10 megacycles being 
chosen as favorable operating frequencies. 
Most considerations indicated that the higher 
frequency should be used, the principal objec- 
tion being the inherent difficulties encount- 
ered in high-frequency transistor circuitry. 
At 10 mc the number of scatterers one wave- 
length or greater ( ^ = .iSmm) in size is 
quite large, with small marine organisms, 
particulate matter, and minute bubbles abound- 
ing. 

For a stationary transducer-pair and moving 
target (scatterers), the frequency of the re- 



* Superior numbers refer to similarly numbered references at the end of this paper. 



194 



turned signal is 



(1) 



where f^ is the frequency of the volume re- 
verberation signal at the receiver, v^ is the 
velocity of flow along the axis of the trans- 
ducer-pair, c is the speed of sound in the 
medium, and f is the transmitting frequency. 
The velocity v^ is considered positive in the 
direction the transmitted wave is projected. 
The received signal beats with the transmitted 
tone, the beat frequency being the Doppler 
frequency. The Doppler frequency is given by 



/if = f-f„ =f-(f 



!i) f 



- 2vv 



c + Vx 



(2) 



Since the speed of flow is small compared to 
c, the Doppler shift may be approximated by 



Af 



2Vy 
c 



It is convenient to use the quantity 

^ = i X 106, 
c 



(3) 



(1*) 



the normalized sensitivity for Doppler-shift 
devices, which has the units cps/mc/m/sec , 
The normalized sensitivity for sea water is 
about 1300 cps/rac/m/sec. Rewriting (3), we 
have 



A f - <(^Vx f 



(5) 



where f ' is the transmitting frequency in 
megacycles. It is desirable to have f ' as 
large as possible for good resolution. The 
normalized sensitivitj; f - i^cc), is dependent 
on the speed of sound in the water; therefore, 
if very accurate measurements of flow rates 
(less than +5^ error) are to be made, it 
would be necessary to determine or estimate 
the speed of sound at the point of measure- 
ment. Although the speed of sound varies 
widely in the ocean, it is possible to estim- 
ate the speed of sound at a point of measure- 



ment closely enough to ensure satisfactory flow- 
rate determinations. 

The sensitivity at 10 mc is about 13,000 
cps/m/sec, making practical an instrument with 
a working range of 1 ram/sec to 10 m/sec. If it 
is desired, the range can be extended to higher 
and lower flow rates with little additional 
effort. 

The transmitting frequency must be held ccn- 
stant for accurate measurements to be made. 
Ztvots can be caused by short- or long-term in- 
stability in the transmitting frequency, iirrors 
due to short-term instability occur when changes 
in frequency occur during the time it takes a 
transmitted wave to return to the receiver. 
This round-trip time is on the order of cme 
millisecond; hence, the frequency drift rate 
would have to be extremely high to introduce any 
appreciable error. Long-term drift of the oscil- 
lator frequency produces an error in the Doppler 
signal that is proportional to the error in the 
transmitting frequency. 

A change in the sense of Vj^ results only in 
a 180° phase change in A f ; therefore, if the 
instrument is to determine sense as well as 
speed, it is necessary to beat the returning 
signal with a reference signal differing in fre- 
quency from the transmitted wave by more than 
the maximum Doppler frequency to be measured. 



S f - (f» - f ) 



2V2 
c 



(6) 



Here f* is the reference frequency (assumed 
greater than f for this discussion) and 8 f is 
the new difference frequency. For zero flow, 
the difference frequency is not zero, but is the 
offset frequency f* - f. When fif is less than 
the offset frequency, this corresponds to a 
negative v-^, or flow toward the transducer-pair. 
If f* is assumed to be less than f , similar re- 
sults are obtained. If the current meter is 
oriented facing the current by a vane arraa ge- 
ment, the sense information would not be re- 
quired. 

One further advantage was gained by using 
a transmitting frequency of 10 mc, that being 
the control over the region in which the current 
is to be raeasxired. Attenuation at 10 mc is 
about 20 db/m, which effectively limits the dis- 
tance the instrument "sees". There is an area 
immediately in front of the transducer-pair 
which gives no return, because the transducers 
are spaced a small distance apart. The beam 
width of the transducers is narrow, so the 
lateral area covered is small. Because of these 
conditions, the region of observation is limited 
to a narrow volume extending from about I4O to 



195 




~v / 



Fig I The Doppler shift ocean current meter. 




Fig. 2 Photo of the meter showing the construction. 



196 



70 cm in front of the transducer-pair, in the 
clear water where the flow pattern is unaffected 
by the presence of the meter. 

Since the current meter has no moving parts 
it can respond almost instantaneously to flow 
changes, being limited by the transit time of 
an acoustic wave from the point of measurement 
to the receiver (less than 1 ms). Spectrum 
broadening and rapid shifts of frequency of the 
returned signal can be expected in turbulent 
flows and should provide a reliable index of 
turbulence in the measured current. 



DESCRIPTION OF THE CURRENT METER 

The current meter consists of an oscillator 
driving the transmitting crystal, an amplifier 
tuned to the oscillator frequency (10 mc) and 
driven by the receiving crystal, a detector, 
and an audio frequency stage with emitter fol- 
lower output. These elements are enclosed in 
a pressure-tight case. The instrument operates 
on 1«5 V and, except for the battei^r, is com- 
pletely enclosed in a cylindrical package about 
12 cm long and 3.2 cm in diameter. The crystal 
transducers are mounted on one end of the cyl- 
inder, while the electrical connectors exit 
from the other. The complete current meter is 
shown in Fig. 1. 

Complete isolation of the oscillator and 
amplifier stages is provided by the internal 
shields shown in Figs. 2 and 3. The outer 
case provides structural strength to withstand 
the water pressure and is sealed at both ends 
with 0-rings. The two electrical conductors, 
one for -1.5 v and the other for the audio 
signal output, pass through small O-ring stuff- 
ing boxes to prevent leakage around them. 

The transmitting and receiving crystals 
are standard stock barium titanate discs 6.5 
ram in diameter and about .25 mm thick. The 
thickness-resonant frequency is about 10 rac. 
The theoretical half-beamwidth of these crys- 
tals at 10 mc is 1.7° and the actual measured 
half-beamwidth is about 2.5°, as shown in 
Fig. li. The crystals are mounted 6 mm on 
centers and backed with .8 mn of epoxy circuit 
board. 

The oscillator is of unique design, employ- 
ing a single tunnel diode as the active element. 
The tunnel diode is superior to conventional 
transistors in this application because of its 
small size and excellent current-handling 
ability at high frequencies. Although the im- 



pedance of the crystal is low at 10 rac, it is 
possible to apply 2.0 v peak-to-peak across the 
crystal with the tunnel diode. 

The tuned amplifier stages employ KADT, 
high-frequency transistors operating well below 
their rated voltage. There are three stages 
with a gain of about 20 per stage. There is 
enough acoustic coupling between the transmit- 
ting and receiving crystals to provide the 
reference frequency; hence, no electronic mixing 
is required. The Doppler frequency appears as 
amplitude modulation on the 10-mc carrier. 

The Doppler frequency is extracted from the 
10-mc carrier with a highly sensitive backward 
diode detector, then amplified. The Doppler 
frequency shift for a flow range of 1 mm/sec to 
10 m/sec is 13 to 130,000 cps. In this form 
the data can be processed for recording on tape 
recorders or for telemetering to data-gathering 
stations. 

The Doppler-shift flowmeter requires very 
little power and operates on 1,5 v, drawing only 
50 ma. It could be operated continuouslj' on a 
single rechargeable flashlight cell for about 
I46 hours. 



RESULTS 

The Doppler-shift ocean-current meter has 
been tested in the laboratory in a flow tube. 
Results indicated that, if sufficient scatterers 
are present, the instriunent will function well, 
although it was necessary to add scatterers to 
Palo Alto tap water to get satisfactory returns . 
The observed Doppler frequency checked closely 
with the measured velocity in the tube. In 
order to try the meter in "ocean" water, it was 
taken to Palo Alto Yacht Harbor on San Francisco 
Bay for additional tests. Sufficient scatterers 
were present in the yacht harbor water to get 
return, and the meter performed as anticipated. 
The signal-to-noise ratio was low, but work is 
underway to decrease the noise level. 



CONCLUSIONS 

This paper describes an ocean-current meter 
which uses the Doppler shift in continuous-tone 
volume reverberation to measure flow rates. 
Operation of the instrument depends on suf- 
ficient scatterers being present in the water 
that is to be measured. It is assumed that, at 
an operating frequency of 10 mc, there are 



197 




Fig 3 Photo showing the electronics. 




3 2 10 12 3 4 

ANGLE e DEGREES 
Fig. 4 Transducer pressure pattern at 10 mc. Solid curve Is the theoretical 
pattern. 



198 



enough of the necessary scatterers present to 
operate the instrument satisfactorily in ocean 
water. Although the device described was de- 
signed to operate over a range of 1 mm/sec to 
10 m/sec, it is reasonable to assume that, with 
minor modifications, it would operate over a 
much wider range. This instrument should pro- 
vide a reliable index of turbulence in ocean 
cuorrents because of its excellent response to 
rapidly changing flows. 



NOMENCLATURE 

c = speed of sound, m/sec 
f,f* = transmitting frequency, cps 
f ' - transmitting frequency, rac 
A f = Doppler frequency, cps 
S f = difference frequency, cps 
fy " returned frequency, cps 

P/Pq = relative pressure, dimensionless 
V ■■ velocity of flow along the axis of the 
transducer-pair, m/sec 

e e an angle, deg. 

y = normalized sensitivity, cps/rac/m/sec 



REFEREMCaS 

1. J. W. Johnson and R. L« WLegel, "Investiga- 
tion of Current Measurement in Estuarine 
and Coastal VJater", September 1958, Cali- 
fornia State Water Pollution Control Board 
Publication #19, Sacramento, California. 

2. G. A. Klotzbaugh, "Theory of Continuous- 
Tone Reverberation", J. ACOUST. SOC. m. 
27, No. 5, September 1955. 



199 



HIGH- ACCURACY, SELF- CALIBRATING ACOUSTIC FLOW METERS 

by R. A. LESTER, Research Engineer 
Westinghouse Research Laboratories 
Pittsburgh, Pennsylvania 



ABSTRACT 

A number of acoustic flow meters have been 
developed and tested for a variety of uses- All 
of the units transmit in opposition and compare 
the received phases; the phase difference is a 
function of the water velocity. The first unit 
was one which used an amplitude-modulated con- 
tinuous wave signal and measured speeds from 
0.15 ft/sec to 15 ft/sec to an accuracy of Vy. 
A second type compares the carrier frequency and 
measures speeds from approximately O.OO5 ft/sec 
to 0.5 ft/sec with an accuracy of Vfo. A third 
pulse-type system is being developed ; it is 
simpler than the original unit and eliminates a 
number of the Inherent inaccuracies of the above- 
mentioned units. One of the desirable features 
of all of these units is the ability to be 
calibrated or checked for zero reference in the 
field. 



IMTRODUCTION 



For monitoring ocean currents, wave particle 
velocities, flows about ships and models, and 
flows in pipes, flow meters which are both 
accurate and dependable are required. Acoustic 
flov; meters show great promise of fulfilling this 
need. Acoustic meters have several salient 
features: one, they are nonfouling since there 
are no moving parts; two, they are linear devices 
with good accuracy; three, they are directive; 
last, but no means least, they may be calibrated 
in the field. Several acoustic flow meters have 
been built and tested to measure flows in the 
ocean. The construction and limitations of these 
meters will be discussed. 



OFERATDIG PRINCIPLE 

These flow meters, like most acoustic flow 
meters, measure the difference in travel time of 
sound in the upstream and downstream directions 
of the flow. The fluid velocity is then: 



At C 
2L 



if V « C 



where 



V = velocity of the fluid, 
L = distance the sound travels, 
C = speed of sound in the medium, and 
At = difference in time delays. 



To get an order of magnitude of the numbers 
involved, consider a flow of 1 ft /sec in water. 



If L is 10 feet, then At = 2 LV/C 



,2 



0. 



usee. 



To obtain accuracies of .1 ft/sec this system 
must be capable of resolving time delays of less 
than 1 usee. This is most conveniently done by 
measuring the relative phases of two sinusoidal 
signals. Since the measurements of the upstream 
and dovmstream travel times are to be made 
simultaneously, there must be two sets of receiv- 
ing equipment with their associated time delays. 
Therefore, an error in the measurement of At will 
be introduced unless the two receivers have equal 
time delays. In the meters described here, 
provision is made to balance the receiving equip- 
ment and thus "zero calibrate" the meter from 
time to time to insure accuracy. In the first 
two of these meters, this "zero calibration" may 
be made in the presence of a flow. The third 
meter must be "zero calibrated" \mder zero flow 
conditions; thereafter, its calibration is a 
function of the stability of quartz crystal 
oscillators. 



THE EQUin-IEMT 

The first meter built was a CW dual 
frequency system which was designed to measure 
flovf up to 15 ft/sec. For the particular appli- 
cation, it was desirable that the flow be averaged 
over a ten- foot distance. This system represents 
perhaps the most straightforward electronic 
circuitry which will make the measurement (see 
Fig. 1). Four transducers are used in this flow 
meter, two on each probe. The pairs of trans- 
ducers are separated by about an inch. In order 
to get a narrow acoustic beam width, high frequency 
carriers of 1.1 and 1.6 mcps are used. These are 
modulated at 20 kc. The received signals are 
amplified, detected, and applied to the phase 
meter. The relative phase of the 20 kc signals 
is then proportional to the flov/. Zero calibration 
is accomplished by reversing the direction of the 
acoustic path of one of the frequencies. With 
the signals in the same direction the water path 
time delays of both signals are identical; hence 
the electrical delays of the system may be 
adjusted to "zero". 

This system, although quite simple electronically, 
has a number of potential weaknesses. To begin 
with, it requires 2 cables to each post, 2 trans- 
ducers in each post, 2 transmitters operating at 



200 



2 widely separated frequencies and, because of 
the physical separation necessaiy due to trans- 
ducer size, tvo acoustic paths are required. 
Errors may occur because of electrical leak- 
through or due to acoustic path separation in a 
highly inhomogeneous medium; it is also possible 
that errors of a secondaiy nature may occur due 
to the large frequency separation of the trans- 
mitted signals. 

The following system, shown in Fig. 2, was 
constructed to circunrvent these two weaknesses. 
In this flow meter, the high frequency carrier 
with a 20 kc modulation is again used. T\ro 
transducers are driven from the same pulsed 
1.1 mcps transmitter. The transmitter Is turned 
off when the space between the transducers Is 
filled with acoustical energy. The signals are 
detected and again the phase difference of the 
20 kc signal is proportional to the flow. A 
sampling circuit after the phase meter remembers 
this phase difference until the phase is altered 
by the next received signal. In this way, 250 
samples of the fluid velocity are taken each 
second. The resistors shown are included to 
insure that the transducers will see the same 
impedance when transmitting as when receiving, 
thus insuring their reciprocity. This system 
uses a single cable to each post, one transducer 
in each post, a single acoustic path and a single 
frequency. Crosstalk problems and acoustic path 
problems are minimized and equipment problems 
due to water exposure are halved. 

The third system, shown in Fig. 3, is a 
pulse system which uses free rxmning crystal 
oscillators to store the phase Information. It 
was built to measure flows of less than two knots 
maximum velocity. In this meter the transducers 
are spaced at a two foot interval. A pulsed 
1 mcps signal is applied to the two transducers 
for too usee. This signal is received and used 
to lock two slave oscillators. These slave 
oscillators are then heterodyned with a local 
oscillator and the resulting audio signals are 
applied to the phase detector. The output of 
the phase detector then indicates the flow. 
During the time no energy is received, the slave 
oscillators free-run, thus providing continuous 
information to the phase meter. The range of the 
velocities to be measured or the post spacing 
may be varied by changing the carrier frequency. 



SOURCES OF ERROR 

The error of these systems due to the 
electrical circuits is quite small. The phase 
meter has been the limiting component and its 
error is approximately 0.3^. 

In homogeneous water the accuracy of the 
instantaneous readings is limited by the vortices 
created by the leading transducer when the 
acoustic beam is in the wake of this probe. 
This vortex shedding causes a fluctuation in the 



output vfhich increases In magnitude and frequency 
with increasing speed. For the 2-3/8" probes 
used, the measured velocity fluctuated about 0.2 
knots at a speed of 8 knots, and the fluctuation 
had a frequency of about 17 cps. If the flow 
meter is run at an angle to the flow, such that 
the acoustic beam is not in the wake of the lead- 
ing transducer, there is no error due to vortex 
shedding. 

In inhomogeneous water, the errors introduced 
are a function of the velocity of the fluid, the 
magnitude of the velocity anomalies, the patch 
size and the distance between transducers. These 
inhomogenelties can introduce errors in several 
ways. 

One mechanism which can cause errors is the 
phenomenon of multiple path transmission which 
results in signal amplitude fluctuations. This 
occurs ^Jhen parts of the acoustic beam are re- 
fracted in a nonuniform manner so that they arrive 
at the receiving element out of phase. This 
effect varies as the distance between the trans- 
ducer elements; however, the exact manner in which 
it varies is, at present, not completely 
understood. The effect of this secondary 
path is to add to the direct signal another sig- 
nal of slightly different phase. The sum of 
these two signals results in a fluctuating 
received amplitude. Tests were conducted at sea, 
at Scripps Institute, and in the Laboratory to 
determine the magnitude of this effect. It was 
determined that the signal level fluctuated 
approximately 12 db under fairly severe thermal 
conditions. Using this as a figure for the kind 
of fluctuation one might expect at sea, the 
velocity error due to the multiple path trans- 
mission may be calculated. If it is assumed that 
the second path signal is equal in magnitude to 
the direct signal, a delay of l66 electrical 
degrees of the carrier frequency would be required 
In order for the resulting amplitude to change to 
one-fourth of its original value. The resultant 
phase of the received signal would then be 83 
different from the phase of the direct path. 
This condition would lead to an apparent time 
delay of about 0.25 usee or an instantaneous 
error of about 0.3 ft/sec in the measured 
velocity. This error does indeed occur occasion- 
ally under severe thermal gradients in the order 
of 1 to 2 F per foot. A secondary effect of 
the multiple path is the effect of the amplitude 
change on the time delay of the receivers. The 
receivers may be designed so that error due to 
amplitude fluctuations are negligible. 

Inhomogenelties can also cause errors due to 
the fact that the acoustic signals traveling in 
opposite directions are not in the same water at 
the same time. If the water velocity is large 
enough and the thermal patches sufficiently 
small, the sound traveling in one direction will 
travel through different water than the sound 
traveling in the opposite direction. This effect 
is quite difficult to separate from the effect of 



201 



1.1 m. c. p. s. 
Transmitter 




Receiver 



]□!-■ 



Phase 
Shifter 



20 kc 
Modulation 






Phase 
Meter 



Output 



1. 6 m. c. p. s. 
Transmitter 



Receiver 



Jlock Diagram of 0-15 ft. /sec. Acoustic Flow Meter Using 
Four Transducers 



Fig. 1 



Pulsed 
Transmitter 



loon 



20 kc 
Modulation 



l/4-l/2n 



-^A/VVV- 

100 a 



-HdI \n\ — - 



i 



*■ Receiver — i i — Receiver ■• 



_!_ 



Phase Meter 



Sync 



Low Pass 
Filter 



Sampling 



Output 

Block Diagram of 0-15 ft. /sec. Acoustic Flow Meter 
Fig. 2 



202 



1635 Kcps 

Xtal Oscillator 



fl-- 



iDl- 



Slave 
Oscil. 






Slave 
Oscil. 


\ 


/ 








^ ' 


Mixer 




Local 
Oscil. 




Mixer 
























Phase 
Meter 


/ 














"^ 





Output 

Fig . 3 Block Diagram of 0-2 Knot Flow Meter . Switches ore Electronic . 



1.5 

1.4 

1.3 

1.2 

1.1 

1.0 

.9 

.8 

.7 

.6 

.5 

.4 

.3 

.2 

.1 







1 1 


1 1 1 1 1 


1 1 1 1 


/ - 


- 




Run #5 — ^ 


V- 


- 




// 


'^Run #11~ 


— 


0° to Flow 


-/ y 


~ 


— 


; 


Y j^ 


— 


- 


Run #K z' J 


iT 


— 


— 


P If 


'--38° to Flow 


— 


- 


/y 




— 


- 


/jr 




- 


- 


Pjr^^m m 




- 


- 


Jrf 




— 


~ / 


cr 




- 


r\ 


1 1 1 1 1 


1 1 1 1 


1 i 



1 2 3 4 5 5 7 8 9 10 U 12 13 14 
Speed, ft. /sec. 

Flow Meter Output vs. Carriage Speed 



203 



multiple path transmission and since the errors 
which were measured can be accounted for "by the 
multiple path effect, the errors due to very- 
turbulent water are assumed to be small or at 
least rare . 

Water tank tests have been conducted vrtiich 
indicate that selective fading of the carrier or 
side bands does not occur, or at least does not 
detract significantly from the accuracy of the 
system. Also, there does not seem to be a 
sufficient density of scatterers in the ocean at 
these frequencies to seriously affect these 
systems. 



RESULTS 

The meters were tested at David Taylor Model 
Basin. Fig. 4 shows a graph of the output of the 
two frequency 10-foot model of the flow meter vs 
carriage speed for two different alignments to the 
flow. The graph shows that the meter is accurate 
to better than 1^ and is linear to its maximum 
velocity. Similar results were obtained for the 
other two meters. 

The two-frequency meter has also been tested 
at Scripps Institute and at sea aboard the USS 
Redfin. Under operating conditions at sea the 
error in the readings can be measured by putting 
the flow meter in the "zero calibrate" mode. 
Any indicated velocity is then a noise signal or 
error of the system. Here It was found that the 
accuracy varied with thermal conditions from 
0.5 ft/sec or 35^ of full scale for severe thennal 
conditions, to better than .08 ft/sec in iso- 
thermal vfater. The average meter reading under 
all sea conditions approaches the accuracy of the 
electronic equipment or about 0.3^. Indications 
are that the 2-foot meter will perform better 
under nonisothermal conditions, but it has not 
yet been tested. 

The accuracy obtained by these meters is 
sufficient for many applications, especially at 
depths where isothermal water is found. The 
"zero calibration" and the nonfouling feature 
makes them ideally suited to long-term installa- 
tions. Their directivity indicates the flow 
direction. Work is proceeding to improve oper- 
ation under inhomogeneous conditions. 



ACKHOt'flLEDGMEMT 

The contributions of 0. J. Allen to the 
development of the two-foot flow meter are grate- 
fully acknowledged. 

(a part of this work was done under 
Contract WOrd I8783) 



204 



CURRENT MEASUREMENTS FROM MOORED BUOYS 

by WILLIAM S. RICHARDSON 
Woods Hole Oceanographic Institution 
Woods Hole, Massachusetts 



The history of the direct measurement of 
currents in the deep water of the open ocean is 
a rather short one. Indirect methods based on 
the distribution of various chemical and physi- 
cal properties provide us with a general picture 
of the deep circulation and calculations based 
on the distribution of density provide quantita- 
tive data which it would be desirable to check 
by direct measurement. 

Many techniques for direct current measure- 
ment have been proposed but few have been used 
to any great extent. Perhaps the most powerful 
and widely used has been the Swallow float. 
This technique, developed by Dr. John C. Swallow 
of the National Institute of Oceanography, 
utilizes a neutrally buoyant drifter which can 
be adjusted to drift at any desired depth. The 
float is tracked acoustically from a ship and 
may be followed for a period of days or even 
weeks. This technique in the hands of Swallow, 
Volkmann, Knauss and others has given us our 
first glimpse of the details of the movement of 
the deep water and has contributed greatly to 
our knowledge of several major current systems. 
Deep water measurements by this technique in 
areas well removed from major current systems 
have shown the currents to be swifter and more 
variable than had been expected. This points 
to the necessity for longer time series of 
current measurements over more extended areas 
than are easily undertaken with Swallow floats. 
To provide such measurements, a program of 
current observations from anchored buoys has 
been undertaken and as an initial effort a line 
of stations between Martha's Vineyard and 
Benmida has been set. (see Figure 1) 

The stations themselves are rather simple. 
The surface float is a foam filled fiberglass 
doughnut eight feet in diameter with a three f 
foot hole. It has about 6000 pounds of buoyancy 
which is sufficient to part the mooring warp 
if the mooring strain builds up excessively. 
The float carries a ten foot high tripod tower 
on which is mounted a light, a low powered 
radio beacon for location purposes and a 
recorder for wind speed and direction. The 
float is connected to the warp by means of a 
3 point, 45° bridle and a 30 foot leader of 
1/2 inch galvanized chain. The warp itself is 
polypropylene rope about 1/2 inch in diameter 
and having a breaking strength of about 5000 
pounds. The rope is somewhat positively buoy- 
ant in water and therefore contributes no dead 
weight strain to the moor. It will stretch 
about 407. before breaking and this permits the 



mooring to be set with little or no scope, 
this being provided by stretch as required. 
The warp is provided in 500 meter lengths 
with eyes spliced in each end; instruments 
are inserted as links between the lengths and 
must be capable of supporting the full tensile 
load of the warp. They can therefore be located 
at any 500 meter multiple in depth or at other 
depths if special lengths are made up. The 
bottom end of the deepest length of the warp 
is connected to a weak link having a strength 
of about 4000 pounds. This link should part 
during recovery of the mooring if the anchor 
is fouled. The ground tackle consists of a 
cast iron clump weighing 800 pounds followed 
by 200 feet of 1/2 inch chain (600 pounds) 
and a 90 pound Danforth anchor. 

Because the mooring warp is ordinary rope 
there is no electrical connection between the 
various instruments and the surface float. 
Therefore each instrument must be designed 
to record internally and the mooring must be 
pulled in order to retrieve the records. In- 
dividual instruments are designed to provide 
about four months recording so recovery three 
or four times per year should suffice if the 
stations last well. The Bermuda line, if fully 
in place, involves about 150 instruments of 
various types, current meters, wind recorders, 
inclinometers, depth recorders and tension 
recorders. Each of these is capable of storing 
about 10,000 readings of the variable being 
measured. This leads to an ultimate data re- 
duction problem with a potential load of 
1,500,000 readings, most of which involve more 
than one measurement, i.e. a current measure- 
ment is both speed and direction and the direc- 
tional measurement is made up of two parts, the 
orientation of the instrument in the earth's 
magnetic field (compass) and the relative 
direction of the current as detected by a vane. 
Because of this potentially large data reduc- 
tion problem the recordings in each instrument 
are made in a digital format on photographic 
film. The film can then be scanned photo- 
electrically and the data buffered to a com- 
puting machine for processing. Photographic 
film was selected as the recording medium 
because many parallel data channels are re- 
quired and power consumption is less for this 
type of recording than for magnetic tape or 
other media. 

As an example of the instrumentation we 
may consider the current meter. This is shown 
in Figure 4. The instrument is cylindrically 



205 




78° 77° 76° 75° 74° 73° 72° 71° 70° 69° 68° 67° 66° 65° 64° 63° 

■"Igure 1 The buoy line. 



SURFACE 



1000 



2000 



3000 



4000 



5000 



6000 




IOO:l 



Figure 2 Section of the buoy line. 

206 







.-ANEMOMETER 
r WIND DIRECTION 
- RECORDER 




A BUOY STATION SHOWING 
TYPICAL INSTRUMENTATION 




-j CHAIN 
-TENSION 

f POLYPROPYLENE 
IN 500 M SHOTS 

CURRENT METER 



f POLYPROPYLENE 
CORROSIBLE LINK 
WEAK LINK 
POLYPROPYLENE (50' ) 



^ i CHAIN (200 ) 

901b DANFORTH 

Figute 3 Mooring syile 





Figure 4 Current meter. 



rii 




207 



16 mm film 
stop 

f oto 



otor 1 

tort / read — , j 



Figure 5 Formot of current meter. 




Figure 6 Hurricane tracks. 



208 



symmetrical and does not require orientation 
into the current. Current direction is sensed 
by a vane in the upper cage which will orient 
to within 10° of the current direction at .01 
knot. The vane carries a magnet which couples 
through the end cap of the pressure case to a 
jewel bearing mounted magnet and seven level 
gray binary encoding disc. When a light is 
flashed behind this disc the light passing 
through the seven channels is "piped" to the 
field of view of the camera by small plexiglas 
light guides where it appears as seven spots 
on the film, either present or not present de- 
pending upon the orientation of the vane rela- 
tive to the pressure case. A similar seven 
level gray binary number is obtained at the 
same time from a compass mechanism which also 
carries an encoding disc. This encodes the 
magnetic orientation of the instrument as a 
whole and the difference between the vane and 
compass readings is the direction of the 
current. These seven level binary numbers give 
directions individually accurate to about 2 1/2 
or current direction to 5° when they are sub- 
tracted. The current speed is sensed by a 
Savonius rotor the bearings of which permit it 
to start rotating at speeds of less than .01 
knot. The rotor is also magnetically coupled 
through its end cap to a jewel bearing mounted 
light chopper which provides one pulse of light 
for each rotation of the rotor. This pulse is 
"piped" to the field of view of the camera by 
a fiber optics light guide. The film is ad- 
vanced at a slow uniform rate by the camera 
motor (1/8 inch per minute) and the rotor 
pulses appear as a succession of spots on the 
film which can be counted photoelectrically . 
An illustration of the film format is shown in 
Figure 5. 



was to be a serious problem. Stations I and J 
(the remaining Gulf Stream stations) were opera- 
tive for several weeks but were not found when 
the line was visited for recovery of records 
in late July. The surface float of station I, 
together with the upper-most current meter, was 
recovered by a freighter in October but was set 
adrift again without retaining the instrtiment. 
Thus a good set of Gulf Stream current measure- 
ments is still drifting around in the ocean. 
The surface float from station J has never been 
reported. Stations A, B, C, D, E, F, K, L and 
M have been maintained with reasonable success 
from May or June until late September. The 
visitations of Hurricanes Esther and Frances, 
the tracks of which are shown in Figure 6, 
caused considerable difficulty. The deep 
stations at D, E, F, K, L, and M which were 
in place at the time of the storms have sur- 
vived with only damage to their towers. The 
shallow stations A, B and C however, are now 
adrift, although it appears that C was on 
station some ten days after the passage of 
Frances. 

To suDiBiarize, we have been quite success- 
ful with deep stations except those in the 
Gulf Stream where we have had no success at 
all. The shallow stations (less than 100 
fathoms) have been reasonably successful 
during the summer months but have fallen 
victim to the fall storms. 

At the time of this writing the work of 
data reduction has just begun. Hopefully we 
will be able to report on this in the near 
future. 



Tests of the mooring system were made in 
1500 fathoms off Bermuda during December and 
January 1960-61. Tension measurements were 
made which showed a maximum during this period 
of about 800 pounds under heavy storm conditions 
and a typical tension of 100 to 300 pounds. It 
thus appeared the design was reasonably con- 
servative for a moderate current environment 
and the instruments required for the line as 
shown in section in figure 2 were constructed 
during the spring of 1961. Stations A, R, C 
and D (Figure 1) were set in early May. Fail- 
ures of the shallow stations A, R and C occurred 
after a week or two and this was traced to 
failure of the bails on the current meters 
caused by vibration. This fault was corrected 
and the rest of the line was set in early June. 
Station H failed and was recovered on a chance 
encounter of the surface float with R/V ATLANTIS. 
Failure was attributed to stress corrosion of 
the tie rods of the upper-most current meter, 
possibly caused by overstressing during assembly, 
and the entire moor was lost. Station G failed 
a few weeks later for the same reason, although 
evidence for this mode of failure was not avail- 
able soon enough to allow realization that this 



209 



DEEP CURRENT MEASUREMENTS NEAR BERMUDA 

by RAYMOND F. McALLISTER 



INTRODUCTION. 
It has been customary for years to iieasure 
deep ocean currents indirectly^ deducing them from 
dynamic topography. hore recently the jog-log^ para- 
chute drogues and neutral density floats, along with 
anchored buoy recording stations, have been used, 

All OF THESE METHODS SUFFER FROM THE SAME 
difficulty: they filter out high FREQUENCY FLUCTUA- 
TIONS IN CURRENT SPEED AND DIRECTION, EITHER BY THE 
LONG TIME BETWEEN SUCCESSIVE RECORDINGS, BY MECHANICAL 
FILTERING DUE TO THE LONG CONNECTING LINE TO THE SUR- 
FACE, OR BY THE DIFFICULTY IN OBTAINING ACCURATE GEO- 
GRAPHIC LOCATION, This is not to say that these are 

NOT EXCELLENT METHODS OF MEASURING CURRENTS, BUT 
RATHER THAT THEY COULD NOT SATISFY THE OBJECTIVES OF 
THIS STUDY, FOR WHICH A CONTINUOUS RECORDING CURRENT 
METER WITH A HIGH SPEED OF RESPONSE TO CURRENT CHANGES 
WAS NEEDED, ThIS REPORT DETAILS THE METER DEVELOPED 
AND SOME OF THE INTERESTING RESULTS ACHIEVED, 



210 



THE METER. 
In 1960^ THE Office of Naval Research agreed 

TO SUPPORT THE CONSTRUCTION AND INSTALLATION OF A 
SERIES OF CABLE CONNECTED CURRENT METERS, DESIGNED TO 
GIVE CURRENT SPEED, AND ULTIMATELY DIRECTION, TO RE- 
CORDERS PLACED ON THEIR TeXAS ToWER RESEARCH PLATFORM 

ON Plantagenet Bank, Bermuda, This tower, called 
"Argus Island", is situated on the Bank, in 194 feet 
OF water, about 25 miles from Bermuda, Its location 
IS SHOWN IN Figure I, at the tip of the arrow. 

The first meters installed were Savonius Rotor 

SPEED UNITS AT 200 AND 500 FATHOMS, CONNECTED TO ArGUS 

Island by a two conductor plastic insulated cable with 
sea return and a three conductor double armored cable 
respectively, power was provided from the surface to 
light a grain of wheat bulb with near infinite life 

AT RATED VOLTAGE, ThE SPEED SIGNAL WAS GENERATED WHEN 

the light from the bulb, falling on a photosensitive 
device, was interrupted by a segmented skirt on the 
Savonius RotoRo This is, in essence, the photo electric 

PICKOFF developed IN Wl, RiCHARDSOn's LAB AT WHOI , A 
CLEAR "go-no-go" SIGNAL RESULTED, WHICH WAS EXTREMELY 
DEPENDABLE AND READABLE EVEN THROUGH A HIGH LEVEL OF 
ELECTRONIC NOISE FROM THE RECORDER OR CABLE, 



211 




LOCATION OF METERS 



APPROACHES TO BERMUDA ISLANDS 



HO.- 5723 



Figure I. BERHUDA,. Associated Banks and the Location 

OF Argus Island c 



212 



subsequentlyy a unit was placed on top of 
Plantagenet Dank at a depth of 21 fathoms, and later 
yet another was installed at 500 fathoms, but in a 

DIFFERENT LOCATION ON THE FLANK OF THE BANK. AlL OF 

these units j and a later one which measured relative 
direction, were floated 50 feet off bottom to get away, 
if possible, from near bottom effects, figure 2 shows 
the location of the various units, and figure 3 the 
current meter. installed on bottom. 

Flantagenet Bank shows a large magnetic anomaly, 

AND magnetic direction SENSING DEVICES WERE ELIMINATED 
AS POSSIBILITIES FOR DETERMING CURRENT DIRECTION IN 
THE AREA. A RELATIVE DIRECTION MEASURING DEVICE, CON- 
SISTING OF A CONTINUOUS ROTATING POTENTIOMETER WITH A 
VERY LONG LIFE EXPECTANCY, WAS BUILT. IHE POTENTIOMETER 
IS CONNECTED TO A VANE WHICH HAS NEAR NEUTRAL BUOYANCY, 
AND IS RUN UPSIDE SOWN IN LIGHT OIL. A SMALL TIMING 
MOTOR AT THE INSTRUMENT END OF THE CABLE PROGRAMS THE 
SPEED AND RELATIVE DIRECTION UNITS, IF DESIRED, AND 
SENDS A ZERO AND oOO° CALIBRATION MARK UP THE CABLE AT 
REGULAR INTERVALS. FiGURE 4: SHOWS BOTH SPEED AND DI- 
RECTION UNITS BUILT FOR DISPLAY PURPOSES, WhEN THE 
RELATIVE DIRECTION UNIT IS USED, THE WHOLE PACKAGE IS 
MOUNTED AT THE TOP OF A 3/8" SOLID STEEL ROD TO PREVENT 
ROTATION WITH RESPECT TO THE BOTTOM. 



213 




Figure 2. Location of 5 Current Meters on the Flanks 

OF Plantacenet Bank. 



214 



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FjavRS i, Sp£2:> 



■:tz 'J'-'SLT roR DisPl>*x. 



215 



RESULTS. 
Thus far six meters rave been installed and 

HAVE GIVEN RECORDS FOR SOME TIME, CnE FAILED AFTER 
SEVERAL DAYS J BY DEVELOPMENT OF A SHORT UNDER 2000 FMS 
OF WATERj AFTER R.ETURNING A SHORT SEQUENCE OF CURRENT 

SPEEDS. The 750 fm unit was intended to give speed 

AND DIRECTION^ BUT THE SPEED SENSOR FAILED TO OPERATE 
AND ONLY RELATIVE DIRECTION WAS OBTAINED, ThE REC0P,D 
CEASED WHEN AN ATTEMPT WAS MADE TO RECOVER THE INSTRU- 
MENT FOR REPAIR, The REST OF THE UNITS GAVE SPEED 
SIGNALS FOR PERIODS UP TO TWO MONTHS j AND ALL FAILED 
BY CABLE BREAKS AT THE ArGUS IsLAND END EXCEPT THE 
21 FM UNIT WHICH, PREDICTABLY, FOULED AFTER ABOUT TWO 
WEEKS OF OPERATION, It IS INTERESTING TO NOTE THAT 

one of the cables was probably broken by a migrating 
humpback whale at the point where it extended from the 
tower to the sea-floor in a big catenary, 

On this same Bank, one inch steel buoy chain 
has parted on a number of occasions during storms, and 
expanded mesh platforms have been curled up and 

CARRIED AWAY BY STORMS, GaBLE TERMINATION HAS THERE- 
FORE PRESENTED A PROBLEM, BUT IN SPITE OF THE RELA- 
TIVELY SHORT CABLE LIFE OF THE SEVERAL UNITS, PROPER 
SHORE TERMINATION OF FUTURE CABLES IS EXPECTED TO IN- 
CREASE LIFE BY A FACTOR OF 10 OR MORE, 

216 



a typical speed record is shown in figure 5, 
at a tiiie when three heters were running simultaneously, 
Plots of a portion of the three unit record are shown 
IN Figure 6, and of the 750 fm direction signal in 
Figure 7. 

In general, current speeds at depths of 200 
and 500 fhs are fairly high, a haxi21um current of 
i»i6 knots was recorded at 200 fnsj with currents in 
excess of 0,75 knots relatively cohhon. spurt currents 
of up to 0,64: knots in one second have been observed 
at this depth, while currents below the heter threshold 

OCCUR AT OTHER TIMES, NeTER THRESHOLD IS ABOUT 0,04 
KNOTS, At 500 FHS THE MAXIMUM RECORDED CURRENT SPEED 

was 0,58 knots, although this did not occur at the 
time of year during which drogue measurements indicate 
the highest speeds at this depth, reference to 
Figure 6 will show that no ready correlation exists 
between the 21, 200 and 500 fm records, longer records 
are equally inconclusive in this respect, currents 
reported from the short lived 2000 fm meter ranged up 
to 0,13 knots, with this meter 30 feet off the bottom 
for easier handling of the unit, 

Current directions from the 750 fh unit show a 
fantastic change in azimuth with time, figure 7 shows 

CHANGES OF 50^ IN 30 SEC, 80° IN 60 SEC, 130 IN 4r MIN, 

180° IN 8-1/2 MIN, AND 360° IN 77 MIN, Other portions 

217 









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Figure 5, "Hot Pen Paper Record of 3 Cupment Speed I'.'eters 

k'OR KIN G S I?r UL TA NE OUSLY, 



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Figure 6, 15 Hour Plot of Current :^peeds at Three Depths 
IN Plantagenet Bank Area. 



219 






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OF THE RECORD SHOW 40 IN 4 SECj AND IIO'^ IN 30 SEC, 

220° IN 50 SEC, AND 180'^ IN 4 NiN, These results, 

COUPLED WITH THE SPURT CURRENT SPEEDS AND WITH SOME 
RESULTS OBTAINED IN EARLIER YEARS WITH THE PARACHUTE 

DROGUES, HAKE ONE SUSPECT THE PRESENCE OF EDDIES AND 
GENERAL TURBULENCE IN THE LEE OF THE BaNK, AND PERHAPS 
ALSO IN THE LEE OF RIDGES AND PROJECTIONS ON THE FLANK 

OF THE Bank, It is planned to place a group of three 

HETERS at accurately KNOWN SPACING, ROUGHLY IN A 

triangle, with the objective of measuring scale and 
duration of the eddies, 

Maurice Blaik, at Hudson Laboratories of Co- 
lumbia University, is studying turbulence in the sea, 

AND HAS run A SPECTRAL DENSITY ANALYSIS OF ONE 72 HOUR 
RECORD, He finds a SERIES OF PERIODICITIES RANGING 
FROM li CYCLES PER DAY (cPd), AND A RATHER STRONG 
2 CPD, TO A VERY WEAK 26 CPD, WITHOUT CURRENT DIREC- 
TION, SOME OF THE CYCLIC INFORMATION MAY BE UNDECIPHER- 
ABLE, SINCE THE METER REACTS TO ALL CURRENTS IN A 
HORIZONTAL PLANE, BOTH FORWARD AND BACKWARD, HiS 
FINDINGS, ADMITTEDLY BASED UPON A SHORT SAMPLE AND 
NECESSARILY TENTATIVE, ARE AS FOLLOWS: 



221 



Peak frequencies :- cycles/day at 200 fm 500 fm 

li 2 

7i 

9 
12 

14 i 14 

18 

20 20 

26 26 

Mo INTERPRETATION OF THIS DATA IS ATTEHPTED, 

It is FELT THAT THE PROGRAM OF CABLE CONNECTED 
CURRENT METERS AND OTHER SENSORS IS A PROMISING ONE AND 
FURTHER WORK WILL BE DONE TO IMPROVE IT, SeRIAL SAMPLING 
OF SEVERAL SENSORS AND TRANSMISSION OF THE DATA ALONG 
A SINGLE CONDUCTOR AND SEA WATER GROUND IS POSSIBLE 
V/ITH THE PRESENT STATE OF THE ART, AS IS SIMULTANEOUS 
TRANSMISSION OF SEVERAL FREQUENCY SEPARATED SENSOR 
OUTPUTS. It is expected that THIS PROGRAM WILL CON- 
TINUE AND BE EXPANDED, 



222 



SEA STATE - EFFECTS AND PROBLEMS 

by LEE iVl. HUNT, Technical Assistant 
Committee on Undersea Warfare 
National Academy of Sciences 
Washington, D. C. 



ABSTRACT 



Sea state exerts a greater overall effect 
on the Navy and merchant marines than any 
other single environmental factor. This paper, 
in order to emphasize this point, discusses the 
effect of wave height on background noise and 
surface reverberation which imposes limita- 
tions on sonar and radar effectiveness, and 
its effect on ship speed and ship damage. Wave 
forecasting, wave height observations, and the 
sea state code are also discussed from the 
standpoint of present practice and needed im- 
provements. 



INTRODUCTION 



Since man first went down to the sea in 
ships, or canoes for that matter, his worst 
enemy has been heavy seas. What astronom- 
ical value figure could we attach to the vessels 
lost and damaged by this age old enemy -- how 
many thousands of lives have been lost to its 
whim? We will never know, but some insight 
is gained by considering the fact that during 
the latter phases of World War II this enemy 
did more damage to our Pacific Fleet than did 
the Japanese. In one encounter off the 
Philippines in December 1944, 3 destroyers 
(HULL, SPENCE, MONAGHAN), 200 aircraft, 
and 790 men were lost. Twenty-eight ships 
were damaged, and 9 so badly that they re- 
quired major overhauls. Admiral Nemitz 
called this, "The greatest loss that we have 
taken in the Pacific without compensatory re- 
turn since the First Battle of Savo. " 



The "battle of the interface", however, 
has not been entirely one-sided. Man has 
made some progress beginning with Maury's 
sailing charts which, among other things, re- 
duced the average sailing time between London 
and San Francisco by 47 days. Sverdrup and 
Munk developed the wave and surf forecasting 
technique by which countless lives were saved 
during the amphibious landings of World War 
II. More recently, Pierson, Neumann, and 
James formulated the Wave Spectrum Method 
of wave forecasting used in the Navy's Ship 
Routing Program through which the average 
sailing time for Atlantic crossings has been 
reduced by 1 day and that of the Pacific by 5 
days. In addition, it has resulted in a drastic 
reduction in ship and cargo damage due to 
heavy seas. Backing up wave forecasting has 
been the indispensable progress in meteorology 
which provides the basic imputs to the wave 
forecasting machinery. 

The interface battle, however, is no 
longer concerned only with the loss of ships 
and lives in the direct sense. The battle be- 
came multifronted with the introduction of the 
submarine as an efficient and highly effective 
weapon during World War I. Its performance 
in sinking nearly 5 percent of the total British 
shipping during a single month (April 1917), and 
accounting for 69 percent of the 21, 000, 000 
gross tons of Allied shipping lost to enemy 
action during World War II has clearly made 
it a weapon to be countered. But countering 
must be preceded by detection, and for this we 



"Superior numbers refer to similarly numbered references at the end of this paper. 



223 



depend primarily upon sound about which it 
has often been said, "the only thing constant 
about sound in the sea is its variability. " 

Since sea water is virtually opaque to 
electromagnetic waves, we can expect sound 
to continue to be the cornerstone of our de- 
tection systems for some time to come. We 
do and will continue to depend upon it not only 
for the detection of submarines by hull mount- 
ed, towed, and bottomed systems, but as the 
sensing element in homing torpedoes, in the 
location of mines, and to provide the guidance 
by which future submarines will maneuver 
through the mountains and valleys of the ocean 
bottom. We can expect, then, that the evolu- 
tion in sonar systems will continue towards 
greater sensitivity and range. One of the 
greatest stumbling blocks in the path of this 
evolution is the environment through which 
sound must propagate, and, not the least of 
the parameters involved is sea state. 

The following discussion is designed to 
review the most important effects of sea state 
on naval and merchant marine operations and 
to point out some of the present and future 
problems. Some areas of the discussion will, 
of necessity, be limited either by classifica- 
tion or the lack of adequate data. 



THEORY OF OPERATION 



EFFECTS 

Ambient Nois e 

The "composite noise from all sources 
in a given environment excluding the desired 
signal and noise inlierent in the measuring 
equipment and platform" "* may be considered 
ambient noise. Although there are many 
sources of this noise ranging from the thermal 
agitation of water molecules to biological and 
man-made noise, the dominant noise, under 
open-sea deep-water conditions, orginates at 
the sea surface and increases with increasing 
sea state. Its importance to the Navy lies in 
the fact that as sonar systems and platforms 



are made quieter it may provide the limiting 
noise background in which a signal must be 
detected. Indeed, under proper conditions 
it serves this purpose now. 

During World War II deep-water ambient 
noise was studied extensively and the results 
of many wartime measurements have been 
summarized in the form of the well-known 
"Knudsen" curves showing the spectrum of 
deep-water noise and its dependence on sea 
state. 5 These curves, reproduced in Fig. 1 
are still accepted as representative of average 
ambient noise levels in the frequency range 1 - 
25 kc. Over this range the curves indicate a 
noise level increase of about 25 db as sea 
state increases from to 6, with a similar 
increase at a given sea state as the frequency 
decreases from 25 to 1 kc. More recent inves- 
tigations have shown that thermal noise poses 
an absolute limit to the Knudsen curves at about 

n 

50 kc , and that at frequencies below 500 cps 
the values deviate somewhat from the extra- 
polated Knudsen curves. 

It is worth emphasizing that the Knudsen 
curves represent the gross averages of many 
measurements made at the various sea states. 
No distinction is made between sea and swell 
nor do the curves indicate the stage of develop- 
ment or decay of the waves under which the 
measurements were made. It is possible that 
the correlation between wave height and am- 
bient noise is such that sea state can be deter- 
mined by measuring the noise level. Far more 
detailed measurements with respect to sea 
conditions will have to be made, however, 
before this can be demonstrated. Regardless 
of this application, the unrelenting war on 
background levels alone requires a better 
distinction between ambient noise levels and 
sea conditions. 

Although the correlation between ambient 
noise level and sea state has been well dem- 
onstrated, the method by which the noise is 
produced at the surface is little understood. 
It has been suggested that such things as 
breaking waves or white caps, bubbles bursting 
at the surface after being entrained by breaking 



224 




(jUJO/BNAQ I -\3U 8a) n3A31 WrUdl33dS 



225 



waves, the pressure effect of capillary wave 
trains, or atmospheric turbulence created by 
wind over tlie -roughened water surface may be 
responsible. Certainly, the first two of these 
produce some noise, but these conditions do 
not become prevalent until about sea state 3. 
Fig. 1 shows that of the 25 db increase in 
spectrum level between sea state and 6, 19 db 
of this occurs between sea state and 3, and 
10 db between sea state and 1 with the maxi- 
mum significant wave height being 4 feet and 
1/3 foot respectively. This indicates that the 
greatest portion of the noise increase must be 
explained by factors other than breaking waves 
and bubbles entrained by such waves. 

The declining increment in noise level 
above sea state 3 itself may be due to the 
filtering effect of a shallow bubble layer which 
scatters the sound back to the surface thereby 
preventing a large portion of it from reaching 
the hydrophone. 

While ambient noise can be produced by 
fluctuations in hydrostatic pressure, it is 
doubtful that capillary waves contain enough 
energy to account for much of the observed 
noise. Wind, on the other hand, certainly 
possesses enough energy and may play a 
significant role in sound production, but more 
investigation is needed before this can be de- 
termined. 

As sonar systems become more sophis- 
ticated, high ambient noise levels will become 
increasingly bothersome unless discriminated 
against or operated around. Too, since the 
noise is virtually independent of depth, sonar 
systems designed to escape surface reverber- 
ation, adverse thermal conditions, and platform 
noise will still have to contend with ambient 
noise. The Knudsen curves coupled with wave 
forecasts will make it possible to do a passable 
job of forecasting ambient noise levels under 
deep-water conditions. Forecast accuracy 
cannot be improved, however, without a more 
detailed knowledge of noise level with respect 
to sea conditions. 



Surface R everberation 

Reverberation in underwater sound is the 
sound scattered back towards the source by 
various inhomogeneities of the environment. 
It is customarily designated surface, volume, 
or bottom reverberation depending upon the 
source of the scatterers. The irregularities 
of the surface and bottom are primarily re- 
sponsible for the reverberation originating at 
these two surfaces, while biological organisms, 
particulate matter, and possibly turbulent and 
thermal microstructures are considered re- 
sponsible for volume reverberation. 

With observed increases in surface back- 
scattering strength of around 28 to 30 db at 
wind speed as low as 18 knots, providing a 
level of about-26 db for low grazing angles and 
considerably greater for high angles (see Fig. 
2), the importance of surface reverberation to 
the Navy is obvious. In deep water it will often 
provide the limiting noise level, a fact that, as 
in the case of ambient noise, can only become 
more serious as the noise from other sources 
is reduced. 

Although there can be little doubt that 
surface reverberation is caused by surface and 
near-surface irregularities, and increases 
with increasing sea state, the data from most 
investigations have been more easily correlated 
with wind speed than with sea state. Since the 
wind can only influence surface reverberation 
through its effect on the sea surface the reason 
for this better correlation with wind speed may 
be due to one or more of the following: (1) the 
lesser accuracy to which sea state is usually 
measured as compared to wind speed; (2) the 
present lack of accurate correlation between 
bubble density and sea state; (3) very high 
frequency waves are a more rigid function of 
wind speed than of sea state; and/or, (4) the 
mere determination of the significant wave 
height does not, by itself, give any idea of the 
stage of development of the wave spectrum. 



226 





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Fig. 2, which results from tests conduct- 
ed by the Ordnance Research Laboratory 
(University of Pennsylvania) °, and the Applied 
Physics Laboratory (University of Washington) 
off Key West, Florida, and Dabob Bay near 
Seattle, shows the effect of wind speed and 
grazing angle on surface backscattering 
strength. Surface reverberation is little 
affected by frequency, but, as shown, it is 
strongly dependent upon grazing angle and more 
strongly so at low wind speeds when the grazing 
angle is high. Although not shown on the curves, 
volume reverberation probably provides the 
dominant noise at very low grazing angles 
which indicates that surface reverberation, 
for most sound pathes, is troublesome only 
at relatively short ranges. 

Q 

Hoover and Urick have offered an ex- 
planation for the shape of the curves in Fig. 2. 
The flatness of the curves at low grazing angles 
is thought to be due to a near surface scattering 
layer, possibly bubbles, which was observed 
during the ORL tests when the wind speed ex- 
ceeded 10 knots. It might be added here that 
this scattering layer was not observed during 
the APL tests in Dabob Bay. The gradual rise 
at intermediate grazing angles is thought to be 
due to actual surface roughness such as ripples 
and wavelets, whereas, at higher angles 
(greater than 70 degrees) some sort of specular 
reflector is indicated. This is due, possibly, 
to small wave facets oriented normal to the 
sound beam. 

An interesting feature of the curves 
shown in Fig. 2 is that, in the APL tests, 
a plateau occurs at a wind speed of 14 knots 
with no further increase in backscattering 
strengthto the 30 knot limit of the test. The 
ORL curves do not show this plateau eve n at 
17. 5 knots, but the increase in backscattering 
strength over the 2. 5 knot increment falls 
off with increasing wind speed indicating that 
it may be approaching a plateau. World War 
II 24 kc data using a grazing angle of 3 degrees 
shows a plateau at a wind speed of 23 knots 



(see inset. Fig. 2) which lends support to this 
idea. The difference in the wind speeds at 

which the World War II and the APL rever- 
beration levels reach a plateau may be due, 
at least in part, to the fact that Dabob Bay is 
almost completely surrounded by mountains 
limiting the wind to either a 5 or a 25 mile 
fetch. Six inch waves under a 20 knot wind 
have been observed in the Bay indicating a 
considerable departure from open sea con- 
ditions. 

The reason for this plateau may be due 
to the fact that the amount of small scale 
roughness that can be superimposed on a 
wave form of given dimensions is finite, and 
in fully developed seas at higher and higher 
wind speeds the tendency is towards longer 
period waves. In other words, as seen by a 
sound beam, the number of surfaces oriented 
normal to it reaches a point of diminishing 
return as wind speed or sea state increases 
beyond a given point. In any event, it is 
important that the position of this plateau be 
firmly established under open sea conditions 
and the reason for its existence determined. 

Much of the effect of surface reverber- 
ation can be circumvented by divorcing the 
sonar system or sound path from the surface, 
but hull mounted systems and active acoustic 
homing torpedoes must continue to face this 
background noise problem at short ranges. As 
in the case of ambient noise, backscattering 
levels can be forecast through a prior know- 
ledge of wind speeds or sea state, but with 
considerably less accuracy. An adequate 
correlation with sea state has not been made, 
extensive measurements in sea states greater 
than 3 have not been taken, and the scatterers 
responsible for the various portions of the 
curve have not been clearly identified. 

Hydrodynamic Noise 

The noise produced directly or indirectly 
by the motion of a ship through the water is 



228 



classified as hydrodynamic noise. It is pro- 
duced by cavitation and turbulence about the 
hull, bubbles striking the sonar dome, wave 
slap, and quenching. The noise level depends 
upon hull design, sonar dome design and lo- 
cation, and heading with respect to the sea. 
Its intensity increases with increasing ship 
speed and sea state. 

Under sea state conditions the noise 
produced by flow about the dome and hull 
would be the major source of hydrodynamic 
noise, but rolling and pitching caused by 
higher seas bring the other sources into play. 
Cavitation is produced by violent motion of 
the bow, while bubbles, either trapped or 
created by bow motion, cause crashing 
sounds when they strike the sonar dome. 
The sound produced by waves striking the side 
of the ship is obvious even at low speeds, and 
quenching occurs when the bow and sonar dome 
clear the water during severe pitching. Each 
of these sources cause periodic noise, and 
under proper conditions they may make 
listening impossible a large percentage of 
the time. 

Little unclassified information on hydro- 
dynamic noise levels as a function of ship 
speed and sea state exists, nor is it even 
adequately known. It is sufficient here, 
however, to say that as ship speed and sea 
state increase, hydrodynamic noise rapidly 
becomes the dominant source of undesirable 
background noise considerably exceeding sea 
state 6 ambient noise at relatively high fre- 
quencies. It can be, and has been to some 
extent, reduced by streamlining the sonar 
dome and other protrusions and by hull de- 
signs which improve the ship's seakeeping 
capabilities. In spite of this, however, the 
operation of hull mounted sonar at high speeds, 
especially in high seas, can only be accom- 
plished at the expense of detection ranges such 
that it is of questionable value in the vicinity 
of sea state 6. 



As in the case of the other noise sources 
discussed, a prior knowledge of wave con- 
ditions to be encountered will allow avoidance 
of unfavorable conditions or time for tactical 
changes for the best utilization of ships and 
systems under adverse sea and sound condi- 
tions. 

Radar 

In the detection of snorkeling of sur- 
faced submarines, airborne radar has the 
advantage of providing precise range and 
bearing values as well as a high search rate. 
In a manner similar to that of the surface 
backscattering of acoustical energy, electro- 
magnetic energy is also backscattered by a 
rough sea surface. ^^ In a phenomena known 
as "sea clutter" transmitted energy is re- 
flected back to the radar from waves causing 
a bright spot in the center of the PPI scope, 
the extent of which increases with antenna 



altitude and sea state. 



12 



Unlike the backscattering of sound from 
the sea surface, the returned electromagnetic 
energy is dependent upon the relative bearing 
and direction of the reflecting waves with 
reception being better when looking in the 
direction of wave propagation. If sound 
experiences this effect the results are 
obscured by continual fluctuations in 
intensity. Fig. 3 shows the effect of sea 
state and look-direction on the blip-scan 
ratio of an AN/APS-15a radar at an altitude 
of 500 feet. As indicated, the effectiveness 
of airborne radar is considerably restricted 
by state 3 seas, and of dubious value at sea 
state 4. Some improvement has been made 
through the introduction of the doppler 
principle, but sea state is still a major 
deterrent to the use of airborne radar for 
surfaced submarine detection, as well as 
for detecting submarine snorkles or periscopes. 



229 



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S hip Spee d 



The fact that surface vessels have not 
undergone the same degree of evolution in 
speed as have various other means of trans- 
portation does not detract from the consid- 
erable economic and military importance of 
greater speed to the Navy and merchant 
marines. A part of the reason for this slow 
evolution is that although the speed of any 
ship is basically dependant upon its design 
characteristics, it is further limited by 
such factors as currents, winds, and most 
important of all, by sea state which serves 
to reduce speed through the following effects: 
(1) added resistance due to wave reflection, 
especially in short waves; (2) rolling; (3) 
pitching; (4) indirect effect of added re- 
sistance to propulsion; (5) propeller racing; 
and (6) voluntary reduction in speed to ease 
severe motion of the ship. 

It is difficult to correlate the speed of a 
given ship with sea state. For one thing, 
the period of the waves and the frequency 
of encounter must be considered along with 
wave height. Too, the degree of voluntary 
reduction in speed varies with captains and 
conditions. Voluntary speed reduction. 



especially in merchant vessels, is an im- 
portant factor as indicated in Fig. 4 which 
shows the reduction in speed computed from 
drag alone, and the average voluntary re- 
duction experienced by a number of merchant 
ships transiting the North Atlantic. ^^ The 
computed reduction due to drag at the upper 
limit of sea state 6 was 14 percent, whereas, 
the actual reduction amounted to 56 percent 
of the sea state speed. 

As a result of many actual measurements, 
James '■■^ has been able to construct ship speed 
versus wave height curves for several mer- 
chant ship classes. These curves give average 
speed reduction values for head, beam, and 
following seas and are presently being used 
to construct Least Time Tracks in the Navy's 
Ship Routing Program. Table 1, taken from 
these curves, shows the effect of head and 
following seas of various heights on the 
speed of several classes of merchant ships. 
Of interest here is the fact that following 
seas also cause a consideration reduction 
in speed. 



TABLE 1. THE EFFECT OF WAVE HEIGHT AND HEADING ON SHIP SPEED 





SHIP TYPE 


Wave 


T5-S-12A 


T2-SE-A2 


T2-SE-A1 


VC2-AP3 


VC2-AP2 


Ci-M 
- Al/1 


P2-S2 
- R2 


LSD 


Ht. 




SHIP SPEED (in knots) AND HEADING 








(feet) 


H- F* 


H F 


H F 


H F 


H F 


H F 


H F 


H F 





18.5 18.5 


16.0 16.0 


14.5 14.5 


17.1 17.1 


16.0 16.0 


10.5 10.5 


19.3 19.3 


12.3 12.3 


10 


17.5 18.5 


15.1 15.8 


13.6 14.5 


15.9 17.3 


14.2 15.8 


9.0 10.4 


18.0 197V 


11,2 12.1 


20 


14.1 17.0 


12.7 14.4 


10.8 13.4 


11.1 15.5 


9.0 13.8 


5.2 8.1 


13.8 12.5 


7.8 9.9 


30 


11.0 15.4 


10.8 13.0 


8.5 12.0 


7.4 13.4 


5.9 11 .5 1 3.3 5.7| 9.8 15.8 


4.9 7.8 



H - Head Seas, F - Following Seas 



231 



Figure 4. Effect of Sea State on Ship Speed, Difference in Two Curves Due to 
Voluntary Reduction in Speed. (Victory Ship, North Atlantic - 
Adopted from Fig, 7.2, Ref. 13 .) 



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35 



232 



Ship Damage 



Extensive cost studies on ship damage due 
to heavy seas are virtually non-existant. For 
the most part, the problem has been covered 
by such statements as, "Throughout the war 
(WW II) the cost and time lost in the repair of 
ships damaged by heavy seas were as great as 
for battle damage." No doubt this estimate 

is in the right ballpark, and as such it presents 
the startling fact that we financed two equally 
expensive naval wars - the "shooting" war and 
the "interface" war. Even worse is the fact 
that the latter has never ceased. Of the 32,358 
power vessels of over 500 gross tons register- 
ed with the various governments of the world 
at the beginning of 1954, some 1,021 suffered 
heavy weather damage, 20 foundered and were 

a complete loss, and another 976 were strand- 

15 
ed during the year. 

Townsend , in a detailed study of for- 
ward bottom damage resulting froin slamming 
in heavy seas to 141 American Flag vessels 
over a 26 month period, found that the total 
repair cost amounted to $3, 084, 905 averaging 
$21, 879 per vessel, and requiring a total of 
581 days of repair. These figures represent 
only physical repair and do not reflect the 
cost of the vessel during repair or loss of 
earnings. It should also be emphasized that 
only the damage to shell plating and internal 
members in the forward bottom of the ship 
were considered. Any damage which may 
have been experienced by the rest of the ship, 
either due to slamming or to green water on 
the deck, is not included. 

Of some interest, in the context of this 
paper, is the fact that 56 percent of above 
damage occurred in the North Atlantic, 15 
percent in the North Pacific, 10 percent in 
the Western Atlantic, and 7 percent in the 
North East Pacific. Only 12 percent of the 
ships were damaged in the other parts of the 
world's oceans. Of course, a part of this is 
due to the position of the main trade routes 
rather than the geographical incident of 
heavy seas. 



Since sea state cannot be controlled, the 
cost resulting from ship and cargo damage 
as well as fuel consumption can only be re- 
duced through better hull designs and ship 
routing. The Navy, realizing this, is using 
its Ship Routing Program, which was 
originally designed to reduce the cost 
of MSTS vessel operation, to route an 
increasing number of various fleet units, 
including submarines. The Program, 
developed by the Hydrographic Office and 
operated by the Navy since 1958, has made 
some 163 7 individual routings (not to be con- 
fused with the number of ships routed) as of 
March 1961. As stated in the Introduction, 
this service has resulted in an appreciable 
transit time reduction by providing optimum 
routing through existing sea conditions. Re- 
liable figures for the reduction in ship and 
cargo damage resulting from this program 
do not exist, although various estimates 
indicate a significant reduction. Private 
shipping lines which, in their present heavily 
subsidized economic plight, can ill afford 
unnecessary damage and operating cost, have 
made only token use of this service although 
it is offered by several private concerns. 

WAVE HEIGHT OBSERVATIONS 
AND FORECASTING 

Th e Sea State Code 

The term sea state, as generally used, 
may be defined as the average height of the 
highest one-third of the waves observed in 
a wave train referred to a numerical code 
which covers an increasing range of such 
heights (see Table II). As shown in Table 
III the code may also be applied to swell con- 
ditions, but used alone, as it usually is, it 
makes no distinction between sea and swell. 
In addition the code gives no idea of the 
stage of development or decay of the wave 
spectrum, nor does it allude to the distri- 
bution of periods. 



233 



Table II - STATE OF SEA - WIND WAVES 
(WMO Code 75) 



Code 


Description 


Height(feet) 





Calm - glassy 





1 


Calm - ripples 


- 1/3 


2 


Smooth - wavelets 


1/3 - 1 2/3 


3 


Slight 


12/3-4 


4 


Moderate 


4-8 


5 


Rough 


8 - 13 


6 


Very rough 


13 - 20 


7 


High 


20 - 30 


8 


Very high 


30 - 45 


9 


Phenomenal 


over 45 



NOTE: The exact bounding height is to be assigned 
to the lower code figure, that is, a height of 
4 feet is coded as 3. 



Table III - SWELL CONDITION CODE 



Code 


Height in feet 


Description 


Approximate 
length in feet 





- no swell 







1 
2 


( 1 to 6 - low swell 

' 6 to 12 - moderate 


i Short or average 

( Long 


to 600 
Above 600 


3 


/ Short 


to 300 


4 


Average 

' Long 


300 to 600 


5 


, Greater than 12 - high 

Confused 


Above 600 


6 


i Short 


to 300 


7 


1 Average 


300 to 600 


8 


1 "'=i='S= 

' Long 


Above 600 


9 















There was a time when a general know- 
ledge of the height of the higher waves was 
sufficient for all practical purposes. This is 
no longer the case. Acoustical research has 
indicated that it is desirable to know the sig- 
nificant wave height to within plus or minus 
10 percent. Even if the wave height is 
measured to this accuracy its value is lost 



if it is coded as, say, sea state 6 which 
covers a 7 foot range of height. It also 
is becoming increasingly obvious that 
the high frequency waves in the spectrum 
may be as important in the generation 
and reflection of sound as the lower fre- 
quency waves with their greater height. 
Because of this, some idea of the shape 



234 



of the frequency spectrum will be needed to 
forecast background noise levels as soon as 
these levels have been adequately correlated 
with detailed sea conditions. 

The needs of the naval architect are also 
beginning to be felt. The seakeeping char- 
acteristics of the old as well as the newer 
more advanced ship designs are dependent 
upon wave period as well as height so that 
in order to forecast ship speed and motion 
both should be known. 

The present code evolved to fill a need, 
but the need has increased such that another 
evolutionary step is required. The Wave 
Forecasting Program responding, in part, 
to this reports significant wave heights. 
Even this, however, is not sufficient for all 
needs. For the sake of brevity as well as com- 
pleteness of information a new code is needed 
which clearly distinguishes between sea and 
swell, indicates the period about which the 
maximum spectral energy is concentrated, 
and covers a more practical increment of 
wave heights. The latter is especially needed 
over the range from 2 to 20 feet. 

Wave Height Observa tions 

Wave heights are presently being deter- 
mined with varying degrees of accuracy by 
bottomed pressure elements, upward looking 
fathometers, buoy housed accellerometers, 
various mechanical and electrical devices, 
and visual observation. By far the greatest 
number of day to day observations are made 
by the latter method. They are made from 
merchant vessels, naval vessels, weather 
ships, and oceanographic research vessels 
from which the observers height above the sea 
varies from 6 to 60 feet. This factor alone 
introduces a tendancy for observers close to 
the sea to exaggerate wave heights, and those 
higher above the sea to underestimate them. 



In addition to this source of error 
is the fact that the resulting average of 
the wave heights observed is computed 
from individual observations ranging in 
number from to, hopefully, 50. Where 
the greatest number of reports fall within 
this range is left to the readers imagina- 
tion. It has been stated that "at least 
fifty wave heights (estimates) are needed 
before any confidence can be place in the 
computed average wave height." '-'* For 
instance, on the basis of 9 observations 
from which the significant wave height is 
computed to be 14. 2 feet all that can be 
said theoretically is that the true value 
lies somewhere between 11.0 feet and 
19. 8 feet, or a possible error of 28 percent. 
Nearly three times greater than the desired 
error for acoustical purposes. On the basis 
of 50 observations, however, the true value 
would theoretically lie between 12. 6 feet and 
15. 9 feet, or a possible error of 10 percent 
which places it within the desired acoustical 
error range. 

It is obvious that wave height obser- 
vations must be instrumented if the desired 
accuracy is to be achieved. The need for 
wave recorders on mobile platforms such 
as ships and planes is continually increas- 
ing. This need will be partially filled by 
the shipboard wave recorder now being 
developed for the Hydrographic Office. 
Whether it will provide the accuracy needed 
for acoustical work is yet to be seen. 

Wave Forecasting 

Twenty-four hour wave forecasts are 
issued daily by Fleet Weather Central in 
Suitland, Maryland and Honolulu, Hawaii, 
as well as the Fleet Weather Facilities in 
charge of ship routing at Norfolk, Virginia 
and Alameda, California. The service is 
also provided by several private concerns on 



235 



a commerical basis. Wave heights are fore- 
cast, as previously stated, by the Wave 
Spectrum Method developed by Pierson, 
Neumann, and James in 1955. The meteoro- 
logical inputs to the method are supplied by 
synoptic data and the 5 day weather forecast 
maps of the Northern Hemisphere issued 
every Monday, Wednesday and Friday by the 
Extended Forecast Section of the Weather 
Bureau, 

The observational network which supplies 
the data for the overlapping 5 day forecasts, 
in addition to continental and island based 
stations, is made up of 10 weather ships in the 
North Atlantic (positioned between 35 and 68 
degrees north latitude), and 3 in the Pacific. 
Augmenting the observations made by these 
stations are those made by naval, coast guard, 
and merchant vessels. The data from these 
sources are, of course, variable both in space 
and time. As a general practice, for instance, 
aircraft carriers report weather observations 
every 6 hours, destroyers every 12 hours, and 
merchant vessels every 24 hours. 

On an average day there is an estimated 
4000 ships at sea in the Atlantic area. Con- 
sidering the fact that weather forecasting over 
the ocean is considered to be simplier than 
over land this coverage, at first glance, would 
seem to be more than adequate. Most of this 
niunber, however, is made up of merchant 
vessels, only a small percentage of which 
make regular weather observations. This, 
coupled with the fact that ships tend to con- 
centrate along well defined trade routes, con- 
siderably reduces the potential number and 
distribution of mobile weather stations. A 
further restriction on the number of weather 
reports fed to the forecast centers is imposed 
by communication delays. Of the overall total 
of about 10, 000 weather observation stations 
in the Northern Hemisphere that could report, 
an average of only 3000 are received. ° The 
end result is that weather maps must occa- 
sionally be extrapolated over considerable 



areas having insufficient data. It should 
also be mentioned that the sea based 
observational network, inadequate now 
from the standpoint of optimum distri- 
bution, will deteriorate rapidly under war 
conditions. 

Very little data is readily available 
on the forecast accuracy of the present 
program. James reported early in 
the development of the program that a 
comparison of the forecast and observed 
wave heights at some 50 grid points across 
the North Atlantic during winter months 
showed that 85 percent of the forecast 
wave heights were within plus or minus 
4 feet of the observed heights. Since many 
of the waves measured were 25 feet and 
greater in height this was considered an 
acceptable error at the time. An un- 
published average error estimate of plus 
or minus 21 per cent has been expressed by ■ 
one of the forecast units. Either of these 
errors would have to be reduced by approx- 
imately 50 percent in order to provide the 
accuracy desired for the prediction of those 
sound conditions depending upon the state 
of the sea. Some researchers believe that 
a 90 percent accuracy can be achieved , 
but much work will be required before this 
goal is reached. 

A significant increase in the present 
forecast accuracy will require effort on 
several fronts. Weather forecasts can, 
at best, be only as accurate as the data 
upon which they are based. It goes without 
saying that, due to the human factor in- 
volved and such easily corrected things as 
the lack of anamometers on many of the 
reporting merchant vessels, improvements 
can be made in data acquisition. Even with 
adequate and accurate data, however, our 
present level of understanding of the basic 
meteorological and oceanographic forces 
involved is not such that perfect forecasts 
could be made. 



236 



The accuracy of the Wave Spectrum 
Method of forecasting itself is a matter of 
controversy between its authors and users 
and those of the several other methods in use 
here and in other countries. With regard to 
the differences between these various methods 
it has been said, "One would almost question 
whether the different authors were working 
on the same planet with the same weather 
conditions". In order to resolve the differ- 

ences in these forecast methods a rigidly con- 
trolled comparison test will have to be con- 
ducted in an area such as the North Atlantic 
where variable sea conditions are available 
and the weather and wave height observations 
are reasonably adequate. 

The brightest hope for more accurate 
wave forecasts is NANWEP (Navy Numerical 
Weather Problems Group), a computer approach 
to atmospheric and oceanographic forecasting 
now evolving at the Navy Post Graduate School 
in Monterey, California. With all its automatic 
data processing equipment operating this system 
can, by making 300 million computations, pro- 
duce a complete pressure pattern forecast in 
40 minutes. From this forecast the NANWEP 
computer can forecast wind direction and 
velocity and from this the wave heights. 



CONCLUSION S 

The following conclusions are drawn 
from the foregoing discussion: 

1. Undesirable noise resulting from 
the interaction between acoustical energy, 
electromagnetic energy or the platform 
with the sea surface is sufficiently corre- 
latable with sea conditions that it is possible 
to forecast their levels provided the state 

of the sea is known. 

2. The accuracy with which this can 
be done at present is not sufficient. A better 
correlation is needed between background 
noise and surface reverberation, and the 
state of the sea. 

3. The value of routing, both from 
the standpoint of ship speed and ship damage, 
has been demonstrated such that non-military 
vessels are justified in availing themselves 
of this service to a greater extent. 

4. The benefits to be derived from a 
greater accuracy in wave forecasts are such 
that an intensified effort to improve them is 
clearly warranted. 



The automation of data processing in 
weather and wave forecasting is a big step 
forward, but the full potential of this step 
will not be realized until data acquisition is 
equally automated. It seems inevitable that 
meteorological and oceanographic observa- 
tions for forecasting purposes will eventually 
be made by stationary and adequately spaced 
instrumented buoys. Towards this end a 
technical and economic feasibility study con- 
ducted in the near future would not, in the 
author's opinion, be premature. 



237 



REFERENCES 



1. "Geophysics and Warfare", Landsberg, 
Helmut E. , Research and Development 
Coordination, Committee on General Science, 
Office of the- Assistant Secretary of Defense, 
Research and Development, March, 1954, 

p. 30. 

2. "United States Destroyer Operations in 
World War II", Roscoe, Theodore, US 
Naval Institute, Annapolis, Maryland, 1953, 
pp. 448-452. 

3. "Der Seebrieg", Ruge, Friedrich, Vice 
Admiral (Navy of the German Federal 
Republic), US Naval Institute, Annapolis, 
Maryland, 1957. 

4. "Supplementary Definitions for Underwater 
Acoustical Terminology", Subcommittee on 
Underwater Noise Standards, BuShips Noise 
and Shock Panel, BuShips, INST. 3985.1, 
August 1952. 

5. "A Survey Report on Basic Problems of 
Underwater Acoustics Research", Panel on 
Underwater Acoustics, Committee on 
Undersea Warfare, National Research 
Council, 1950. 

6. "The Thermal Noise Limit to the Detection 
of Acoustical Signals In Water", Mellen, 
R. H, , US Navy Underwater Sound Lab. , 
Tech. Memo. D161d, Ser. No. 946-45, 
March 12, 1951. 

7. "Some Notes on Ambient Noise From Sur- 
face Disturbances", Rhian, Elliot, Memo 
to FF Koczy, Univ. of Miami, July 1,1960. 

8. "The Back Scattering of Sound From The 
Sea Surface: Its Measurement, Causes, 
and Application to the Prediction of 
Reverberation Levels", Urick, R. J., and 
Hoover, R.M., J. Acoust. Soc. of Amer. , 
Vol. 28, No. 6, Nov. 1956. 

9. "Measurement of the Back Scattering of 
Underwater Sound from the Sea Surface", 
Garrison, G.R., Murphy, S.R. 

and Potter, D.S., J. Acoust. 
Soc. Am., Vol. 32, No. 1, 
Jan. 1960 



10. "Limitation of Echo Ranges by Rever- 
beration (Deep Water)", UCDWR File 
Report M361, File No. 01.90, Sept. 1945. 

11. "Sea Clutter in Radar and Sonar", Hoover, 
R.M., and Urick, R. J., IRE Convention 
Record, Vol. 5, Part 9, 1957. 

12. "Search and Screening", Operation 
Evaluation Group, Office of the Chief 
of Naval Operations, Rpt. No. 56, 1946 
pp. 62-74. 

13. "Application of Wave Forecasts to 
Marine Navigation", James, Richard W., 
US Navy Hydrographic Office, Spec. 
Pub. No. SP-1, July 1957, pp. 20, 32 

14. "Practical Methods for Observing and 
Forecasting Ocean Waves by Means of 
Wave Spectra and Statistics", US Navy 
Hydrographic Office, HO Pub. No. 603, 
1955, pp. 223, 152. 

15. "Collision at Sea", Sharpley-Schafer, 
J.M., J. of the Inst, of Navigation, 
Vol. 8, No. 3, 1955. 

16. "Some Observations on the Shape of Ship 
Forebodies with Relation to Heavy 
Weather", Townsend, H.S., Paper pre- 
sented at the April 28, I960 meeting of 
the Society of Naval Architects and 
Marine Engineers. 

17. "The Environment and Undersea Warfare", 
forthcoming report by the Panel on 
Environment and Undersea Warfare, 
Committee on Undersea Warfare, National 
Academy of Sciences. 

18. "NANWEP; Weather by the Numbers", 
Underwater Eng. Vol. 1, No. 3, Nov. 15, 
1960. 

19. "Known and Unknown Properties of the 
Frequency Spectrum of a Wind Generated 
Sea", Pierson, Willard J. , Jr., and 
Neumann, Gerhard, Paper presented 

at the Conference on Ocean Wave Spectra, 
Easton, Maryland, May 1961. 



238 



ABSTRACT 



THE BATHYPAGE 

by DR. A. A. MILLS 

Assistant Professor, Institute of Oceanography 

Dalhousie University 

Halifax, Nova Scotia 



A design study for an apparatus to 
obtain living specimens of the bathypela- 
gic fauna. 



IMTRODUCTIOM A^D PREVIOUS WORK 

It has for long been recognised that 
possession and maintenance of living speci- 
mens of the bathypelagic fauna would greatly 
aid investigation of orientation, sensiti- 
vity to light, sound production, biolumine- 
scence, and other characteristics of these 
little-known inhaliitants of the deep sea. 

So far, most investigators have fol- 
lowed methods originated on the 'Challenger' 
'Blake '"^ and 'Michael Sars'3 expeditions, 
using bottom and mid-water trawl nets. 
Although improvements in the construction 
and use of this equipment have been made, 
^j5,o examination of the literature dis- 
closes few attempts to devise alternative 
or supplementary methods for collection of 
pelagic organisms other than the plankton 
ij°>°. The researches of H.S.H. Prince 
Albert I of Monaco on the new, and some- 
times gigantic, squid and cuttlefish found 
in the stomach of the sperm-whale are well 



known 



10 



la 



less familiar is his use of large, 
baited traps ("nasse") and submarine elec- 
tric lamps, to obtain specimens from below 
1000 metre'^!*"'*Quite recently, ISAACS and 
SCHICK have successfully attached similar 
traps to deep-sea free instrument vehicles 

Cameras '-^ and television have been 
used to record underwater life, and marine 
biologists have themselves descended in 
bathysphere^ or bathyscaphe-^ 'j-'-"j -'■9 to 
observe and photograph the indigenous 
faxina20-23. Attempts to use baited hooks 
or a wire trap to capture specimens seen . 
fpom these vehicles were unsuccessful ''' 

Thus, the only living examples of the 



2U 



bathypelagic fauna which have been studied 
under laboratory conditions are:- 

i) Species able to rise naturally to the 
surface; often at night -", or during 
some stage of their life-cycle26_ 

ii) Those cast up by natural phenomena ' 

iii) Representatives of certain species which 
have survived trawling from deep water 
16,26,28,29,30 



It is generally believed that the abrupt change 
in temperature, together with abrasion in the 
net, is of more importance than the decrease 
in hydrostatic pressure in causing the heavy 
mortality associated with deep-sea trawling 
lo,2o,31,32_ However, this hypothesis may 
need qualification in view of W. B. MARSHALL'S 
recent identification of well-developed swim- 
bladders in many genera of deep-sea fish^">^^. 
It appears that the swimbladder is absent in 
those bathypelagic forms centred below the 
1000 m level, but is present in many species 
above this depth, and re-occtirs in numerous 
benthic species fotmd near the sea-floor far 
below^'*. 

There is, therefore, a need for apparatus 
which will enable living specimens of the 
bathypelagic fauna to be captured and recovered 
without injury^-', and with minimum disturbance 
of their normal environment. This requirenent 
has been recognized for many years'^"'-'"^ j^^^^ 
little appears to have been achieved. 



The Bathypage 

This paper reviews some possible methods 
for the realisation of such apparatus, which 
would appear to be best met by development 
of the trap, rather than the net, concept. 
The name 'bathypage' is proposed for the 



"Superior numbers refer to similarly numbered references at the end of this paper". 



239 



device, from the Greekpaflvj- deep, and 
TToy''7- a snare oT trap. 



Size 

The first point to be considered is size. 
HAJ-iDY-^-'- warns us against imagining that the 
rather frightening pictures sometimes repro- 
duced (without accompanying scale.') in the 
'popular' press represent creatures of 
enormous size. In fact, most of the captured 
specimens average 2-3 inches in length, niea- 
surements of 10-12 inches and above being 
exceptional. On the other hand, BEEBE with 
his bathysphere-'-"'^^, and later observers in 
the bathyscaphes, consistently report much 
larger creatures - 10 feet or more in length 
^'^. It would seem that the larger fish and 
invertebrates have sufficient power and 
agility to evade the relatively cumbrous and 
slow-moving deep-sea nets. 

Direct observations have also tended to 
refute other long-established conventions 
concerning life in the deep sea; such as its 
supposed scarcity37, decreasing abundance 
with depth, and inactivity^"; ^°' 20, 29,31. 
This should be remembered when designing 
apparatus for use in this region. 

It would therefore seem best to build 
the trap as large as can be conveniently 
handled by the available research vessel. 



Thermal Insulation and Flotation 

The need for some form of thermal insu- 
lation of the contents of the trap has 
already been mentioned. Obviously, those 
substances normally employed for this purpose 
would rapidly become saturated and ineffi- 
cient unless enclosed in a pressure-resistant 
housing. A material which does appear most 
suitable for this application is gasoline 
gelled with 'Wapalm'58)39. Prevention of 
convection currents reduces the thermal 
conductivity of this material'-iO to approxi- 
mately 3 X 10-^ cal.sec."^ cm"-"- per degree 
- comparable with the conductivities of 
cork, cloth and firebrick, and about three 



times that of glass wool^ . As it is thixo- 
tropic and capable of flo'tr''^ the gel may be 
exposed to the hydrostatic pressure. 

Besides being inexpensive, another advan- 
tage of this gel is that its low specific 
gravity (ca-0.7) enables the insulating jacket 
to act as a float. Other greases and waxes 
(e.g. petrolatum) may bear a closer resemblance 
to the blubber of the whale, but are denser 
(S.G. ca 0.9) and cannot be gelled in situ in 
the cold. These and various microcrystalline 
waxes, polythene, etc. may be applicable where 
the apparent weight is not critical. 



Pressure Resistance 

So far, then, the apparatus is concei-ved 
as a fairly large chamber, constituting the 
live trap proper, surrounded by gelled gasoline 
to provide thermal insulation and flotation. 
To preserve the original hydrostatic pressure 
necessitates an excessively thick and heavy 
chamber if alloy steel be employed, but there 
is some possibility that filament-wound glass 
f ibre-and-plastic vessels might serve above 
hadal depths. In the exploratory models it 
is proposed to allow water to escape through a 
valve to equalise pressures. Provided the rate 
of ascent is sufficiently slow, those species 
with well-developed swimbladders might be able 
to resorb sufficient gas to avoid permanent 
injury. 



Luminous Lures and Bait 

If the apparatus is to fulfil its inten- 
ded purpose within a reasonable period of time, 
it is presumably advisable to employ some form 
of lure or bait. The vicious circle resulting 
from the paucity of our knowledge of the habits 
and responses of these creatures can only be 
broken by an empirical choice of technique, 
based on the fragmentary observations which 
have been made of those fish surviving for up 
to thirty-six hours^^. L-uminescence being one 
of the most obvious characteristics of the 
deep-sea fauna, it must surely serve some pur- 
pose in attraction of mates or prey. BEEBE^3 
records that a Pacific myctophid (lantern-fish) 
reacted to the intermittent exposure of a lumi- 
nous wrist watch, but was unaffected by the 



much stronger beam of a flashlight. RARSHALL 



26 



240 



mentions the use of natural luminous bait 
by fishermen, and describes the flashes of 
coloured light emitted by different species 
of deep-sea angler fish (Ceratioidea). Thus 
it would seem that a low intensity source of 
light (perhaps greenish or bluish)"^" is 
indicated, and that intermittent operation 
might be beneficial. JERIXiV'S^'^ demonstra- 
tion of the transparency of deep oceanic 
waters means that even a faint light would 
be visible from a considerable distance. 



radar reflector and flashing light would 
facilitate recovery. 

An alternative method might be considered 
when the bathypage is to be used off an ocea- 
nic island such as Bermuda. Where deep water 
is available within a few miles of shore, and 
a fairly continuous watch could be maintained, 
closing of the trap could be arranged to 
operate the weight release mechanism. 



It is proposed to try both fish muscle 
inoculated with luminous bacteria ( Photo - 
bacterium f ischeri ) and plastic phosphors 
for this purpose. 



Triggering Mechanism 

The trap may be designed to close on 
contact with the bait, by means of a simple 
mechanical linkage'''5 to spring-loaded lucite 
doors. This tripping mechanism could be 
made quite delicate if a soluble plug or 



magnesium link" 



,6, U6 



were arranged to act as 



a 'safety catch' during descent. The lucite 
doors should have opaque covers to protect 
the catch against the possible adverse 
effects of sunlight. 



Laying and Recovery 

Suspension of the apparatus by means 
of a wire or nylon^'^ cable attached to a 
vessel (or buoy) at the surface suffers 
from many obvious disadvantages, although 
it has some merit for initial trials. 

It is preferable that the device should 
descend freely and rise automatically. For 
sampling the fauna within, say, 1000 feet 
of the bottom, it is a simple matter to 
weigh down the buoyant trap with a sinker 
attached to an appropriate length of cable. 
Sampling the mid-water life is more diffi- 
cult, but it is hoped that the addition of 
a cluster of sealed aluminum tubes to the 
bathypage will enable it to become neutrally 
buoyant at a predetermined depth in the 
manner of the Swallow float'io. 

In either of the above methods, corro- 
sion of a magnesium link"'^" or the opera- 
tion of a clockwork mechanism", would 
release the trap after a known time. A 



Conclusions 

It is believed that there is a need for 
alternative apparatus complementing the deep- 
sea trawl in the investigation of the bathy- 
pelagic fauna. This should be free of the 
disadvantages of the net, Eind enable the 
collection of living, undamaged specimens for 
laboratory study. Such an apparatus appears 
technically feasible. 



REFEREMCES 

1. Thomson, C. Wyville, "The Voyage of the 

'Challenger'. The Atlar.tic. " Harper 
Brothers, New York, I878, Vol. 1, pp. 
68-70. 

2. Agassiz, A., "Three Cruises of the 'Blake'". 
Sampson Low, London, I888. Vol. 1, p. 26. 



3. 



Murray, J . , 
the Ocean. ' 
pp. 36-51. 



and Hjort, J., "The Depths of 
Macmillan, London, 1912, 



U. Kemp, S. and Hardy, A. C, 'Discovery' 
Investigations. Objects, Equipment, and 
Methods. 'Discovery' Reports , 1929, 
_1 lUl. 

5. Kullenberg, B., The Technique of Trawling, 
in Bruun, A. et al . , "The Galathea Deep 
Sea Expedition, 1950-1952". Allen and 
Unwin, London, 1956, pp. 112-118. 

6. Isaacs, J. D., and Kidd, L. W., University 
of California, Scripps Institution of 
Oceanography., Oceanographic Equipment 
Report, 1953, Wo. 1, S.IO. 

7. Sverdrup, H. U., Johnson, M. W. , and 
Fleming, R. H. "The Oceans. Their 
Physics, Chemistry and General Biology". 
Prentice-Hall, W. J., 19li2, pp. 376-385. 



241 



10. 

11. 

12. 
13. 

111. 

15. 

16. 

17. 
18. 

19. 
20. 
21. 

22. 

23. 

2U. 



Bames, H., "Oceanography and Marine 
Biology." Allen and Unwin, London, 1959, 
pp. l5-h6. 

Agassiz, A., "Three Cruises of the 'Blake'". 
Sampson Low, London, 1888. Vol. 1, p. 36. 

Herdman, W. A., "Founders of Oceanography 
and their Work." Arnold, London, 1923, 
pp. 119-133. 

Richard, J., "Les Carapagnes Scientif iques". 
Monaco, 1900. 



Richard, J., Bull, de L'Institut Oceano- 
qraphigue (Monaco) , 1910, Mo. 162. 

Johnstone, J., "Conditions of Life in the 
Sea." Cambridge Univ. Press, 1908. p. 2li. 

Isaacs, J. D. and Schick, G. B. , Deep-Sea 
Research , I960, J^, 61. 

Edgerton, H. E., Mat. Geoq. Mag ., 1955, 
107 , 523. 

Beebe, W. , "Half Mile Down". 2nd edition, 
Duell, Sloan and Pearce, Mew York, 195l- 

Piccard, A., "In Balloon and Bathyscaphe." 
Cassell, London, 1956. 

Houot, G., and Wi 11m, P., "Two Thousand 
Fathoms Down." Hamilton and Hart-Davis, 
London, 1955- 

Piccard, J. and Dietz, R. S. , "Seven Miles 
Down." Putnam, New York, I96I. 

Cousteau, J.-Y., Mat. Geog. Mag . , 195U, 
106 , 67. 

Peres, J. M. and Piccard, J., Bull, de 

L 'Institut Oceanographique (Monaco) , 1956, 

Mo. 1075. 

Peres, J. M., Piccard, J., and Ruivo, M., 
Bull, de L'Institut Oceanographicp-ie 
(Monaco), 1957, Mo. 1092. 

Fage, L. et al . , Resultats Scientif iques 
des Campagnes du Bathyscaphe F.M.R.S. III. 
Annales de L'Institut Oceanographigue 
(Paris), 1958, Vol. 35, Part U. 

, Houot, G. S., Mat. Geog. Mag ., 1958, 113 , 
715. 



25. Gibbs, R. H., Deep-Sea Research , 1957, 
h, 230. 

26. Marshall, N. B., "Aspects of Deep Sea 
Biology", Hutchinson, London, 195U. 

27. Zahl, P. A., Mat. Geog. Mag ., 1953, lOl; , 
579. 

28. Beebe, W. , Mat. Geog. Mag ., 1932, 61, 6U. 

29. Beebe, W., Proc. Mat. Acad. Sci . 1933, 19, 
178. 

30. Beebe, W., "Unseen Life of New York." 
Duell, Slcan and Pearce, Mew York, 1953, 
Chap. 13- 

31. Hardy, A. C, "The Open Sea. Part I, The 
World of Plankton." Collins, London, 1956. 

32. Colman, J. S., "The Sea and its Mysteries." 
Bell, London, 1958. 

33. Marshall, N. B. , "Swimbladder Structure of 
Deep Sea Fishes in Relation to their Sys- 
tematics and Biology." ' Discovery' 
Reports , I960, Vol. 31- 

3ii. Annual Report of the National Oceanographic 
Council (U.K.) 1959-60, p. 27. 

35. Eineiy, K. 0. , "The Sea off Southern Cali- 
fornia". Wiley, New York, I96O, p. 162. 

36. Pettersson, H., "The Ocean Floor". Yale 
Univ. Press, New Haven, 195h, p. I6I. 

37. Glinther, K. and Deckert, K. , "Creatures of 
the Deep Sea." Charles Scribner's Sons, 
New York, 1956, p. 81. 

38. Fieser, L. F., Harris, G. C, Hershberg, 
E. B., Morgana, M., Novello, F. C, and 
Putnam, S. T., Ind. Eng. Chem . , 19^6, 38, 
768. 

39. Rueggeberg, W. H. C, J . Phys. and Colloid 
Chem., 19ii8, 52, Ihhh- 

[jO. Langstroth, G. 0. and Zeiler, F. , Can. J . 
Research , 19li8, 26A, 50. 

111. Hodgman, C. D. Ed., "Handbook of Chemistry 
and Physics", l^lst ed. , Chemical Riobber 
Pub. Co., Cleveland, I96O, pp. 2ii36-2Uli3. 



242 



l42. Agoston, 0. A., Harte, W. H., Hottel, H. 
C, Klemm, W. A., Mysels, K. J., Pomeroy, 
H. H., and Thompson, J. M., Ind. Enq . 
Chem. , 1951i, ^6, 1017. 

U3. Beebe, W. and Vander Pyl, H., Zoologica , 
I9hh, 29 {2), 59. 

UU. Jerlov, N. G., Optical Studies of Ocean 
Waters. Rep, of the Swedish Deep-Sea 
Expedition , Goteborg, 1951, 3, 1. 

U5. Chitty, D. and Kempson, D. A., Ecology , 
19li9, 30, 536. 

U6. Van Dorn, W. G. University of California, 
Scripps Institution of Oceanography. 
Oceanographic Equipment Report Wo. 2, 
Ref. 53-23. 

hi- Edgerton, H. E., Cousteau, J.-Y., Brown, 
J. B., and Hartman, R. H. , Deep-Sea 
Research, 1957, h, 287. 

U8. Swallow, J. C, Deep-Sea Research , 1955, 
3, 7h. 



243 



AN EXTERNAL CORE-RETAINER 



by DR. A. A. MILLS 

Assistant Professor, Institute of Oceanography 

Dalhousie University 

Halifax, Nova Scotia 



DJTRODUCTIDM 

For many purposes involving detailed 
study of the sediment-water interface (e.g. 
microbiological examination) it is desirable 
to obtain short cores in which the uppermost 
layers are completely undisturbed. 

The corers most commonly employed with 
this intention!) 2,3 generally incorporate an 
internal core-retainer in which fingers of 
flexible metal or plastic are directed towards 
the axis of the coring tube. It has been 
found that such devices frequently agitate the 
top few centimetres of a loosely-packed or 
flocculent sediment, and also fail to retain 
sand or volcanic ash. 



APPARATUS 

This note describes a device which, by 
replacing the conventional retainer in the 
above corers, facilitates the collection of 
undisturbed samples from a variety of sedi- 
ments. Two models have been developed for use 
with deposits of varying consistency - one for 
stiffer sediments, the other for the more fluid 
silts or sands. 



REFEREMCES 

1. Emery, K. 0. and Dietz, R. S. (19Ul)- 
Gravity coring instrument and mechanics 
of sediment coring. Bull. Geol. Soc. 
Araer. 52, l685-nil(. 

2. Hvorslev, M. J . and Stetson, H. C. (19U6). 
Free-fall coring tube: a new type of 
gravity bottom sampler. Bull. Geol. Soc. 
Araer. 57, 935-950. 

3. Phleger, F. B. (195l)- Ecology of fora- 
minifera, northwest Gulf of Mexico. Geol . 
Soc. Amer. Mem . U6, 1-88. 



ACKNOWLEDGMEMT 

This device was constructed and used 
aboard Lamont Geological Observatory's re- 
search vessel 'Vema', and special thanks are 
due to Dr. C. L. Drake for helpful sugges- 
tions towards its design and practical appli- 
cation. 



The construction and mode of operation of 
this apparatus are shown in Figure 1. The 
corer is lowered in the open position A. Pene- 
tration in excess of a pre-determined length 
(6 in. has been found satisfactory) forces the 
collar upwards, allowing the supporting arm to 
spring free of the catch. Upon withdrawal from 
the sediment the sliding weight drives the 
retainer down the coring tube, over the bevelled 
edge of the cutting head, into the closed posi- 
tion B. When hauled inboard the corer is held 
vertically, the core-retainer carefully dis- 
placed, and a tightly-fitting cork disc pushed 
through the cutting head into the plastic liner. 
The latter, with the enclosed core, is then 
easily removed and sealed. 



244 







245 



SOME NEW MECHANICAL DEVICES FOR OCEANOGRAPHIC RESEARCH 

by SHALE J. NISKIN 
Institute of Marine Science 
University of Miami 
Miami, Florida 



ABSTRACT 

The areas of principal oceanographic 
interest to the Institute of Marine Science 
of the University of Miami are the Straits of 
Florida, the Bahama Banks, Florida Bay and the 
Caribbean. The field problems arising in these 
areas of research, coupled with the specific 
requirements of the various departments at the 
Institute, has prompted the development of 
several new oceanographic tools. Three simple, 
inexpensive mechanical devices are described 
in this paper: a stabilized oceanographic 
reference marker buoy; a sterile biological 
sampler; and a hydrographic wire slope and 
azimuth indicator. 



OCEANOGRAPHIC MARKER BUOY 
INTRODUCTION 



Intensive studies are conducted by the 
Department of Physical Oceanography of current 
patterns in the Florida Bay area (1. Koczy.F.F. 
et al., 1959). The movements of current drift 
drogues are plotted with ship's radar relative 
to moored reference markers equipped with 
radar reflectors. As the drogue drifts out of 
radar range of the reference marker, another 
such marker is launched and anchored, the 
original marker being recovered later. Employ- 
ing these methods, continuous tracking of 
drogues for extended periods of time has been 
made possible. 

THEORY OF OPERATION 

In order to assure maximum range and 
detection, the marker buoy mast supporting 
the radar reflector must possess a high degree 
of vertical stability. Because of the deli- 
cate construction of the radar reflector, the 
mast must be free from sudden and violent 
movements, regardless of the state of the sea. 
The markers should be relatively light in 
weight to facilitate launching and recovery. 
However, types of marker buoys available in 
the past have been either too cumbersome or 
have not offered the desired degree of 
vertical stability. 



DESIGN The reference marker buoy subsequently 
designed to satisfy the requirements discussed 
in the preceding paragraph consists of a 
ballasted mast, its metacenter located below 
the surface of the water and positioned at the 
center of a buoyant flexible ring by spokes 
radiating from the mast to the buoyant ring. 
Wave- induced movements of the buoyant ring are 
not transferred to the mast, excepting some 
degree of vertical acceleration, which is 
considerably dampened by the spokes and the 
flexible nature of the ring. A mooring line 
is attached to the buoyant ring and, therefore, 
has only slight effect on the stability of the 
mast. Because of its peripheral point of 
attachment, the mooring line is not likely to 
foul on the submerged portion of the mast. 

In detail, (see Fig. 1) the buoyant ring 
consists of a length of polyethylene pipe 
coiled into a ring seven or eight feet in 
diameter, its ends coupled together and 
sealed. Nylon spokes radiating from a metal 
hub which is milled to receive the mast are 
secured to the buoyant ring. These spoke 
lashings also hold the ring coils together. 
One-third of the mast length extends below the 
central hub. Ballast is secured to the mast 
heel. The mast is prevented from slipping 
through the hub by a taped serving, which is 
applied to the mast. To meet our specific 
requirements , a radar reflector was secured 
to the top of the mast. 



HYDROGRAPHIC WIRE SLOPE AND AZIMUTH INDICATOR 
INTRODUCTION 

Hydrographic wire configurations produced 
by a combination of the Gulf Stream current 
and vessel drift in the Straits of Florida 
tend to complicate hydrographic instrument 
positioning. The usual technique of employ- 
ing unprotected thermometers for determining 
instrument location has not proven adequate 
for the task. A knowledge of wire slope and 
set can be useful for defining location of 
instruments attached to the hydro-wire. 
Furthermore, this information may yield indi- 
cations of sub-surface currents and their 
direction. 



"Superior numbers refer to similarly numbered 
references at the end of this paper." 



246 



A detailed discussion concerning the 
significance of hydrographic wire angle and 
azimuth information has been provided by 
Carruthers (2. Carruthers et al., 1954). 

In a subsequent paper (3. Carruthers, 
1959) he has described an instrument for 
measuring wire angle and set. Due to various 
mechanical disadvantages of the Carruthers 
indicator its performance in the field proved 
to be somewhat unreliable. A new design 
approach was pursued, resulting in the devel- 
opment of a more efficient hydrographic wire 
slope and azimuth indicator. 



THEORY OF OPERATION 

In this new indicator, (Fig. 2) a verti- 
cally orienting and magnetic north-seeking 
unit of practically neutral buoyancy is housed 
spherically to allow the inner unit to pre- 
serve its northward and vertical orientation, 
regardless of the disposition of its housing. 
A float secured to one end of the inner mem- 
ber insures its vertical orientation, while 
magnetic needles attached to this unit cause 
it to seek magnetic north. The spherical 
shape of the inner member permits its being 
locked accurately, relative to the wire 
orientation. 

DESIGN The plastic hollow inner sphere is 
provided with a spherical glass float at its 
upper pole. Two magnetic needles are mounted 
along the horizontal axis of the inner sphere. 
Sufficient ballast to cause the inner sphere 
to approach neutral buoyancy in salt water is 
attached to its lower pole. A glass bead 
bearing is fixed to either pole of the inner 
sphere. The outer housing is composed of two 
flanged plexiglass hemispheres bolted to- 
gether through short plastic spacers placed 
between the flanges. This space is occupied 
by a pair of caliper clamps, each of which is 
pinned at one end and free to swing horizon- 
tally between the flanges. The unpinned 
clamp ends are bound together with elastic 
bands. Upon messenger impact a wedge spread- 
ing the clamp ends apart is removed, allowing 
the clamps to lock securely under elastic 
tension around the inner sphere. Both inner 
sphere and outer housing are free-flooding. 

The upper hemisphere of the outer housing 
is inscribed with latitudinal lines represent- 
ing the degrees of inclination. The inner 
sphere is marked around its equator with a 
compass rose; longitudinal lines pass through 
every 10 . Thus both wire slope and azimuth 
may be read directly. Due to the convergence 



of the longitudinal lines at the poles of the 
inner sphere, precise reading of azimuth becomes 
increasingly difficult with wire slopes of 7 
or less. Because the diameter of the inner 
sphere is slightly less than that of its 
spherical housing, slight horizontal displace- 
ment is possible. However, the caliper clamps 
are designed to correctly re-center the inner 
sphere if this displacement occurs. A framework 
supports the outer housing longitudinally and 
may be clamped to the hydro wire with a slotted 
bolt-and-wing nut arrangement. This framework 
contains the caliper clamp releasing wedge and 
plunger rod, as well as the messenger release 
mechanism, which consists of a short rod butted 
against the plunger rod and mounted on a compress- 
ion spring. 



STERILE BIOLOGICAL SAMPLER 



INTRODUCTION 

Investigations by the Department of 
Microbiology concerning the distribution and 
biology of salt water yeasts and fungi have 
given rise to a need for water samples of two 
liters or more which are free from micro- 
biological contamination from sources other than 
the point at which the samples are gathered. 
Available sterile samplers (4. ZoBell, 1946 and 
5. Sirokin, 1951) have had inherent depth and 
capacity limitations. 



THEORY OF OPERATION 

DESIGN The sampler subsequently designed 
operates on the principle of a bellows. (Fig. 3). 
A pliable air evacuated and sterilized container 
is fitted with a tape-sealed check valve and 
secured to a hinged framework by means of 
pockets attached to both sides of the pliable 
container. This framework consists of two 
fork-ended plates, hinged together, under- 
spring torsion. Upon messenger impact, a plunger 
rod is depressed simultaneously disengaging two 
levers which hold the plates together, thus 
permitting the hinged plates to swing apart. 
The lower lever also serves to remove the tape 
seal from the valve. The collapsed pliable 
container is thereby pulled open into its full 
3 dimensional configuration, and, in so doing, 
water is forced into the container. After 
equilibrium is achieved, no more water may 
either enter or escape from the container. 
The messenger release mechanism is activated by 
the plunger rod upon messenger impact. A small 
quantity of sterile salt water, initially intro- 
duced into the container facilitates valve 
action. 



247 




STABILIZED OCEANOGRAPHIC REFERENCE MARKER BOUY 



FIG. 2 




HYDRO WIRE SLOPE AND AZIMITH INDICATOR 



248 





DC 
Ijj 



< 
CO 

cr 

UJ 

< 



< 
o 

o 
o 

_l 
o 

CD 

UJ 
_J 

q: 

UJ 

I- 
cn 



^^:33i^St^ 




249 



The plastic containers are inexpensive 
enough to be considered disposable. Our micro- 
biological group is currently investigating 
the possible deleterious effects of various 
types of plastic material on the microorganisms 
in water samples. 



CONCLUSION 



The oceanographic reference marker buoy 
and wire slope and azimuth indicator are now 
generally used in our oceanographic survey 
work. Though it has not been used extensively 
at sea, the sterile biological sampler has 
been successfully tested. 



REFERENCES 



1. "The current patterns on the Tortugas 

Shrimp grounds". F. F. Koczy, et al.. 
Proceedings of the Gulf and Caribbean 
Fisheries Institute 12th annual session, 
November 1959 pages 112-125. 

2. "On instrumental measurement of the line 

shape under water. Concerning the 
determination of vertical distribution of 
slope (magnitude and direction) down 
oceangr. wire, and the measurement of 
current-caused obliquity of a rope strain- 
ed between an anchor and a sub- surface 
buoy." Carruthers, J. N., et. al., Dt . 
Hydrogr. Z 7 1954, page 22. 

3. "On instrumental measurement of hydro wire 

slope" Carruthers, J. N. Dtsh. Hydrogr. 
Z 12 1959, 167-171. 

4. "Marine microbiology" Zobell, C. E. pub- 

lished by Chronica Botanica Co., Waltham, 
Mass. 1946. 

5. "A sampler for the selection of samples 

of water for bacteriological analyses." 
Sorikin, I. Institute of Reservoir 
Biology Academy of Science, U.S.S.R, 
bulletin No. 6, 1960, pages 53-54. 



ACKNOWLEDGEMENT 

The development of these devices was 
supported in part by the Office of Naval 
Research, Contract No. 840(01), under the 
supervision of Dr. F. F. Koczy, Chairman of 
the Division of Physical Sciences, Institute 
of Marine Science, University of Miami. The 
aid and cooperation of the following staff 
members in the preparation of this paper are 
gratefully acknowledged: Dr. Koczy for his 
valuable advice and appraisal; Dr. Gene 
Rusnak for his corrections and comments; and 
Mr. M. Rinkel for his cooperation in the field 
tests of these devices. 



250 



USE OF THE PRECISION GRAPHIC RECORDER (PGR) IN OCEANOGRAPHY 

by S. T. KNOTT, Research Associate in Engineering 
Woods Hole Oceanographic Institution 
Woods Hole, Massachusetts 



ABSTRACT 

This paper briefly describes the Precision 
Graphic Recorder. How its timing and correla- 
tion capabilities are used for collecting acousti- 
cally derived data in bathymetry, seismic 
reflection and refraction profiling, instrument 
location, navigation and various biological 
studies is reviewed. 



INTRODUCTION 

The roots of the name "graphic recorder" 
are found in early bathymetric work, such as 
that of Veatch and Smith^, in the 1930's. The 
PGR , however, might better be described as 
an event correlation recorder, although its 
presentation is substantially the same as that 
of recorders in modern echo-sounders where 
a recording stylus repeatedly sweeps across 
a long narrow strip of sensitized paper. It is 
similar, also, to a delay-triggered "Z" axis 
modulated oscilloscope, but presents successive 
samples of time-related data side-by- side for 
visual correlation. Such a series of samples, 
each taken at a precise repetition rate on a 
common, accurate time-base, produces a 
graphic plot of the data as a succession of offset 
measurements in time. 

Prior to 1954 when Luskin et al"^ 
discussed the precision measurement of ocean 
depths, the geophysical research groups at the 
Woods Hole Oceanographic Institution and the 
Lament Geological Observatory had found 
commercially available echo- sounding recorders 
to be less precise than was required for their 
problems. Nor was there an adequate choice 
of recording resolution available in one 



instrument. Both laboratories decided to 
develop instruments, and a healthy scientific 
competition evolved. Lamont's instrument, 
the Precision Depth Recorder (PDR), was 
first in the field. It provides recording 
resolutions of about 25 and 50 milliseconds per 
inch for travel time measurement on a time 
base controlled to better than 1 part in 10^. 
Our recorder appeared about six months later. 
The group at Lamont Observatory conceived 
a reliable and moderately simple device for 
the measurement of ocean depths. Our record- 
er was somewhat more complicated because 
our objective was a multipurpose tool. Like 
the PDR, the PGR measures travel-times 
precisely and with predictable accuracy, but 
in addition it provides considerably higher 
resolution for a finer measure of time 
differences. From its twelve writing rates we 
obtain recording resolution from 3 milliseconds 
to 400 milliseconds per inch^. Some ten 
programing arrangements are available to 
gate the transmission and reception of signals. 
Its frequency response is flat from less than 
100 cycles to over 20 kilocycles per second, 
and its usefulness extends to beyond 80 kilo- 
cycles. Both research groups found facsimile 
recorders most useful; Lamont uses the Times 
Facsimile recorder, and we, the Alden. 

A tuning fork in the PGR establishes the 
time base. Its signal controls the synchronous 
drive of the sweep mechanism and programing 
switches. The sweep, generated by the inter- 
section of a rotating helix and a straight 
printing blade is sharply defined and rectilinear, 
with a timing accuracy of the order of the fork. 
Signals appear as a darkening on the paper 
between the helix and blade and must be 
rectified before recording because the marks 
are caused by an electrolytic deposition of 



Superior numbers refer to similarly numbered references at the end of this paper. 



251 



ferric ions from the printing blade. In general, 
full- wave rectification is used in studies where 
signal envelopes are to be correlated, and half- 
wave for effectively correlating wave forms 
within envelopes. Signal phase may be deter- 
mined by selecting either the positive or the 
negative excursions of the signal. Scale or 
timing lines generated directly from the fork 
signal serve two purposes, measurement and 
indication of recorder synchronization. 



USES: Bathymetry 

The first use of this recorder in 
bathymetry still remains an important part 
of its job. During research cruises, the 
PGR's are routinely put to this task 24 hours 
a day. Consider what information is to be 
gained from echo- sounding. Travel time is 
the most obvious and is now measured with 
great accuracy. For the most part, resolution 
of about 30 milliseconds per inch is adequate. 
This resolution presents a 200-fathom depth 
interval across eighteen inch paper. In 
addition to its obvious use in hydrographic 
charts, this accurate information has been 
used by physical oceanographers at Woods Hole 
to guide their Nansen bottle lowerings to within 
a few feet of the bottom. More recently, 
however, they have used the acoustic pinger 
technique described later. Mooring deep-sea 
buoys also requires this knowledge of depth, 
for in one method used here, moorings are 
cut to match the water depth. 

The PGR's fastest sweeps (< 10 milli- 
seconds per inch) are useful in the detection 
of subtle changes in travel time caused by 
gradual slopes found in the abyssal plains and 
elsewhere. The FOR can make these measure- 
ments because of the constancy of its timing. 
It is easily seen that cumulative sweep- time 
errors resulting from inconstant timing would 
raise havoc on a 50 -millisecond sweep when 
displaying travel times several seconds long. 

The high resolution of which the PGR 
is capable has led to the discovery of small 
rough features of the bottom and also to areas 
of sediment ponding^. The vertical dimensions 
of these features seen with sounders are 



relatively small. The in- the- water length of 
the pulse cannot be much greater than the 
dimensions of the features for the pulse alone 
will cause the detail we seek to be hidden. 

There is a part of the Blake Plateau, 
for instance, where, (see Fig. la and b) in 
spite of many crossings, several canyons and 
many peculiar bumps having only a few fathoms 
relief had not been detected with older sounders. 
These were discovered when we surveyed the 
area with a PGR, using resolution of less than 
30 milliseconds per inch and short pulses of 
less than one millisecondS. Some indications 
of these features can be found on the old records, 
but the changes in the travel times defining the 
features are of the same order or less than 
the expected errors of the older equipment. 

In the sediment ponds, where a long 
pulse hides, Fig. 2 (from Hersey"'), the 
existence of reflecting horizons below the sea- 
floor, the PGR controls pulse length to in-the- 
water dimensions which are hopefully less than 
twice the distance between the reflecting hori- 
zons. The structure of the echo- train reveals 
the presence of the horizons which is most 
important to display. Much of this work has 
been done with 0. 2 millisecond pulses. The 
PGR provides the bandwidth, 5000 cycles, 
necessary to permit these short pulses to 
pass to the recorder without distortion. 

Echoes' structures often change rapidly. 
Fig. 3, especially at ship's speeds of ten knots 
or more, yet the validity of these sub- sea- 
floor reflections depends upon the continuous 
correlation of particular returns over 
considerable distances. Strong correlation is 
obtained because the samples are taken closely 
enough in space and time so that substantially 
the same reflection recurs, because changes 
in transmission path geometry occurring 
between samples are less than the dimensions 
of the irregularities in the bottom, and because 
each of these samples is initiated on a precise 
time schedule. To achieve the necessary high 
sampling rate, we cannot wait to receive the 
echo from one pulse before sending another, 
but must have as many pulses as possible 
simultaneously in transit to and from the 
bottom. The PGR offers such a program. It 
is designed to have "windows" in the pulse 
schedule during which echoes may be received 



252 



uncluttered by the direct reception of the pulse 
and its reverberation. Programs are based 
upon a count of integral recorder sweeps. 
They require the sweep period to be several 
times less than the travel times in deep water. 

The reflecting horizons below the sea- 
floor are often the boundaries of lenses of 
differing materials; they may be pinched out 
at the sea floor and more ancient formations 
exposed. The PGR gives a permanent display 
of their echo structures, which may be used 
for later study or for immediate use in 
coordinating coring operations. Since 12 kc 
attenuates rapidly in the sediments these 
reflections are most often only tens of feet 
deep, but they are within the reach of deep-sea 
corers. 

It might be asked why an oscilloscope 
isn't used. A scope is usually a part of the 
instrumentation, but scope photographs, are 
not easily compared with one another at a 
rate of several thousand an hour. Although 
they give needed amplitude information it is 
often difficult to obtain representative 
amplitude differences within the echo structure 
from only a few samples, because of the fluc- 
tuation fovind in such measurements. A visual 
integration of the returns on the PGR record 
is a useful guide in these bottom reflectivity 
studies. 

We also use precision soundings for 
navigation, '^ ' 2 and often moor deep sea buoys 
on a particular bottom contour, a line of 
position easily followed with the PGR. 

Seismic Reflection and Refraction 
Profiling 



penetration of the sea- floor from these 
relatively weak sources, and attribute a great 
part of this success to the correlation 
capabilities of the PGR. These electrical 
sources are designed to follow the moderately 
high repetition rates of the PGR, which are at 
least an order of magnitude greater than those 
used in conventional explosive methods. The 
signal is coherent and generally remains so 
after sea- surface, sea- floor, and sub- sea- 
floor reflections, see Fig. 5. The wave 
length in water at these low frequencies is 
great enough and the sampling rate fast enough, 
that changes in geometry or sub- sea- floor 
structure do not erratically interrupt the 
correlation of the wave forms in the returning 
signals. Weak signals are traced through noise 
with unusual ease, (Fig. 6) for the PGR is in 
fact an autocorrelation device when it can 
control the timing of events. 

The PGR /ecord from vertical seismic 
reflections gives us a cross- section profile 
of the structure below the bottom, but the 
depth scale must be determined and corrected 
by propagation velocities obtained from oblique 
reflection and refraction data taken with the 
same system. Refraction arrivals, when 
present, can be immediately identified (Fig. 7) 
and compressional wave velocities readily 
computed. In their absence there is an 
overabundance of reflection data for a more 
complicated velocity determination 12,13. 
An oscilloscope and tape recorder are necessary 
accessories to this instrument, however; the 
scope for instantaneous observations and 
photography, the tape for storage and future 
analysis. There are simply not enough PGR 
channels available at one time, even if 'master 
and slave" techniques are used. 



We record seismic reflections in a 
system made up of a broad spectrum sound 
source actuated by the triggering mechanism 
of the PGR wnich in turn records the signals 
received by a broadbsind hydrophone suspended 
from the ship. Adjustable bandwidth filters 
are used to filter the signal in differing 
frequency bands for each channel of the PGR. 
This system is known as the Continuous 
Seismic Profiler 2, 9, 10 jrig_ 4_ i^ ^^s 
development at Woods Hole the sources most 
used have been the underwater spark and the 
E. G. and G. "Thumper". Both have higher 
peak pressures than most sounders, but in 
narrow bandwidths at the necessary low 
frequencies their output is generally below 
100 db above a microbar. Yet we obtain good 



Location of Instruments and other 
Objects 

In addition to high resolution echo sound- 
ing studies, the PGR is used for echo location, 
the finding and identifying of objects suspended 
in the water. These objects may be animal, 
as in the case of fish, porpoises, or scattering 
layer-'-'*; they may be instruments, buoys which 
can be tracked and recovered, cameras^^, 
corers-"^, nets and dredges-''^, whose lowering, 
placing and raising can be accurately monitored 
with this system. 

Echo location techniques employ not only 
the shipboard transducers of sounders or 



253 



ranging equipment, but also pingers which are 
attached to cable- suspended and free instru- 
ments. The difference between the arrival 
times of the directly received and bottom 
reflected signals from this pinger indicates an 
instrument's height above bottom, (Fig. 8). 
The signal structure and timing of these arrivals 
displayed on the PGR disclose such details as 
when a corer triggers, or the attitude of a 
dredge e. g. whether or not it is kiting during the 
lowering. Cameras can be manuevered within 
their focal lengths above the bottom in water 
several miles deep. We can tell whether the 
cameras are over smooth, muddy bottom or 
rough, rocky bottom. The guesswork in these 
many operations has for the most part been 
eliminated. We no longer speculate whether 
a dredge is on bottom, a camera in focus, cable 
payed out too fast or a Nansen bottle cast 
dragged on bottom. 

Where depth must be accurately known, 
for such instruments as the Bureau of 
Standards Velocimeter, the simple pinger 
technique is not adequate '■°. However, the 
additional travel path geometry provided by 
the inverted echo sounder described by Dow ^^ 
solves this problem. 

Navigation techniques involving acoustic 
pingers and transceivers, and sonobuoys are 
also used with the PGR. The motion of freely 
drifting pingers with precisely timed repetition 
rates can be tracked by measuring the change 
in time interval between received pings. When 
sonobuoys and acoustic transceivers are used, 
a simple travel time measurement is used to 
comDUte one's range from them. 

Studies of Sea Life 



and high resolution. Fig. 10. 



CONCLUSIONS 

Some of the salient jobs of the PGR have 
been mentioned. There is good probability' 
that there will be more. We have not yet used 
it to measure oceanic tides, for example. 
Studies of the scattering layer and newly foimd 
groups of larger sea life continue. New 
advances in navigation are most encouraging 
for those studying bathymetry, for our depth 
measurement capability is all- too- often better 
than our navigation. New and more powerful 
broadband sound sources hold promise of 
making continuous seismic profiling as routine 
as echo sounding. Even without the use of new 
inverted sounders, heat probes, and other 
equipment there is without a question much 
future use for the PGR. 



ACKNOWLEDGMENTS 

The development of the recorder and 
much of the Continuous Seismic Profiler was 
c arried out by WHOI under U. S. Navy Bureau 
of Ships' Contracts NObs-43270 and NObsr-72521 
as has been previously reported. Other work 
summarized here have been supported by WHOI 
under Office of Naval Research contract Nonr- 
1367(00), and NSF grants. 

This is Contribution No. 1223 of the 
Woods Hole Oceanographic Institution, Woods 
Hole, Massachusetts. 



Scattering layer records from the PGR 
see Fig. 9a and b, often a by-product of 
bathymetry, show the diurnal migration and 
distribution of these groups of sound 
scatterers ^^. Interesting work has been done 
by lowering a sounding transducer into the 
layers to learn more of the size, population 
and movement of individual animals ^^- 20 _ 
Echoes are read out on the highest writing 
speed of the PGR. Earlier this information was 
used to determine when to trigger an underwater 
camera; now the camera and its acoustic range 
finder are in one submersible package. 

Fish schools are studied by sounding 
and echo ranging. A PGR record from such 
a study illustrates this use of short pulses 



REFERENCES 

"Atlantic Submarine Valleys of the United 
States and the Congo Submarine Valley", 
Veatch, A. C. and Smith, P. A. , Geol. 
Soc. of Am. , Special Papers No. 7, 1939. 

2. "High Resolution Echo Sounding Techniques 
and their Use in Bathymetry, Marine 
Geophysics and Biology," Knott, S. T. and 
Hersey, J. B. , Deep- Sea Research, Vol. 4, 
No. 1, 1956, pp 36-44. 



254 



3. "Precision Measurement of Ocean Depth", 
Luskin, B. , Heezen, B. C. , Ewing, M. , 
and Landisman, M. , Deep- Sea Research, 
Vol. 1, No. 3, 1954, pp 131-140. 

4. "Instruction Manual for the Precision 
Graphic Recorder (PGR)", Knott, S. T. 
and Witzell, W. E. , Woods Hole Oceano- 
graphic Institution, Ref. No. 60-38, 
October 1960, pp 1-42 + Appendix (86 pp). 

5. "Evidence for Ponding in Deep Sea 
Sediments", Hersey, J. B. , given at 
lUGG, Helsinki, Finland, August 1960. 

6. "Geophysical Investigation of the 
Continental Margin between Cape Henry, 
Virginia and Jacksonville', Florida", 
Hersey, J. B. , Bunce, Elizabeth T. , 
Wyrick, R. F. and Dietz, F. T. , Bull. 
Geol. Soc. Amer. , Vol. 70, April, 1959, 
•pp 437-466. 

7. "Reconnaissance Survey of Oriente Deep 
(Caribbean Sea) with a Precision Echo 
Soimder, Hersey, J. B. and Rutstein, M. 
S. , Bull. Geol. Soc. of Amer. , Vol. 69, 
No. 10, 1958, pp 1297-1304. 

8. Bunce, Elizabeth T. , 1961, personal 
communication on a bathymetric survey 
of the Romanche Trench. 



16. 



17. 



19. 



20. 



"Acoustically Monitored Bottom Coring", 
Hersey, J. B. , Deep-Sea Research, Vol. 
6, No. 2, 1960, pp 170-172. 
"Improved Techniques of Deep- Sea Rock 
Dredging", Nalwalk, Andrew, Hersey, J. 
B. , Reitzel, John and Edgerton, H. E. , 
Deep-Sea Research (In press). 
"Comparison of Directly Measured Sound 
Velocities with Values Calculated from; 
Hydrographic Data", Hays, Earl E, The 
Journal of the Acoustical Society of 
America, Vol. 33, No. 1, 85-88, January 
1961. 

"Inverted Echo Sounder", Dow, Willard, 
Stillman, Stephen L. , ISA-ASLO, Marine 
Sciences Conference, September 11-15, 
1961, Woods Hole, Massachusetts. 
"A Scattering Layer Observation", 
Kanwisher, J. , Volkmann, G. , (1955), 
Science 121 (3134), 108-109, 



9. "Continuous Reflection Profiling", 

Hersey, J. B. , The Sea, (In press). 

10. "Geophysical Investigation of Cape Cod 
Bay, Massachusetts using the Continuous 
Seismic Profiler", Hoskins, H. and Knott, 
S. T. , Journal of Geology, Vol. 69, No. 3, 
1961, pp 330-340. 

11. "Sonar Uses in Oceanography", Hersey, 
J. B. , Edgerton, H. E. , Raymond, S. O. , 
and Hayward, G. , Instrument Soc. of 
America - Fall Instrument- Automation 
Conference and Exhibit, New York City, 

N. Y. , Preprint Number 21-60, 
September 26-30, 1960. 

12. "Analysis of Reflection and Refraction 
Records taken with the Continuous Seismic 
Profiler", Hoskins, Hartley, Woods Hole 
Oceanographic Institution, Reference No. 
60-37, 1960. 

13. "A Deep-Sea Seismic Reflection Profile", 

Officer, Charles B. , Geophysics, Vol. 
XX, No. 2, April 1955, pp 270-282. 

14. "Suspended Echo- Sounder and Camera 

Studies of Mid- Water Sound Scatterers", 
Johnson, Henry R. , Backus, Richard H. , 
Hersey, J. B. and Owen, David M. , Deep 
Sea Research, Vol. 3, 1956, pp 266-272. 

15. "Uses of Sonar in Oceanography", Edgerton, 

H. E. , Electronics, Jirne 24, 1960. 



255 



Fig. 1. Echo sounding profiles across (a) a small canyon and (b) small 

isolated bumps on the relatively flat sea floor of the Blake Plateau. Resolution: 
15 milliseconds per inch. Vertical exaggeration: 30 to 1. 

Fig. 2. High resolution soundings indicating sediment ponding. In (a) the 

ship's motion on the ocean waves causes oscillations in the echo sequences from 
the bottom. In (b) the effect of two pulse lengths, not greatly different, is compared 
(From Hersey ^) 

Fig. 3. High resolution echo soundings of the Nares Abyssal Plain. Indications 

of sediment ponding are interrupted by a small seamount at the right end of record. 
Resolution: Approx. 15 milliseconds per inch. Pulse Length: 0. 2 millisecond. 
Vertical exaggeration: 40 to 1. 

Fig. 4. A Block diagram of the Continuous Seismic Profiler. The two- 

channel Precision Graphic Recorder is a part of this system. 

Fig. 5. A seismic reflection profile across the southern tip of Stellwagen 

Bank, Massachusetts Bay. Successive signals maintain their similarity after 
many reflections. (From Hoskins and Knott ^^) 

Fig. 6. Seismic reflection records across Georges Bank taken on two, 

synchronized PGR's. The rippled trace on the left is the sea floor and arrows 
indicate seismic reflections from deeply buried acoustic and probable geological 
discontinuities, which are accentuated by this oblique view. Note that these returns 
correlate and background noise generally does not. 

Fig. 7. In an oblique seismic reflection and refraction profile, the travel 

time of the direct arrivals changes as the source and receiver are separated on 
the sea surface. Refracted signals having travelled at greater compressional wave 
velocities than that of water arrive earlier than the directly received water-borne 
arrivals 10. 

Fig. 8. Pinger controlled instrument lowering. The difference in travel time 

between the direct and bottom reflected pings is measured between the traces 
displayed on the PGR record. 

Fig. 9. (a) Scattering layer migration at sunrise, (b) High resolution echoes 

from individual scatterers detected by lowering the sounding transducer among the 
scatterers. 

Fig. 10. Echo ranging on fish schools. One of the fish schools in the record 

to the left is examined with high resolution in the record to the right". 



256 



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262 



INVERTED ECHO SOUNDER 



by WILLARD DOW, Electronics Engineer 

and STEPHEN L. STILLMAN, Research Assistant in Engineering 

Woods Hole Oceanographic Institution 

Woods Hole, Massachusetts 



PART 1 - Willard Dow 



ABSTRACT 

The Inverted Echo Sounder is an instrument 
primarily designed to provide a continuous and 
precise measurement of the depth of other 
instruments, such as the velocimeter being 
lowered along with it into the sea. 

The device has also been used for detailed 
survey of the ocean bottom in deep water and 
by simple alteration of its suspension can be 
used for high powered short pulse echo ranging. 



INTRODUCTION 



Instruments are now available which are 
capable of measuring sound velocity, tempera- 
ture, and salinity to a high degree of precision. 
However, the value of these measurements is 
greatly reduced if the depth of the instrument 
is not also known simultaneously and with 
comparable precision. 

Most devices for such depth measurement 
incorporate bellows or bourdon tubes which 
although they can be made sensitive to small 
pressure changes in shallow water, become of 
necessity stiff and insensitive to such changes 
when designed to withstand the high static 
pressures of the deep ocean. 

The Inverted Echo Sounder when coupled 
to a precision recorder has provided highly 
precise depth measurements down to at least 
16, 000 feet, and when perfected should 
operate considerably deeper. 

When towed close to the bottom, the 
instrument also provides a highly detailed 
survey of the area showing bottom configu- 
ration impossible to resolve with conventional 
surface echo sounders. 



THEORY OF OPERATION 

The device consists of a high powered 
"pinger" as a short pulse transmitting unit 
mounted along side a sensitive fixed tuned 
receiver. Both units are connected to a com- 
mon transducer which is used both as a 
projector and as a receiving hydrophone. The 
apparatus is self-contained and battery operated. 

When submerged, the transmitter directs 
short pulses toward the surface at a one second 
repetition rate (Fig. 1). The surface reflected 
pulses are detected by the deep receiver, 
amplified and sent up via a single conductor 
oil well logging cable to the surface vessel. 
Here the signal is amplified further and applied 
to a precision graphic recorder normally used 
for echo sounding. From this record the depth 
of the instrument may be read directly. ( Fig.lA) 

Although the main lobe of the transducer is 
always directed toward the surface during 
instrument lowerings, there is also a weaker 
back lobe directed toward the bottom. There- 
fore when the gear is lowered to within 600 
feet or so of the ocean floor, the bottom also 
becomes visible on the recorder chart and the 
winch can be stopped in time to avoid dragging 
instruments in the mud. 

This same back lobe is made use of in 
bottom survey operations. In this case the 
sounder is lowered to between 30 and 100 feet 
of the bottom, and towed slowly across the 
region of interest. Under these conditions 
the area covered by the transducer beam at 
any given moment is comparatively small and 
details of bottom structure may be observed 
without the ambiguity produced by side re- 
flections or the losses encountered in sound 
transmission through thousands of feet of 
water. 



263 



Since the surface is constantly being 
recorded as well, the depth of bottoni features 
below the surface can also be determined from 
the recorder chart. 

When a velocimeter is used with the gear 
its output signal passes through a mixer- 
driver stage in the inverted pinger where it 
is mixed with the receiver signal for trans- 
mission to the surface via the logging cable. 
At the surface the two signals are again 
separated by filters, the velocimeter signal 
being channeled to a counter and printer and 
the depth pulses to a precision graphic record- 
er as indicated above. 



ELECTRONIC DESIGN 

A. The Transmitter 

Fig. 2 is a schematic diagram of the 
transmitter or "pinger" circuit. The trans- 
istor power supply consists of two 2N278 
transistors in a miultivibrator circuit operat- 
ing at about 800 cycles. The high voltage 
secondary of the multivibrator transformer 
drives a voltage doubling rectifier circuit 
which in turn delivers approximately 1000 
volts to the load. 

The load consists of the two capacitors 
C ;i and C2 in series, which in turn are con- 
nected to the plate and grid circuits of the 
thyratron as shown. When switch SW-1 
closes, the high voltage is applied to the grid 
of the thyratron and the thyratron fires, dis- 
charging capacitors C^ and C2 through the 
primary of output transformer T2- Tg is a 
step-up transformer, the secondary of which 
is tuned to the 12 kc resonant frequency of 
the crystal transducer. A 14 kv, 400 micro- 
second ringing pulse is thus developed across 
this transducer and an acoustic "ping" is 
produced. 

In the first experimental versions of this 
instrument, switch SW-1 was closed at a one 
second repetition rate by a motor driven cam. 
This motor, governor controlled for precision 
timing, was pre -synchronized to the read- 
out recorder on the ship so as to produce a 
more legible record. However, this timing 
system is not entirely satisfactory and an 
electronic timer of higher accuracy is being 
developed. 



B. Receiver 

Fig. 3 is a schematic diagram of the 
receiver. This unit is fully transistorized and 
comprises three single ended stages fixed 
tuned to 12 kc, a push-pull driver and a 10- 
watt class AB final used as a cable driver. 
The first two stages are designed for low noise. 

The input circuit is somewhat unconven- 
tional and therefore should be explained in 
some detail. 

As indicated in Section A, the transmitter 
develops a 14 kv pulse across the transducer. 
Since this same transducer is used as a re- 
ceiving hydrophone during the listening peri- 
ods, it is essential that the receiver be 
electrically isolated and protected during the 
transmission of the 15, 000 volt pulse. It is 
also important that the receiver input imped- 
ance be high compared to that of the 12 kc 
tank circuit formed by the output transformer 
and the crystal transducer. Otherwise, load- 
ing and detuning effects could easily absorb 
most of the power in the transmitter pulse. 

The solution to the problem is shown in 
the receiver diagram. A 15, 000 ohm high 
voltage resistor connects the transducer to a 
limiter circuit comprising two 10 watt zener 
diodes back to back. The resistor value is 
high enough to prevent loading the transmitter 
and also limits the zener current to a safe 
value. The zeners clip the receiver input at 
about 4 volts. As this signal would still over- 
load the receiver, a second clipper follows 
the zeners consisting of reversed silicon 
diodes which have a conduction threshhold of 
about 0. 3 volt, a reasonable input level. 



C. The Cable 

The oil well logging cable used to support 
the instruments and conduct the signals to the 
surface is essentially conventional in design. 

It consists of an electrical conductor of 
No. 19 stranded copper over which is drawn 
a thin hard layer of extruded nylon. This in- 
sulated center conductor is separated from the 
external sheath by a waterproof soft rubber 
compound which keeps the cable flexible and 
provides additional insulation. 



264 



The outside sheath consists of two layers of 
galvanized steel strands in opposed lays to 
prevent twisting and kinking. The overall 
diameter of the cable is slightly less than 
1/-1" and it has a breaking strength of 4, 265 
pounds. 

This cable was selected because it is 
strong, small in diameter, relatively cheap 
(17 cents/foot in 30, 000 foot lengths), and 
readily available. Although its attenuation 
is high at the higher frequencies, the trans- 
istorized Class B cable driving stages in the 
receiver and velocimeter amplifiers have 
more than sufficient power to overcome the 
losses in a six mile line at the expense of an 
average battery drain of only a few mili- 
amperes. 



PART #2 - Stephen L. Stillman 



STRUCTURAL DESIGN 

A. Orientation 

In order to obtain the strongest signal 
return from the water surface, it is neces- 
sary to hold the axis of the main lobe of the 
transducer perpendicular to the surface. This 
requirement dictates a self -aligning hydro- 
dynamic design containing components so 
located as to produce balanced drag effects 
and to properly locate the center of buoyancy. 



B. Vertical Stabilization 



D. Accuracy 

The accuracy of the depth measurement 
depends, of course, upon the velocity of 
sound in the water at the place where the 
lowering is being made. This velocity in 
turn depends on the temperature, density, 
and salinity of the water through which the 
sound travels. The more accurately these 
factors are known, the more precise the 
measurement since the resolving power of 
the gear is sufficient to indicate vertical 
changes of a few feet regardless of the depth 
of the instrument. 

When an accurate velocimeter is lowered 
with the sounder so that the sound velocity is 
known throughout the transmission path, it 
is certainly safe to assume that a deep 
measurement is good to a fathom and perhaps 
better. Expressed in the usual way, as per 
cent accuracy of full scale, this would cor- 
respond to an accuracy of at least 0. 04%, if 
full scale were considered to be 15, 000 
feet for example. 



Static stabilization of the gear is achieved 
by pivoting a towing support bail (Fig. 4 at A) 
at a point just below the center of buoyancy. 
A strong righting moment is thereby produced 
about this towing-pivot point thus providing 
the primary vertical aligning force. When 
towing, the hydrodynamic drag developed a- 
bove the towing pivot point must be balanced 
by the drag below this point. This is accom- 
plished by adding a vane at the top (Fig. 4 at 
B). It was found necessary to add a second 
vane to provide a moment of force about the 
vertical axis. This orients the instrument in 
the direction of tow allowing the upper vane to 
position the entire instrument and develop the 
proper drag for balance. Since the. gear will 
remain vertical regardless of cable angle, 
towing speeds up to 4 knots even in rough seas 
are permissable. 



External Frame 



Damage to instruments while handling on 
deck and over the side has often in the past 
been disastrous especially when the ship is 
rolling severely. Mildly rough seas average 
a good part of ship time at sea, and productive 
use of this time is obviously advantageous. 
The instrument described has been developed 
for use under these conditions. 



265 



For example, to avoid damage to the 
Inverted Sounder and velocimeter a lightweight 
aluminum tubular frame is constructed around 
the principal components (Fig. 4 at C) and 
mounted to the internal structure by neoprene 
and plastic shock absorbers (Fig. 4 at D and 
E , for example). The support points of the 
whole assembly are located on the internal 
structure itself, not the frame. Therefore, 
damage to the frame is not apt to affect op- 
eration of the instrument. 

During bottom survey work a possible 
cause of loss is snagging the instrument on 
the bottom. To guard against this, the rub- 
ber and plastic shock material present weak 
links which will part before the supporting 
steel cable. 

An additional way of retrieving snagged 
gear is provided in a safety cable. One end 
is fastened at the lower end of the instrument 
(Fig. 4 at F) the other to the steel support 
above the clamp (Fig. 4 at G). All external 
aluminum metal surfaces are coated with an 
epoxy type paint to resist surface corrosion. 
Teflon bearing material was used on the bail 
pivot to reduce noise. 



no longer manufactured, a special feed through 
designed for the purpose is used on the current 
model. 

After considerable investigation it was 
found that a certain commercial weather- 
stripping putty had excellent insulating quali- 
ties for high voltage even when subjected to 
high pressure in salt water. This material 
was therefore used directly to insulate the 
high voltage terminal described above. The 
entire high voltage assembly is protected by 
an external aluminum housing (Fig. 6 at C). 

An internal bulkhead incorporating an O- 
ring seal is placed within the transmitting 
tube to separate the battery compartment 
from the high voltage transmitter (Fig. 6 at D). 
This precaution was taken because silver zinc 
batteries, when defective or subjected to heavy 
drain, have been known to emit enough hydrogei 
to cause an ex-plosion when mixed with air and 
ignited by a spark such as might accidentally 
be generated by a defect in the high voltage 
system. 



E. Internal Construction 



D. Watertight Electronic Chambers 

The two watertight compartments contain- 
ing the transmitter and receiver respectively 
consist of two 7075-T6 aluminum tubes, 
(Fig. 5) and end caps of the same material. 
These compartments will withstand 10, 000 
P. S. I. and are sealed with double O-rings 
mounted on the caps. (Fig. 6 at A and B). 
One O-rtng is located as near as possible to 
the perimeter of the cap to prevent corrosion 
from developing between cap and tube surfa- 
ces. Such corrosion would cause considerable 
difficulty in removing the end caps. Each cap 
is held to its tube by four quick acting stain- 
less steel drawhook latches. Eight standard 
Joy plugs provide electrical connections 
through the caps. 

The earlier niodels of the instrument 
employed a standard model airplane engine 
spark plug as the high voltage feed -through 
which conducts the 15, 000 volt pulse through 
the end cap. These plugs are capable of 
withstanding the 14, 000 P. S. I. required for 
deep submergence. Because these plugs are 



Stainless steel was used for chassis con- 
struction where possible to prevent salt air 
corrosion. The transmitter and receiver 
chassis are mounted on the end caps, thus 
eliminating several connectors. The receiver 
battery is contained in a plug-in chassis, on 
which is also mounted the velocimeter mixer - 
amplifier (Figs. 7 and 8). A fibreglass cover 
protects the components from salt spray when 
the battery chassis is removed from the tube 
on deck. To reduce acoustic noise, the timing 
motor is suspended by neoprene strips and 
entirely encased in a sound absorbing plastic 
foam. 



F. Velocimeter 

A N. B. S. velocimeter may be attached 
below the internal assembly, where it is pro- 
tected by a tubular structure and shock mounts 
(Fig. 4 at H). This instrument is designed 
for 20, 000 P. S. I. If it becomes desirable to 
also operate the sounder under such pressure, 
this can be accomplished by a slight increase 
in the wall thickness of the aluminum tubes 



266 



housing the electronic units 



CONCLUSION 

This paper has been concerned with a 
combination precision depth meter and bottom 
survey instrument, with provision for also 
transmitting sound velocity information to the 
surface. Since velocity information is not 
complete without a precise depth measure- 
ment, and since the depth measurement 
becomes far more accurate when the true 
velocity is known, these two instruments 
complement each other rather nicely. How- 
ever, to complete the velocity picture the 
factors which affect velocity should also be 
known. Therefore, we are now preparing to 
add precise temperature determination and 
possibly salinity to the velocity and depth 
determinations. 



ACKNOWLEDGMENTS 

This gear was developed under Office of 
Naval Research Contract No. 1367. 



The authors of this paper wish to thank 
J. B. Hersey for promoting and supporting 
the development of the equipment. 

They also greatly appreciate the coopera- 
tion and assistance of Earl E. Hays who 
developed successful techniques for using 
the gear as a survey instrument for detailed 
examination of the bottom. 

This is Contribution No. 1222 of the 
Woods Hole Oceanographic Institution of 
Woods Hole, Massachusetts. 



LIST OF FIGURES 

Block diagram of system components. 
PGR record of typical lowering(photo) . 
Schematic diagram of transmitter. 
Schematic diagram of receiver. 
Structure of deep unit (photo). 
External view of watertight compart- 
ments (photo) . 
Transmitter chassis. 
Receiver and velocimeter amplifier 
chassis (photo) . 
Bottom view of receiver and 
velocimeter chassis showing plug- 
in arrangements. 



Fig. 


1 


Fig. 


lA 


Fig. 


2 


Fig. 


3 


Fig. 


4 


Fig. 


5 


Fig. 


6 


Fig. 


7 



Fig. 8 



VELOCITY SIGNAL 




VELOCIM ETER 



Figure I 



267 



RETURN 
TO SURFACE 



SEA 

SURFACE 
ECHOES 
(RAISING) 



ECHOES 
FROM 
BOTTOM 



TRANSMITTED 
PING 

SEA 
SURFACE 

ECHOES 

(LOWERING) 



SHIP'S HULL 
ECHOES 

STARTING 
DOWN 































y 



*« 













-r-U^ 




METER 
WHEEL 
READINGS 



TRAVEL TIME 



Figure 1A 



268 




2NI75 2NI75 ,k 



20 K :; 16 K ;| 1 20 K :■ 




6316 

006 



120 K 5 18 



::6.K 



'^^ — T ^ 



Tfi-4 2 5 WATT 
3 3 1 

280 
IWATT 



< 



i 



' MUX-3 ~|~ 



EXTERNAL TO RECEIVER 



I I , TRANSDUCER 



ALL RESISTORS 1/2 WATT UNLESS OTHERWISE SPECIFIED 
ALL ELECTROLYTIC CAPACITORS 12 W V D C 



SIGNAL OUT 

12 KC 



^-^10 Mi2 Z 



., L-^w O -12 



WOOM HO(_I OC«ANOGI»*FMIC iNrrTTUTVJN 
WOOD« HOI-K. MAS* 

INVERTED ECHO 
SOUNDER RECEIVER 


°"— "C 1 


•"'-' 1 ""'2 JUNE 60 


'"° W 80 W 




'""1367-1 



Figure 3 

269 




DRAG A 



CENTER 

OF 
BUOYANCY 



TOW 

SUPPORT 

POINT 



DRAG B 



270 




61 



\ 









271 





272 



A BOTTOM STRIP MAP CAMERA 

by DR. ANGELO J. CAMPANELLA, Senior Physicist 

HRB-Singer, Inc. 

State College, Pennsylvania 



ABSTRACT 



A prelimjnary investigation of photographing 
a lake bottom using a scanning-type system is 
reported. An exannple of the results of tests 
conducted with a line-scan camera system Is 
presented. 



INTRODJCTION 

In ocean and lake bottom photography, large 
area coverage at a suitable illumination level is 
difficult to obtain. To date, successful bottom 
photography has consisted of photographs of local 
coverage on the order of several feet in range in 
relatively clear water. 

The feasibility of a line scan strip nnap 
technique for underwater bottom photography is 
demonstrated herein. This experimental camera 
system offers the advantage of contrast en» 
hancement, minimum light level requirements, 
and the ability to trade resolution for sensitivity. 
This system was installed in a glass bottomed 
boat and bottom photographs taken of a shallow 
mountain lake are shown. 



CAMERA 

Figure 1 illustrates the canriera's principle. 
A line scan motion is produced by rotating a 
plane mirror on an axis inclined 45 with respect 
to its surface. This mirror reflects light into 
an objective aperature which focuses the light 
onto a photomultiplier cathode. The area of this 
image impinging onto the cathode is limited by a 
small variable aperture. The image of the 
aperture may be considered as being projected 
onto the ocean bottom. This spot is rapidly 
swept across the bottom surface in a lateral 
direction via the rotational motion of the scanner 
mirror. 

The maximum scan rate used was about 60 
lines per second. The forward motion of the 
vehicle carrying the camera unit provides the 
longitudinal scanning. A contiguous coverage of 
the bottom will occur for scanning speeds as 
fast as or faster than that required to lay one 
scanned strip adjacent to the previous. It is 
conventional to scan at a slightly greater RPM 
than that required for contiguity. This minimizes 
the raster effect in the recorded photograph. 



The instantaneous signal amplitude received 
at the detector, in this case a photomultiplier, 
is amplified and its dc level carefully controlled 
so as to have a minimum bottom brightness 
encountered correspond to the threshold of the 
recording film. Recording film illumination is 
accomplished by feeding the signal from the 
control box into a glow lamp whose light output is 
a confined spot of brightness proportional to the 
input current. The recording film is wrapped 
around a barrel containing a rotating microscope 
objective, so that the film remains in the focal 
plane of the objective. The glow lamp output is 
projected along the axis of the barrel, folded 
90° by a mirror, and then enters the objective 
lens. The spot is projected on the recording 
film by the microscope objective. A common 
Plus X type film has been found to have ample 
sensitivity. 

The film is moved past the barrel at a speed 
proportional to the velocity of the vehicle and 
inversely proportional to the distance to the 
bottom. The film speed used for these experi- 
ments corresponds to a vehicle velocity of about 
one foot per second and a bottom distance of 
seven feet. Gyro-stabilization of the roll axis 
is provided. 

The camera system can accomiTiodate a 
wide range of illunnination levels by the vari- 
ation of the area of the aperture before the 
photonnultiplier detector. In particular, reso- 
lution can be exchanged for sensitivity. (This 
is impossible in a conventional camera.) The 
resolution-sensitivity product is proportional to 
the area of the collecting aperture. Sensitivity 
greater than that of film can be achieved with 
some loss of resolution. 

Figure Z is an example of a photograph that 
a line-scan system has produced. The resolution 
and dynamic range illustrated here are typical. 



DESCRIFTIO.Nf OF WATER-BORNE EQUIPMEisIT 

The vehicle used to carry the camera equip- 
ment was a 12-foot, all-aluminum pram 
modified as shown in Figure 3. 



273 




Parabolic Mirror 
Objective Aperture 



Scanning Mirror 
Light from Scanner Spot 



Glow Lamp 

Printer Objective 
Lens 



Fig. 1 - Basic Camera Scheme 




Fig. Z - A Line Scan Strip Map 
274 



The center seat of the boat was removed, a 
6-inch by 34-inch hole was cut athwartships in 
the bottom, and a like-size section of auto safety- 
glass window was installed. The area adjacent to 
the window was painted dull black to minimize 
stray reflections. An electric trolling motor, 
powered by two 6-volt auto batteries, propelled 
the boat. Two crewmen were used to maneuver 
the craft and operate the system. 

High voltage for the photomultiplier was 
obtained from the control box cathode ray tube 
power supply. The control box and battery (two 
12-volt auto batteries in series) were installed in 
the boiv along with a 400-cycle inverter. 

The window, which extended the full width of 
the boat bottom, was wide enough to accommcdate 
the 3-inch wide scanning aperture and to provide 
an approximately 80° lateral field of view after 
refraction at the air-water interface. 



EXPERIMENTS 

Roosevelt Lake, a small artificial lake near 
State College, Pennsylvania, was chosen as the 
site at which photography with the water-borne 
equipment would be tried. The bottom of this 
lake slopes gently from the beach to a maximum 
depth of about 12 feet. 

Two targets were prepared for the tests. 
The first was a one-foot square sheet of aluminum 
painted to produce a black and white checker- 
board comprising four 6~inch squares; the second 
target was a pair of 6-inch by 18-inch aluminum 
strips set in the form of a cross. One strip was 
painted black, the other white. These targets 
were placed near each other on the lake bottom 
and their position marked by a buoy. 

Both natural light and artificial light photo- 
graphs were planned, but time limitations pre- 
vented the latter. The water was relatively 
clean, enabling the bottom to be seen through the 
glass window. A coating of moss and silt signifi- 
cantly reduced the r eflectivity and contrast of 
the bottom, resulting in very low contrast objects. 
This bottom situation, probably representative 
of the worst conditions to be encountered, points 
up the need for contrast-increasing devices 
including side lighting. Under conditions of 
little or no silt, considerably better results are 
naturally expected. 

It was possibly to vary the speed of the 
pram in six steps from less than 1/2 knot to 
about 3 knots. A maximum of about 2 knots was 
used daring the photographic runs because 
higher speeds caused lapping under the bow, 
producing an accumulation of air bubbles under 
the blass window. Since the recording film speed 
mjst be matched to the boat's velocity in relation 
to depth, the maximum available film speed of 
one foot per minute dictated a boat speed of one 
foot per second when the depth was seven feet, 
the depth at which the targets were planted. 
Future models of a system could accomnn.date 
considerably greater velocities. 



Figure 4 shows a photograph which was 
taken with this gear. The angular size of the 
scanning spot was three milliradians. The left- 
hand side of the upper photo shows some tree 
branches or, perhaps a tree stump. The boat- 
shaped object in the center appears to be a sunken 
canoe. The checkered target appears at the 
center-right, and the cross in the upper right 
corner. It is noted that the whites of the targets 
are extremely bright while the blacks are not 
immediately evident. This is a consequence of 
the poor reflectivity and the presence of some 
scattering particles in the water respectively. 
The uniform lateral striations are spontaneous 
variations of the electronic level at very low 
frequencies. More recent developments have 
minimized these lines. The day on which this 
run was made was very cloudy with intermittant 
drizzle. The second photo was made on a sunny 
day. The shadow of the boat is evident as a 
black stripe down the photo. Bottom objects, 
such as tree stumps and a silt-covered plank 
are evident with better contrast. Surface wave 
patterns caused occasional light patterns. In 
the left portion, the checkered target is evident 
despite the boat's shadow. 



CONCLUSIONS 

Acceptably identifiable photographs of targets 
on a shallow lake bottom have been obtained 
using a scanning-type system. These results 
are encouraging, and further work is required 
to illustrate the ultimate worth of the system for 
oceanographic research. 

In order to simulate the lighting conditions 
which are found at the ocean floor, a series of 
photos should be taken at night using artificial 
illumination. Figure 5 shovvs one possible 
mounting configuration of these lights, which 
would be encased in a watertight container and 
immersed in the water. 

A high intensity beam spot which would scan 
along with the camera so as to coincide with the 
look spot of this equipment is another possibility. 
This configuration permits either an increase in 
brightness or a decrease in power requirements 
or both over the system utilizing fixed lights. 

The scanning beam source would be as much 
displaced from the scanner aperture as physically 
feasible. 

Although intense scattering from the beam 
would find its way into the instantaneous field of 
view of the scanner aperture, the contrast- 
enhancing capabilities of the electronic process- 
ing system permit the large steady component of 
the signal due to backscattering to be cancelled. 
Moreover, the volume of water directly illumi- 
nated by the light beam would be relatively small 
since it is necessary to provide light flux for 
only a small picture element at any given instant. 
This reduces the amount of cross-scattered light 



275 



Storage 
Battery 




Control Box 



Opei-ator 



Storage Battery 



Propulsion Motor 



NOTE: Over-all length 12' 
Beam 36" 



Fig. 3 - Experimental Boat 





Fig. 4 - Photi.)graph of Lake Bottom 



276 




CI 

o 

•1-1 

n) 

a 

•l-l 
m 

a 
o 

o 

00 



13 
en 



-.H 



277 



that travels from the illuminated column to the 
viewed volume. 

It is noted that the brightness required at the 
target and, hence, the flux density in the illumi- 
nating beam are no greater than that required 
for normal camera photography, assuming that 
the line scan system is adjusted to have the same 
sensitivity as the film. Conversely, vi'ith some 
sacrifice of resolution, photographs can be taken 
under light conditions insufficient for normal 
camera photography. 

It is realized that the system set forth has 
the shortcommg for deep oceanographic photo- 
graphy, of requiring a large slot-shaped window. 
This can be overcome by utilizing conical scan 
instead of linear scan. This requires a small 
circular-shaped window, whose inner diameter 
may be smaller than its outer diameter. This 
then allows the use of conventional conical deep- 
vehicle windows. Power requirements for the 
camera unit exclusive of illumination would be 
modest. One or two automotive type storage 
batteries would be sufficient for a few hours of 
continuous operation. The system can be 
slowed down for slower line rates in the event 
that telemetering to the surface over low band- 
width cabling is desired. 



278 



SOME RECENT ADVANCES IN UNDERWATER CAMERA EQUIPMENT 

by HAROLD E. EDGERTON, Professor of Electrical Engineering 

Massachusetts Institute of Technology 

Cambridge, Massachusetts 

and SAMUEL O. RAYMOND, Senior Engineer 

Edgerton, Germeshausen&Grier, Inc. 

Boston, Massachusetts 



ABSTRACT 



There is a continuing need in the field 
of deep sea ocean floor photography to take pic- 
tures at greater distances above the ocean floor 
so that more area of the bottom can be covered 
with each picture. With this technique, a means 
for photographically "mapping" the ocean floor 
might approach the means of mapping land areas 
as used in aerial photography, but on a much 
smaller scale. Recent advances using faster 
lenses, more light, and better light placement 
are discussed. 

INTRODUCTION 

Aerial photography is a technique that 
has been of tremendous value in mapping the sur- 
face of the earth. A pair of stereo photographs 
taken from an altitude of 30,000 feet can map in 
detail an area of over 20 square miles. It 
might take a land surveyor years to map this 
area in equal detail. Aerial photography has 
moved up to 80,000 feet and beyond into the field 
of earth satellites and rockets which travel hun- 
dreds of miles above the earth, covering corres- 
pondingly greater areas of the earth's surface 
with each picture. 



If deep sea ocean floor photography 
could be advanced to equal even 5% of what has 
been possible with aerial photography of land, 
the benefits to oceanographers , hydrographers , 
and marine geologists would be tremendous. There- 
fore, the trend in deep sea ocean floor photo- 
graphy is toward taking pictures farther and far- 
ther off the ocean floor covering more and more 
area. Until several months ago, most deep ocean 
photography was being done at a distance of about 
10 feet above the ocean floor covering an area of 
about 50 square feet. The camera used was the 
type shown in Figure 1. ,The electronic light 
source was essentially the same distance above the 
ocean floor as the camera. The light was rated at 
100 watt-seconds. The lens used was the F-11 under- 
water lens designed by Professor Robert Hopkins of 
the University of Rochester for underwater use be- 
hind a flat glass window. (If a normal camera lens 
which is designed for use in air is used underwater 
behind a flat glass window, "pillow" distortion 
occurs as shown in Figure 2. Professor Hopkins' 
lens is calculated to overcome this distortion. 
A photograph taken with it is shown in Figure 3. 
Of course, if the Hopkins lens is used in air, the 
pictures will have "barrel" distortion.) 



279 




Figure 1. Deep sea camera employing one 100 watt- 
second electronic flash light source and two 35nim 
cameras with Hopkins F-11 lenses for stero use. 
The object on the center of the framework is an 
experimental "sonar pinger", a sound device for 
positioning the camera the proper distance above 
the ocean floor. 




Figure 2. A photograph of the tile on the side 
of the M.I.T. swimming pool showing distortion 
obtained when an ordinary camera lens is used 
behind a flat glass window underwater. 

The success of the lens was very im- 
portant because of the high quality of the photos, 
but the need for a faster lens was felt so that 
pictures could be taken farther off the ocean 
floor. Under sponsorship of Woods Hole Oceano- 
graphic Institution, Professor Hopkins next de- 
signed an F-4. 5 lens for underwater use. The de- 
sign was completed in August, 1960, and these 
lenses with an optional shutter are standard on 
all EG&G underwater cameras. The new lens will 
not fit old model EG6eG cameras without a longer 
pressure case, but the longer cases are available. 




Figure 3. A photograph taken using the new 
Hopkins F-4. 5 underwater lens. Compare the par- 
allelism of the tile lines with those in Figure 2. 
The"data chamber"on the right is an internal part 
of the camera and records, date, time, and depth 
of each picture. The "data chamber" in the camera 
has been found to be invaluable in preve/iting the 
accidental switching of films. A small photo is 
taken with each photograph of pressure (depth)^ 
time on a 24-hour basis, and written in longitude 
and latitude information as well as the ship. 
date, etc. 

In April, 1901 plans were being made 
for the June, 1961 cruise of Woods Hole's Research 
Vessel Chain to the Puerto Rican Trench. Chief 
Scientist J. B. Hersey needed a camera that would 
take pictures showing a fairly wide continuous 
strip of ocean floor at depths of 20,000 feet. 
This was to be the first use of the new F-4. 5 lens. 

In order to get the cameras farther off 
the ocean floor, a special camera rack was used 
which placed the light closer to the bottom than 
the cameras. The new rack is shown in Figure 4. 
This new rack reduces the light source-to-bottom 
distance, thus increasing the illumination of the 
subject. The camera was wired such that it took 
pictures at 6-second intervals with a light source 
output ratings of 50 watt-seconds. Two of these 
camera assemblies were used, and hundreds of 
photographs were obtained. A sample photograph is 
shown in Figure 5. 

The results of the Puerto Rican Trench 
expedition indicated that still more light should 
be used. Consequently, a new lighting system was 
designed and two assemblies were built. The new 
system consists of the same framework as is shown 
in Figure 5. In place of the one, six volt, 50 
watt-second light source are two, 24 volt, 200 
watt-second light sources giving a total rating of 
400 watt-seconds. This increase by 8 fold in the 
light permits the use of wider angle reflectors 
to produce more even lighting. (The 24 volt light 
sources were originally designed for the bathy- 
scaphs FNRSII Trieste and Archemede . No batteries 
or automatic cycling controls are used since the 
lights are normally powered and controlled manually 
from inside the bathyscaph. ) The automatic control 



280 




Figure 4. Special deep sea camera used by Woods 
Hole Oceanographic Institution from the Research 
Vessel Chain for photographing the Puerto Rican 
Trench at a depth of 20,000 feet. The camera 
features F-4. 5 lens stereo cameras mounted side 
by side at the top of the framework, two electronic 
light sources mounted at the bottom of the frame- 
work and a sonar pinger for positioning the camera. 
The framework original Iv was designed in 1960 by 
Edgerton, Germeshausen & Grler, Inc. for the U.S. 
Navy Hydrographic Office. 

and batteries for the lights on the new assembly 
are inside a separate pressure-proof housing 
which is mounted adjacent to the lights. 

Two of these new F-4. 5 lens, 400 watt- 
second, sloping rack, stereo cameras are presently 
on board the Chain en route to the Mediterranean. 
With their it is hoped that pictures will be ob- 
tained 30 feet off the ocean floor covering an 
area of over 300 square feet. 




Figure 5. A photograph taken in June, 1961, in 
the Puerto Rican Trench at a depth of about 
20,000 feet from the Chain using the camera de- 
scribed in the text with 50 watt-seconds at F-4. 5 
on plus X film. The white object is a compass 
and flow indicator. Special printing is required 
to show the compass needle. 

BIBLIOGRAPHY 

Photography of The Ocean Bottom, M. Ewing, A. Vine, 
J. L. Worzel. Journal Optical Society of America , 
vol. 36, 1946, pp. 307-321. 

Cameras and Lights for Underwater Use, H.E. Edgerton, 
L. D. Hoadley. SMPTE Journal . July 1955, pp. 345-350. 

Deep-Sea Photography, E. N. "arvey, E. R. Baylor. 
Journal of Marine Research (Sears Foundation) , 
vol. VII, No. 1, April 194S, pp. 10-1^. 

Submarine Photography with the Benthograph, 

K. 0. Emery. Scientific Monthly , vol. 55, No. 1, 

July 1952, p. 1. 



A Wide-Angle, Underwater Camera Lens, E.M. Thorndike. 
Journal Optical Society of America , vol. 40, 1950, 
p. 823. 

The High Speed Photography of Underwater Explosions, 
?. M. Fye. SMPTE Journal, October, 1950. 



Underwater Photography, H. Schenck, H. 
Cornell Maritime Press . 1954. 



Kendall. 



281 



BIBLIOGRAPHY (continued) 

Photographing The Sea's Dark Underworld, 

H. E. Edgerton. National Geographic Magazine , 

April, 1955, p. 523. 

Deep-Sea Cameras of The Lament Observatory, 

E. M. Thomdike. Deep- Sea Research , vol. 5, 1958. 

Suspended Echo-Sounder and Camera Studies of Mid- 
Water Sound Scatterers, H. R. Johnson, R. H. Bakus , 
R. H. Hersey, D. M. Owen. Deep-Sea Research , 
vol. 3, 1956, p. 266. 

The Luminescence Camera, H. E. Edgerton, 
L. R. Breslau. Journal of the Biological 
Photographic Association , May 1958. Woods Hole 
Oceanographic Institute Report 58-14 . 

Report No. 768, NEL Type III Deep-Sea Camera, 
C. J. Shipek. U. S. Navy Electronics Laboratory . 
San Diego, California, March 13, 1957. 

A New Deep-Sea Camera, A. S. Laughton. Deep-Sea 
Research , Pergamon Press, Ltd., vol. 4, 1957, 
pp. 120-125. 

J. B. Hersey, H. E. Edgerton, S. 0. Raymond, and 
G. Hayward, Sonar Uses in Oceanography . Instru- 
ment Society of America Conference, Preprint 
#21-NY-60, September 1960. 



282 



A COMPLETE SONAR THUMPER SEISMIC SYSTEM 

by EARLD. VAN REENAN, Senior Geophysicist 
Edgerton, Germeshausen&Grier, Inc. 
Boston, Massachusetts 



ABSTRACT 

A complete continuous seismic pro- 
filing systan consists of the Sonar Thumper 
unit. Sonar Recorder, transducer fish, re- 
ceiving hydrophone, preamplifier if necessary 
and variable filter. Sonar Thumper units are 
available from 1,000 watt-sec models up to 
13,000 watt-sec experimental models. Thumpers 
have been extensively used for marine geo- 
logical studies and dredging surveys. The 
safety and economy of the large thumper units 
make them ideal for reconnaissance off- 
shore oil prospecting. 



I. INTRODUCTION 

Major oil companies and off-shore 
seismic contractors often conduct extensive 
seismic surveys which expend as much as '-> tons 
of explosives daily. High explosives generally 
give great reflection penetrations, but they 
are costly and hazardous to use. Several con- 
tinous sub-bottom profiling devices have been 
developed such as the Sparker, Gas Popper, and 
Marine Sonoprobe. These devices have found 
considerable application to limited depth pene- 
tration problems. 

This report describes a complete 
and effective seismic profiling system con- 
sisting of the Sonar Thumper and Sonar Recorder 



along with all necessary auxiliary equipment. 
The Sonar Thumper is available in the standard 
1,000 watt-sec unit on up to an experimental 
13,000 watt-sec unit. The complete thumper 
seismic system fulfills a need by research 
organizations, educational institutions, and 
government of a safe, simple, effective, and 
inexpensive system for marine geological studies. 
The high power, low frequency pulse generated 
by large thumper units give them a great po- 




Figure 1. Sonar Thumper seismic system with 
all necessary auxiliary equipment. 



283 



tential as an inexpensive offshore oil pros- 
pecting tool. 



II. SONAR THUMPER 

A. General Description 

The standard thumper unit consists of 
a power supply cabinet, capacitor bank cabinet, 
and transducer. The power supply converts ship's 
power or electrical generator power (110 or 220 
volts A.C.) to high voltage D.C. which is fed 
to the capacitor bank cabinet. When the trigger 
circuit is activated by a recorder contact, the 
capacitors discharge into the transducer. The 
epoxy encapsulated flat coil has an aluminum 
plate which is spring loaded against the face 
of the coil. The aluminum plate is violently 
repelled from the coil when the strong pulse of 
current flows through the coil. 

A precisely repeatable positive 
pressure pulse is produced by the repulsion of 
the plate in the water. The standard 1,000 watt 
second thumper gives a pulse duration of 0^5 
milliseconds and a peak pressure of approximately 
1 X 10 dynes/cm^ at one yard. The 5,000 watt- 
second unit gives a pulse duration of 2 milli- 
seconds and somewhat higher peak pressure. 

B. Large Thumper Units 

The unique design of the thumper 
transducer makes it inherently a non-saturable 
type of device. Therefore very high power 
thiaapers can be built using the basic trans- 
ducer design. The first 5,000 watt-second 



transducer was a scaled up version of the stan- 
dard model. Several double coil transducers 
were then designed to eliminate the bulkiness 
of the scaled up version and produce a greater 
concentration of energy. However, the energy 
concentration of the double coil transducers was 
so great, the back pressure of the coils caused 
the eposy encapsulation to shatter. To eliminate 
this difficulty, a symmetrical transducer was 
designed with two coils arranged back to back 
and an aluminum plate mounted against each coil. 
Thus the backward pressure of one coil counter- 
balances the pressure of the opposing coi.1. 
Initial tests of this transducer design at 
powers up to 14,000 watt-seconds have been very 
encouraging. 




D^ 




Figure 3. 13,000 watt-second Sonar Thumper 
system. 




Figure 2. 5,000 watt-second Sonar Thurape-- 
installation on board the R.V. Chain duri.^g 
the June, 1961 cruise to the Puerto Rico Tr^ncl. 



The larger thumper units are com- 
pletely modular in design to give great flexi- 
bility. The standard thumper components can be 
used along with more capacitor bank cabinets for 
greater power storage. The firing rate can be 
stepped up by simply adding more power supply 
cabinets. Figure 2 shows a photo of a 5,000 
watt-second unit consisting of two 2,000 joule 
capacitor banks, the standard triggered capaci- 
tor bank, and two power supply cabinets. This 
particular system was used on a Tune^ 1961 
cruise by Woods Hole Oceanographic Institution 
on the ship R.V. Chain to the Puerto Rico Trench 
area. Figure 3 illustrates a schematic diagram 
of the 13,000 watt-second Sonar Thumper unit. 

C. Installation and Operation of the Thumper 

The installation and preliminary check 
of the Sonar Thumper components can be done in 
a short time. The components are designed to 
be portable by two men. The power supply and 
capacitor bank cabinets are ordinarily placed 
in a cabin or sheltered area to avoid salt 
water exposure. 



284 



The power supply should be situated 
in a well ventilated area near the generator or 
other source of 110 or 220 line voltage. If the 
power supply must be placed at some distance 
from the generator, the thumper should be 
operated on 220 volts to reduce peak currents. 
To change over from 110 to 220 volt operation 
requires a simple change of transformer jumpers. 

The capacitor bank should be placed 
relatively close to the point where the output 
cable to the transducer leaves the ship in 
order to keep the high current cable as short 
as possible. High voltage D.C. from the power 
supply is brought into the capacitor bank and 
charges the 160 microfarad bank to approximately 
4 kv. A 110-115 volt a-c line is also plugged 
into the capacitor bank to power heater lamps, 
safety interlocks, the trigger circuit, and 
indicator lights. 

After installation, the unit can be 
checked by firing into a dummy transducer con- 
sisting of a 2-ohm, 200 watt resistor or a 
standard transducer with aluminum plate removed. 
The standard transducer should never be fired 
in the air without a damping water load. When 
fired, the force is so great the transducer 
plate of the standard thumper will leap 30 to 40 
feet vertically if it is fired in air without 
its retaining bolt. Testing at the dock can be 
carried out by lowering the transducer into the 
water alongside the ship. Proper grounding of 
all units should be checked before firing. 

For operation underway, a towing 
vehicle is necessary for the transducer. A 
number of vehicles have been used. The Naval 
Electronics Lab initially mounted the transducer 
on the hull of the ship and now uses an aluminum 
towing vane. The U.S. Coast and Geodetic Survey 
has used the transducer mounted in an internal 
water filled hull well to transmit pulses through 
the hull. Woods Hole Oceanographic Institute has 
a sled with heavy nose weight which they call the 
"flounder". The National Institute of Ocean- 
ography of England uses a fiberglass dinghy w: " i 
a reaction raass^above the transducer of 200 IbJ. 
of concrete. Two towing vehicles are now 
commercially available. One is a fiberslass 
"V"-fin ^ ' designed with negative lift and the 
other is an arrow-like unit with a counterweight 
in front and the transducer mounted in the 
tail (^). 

The size- of the boat used has varied 
widely from 30 ft or 40 ft fishing boats to large 
naval survey vessels. The only requirement is 
sufficient enclosed cabin space for the thumper 
and recorder components. Towing booms are easily 
rigged for support of the transducer fish. For 
small vessels, a 4" x 4" timber across the stern 
or a boat davit can be used. The transducer 
fish is towed by means of a rope or cable which 



(1) Braincon Corporation Type 108 V-Fin 

(2) EG&G Model 261 Transducer Fish 



should withstand at least 1,000 pounds for an 
adequate safety factor. Cable tension depends 
on towing speed and is considerably leas than 
1,000 pounds unless fast speeds of over ;: ::nots 
are required. Ordinarily, water, and ship noises 
become excessive above 5 knots; tL^vefore towing 
usually will be below this speed. 

The larger thumper units simply require 
a little more space for electronic components 
than the standard model. The symmetrical trans- 
ducer can be mounted horizontally or vertically 
because the frequency of the pulse is so low 
that it creates an essentially spherical wave 
front with equal signal irtensity in all direc- 
tions. 



III. Receiving System 
A. Noise Problem 

Before reviewing possible hydrophone 
setups for a receiving system to use with the 
thumper, a consideration of noise problems is in 
order. The sources of troublesome noise which 
may partially or completely mask the seismic sig- 
nal are: 1) Ship screw noises from propeller 
cavitation and drive shaft vibration, 2) Engine 
vibration transmitted through the ship's hull, 
■) Cavitation or burble produced by the hydro- 
phone and towing element moving through the water. 

Each vessel has its own characteristic 
noise level at various speeds. The optimum opera- 
ting speed is the maximum speed possible at which 
useable records can be obtained. Ship noises can 
be partially eliminated by towing either at a 
considerable distance behind the ship or on large 
vessels a long boom off the bow is sometimes 
effective. Distance between the receiver and the 
sound source can be varied considerably. Separa- 
tions of several hundred feet can be tolerated 
in relatively deep water. For shallow water re- 
flection work, the receiver should be relatively 
close to the thumper if an accurate representa- 
tion of shallow reflection layers is desired. 



B. Hydrophones 

A number of hydrophones are commercially 
available which are adaptable to the thumper 
system. The pressure type hydrophone with wide 
response is preferable. Preamplif ication of the 
signal may be necessary if a considerable length 
of cable is used. The preamplifier can be sealed 
in with the hydrophone unit or it can be used on 
board the vessel before the signal is fed to the 
recorder amplifiers. 

One approach for increasing signal to 
noise ratio is the use of a multiple crystal 
arrangement of detectors hooked in parallel with 
a null along the axis to partially cancel noise. 



285 



The National Institute of Oceanography of Eng- 
land reports good results at ship speeds up to 
7 knots using a multiple crystal arrangement in 
a plastic oil filled hose. EG&G markets an 
effective hydrophone with towing fish, the 
rocket hydrophone (see Figure 4 ). Braincon 
Corporation also markets a special "V"-Fin 
lollipop hydrophone which is suitable for use 
with the thumper system. 




Figure A. E.G.&G. Rocket Hydrophones. 



IV. SONAR RECORDER 

The thumper has been successfully recorded 
with a number of systems. Excellent results 
have been obtained by using the Alden Precision 
Graphic recorder and the EG&G Model 250 Sonar 
Recorder, both of which use Alden Alfax paper. 
These recorders work on the same principle of a 
resilient negative helix electrode and a posi- 
tive moving loop electrode, which provides high 
accuracy and resolution. 

The EG6eG Sonar Recorder was designed spe- 
cifically for use with the Sonar Thumper and 
EG&G's Sonar Finger. Figure 5 shows the Sonar 
Recorder in operation on a contract job for the 
U. S. Corps of Engineers. The recording unit 
is compact and versatile and emphasizes sim- 
plicity and ease of operation. Three recording 
speeds are provided to give basic full-scale 
sweeps of 50 fathoms, 200 fathoms and 800 
fathoms. A record gating system allows presen- 
tation of the first, second, third, or fourth 
sweep after keying; thus the 0-50, 50-100.-.., 
0-200, 200-400..., 0-800, 800-1600... fathom 
intervals can be recorded, depending on water 
depth and scale desired. A middle keying 
feature is also provided to give greater scale 
flexibility. 

Sweep accuracy is .005% derived from an 
internal tuning-fork oscillator. Recording c.-.n 
be either full wave, positive half wave, or 
negative half wave. Connections are provided 
for independent headphone monitoring and oscil- 
loscope display of the signal being recorded. 
The paper feed speed is controlled by a sepa- 



rate shunt wound motor with continuously vari- 
able speed control. An event marker line can 
be recorded either with a panel-mounted button 
or remotely. 

Amplifier response can be selected to give 
either a broad band for thumper recording or 
12-1 "■ locycle peaked response for pinger record- 
ing. A built-in RC filter can be cut in for 
reducing high- or low-frequency noise on the 
broad-band response. A separate variable 
filter can also be used to provide fine control 
of frequency response. 




Figure 5. Sonar Recorder at left. The seis- 
mic returns were also recorded on the tape 
recorder at the right for experimental replay. 



V. ELECTRICAL POWER REQUIREMENTS 

The power requirements for the thumper 
seismic system can be supplied by a ship's gen- 
erator or auxiliary generator. A voltage fluc- 
tuation may be noticeable when the thumper is 
fired because of the high peak currents. There- 
fore it is reconmended to run the thumper on a 
separate generator, if possible, to avoid volt- 
age fluctuations to the recorder. 

Many generators are available for sale or 
rental which are suitable for powering the 
thumper. A portable unit with a minimum of 2 
kilowatts, 110 volts or 220 volts, 60-cycle a.c. 
is perfectly adequate for the standard thumper. 
The larger thumper units require somewhat 
larger generators. For example, a 5000-watt- 
second unit with a firing rate of 2.5 sees 
requires a 4-kilowatt generator or larger. 



VI. FIELD SURVEY PROCEDURES 

Assuming that a specific program with de- 
sired coverage has been outlined, an experimen- 



286 



tal program should be carried out initially to 
optimize filter settings and field procedure. 
The initial program may require several days, 
particularly if the survey area is extensive. 

An experimental program should be carried 
out in a geologically known area if possible. 
If cores or probe information is available in 
an area, initial thumping should be done over 
these areas. Filter settings should be opti- 
mized in a known area to best delineate the 
features of greatest interest, such as bedrock 
depth. If any known structural features near 
the prospect area, such as faults, can be 
initially delineated, it will be of great help 
in recognizing similar features in the unknown 
area. 

Optimum boat speed can be determined 
during initial work. The filter settings, gain, 
paper speed, positive, negative, or full-wave 
recording, and the most efficient procedures 
can also be optimized. 

If radio positioning techniques are used, 
calibration and position-checking can be done 
during the initial program. Whenever a posi- 
tion fix is made, a remotely controlled marker 
can mark the record. For rough reconnaissance 
work, celestial navigation and dead reckoning 
may be sufficiently accurate. If the survey is 
carried out near shore, it may be possible to 
obtain accurate fixes from charted shore land- 
marks. 

It is desirable to keep one man stationed at 
the recorder to record station numbers continu- 
ously and monitor recording results as the survey 
progresses. Any features of particular interest 
can be immediately marked on a map for future 
reference. The surveyor, navigator, or radio 
positioning operator can automatically mark the 
thumper record with the remote event marker when 
a position fix is made. The Sonar Recorder op- 
erator marks the corresponding time or station 
number directly on the record to correspond to 
the event mark. 



VII. APPLICATIONS AND RESULTS 

A. Providence River Channel Survey for the 
U. S. Corps of Engineers 

The Providence River Channel thumper survey 
was done to delineate portions of the channel 
where bedrock or boulder removal will be neces- 
sary for a dredging grade level of 45 feet below 
mean low water. The field survey was commenced 
8 May 1961 and completed 19 May 1961. The first 
day was spent in setting up equipment and the 
second day was used for experimental work. 

The vessel used for the survey was a modern 
40-foot fishing boat with flying bridge. The 
boat was equipped with two-way radio and a 
fathometer. 



Boat positioning was done by sextant angle 
to charted landmarks on the shore. Sextant 
ai.gle charts covering most of the Providence 
River Channel area enabled the surveyors to plot 
station positions continuously as the survey 
proceeded. 

Equipment used consisted of the standard 
Sonar Thumper unit, the Sonar Recorder, a BC50 
Atlantic Research hydrophone, and a Minneapolis- 
Honeywell lollipop hydrophone, and "V"-Fin 
towing fishes for the transducer and the re- 
ceiver hydrophone. Two electrical generators 
were used, one supplying 2 kilowatts for the 
Sonar Thumper and a small auxiliary generator 
to supply the recorder power. 

Three main longitudinal lines were run 
clong the channel, one down the middle, and the 
other two toward the sides of the channel. In 
areas where shallow bedrock or boulders were 
suspected, additional cross lines were run for 
added detail. Preliminary thumping was done 
near the area of previous core information. 
However, the only cores to bedrock in this area 
were in shallow water which was not navigable 
for the vessel. Good core information was avail- 
able soutli of the channel area west of Patience 
Island. A thumper traverse was run in this area 
to correlate to the core information. A portion 
of this thumper record is illustrated in Fig. 6. 
The Sonar Thumper was fired at a half-second 
repetition rate and half power. This faster 
rate gives greater resolution and is recommended 
for seismic studies which do not involve great 
depths. 









Figure 6. Thumper record of a traverse west of 
Patience Island, Narragansett Bay. The 50 
fathom sweep of the Sonar Recorder was used. 
The channel surface is shown underlain by an 
irregular reflection surface at 100 to 120 ft. 
Core information in this area shows bedrock at 
a depth of 111 ft corresponding to the irregular 
reflection surface. 

The optimum filter setting for this survey 
appeared to be 300 cps on the low end and 1200 
cps on the high end. Recording was done on the 
positive half-wave form. Paper speed was nor- 
Aially 2.2 inches per minute. The gain attenu- 
ation setting normally used on this survey was 
db, which represents full gain without a pre- 
amplifier. The recorder has a wide range of 
attenuation settings, from db to 80 db. 



287 



Tide gage readings were recorded continu- 
ously throughout the day at a shore station, and 
these readings were radioed to the ship and then 
recorded directly on the thumper seismic pro- 
files. Fathometer readings were taken at one- 
minute intervals corresponding to sextant po- 
sition fixes on major lines and 1/2-minute 
fixes used for detail work. Corrected mean-low- 
water depths were recorded for each station. 
A lead sounding line was used to calibrate the 
fathometer and a 2-1/2-foot correction was 
added to each fathometer depth. These fathom- 
eter readings were not absolutely necessary. 
However, they simplified the correction factor 
for the depth of the thumper transducer, depth 
of the hydrophone receiver, and distance be- 
tween the transducer and receiver. A constant 
correction factor was readily determinable . 
by comparison of the fathometer depth to tiie 
seismic profile recorded depth. This was ap- 
proximately 5-1/2 feet for the major portion 
of the survey. The transducer and hydrophone 
were towed at depths of approximately 3 feet 
each. The sediment velocity was estimated to 
be approximately that of sea water in the upper 
section of interest. This assumption is based 
on previous velocity studies in the general 
Narragansett Bay area by Woods Hole Oceanograph- 
ic Institution. 



on the basis of point-source parabolic patterns 
on the record. 

Because of the lack of usable core or 
probe information in this area, a probing study 
is recommended to corroborate the existence of 
boulders or bedrock in questionable areas. 
During the probing survey to be conducted, a 
close check on seismic records and correlations 
to probing will give considerably more informa- 
tion than was extracted from the preliminary 
study. 

B. Thumper Field Test by the U. S. Coast 
and Geodetic Survey 

A short familiarization and test run was 
made of the Sonar Thumper on board the U. S. 
Coast and Geodetic Survey vessel, the "Explorer", 
July 20 through July 24, 1961. Comparisons were 
made between the transducer mounted inside the 
ship in a well situated below the water line and 
on an externally towed transducer. The pulses 
from the internal well mounted transducer suf- 
fered considerable transmission losses through 
the hull of the ship. However, usable results 
can be obtained with an internal well mounted 
transducer, although depth of penetration is 
reduced. 




Figure 7. Thumper record from Hydrographers 
Canyon Area. The 200 fathom recording sweep 
was used. The depth scale is on the basis of 
4800 ft/sec water velocity. 



A number of thumper profiles were obtained 
across Hydrographer ' s Canyon. One of these is 
shown in Figure 7. The depth of penetration on 
these tests varied somewhat but was usually on 
the order of 400 to 600 feet and in some cases 
weak, but continuous events were detected at 
depths exceeding 1,000 feet. Water depth gener- 
ally varied from 50 to 300 fathoms. The stand- 
ard thumper was used for these tests and the EGG 
Sonar Recorder was used for recording. The ex- 
ternal transducer was mounted on a V-fin fish. 
A V-fin hydrophone and the EG&G Rocket Hydro- 
phone were used alternatively as receivers. 



A number of areas were located in the c lan- 
nel where bedrock removal or boulder removal 
appears to be necessary if deepening is to be to 
45 feet below mean low water. The best quality 
records were obtained in the southern portion of 
the channel where the probable bedrock surface 
can be delineated at depths of over 150 feet be- 
low mean low water. Some portions of the channel 
are characterized by very strong initial reflec- 
tions and subsequent multiples. This highly re- 
flective channel floor condition often results 
in a serious loss of subsequent sub-bottom re- 
flections at these locations. The high reflec- 
tivity of this initial layer may be caused by 
above-average consolidation of the bottom 
sediments. 

The bedrock surface in this area generally 
appears to be extremely irregular, and it is 
often difficult to determine whether an irregu- 
lar reflecting surface represents bedrock or 
large and irregular boulders. A number of 
boulder areas are suspected in the channel area 



VIII. 



CONCLUSION 



Many off-shore areas of the world have 
never been explored for possible oil structures 
because of the tremendous expense of maintaining 
conventional seismic crews and the expense and 
difficulty of obtaining explosives. Some locali- 
ties also forbid the use of explosives in off- 
shore seismic work because of possible damage to 
fish and navigational hazards to shipping in har- 
bors. Large thumper units of 5000 watt-seconds 
on up can of t en give sufficient penetration to 
be of great value as a reconnaissance tool in 
off-shore oil prospecting. The Sonar Thumper 
is simple, reliable and rugged, and requires 
nothing more than 110 or 220 volts a.c. for 
power. The effectiveness of the Sonar Thumper 
and high powers available, along with continuing 
improvements in receiving and recording equip- 
ment, are all factors which point toward the 
increasing future use of the thumper as an off- 
shore oil prospecting tool. 



288 



THERMOELECTRIC POWER FOR OCEANOGRAPHIC RESEARCH 

by MELVIN BARlvlAT, Manager, Thermoelectric Division 
General Instrument Corporation 
Newark, New Jersey 



The utility of thermoelectric generators in 
oceanographic research is outlined. The 
history and basic technology of thermoelec- 
tricity are briefly reviewed and generators 
currently being developed for oceanographic 
service are mentioned . 



Much of modern oceanograp'.iic research is 
conducted by the collection and transmission 
of data over long periods of time from 
unmanned stations. Furthermore, it appears 
that this trend is increasing in use. There 
are many potential missions in this category, 
but to mention a few 

1. anchored buoys with weather and 
oceanographic instrumentation 

2. bottom mounted instruments for 
current measurement and recording 

3 . freely moving buoys for following 
currents 

One of the most critical components of 
these systems is the source of power. A 
power supply for these missions must have: 

a. long life 

b. high reliability 

c . low volume 

d. freedom from environment 

e. low cost 

Thermoelectric generators now being 
developed for various government agencies 
give great promise towards fulfilling these 
requirements. Before describing these new 
developments I would like to briefly provide 
some background in thermoelectricity. 

In 1823, Johann Seebeck reported to the 
Prussian Academy of Sciences his discovery 
of a magnetic field when a temperature dif- 
ference was applied to the junctions of dis- 
similar metals. This magnetic field was, of 
course, due to the current developed by the 
generated voltage. Eleven years later, in 
183I4-, Peltier announced his discovery that 
heat was developed or removed at a similar 

iunction when a direct current electrical 
potential was applied. These have been 
classified as "thermoelectric" effects 

(See figures 1 and 2) For over fifty years 
these phenomena remained only laboratory 
curiosities, the physicist had too many other, 
more promising phenomena to explore. How- 
ever, in this first half of the present 



century the thermoelectric phenomena was 
widely applied for temperature measurement, 
in fact it remains today the most important 
method for scientific and industrial temp- 
erature measurement. 

It had been recognized for many years 
that these thermoelectric effects could be 
used for electrical power generation if a 
temperature difference were maintained 
between the junctions, or as a heat pump if 
electrical energy was applied to the system. 
However, it was not until the pioneering 
work of Maria Telkes in the U.S.A. and A.F. 
loffe in the U.S.S.R. that intermetalic 
semiconductor materials were utilized, 
resulting in the potentiality of acliieving 
useful efficiency levels. It has been the 
growth of knowledge of semiconductors that 
has given the impetus tc an even more wide- 
spread scientific and industrial interest in 
thermoelectricity. In this country there is 
considerable government supported research 
in the field of material and device develop- 
ment, due to potential applications as 
diverse as submarines and satellites. 

Why has this later work been so fruitful 
as compared to the earlier 130 years? It is 
the result of a happy coincidence; the 
previously mentioned development of solid 
state physics ana semiconductor technology 
coupled with a genuine industrial, commer- 
cial and military need for the kind of 
devices thermoelectricity makes possible. 
Understanding of the reasons for the greatly 
advanced thermoelectric utility of semi- 
conductors will enable us to obtain insight 
into thermoelectric material requirements. 

The properties of a thermoelectric mater- 
ial that govern its performance are: 

*^ Seebeck Coefficient - expressed as 
volts per unit temperature differ- 
ence, usually microvolts/" C. 

^ Electrical resistivity, usually ohm-cm 
K Thermal conductivity, usually watts/ 
cm°C. 

A thermoelectric generator, schematically 
shown in Figure 3 consists of a heat source, 
a cold dump, and a thermocouple (in normal 
practice, a number of thermocouples in 
series) . This device, to be efficient, 
requires a high output voltage, therefore 



289 



(a) 





HOT 
JUNCTION 



(a) 



COLD 

JUNCTION 

n 




POWER GENERATION 



I n 

HEAT PUMPING 



SCHEMATIC REPRESENTATION OF 
THERMOELECTRIC CIRCUITS WHERE 
A&B ARE TWO DISSIMILAR MATERIALS 

FIGURE 1 



THERMOCOUPLE CONSTRUCTION 



(b) 



HEAT ABSORBED 



HEAT EMITTED 



COLD END 



-^AAA- 

LOAD 



^^^■^H ^^^^^^ 


COLD END 






DC 
SOURCE 











POWER GENERATION 



PELTIER HEAT PUMPING 



FIGURE 2 



290 



*^ should be as large as possible and the 
temperature difference, hot to cold, should 
be as large as possible. If the thermal con- 
ductivity, K, is small then a smaller amount 
of heat will be required to maintain a given 
temperature difference. To minimize the 
amount of power consumed internally by the 
generator, the electrical resistivity, g , 
should be small. A figure of merit Z lo 
defined where 



Z = 



(2 /J 

is an index of material efficiency. The 
higher the value of Z the better the thermo- 
electric material. 

Now, with metals it is possible to obtain 
reasonable values ofocandfi, but it is not 
possible to get low values of K. Thus, the 
Z of metals is too low for useful power 
generating or cooling devices. With semi- 
conductors, however, even higher values of 
oC are obtainable and by the proper addition 
of impurities (doping) the relationship 
between ^ and K can be adjusted to give use- 
ful values of Z. 

Some of the intermetaUlc semi-conductor 
materials currently used are lead telluride, 
bismuth telluride, zinc antimonide, silver 
antimony telluride, all with various and com- 
plex dopings . Extensive work is currently 
being done to improve these materials and to 
find new ones with higher figures of merit 
(Z) over wider temperature ranges. 

In addition to the problems of semicon- 
ductor material one of the most serious pro- 
blems facing the designer of a thermoelectric 
device falls into the realm of heat transfer. 
The heat input must be sufficient to main- 
tain the hot junction at the desired temper- 
ature and the cold dump mechanism must be 
sized to maintain the proper cold junction 
temperature. The power level of some gen- 
erator design concepts is directly limited 
by-the cold side heat transfer. In the case 
of generators for oceanographic research, 
however, the sea can usually be used as a 
large and efficient heat sink. 

A thermoelectric device is used to con- 
vert heat into electricity, or vice versa. 
No discussion of. these devices is complete 
without examining the heat sources that can 
be used. All thermal energy sources can be 
classified as: fossil fuels, solar, chemi- 
cal, geophysical and nuclear. All these 
energy sources can, and most are, being 
applied to thermoelectric converters. 
Missions in space vehicles are primarily 
considering solar and nuclear and chemical 
heat sources while terrestrial or air-breath- 
ing applications are relying heavily upon 
fossil fuels. It is in these latter cate- 



gories that generators for oceanographic 
research can be found. 

Since both the initial and operating cost 
of a thermoelectric device will depend on the 
power and voltage level required, some atten- 
tion to this requirement is essential In 
some applications a continuous constant 
power level is required and the generator 
will be directly coupled, with suitable 
voltage transformation and regulation, to 
the utilization equipment. There will, how- 
ever, be many applications where the power 
requirement will be intermittent and an 
average power analysis is retjuired. Such 
applications may be periodic data trans- 
mission systems, alarm devices, flashing 
lights, etc. In these cases a low average 
power output may be stored in chemical 
batteries or capacitor systems, for use as 
required. Average power can be defined as 

Power consumption X 
time of consumption 



Avg. Pwr. 



Time of Cycle 



for example a data transmission system 
required 300 watts for 20 minutes every four 
hours 



300 X 20 
^^S. P^-=2i+0 mins. 



= 25 watts average 



A twenty-five watt power supply has consid- 
erable operating and capital cost economy 
compared to a 300 watt system. 

A second important consideration is 
selection of a heat source for a maximum 
economy, reliability, and availability. 
While nuclear and chemical heat sources have 
a most important role to play in undersea 
applications, fossil fuels, such as propane, 
are preferred in air breathing applications 
for economy reasons. In cases where volume 
is important in long life missions, a 
nuclear heat source can be used, if cost and 
hazard considerations are also in consonance. 

It would be interesting to consider the 
overall efficiency values that might realis- 
tically be expected from presently available 
fossil fueled devices and those that might 
reasonably be expected in the future. 







Near 


Efficiency component 


Present 


Future 


Thermoelectric 






converter 


5% 


8% 


Combustion 


7C^ 


75% 


Voltage conversion 


90P^ 


90% 


Energy Storage 


80% 


80% 


Overall 


2.5% 


M-.3% 



Since cost will always be a significant 
parameter in power sources, selection of 
a cost analysis for a typical application 



291 



CASCADING 



SEGMENTING 




^BH 






1^1 


B 


n 


T3 


A 




D 




ELEC 
CON 








B 






Ts 




T2 












C 




E 






Ti| 






^ 


^1 





CASCADING OR SEGMENTING OF T/E SEMICONDUCTORS TO OBTAIN 
OPTIMUM Z OVER SPECIFIC TEMPERATURE INTERVALS & THEREFORE 
OPTIMIZE DEVICE EFFICIENCY 

FIGURE 3 




FIGURE 4 
292 



will be made. 



Given: 



Power Required: 25 watt (average) 

Fuel: Propane at $20 gallons 

Near 
Present Future 



Fuel Cost per KW-hour 
(approximate) $.30 



.17 



The situation in regard to capital cost 
of thermoelectric generators is extremely 
uncertain at the present time and in the 
near future. Most generators now being sold 
are individually built for evaluation pur- 
poses and are priced at hundreds of dollars 
per output watt. Furthermore the useful 
life of these devices is not really known at 
this time. Thus, the annual costs attribu- 
table to the initial price of an operational 
unit must be based on at least pilot plant 
production and a projected, reasonable life 
time. Industry estimates of generator cost 
for small quantities in the twenty five watt 
region are in the ten to fifty dollars per 
watt range. If a conservative value of 
forty dollars be used, and a five year life 
is expected, the kilowatt-hour cost is 
approximately 80 cents. Comparing this to 
the estimated fuel cost, it can be seen that 
the capital depreciation can be the deter- 
mining factor in overall cost. It should be 
noted however, that these conservative cost 
estimates compare very favorably to all 
types of batteries as \\;ell as silicon solar 
cells . 

Figure ^ depicts a ten (10) watt thermo- 
electric power supply recently developed by 
the General Instrument Corporation for eval- 
uation by the U.S. Coast Guard. It is 
designed for use with shore based lights 
as well as large buoys and obviously is 
directly applicable to oceanographic 
research installations. This device uti 
lizes catalytic combustion of propane fuel 
as a heat source. The use of a catalyst to 
promote the reaction of propane and oxygen 
gives high combustion efficiency due to the 
low reaction temperature and it is virtually 
impossible to extinguish the reaction except 
by interrupting the fuel supply. It is 
designed to operate in near hurricane winds 
(70 mph) and in any position of roll. The 
system has an automatic restart provision in 
the event of excessive winds or swamping. 
The system tries to restart once an hour. 
In this way vie avoid the possibility of try- 
ing to restart under impossible conditions 
and thus depleting the energy storage 
system. 



Utilizing some similar design principles 
and techniques the General Instrument 
Corporation is developing a thirty (30) watt 
thermoelectric generator for the Bureau of 
Standards and the Navy's Bureau of Weapons. 
It is to be evaluated for use aboard their 
Gulf of Mexico based weather boat buoy- 
NOMAD. In comparison to the Coast Guard 
generator mentioned above, we will talce 
advantage of the sea water sink by directly 
coupling the cold junction to the hull below 
the water line. 

Fossil fueled thermoelectric generators 
are available from other industrial sources 
but, in general, these are not specifically 
designed for, nor take advantage of, the 
ocean environment. 

The U.S. Atomic Energy Commission, 
through its office of Isotope Development as 
well as its SNAP (System for Nuclear Auxi- 
liary Power) office of the Division of 
Reactor Development, is developing a series 
of radioisotope fueled thermoelectric gen- 
erators for oceanographic missions and 
environments. These are briefly discussed 
below. 

A five watt demonstration device is being 
developed for a Lament Geophysical Labora- 
tory mission using Cesium - 137 as the fuel. 
It is specifically aimed at the underwater 
environment since little shielding is pro- 
vided for the very penetrating radiations 
(Cs-137 is often used as a teletherapy 
source) . 

Strontium-90 is being employed as the 
heat source for another series of develop- 
mental thermoelectric generators in the five 
to thirty watt range. These units contain 
a considerable amount of shielding and can 
be used on land. The first of these has 
been built and is planned for early 
Weather Bureau service in the Arctic in 
conjunction with an automatic weather 
station. 

The obstacles to the widespread use of 
the above mentioned radioisotope fueled 
generators are; potential hazards and the 
high cost of separated radionuclides. In an 
effort to reduce the cost of radioisotope 
heat sources for the oceanographic environ- 
ment, the General Instrument Corporation, 
under USAEC sponsorship, is developing 
techniques for the utilization of Mixed 
Fission Products in thermoelectric genera- 
tors. The goal of our current effort is a 
demonstration device for unshielded, under- 
water use. There is a very large, existing 
AEC program, including an existing pilot 
plant, for the solidification and concentra- 
tion of nuclear waste materials, that 
directly assists these efforts. 



293 



APPLICATION OF MODERN REMOTE HANDLING TECHNIQUES 
TO OCEANOGRAPHY 

by JOHN W. CLARK 
Nucleonics Laboratory 
Hughes Aircraft Company 



INTRODUCTION 

Oceanography is an eclectic science covering a wide gamut of the older 
scientific disciplines. In accomplishing the objectives of oceanography 
one must, among many other things, obtain physical measurements of the ocean 
floor and the ocean itself. One must also obtain samples of the flora and 
fauna of the ocean, as well as geological or physiographic specimens from 
the ocean bottom. In the following discussion I would like to concentrate 
attention upon this data and sample gathering aspect of oceanography, since 
it is to this aspect that the new art of remote handling can make a genuine 
contribution. 

Modern remote handling technology, which is beginning to be recognized 
as a new subdivision of engineering, might perhaps be better described as 
the technology of accomplishing physical operations in hostile environments. 
This new technology is being created by a combination of electronic control 
engineering, human engineering, and remote handling techniques as developed 
by and for the nuclear industry. 

As a typical example of a modern system for operating within a hostile 
environment, let us consider Figure 1, which shows the Hughes Mark II Mobot 
system. This system, which was developed for use in nuclear laboratories, 
is mobile, being mounted upon a three-wheel chassis. It is controlled by 
means of a three-wire cable which may be as long as a few thousand feet. 
The "hands" and "eyes" of the machine are electronically commanded by its 
operator; practical experience has demonstrated that this system can accom- 
plish such complex functions as pouring, stacking, operating power drills 
or wrenches and the like, employing only electronic communication means be- 
tween operator and vehicle. The experience gained with this and similar 
machines forms an effective starting point from which underwater handling 
systems can be developed to accomplish specific oceanographic tasks. 



REMOTE HANDLING VOCABULARY 

The new technology of remote handling and operation in hazardous areas 
is sufficiently unfamiliar as to justify a preliminary discussion and a few 
basic definitions before exploring in more detail the applications of this 
technology to underwater programs. 

In most general terms, consider Figure 2, which shows a hazardous area 
in which one desires to perform some operation. This area may be hazardous 



294 




PROTECTIVE BARRIER 



HAZARDOUS AREA 




^-^-""^ 


1,-^ 


T 









SAFE AREA 










( 


^ 


A 


i 



GENERALIZED REMOTE HANDLING SITUATION 
Figure 2 



295 



due to lack of air, the presence of nuclear radiation, to high temperature, 
or to any other hostile environment which makes it impossible for a man to 
enter. The operations required may be equally broadly considered. Typi- 
cally, it is necessary to translate objects from one position to another, 
to operate tools, such as screw drivers or wrenches, or to operate measur- 
ing equipment of many kinds. Usually, fixed obstacles are contained within 
the hazardous area, limiting the freedom of motion of any equipment con- 
tained therein. 

A typical problem to be handled by a general-purpose underwater remote 
handling system is that of engaging a power-operated wrench with a nut or 
screw. This engagement and the operation of the wrench itself must, of 
course, be done in a manner which is independent of the separation between 
the operator who controls the operations and the equipment, and it must be 
done even in the presence of numerous fixed obstacles. 

In the past, problems of this type have sometimes been attacked by 
the use of long tongs or forceps. Some of these have become extremely com- 
plex and have employed hydraulic or electromechanical actuators to supple- 
ment the physical strength of the operator. All such devices may be con- 
sidered extensions of the man's arms, and the man himself is just outside 
the hazardous area and protected from it by a suitable barrier or shield. 

Let us approach this problem in a more generalized way, and let us 
assume that the separation between the hazardous area and the safe area is 
so great that tong-like tools cannot be used. This requires us squarely 
to face the problem of operating in areas which are inaccessible. This is 
sometimes done by providing the operator with protective clothing suitable 
to the environment. Movable personnel shields may be used in nuclear en- 
vironments, and the space suit of science-fiction is often proposed for the 
space environment. 

In all such cases we find that we have actually not solved the problem. 
We have, on the contrary, merely changed the geometry. The safe area is now 
contained within the hazardous area, but the operator is still separated 
from his work by his protective system and must use tongs rather than his 
own hands for manipulation. 

From the viewpoint of solving the fundamental problem of operating 
within an inaccessible as well as hazardous area, let us analyze a man as 
a handling system. For this purpose we may ignore many of his more inter- 
esting attributes and note that just four interrelated systems are involved. 
These may be identified briefly as his brain, his eyes, his hands, and his 
feet. More seriously, the eyes and the sensory nervous system provide in- 
formation concerning his surroundings. The hands, as controlled by the 
motor nervous system, are able physically to move objects as desired. The 
feet and legs, controlled by their separate motor nervous system, enable 
the entire organism to move about; and finally, the brain assembles and or- 
ganizes all these data and directs the motor systems as required. 

The three functions symbolized by eyes, hands, and feet may readily 
be extended by modern electronic means over any desired distance. In this 
way, a man's senses and his ability to accomplish useful work may be extended 
to any distance, while his brain, which can be duplicated by no existing com- 
puter, remains in safety and comfort at any desired location. 

296 



This simple concept is the basis of the new technology of hostile en- 
vironment operations. Remote handling systems (' Mobots") ere not to be 
looked upon as competitive with a man in a diving suit or diving bell; 
rather, the effective utilization of such systems v;ill increase the abili- 
ty of the man to accomplish functions in the depths of the ocean. This 
paper is concerned primarily with n preliminary outline of ways in which 
the modern concept of remote handling systems can be applied to several 
realistic underwater situations. 



ANALYSIS OF GENERALIZED REMOTE HANDLING SYSTEMS 

In order to analyze in a systematic manner any hostile environment 
problem, it is highly desirable to consider the basic subsystems which 
make up any remote handling system. Figure 3 presents a generalized 
block diagram of any remote handling system. Consideration of this block 
diagram leads to an understanding of the fundamental elements which make 
up any remote handling system so that the design of such systems may be 
approached in an orderly and systematic manner. 

As noted above, remote handling systems are artificial extensions of 
man's senses and muscles over considerable distances. In order to accom- 
plish this, in addition to the systems which duplicate the senses and 
muscles, a link must be provided actually to bridge the physical gap be- 
tween the man and the remote machine, and a control console must be pro- 
vided with which the man communicates with the remote machine. 

Figure 3 shows the interrelationship among the six subsystems which 
make up any remote handling systems. These subsystems, as discussed in 
somewhat more detail below, may be identified as follows: 

the manipulating subsystems ("hands" and "arms") 

the sensory subsystems 

the locomotion subsystems 

the command and data link 

the power subsystems, and 

the control console. 

As a further addition to the vocabulary of this topic, the term 
"Mobot* Vehicle" has been coined to refer to the mobile remote portion 
of the system. Mobot vehicles are mechanical units and are the most con- 
spicuous portion of remote handling systems in action. One basic psycho- 
logical observation can be made, namely, the ease with which a Mobot oper- 
ator learns to identify himself with the Mobot vehicle and to forget the 
existence of the interconnecting systems. This psychological identifica- 
tion appears to be a basic necessity for successful operation of fully- 
remote handling systems. 

Let us consider briefly the requirements upon the several basic sub- 
systems. 



*Trademark of Hughes Aircraft Company 



297 



The Manipulating Subsystems . It seems impossible to avoid the anthropo- 
morphic terms, hands and arras, to refer to the manipulating devices. In 
general, however, these do not much resemble human hands or arms, but are 
designed specifically to perform tasks as required. It is extremely diffi- 
cult to rival the versatility of the human hand. However, special-purpose 
handlers can usually out-perform the human hand in either dexterity, 
strength, small size, or other specific attributes. In addition to having 
sufficient strength to handle the assigned tasks, Mobot manipulating sys- 
tems must be able to work in the presence of obstacles and to perform com- 
plex and intricate motions. 

The Senses . While all the human senses can rather readily be trans- 
mitted via electronic means, vision is the most important by far, and the 
only one which will be discussed in this brief analysis. 

Spatial orientation is normally accomplished by a variety of methods. 
Parallax, scale, relative motion, and the like, are probably most important 
of these. Binocular vision is surprisingly unimportant, as demonstrated by 
the fact that one-eyed men are but little handicapped in perceiving spatial 
orientations in their vicinity. Based on this analysis, excellent success 
has been obtained with a simple vision system utilizing two TV cameras, as 
sho^\m in Figure 4. These two cameras show the operator two mutually per- 
pendicular projections of the area viewed, from which he can learn to deduce 
the spatial orientation of all objects within his visual field. Learning 
time of a few hours has proven quite adequate for this system. 

Certain special problems are often encountered in underwater viewing 
due to the fact that in many cases the ocean water is turbid or murky and 
presents a rather inadequate optical medium. A variety of methods are 
available to aid the operator's vision. For example, the skillful place- 
ment of artificial light sources may reduce the scattering of light by 
suspended particles in the water and improve operator visibility. The use 
of intense pulsed light sources synchronized with the frame-rate of the TV 
cameras may also be helpful. For long distance vision, sonar systems may 
be preferable to optical systems. While sonar systems are limited in their 
ability to resolve extremely fine details, they may furnish to the operator 
completely adequate information for navigation of his remote handling sys- 
tem until it comes within the rather limited range of the optical systems. 

As a general principle of Mobot system design, the engineer makes 
fullest use of all sensory inputs available to him. These may include, 
in addition to sonar and optical vision, touch, hydrostatic pressure, sys- 
tem attitude and heading, apparent speed and direction of water flow past 
the Mobot vehicle, and a variety of others. 

Locomotion . In order for the Mobot to move freely about in the under- 
water environment, several different means of locomotion are available. 
The remote handling engineer will select the one best suited to the parti- 
cular problem presented to him; in many cases a combination of Mobots em- 
ploying different means of mobility is the most economical solution. 

The distinction between handling and locomotion is an important one 
which is basic to effective handling system design. The term "manipulation" 
is reserved for complex and delicate motions, as described in the section 
preceding. The term "locomotion" refers to the process of bringing the 

298 



fNyiRONMENT 



HoSTiLE 



^A/l'/eONMeMT 






DiS PLAYS 



COMMAfvD 
CONTI?0L5 



COMMAND f DATA UNk: 






MANIPULATOR 
ACTUATORS 






LOCOMOTION 
MOTO/^^ 



Console 



MO&OT VCHICLE 



Figure 3 





299 



manipulating devices within reach of the object to be manipulated. In many 
cases, in addition to methods for moving the entire vehicle about, auxiliary 
locomotion subsystems taking such configurations as telescoping lifts, jack- 
knife booms, or the like, may be employed to enable the operator to position 
his handling arms without requiring him to move the entire vehicle. 

For general-purpose operations, a versatile Mobot may be suspended by 
a cable from a barge or other surface vessel. Gross motions of the Mobot 
are accomplished by maneuvering the surface vessel; fine control may be ac- 
complished by small propellers on the Mobot with which it can locate itself 
precisely . 

A freely-moving Mobot is sometimes preferable. This can be accomplished 
by providing sufficient power to drive propellers which will propel the Mobot 
in any desired direction. Depending upon the situation, one may wish to fur- 
nish Mobots which travel mainly horizontally (like unmanned submarines) or, 
in contrast, Mobots which travel mainly vertically (like an underwater ver- 
sion of a helicopter). 

For maneuvering heavy objects or for detailed exploration of the sea 
bottom or similar applications, bottom-crawling vehicles are desirable. 
These may be adaptations of caterpillar tractors or tanks or, alternatively, 
may use large soft rubber tires; in any case, the familiar techniques which 
may have been developed for off-road vehicles on land can be employed under- 
water as well . 

Command and Data Link . This link is the communication medium between 
the operator and the Mobot. It transmits from the operator to the Mobot the 
command information which directs the Mobot 's motions; and it transmits from 
the Mobot to the operator sensory data which inform the operator of the situ- 
ation at the Mobot. Most important of the sensory data is the television 
information which (unless special systems are employed) requires an extremely 
wide band-width. In addition, sonar information and other data such as tem- 
perature, radioactivity level, pH of the water, and the like, may be trans- 
mitted. This link must obviously be capable of providing command information 
at a sufficiently rapid rate to control the Mobot, and of transmitting sen- 
sory data from Mobot to operator, again at an adequate rate. Since a cable 
must be provided to enable the operator to communicate with the Mobot (this 
is necessary since radio energy does not propagate in sea water), this same 
cable can be used to transmit electrical power to the Mobot. Modern multi- 
plexing technique makes it quite feasible to combine the two functions of 
communications and power in a very small number of electrical conductors. 

For very long distances the mechanical problems involved in handling 
the cable and the electrical problems involved in transmitting energy through 
it become quite formidable. It may therefore be necessary in such cases to 
employ repeaters within the cable to facilitate the transmission of command 
and TV information. This obviously implies the necessity for furnishing 
power by other means. In some cases it may be desirable to construct perma- 
nent underwater conduit installations, thus eliminating the necessity for 
carrying the entire length of cable on the Mobot itself. 

Power Subsystems . Power subsystems for remote handling systems are 
based upon standard power technology. In most cases prime power for under- 
water mobile vehicles is best transmitted through the cable which serves 

300 



as the command and data link. In order to economize on copper, power is 
transmitted at high voltage and a local distribution system is included 
within the mobile vehicle. Hydraulic power is highly advantageous for 
underwater actuators, for handling arms, as well as wrenches, jacks, and 
other auxiliary power tools. Accordingly, one often includes a hydraulic 
power subsystem within the Mobot vehicle. 

Large and heavy vehicles, or vehicles required to operate at very 
great distances from the operator, may more economically generate prime 
power within the vehicle itself rather than transmitting it via cable. 
Any power system capable of operating within the ocean can of course be 
used for such vehicle. The control of the power subsystem is accomplished 
through the Mobot command system which, without difficulty, can accommodate 
the necessary additional command channels. 

Control Console . The control console, or control subsystem, is the 
man-machine link, the only point in which the human operator interacts with 
the Mobot system. Human factors engineering methods are fully applicable 
to control console design. Uppermost in importance is minimizing of oper- 
ator fatigue so that a man can spend long periods at the console without 
undue deterioration of his performance. 

As noted above, an experienced operator becomes completely unaware of 
the mechanics of the console itself and subjectively identifies himself 
with the Mobot vehicle. A most subtle point in console design is facilita- 
tion of this subjective identification. 



SCIENTIFIC APPLICATIONS OF REMOTE HANDLING 
TECHNIQUES TO OCEANOGRAPHY 

In the light of the foregoing general discussion of remote handling 
techniques and methods for operating in hostile environments, it may be of 
interest to describe a few applications of these techniques to oceanography. 
These illustrative examples are not intended to exhaust the subject; on the 
contrary, it is hoped that they will stimulate the thinking of the oceano- 
grapher and that as a result it will be possible to propose new advanced 
handling systems which will facilitate the obtaining of scientific informa- 
tion concerning the oceans and their contents. 

Vehicles for obtaining scientific information in the ocean may be re- 
quired to operate at or near the ocean bottom, or in some cases to obtain 
information concerning the ocean itself. This indicates a need for free- 
swinming vehicles as well as for vehicles which can operate on the ocean 
floor . 

The scientific observer is of course the most vital element in the data- 
gathering process. He may desire to be reasonably close to the site of the 
information to be gathered, in a diving bell, submarine, or Bathyscaphe. In 
some cases, on the contrary, he may prefer to remain in a surface vessel or 
shore station from which he can control the motions of a Mobot vehicle and 
can see, hear, and feel the local situation with as much or more facility as 
if he were physically present. This rather subjective data-gathering process 
is of course added to the more physical capability of gathering specimens. 
It is to be noJted that the specimen-gathering process, as accomplished by 

301 



remote control, is in some respects decidedly advantageous as compared to 
the "blind" obtaining of specimens by various pieces of equipment dropped 
over the side on lines or cables. In the former case one not only obtains 
the specimen, but also considerable information concerning its nature and 
surroundings. 

General-Purpose Underwater Handling System . Figure 5 illustrates a 
general-purpose remotely-controlled underwater handling system which might 
be called a "remote-controlled deep sea diver". This freely- swimming sys- 
tem can maneuver either vertically or horizontally and can rest on the bot- 
tom if desired. It is equipped with general-purpose handling arms with 
which it can gather specimens either biological or geological. Its activi- 
ties are directed by means of TV and sonar; the additional senses, such as 
touch, temperature, pressure, etc., can be added if desired. The cable, 
which contains only three electrical conductors, transmits electric power 
to the vehicle as well as serving as a data and command link. One can 
readily visualize a great variety of uses for a machine of this type in ex- 
ploration of the ocean bottom, in locating and perhaps even reading scien- 
tific instruments on the ocean bottom itself, as well as in the basic pro- 
cess of gathering scientific specimens. 

Accessory System for Bathyscaphe . Bathyscaphes and other vessels in- 
tended for exploration of the very deep ocean offer the important ability 
to bring the man in the near vicinity of the area to be explored. The 
Bathyscaphe, as such, seriously limits the activity of its occupant to 
visual observation of his surroundings and to taking readings on perma- 
nently installed scientific instruments. 

The attachment to the exterior of a Bathyscaphe of even a simple re- 
mote handling system would greatly increase the effectiveness of the scien- 
tific observer, since it would enable him physically to handle and work with 
the items in his surroundings, as well as merely to look at them. Such han- 
dling systems might range from a simple arm mounted upon the exterior of the 
vessel to a complete auxiliary Mobot system, including both handling arms 
and supplementary TV vision which could operate up to some little distance 
away from the Bathyscaphe. This latter combination would eliminate the 
necessity of maneuvering the Bathyscaphe itself, which is a rather diffi- 
cult and power -consuming operation. Systems intermediate in complexity 
between these two can of course be readily engineered to meet the require- 
ments of particular programs. 

It is important to realize that even in the case of manned submersibles 
one is still confronted with the hostile environment operating problem. The 
man is not "really there". He is separated from his surroundings by the 
pressure hull of the Bathyscaphe, and his senses and his manipulations must 
of necessity be accomplished by remote control equipment of some sort. 

Bottom-crawling Systems . It is sometimes desirable to employ remote 
handling systems which move about on the ocean floor as opposed to the free- 
swimming systems discussed in the preceding paragraphs. Figure 6 shows a 
typical system of this type. Like all Mobot systems, it is remotely con- 
trolled by means of a cable. The man who directs its motions may be located 
either on a shore station or on a surface vessel, depending upon the sur- 
roundings. The principal utility of a bottom-crawling vehicle lies in its 
ability to handle heavy objects. It may also be equipped with earth-moving 

302 





303 



equipment, such as a bulldozer blade or a power shovel so that extensive 
excavations or structural work can be accomplished. It is realized that 
this type of effort is not of direct application to scientific oceano- 
graphy; one may however find it necessary in connection with oceanographic 
investigations to excavate the ocean floor or to install rather complex 
permanent structures thereon. 

A bottom-crawling vehicle may be equipped with an "underwater heli- 
copter". This accessory will enable the operator to lift the vehicle off 
the bottom in order to avoid underwater cliffs, crevasses, or other 
obstacles. 



CONCLUSION 

The foregoing sections have outlined some of the major principles of 
hostile environment operating technology and the applications of these to 
oceanography. It is to be hoped that this discussion will stimulate new 
ideas in this general field. Experience to date in both nuclear labora- 
tories and underwater operations has clearly demonstrated that equipment 
of the type discussed is completely practical, and in many cases is also 
economic as compared to alternate methods of accomplishing the same func- 
tion. A great deal of activity is now in progress in this branch of en- 
gineering; it is to be expected that in the very near future numerous sys- 
tems of the type discussed will become a reality and will become a creative 
part of the total complex of equipment available to the oceanographer . 



304 



PORPOISE - OCEANOGRAPHIC RESEARCH VEHICLE 



by W. L. CANNON, Project Engineer 
Chance Vought Corporation 
Dallas, Texas 



ABSTRACT 



A description of an oceanographic research 
vehicle called Porpoise is presented. The 
vehicle, under development by Chance Vought 
Corporation under contract with the Office of 
Naval Research, is essentially an underwater 
glider that utilizes buoyancy control as a 
means of propulsion. The vehicle described is 
12 feet in length with a maximum range of about 
26 nautical miles and a depth capability of 
1,000 feet. Performance increases are predicted 
for various sizes of vehicles using several 
types of gas generators. 



INTRODUCTION 

Porpoise is an underwater g_; ider that 
utilizes buoyancy control as the motivating 
force to obtain forward velocity. The vehicle 
is being developed as an oceanographic research 
vehicle by Chance Vought Corooration, under a 
license agreement with Oceanic Systems 
Corporation. At the present time Chance Vought 
has a contract with the Office of Naval Research 
to design and fabricate one vehicle for demon- 
stration of the feasibility of the concept for 
oceanography . 



CONCEPT AND OPERATION 

Fig. 1 shows a sketch of the Porpoise 
vehicle and a portion of a typical mission 
profile. The mission would begin with launch 
of the Porpoise vehicle from an oceanographic 
vessel. The launch operation would consist of 
simply lowering the vehicle into the water 
from the deck of the ship and releasing the 
vehicle on the desired heading. The vehicle 
will take on water through the flood valve 
while the entrapped air escapes through the 
vent valves located along the upper surface 
of the vehicle. Since the flooding begins 
forward of the center of gravity, the Porpoise 
vehicle will pitch over and, as it becomes 
negatively buoyant, begin its descent. At a 
preset depth below the ocean surface, perhaps 
60 feet, a hydrostatic pressure sensing con- 
trol mechanism will close the flood valve and 
the vent valves. At this point, the vehicle 



will be full of water and will descend at an 
angle of approximately Ik degrees with a ve- 
locity of about 10.5 knots. Then, at a pre- 
set depth, the compressed gas control valve 
will be opened, allowing the air or nitrogen 
from the storage tank to enter the ballast 
compartment. The water is then expelled from 
the ballast compartment through the ballast 
outlet valve which is a spring loaded valve. 
Since the water is expelled from the forward 
portion of the vehicle first, a moment is 
obtained which causes the vehicle to begin a 
pitch-up maneuver. When the water is completely 
expelled from the vehicle, and the gas flow 
terminates, the pressure across the hull 
equalizes and the spring loaded ballast out- 
let valve closes. The vehicle now is posi- 
tively buoyant and is rising at an angle of 
about 14 degrees and a velocity of approxi- 
mately 10.5 knots. As the vehicle approaches 
the surface, the depth sensing mechanism opens 
the flood valve and the vent valves to again 
flood the vehicle. Then, of course, the 
vehicle becomes negatively buoyant, pitches 
over, and begins another cycle. 

The wing configuration is designed to pro- 
vide high roll stability, and the wings have 
equal angular travel (ll ) both up and down 
since the wings will be up when the vehicle 
is gliding downward and down when the vehicle 
is gliding upward. 

The instrumentation payload is located in 
the nose of the vehicle. The payload case 
will be separated from the ballast compartment 
by a double watertight bulkhead to facilitate 
instrumentation payload installation and re- 
moval. This allows all instrumentation check- 
out, calibration, and maintenance to be done 
in the laboratory, then installation of the 
payload case on the vehicle just before the 
vehicle is launched. By providing a number of 
payload cases with different instrumentation 
configurations, a good flexibility of mission 
types would be available with a minimum of 
change to the vehicle or any payload case. 

The flotation and marker system will be 
actuated on the final cycle of the mission as 
the vehicle reaches the surface. The flota- 
tion bag is inflated to a diameter of about 



305 




INITIATE BALLAST 
EXPULSION 



OPEN VENT VALVES ' AND 
FLOOD VALVE i TO FLOOD VEHICLE 



g^s/(?/v crA</ij&fer^/^.sr/es 



• CONFIGURATION 

LENGTH 

MAXIMUM DIAMETER 

WING SPAN 

SEMI-MONOCOQUE STRUCTURE 

HULL MATERIAL 

WING- MATERIAL 

TAIL MATERIAL 

WEIG-HT IN AIR 

PISPLACEMENT 

PROPULSION SYSTE^\ 

RECOVERY SYSTEM 



12 FT. 
20.S8IN, 
76 IN. 

100 6061 ALUMINUM 
O.SS 6061 ALUMINUM 
0.)2S 6061 ALUMINUM 
620 LB. 
108OLB. 

NITRO&EN 3OO0PSI 
INFLATABLE SPHERE 



PERFORMANCE 




PIVE AND ASCENT ANGLE 


14- DE&. 


VELOCITY 


10.E KT 


PERTH 


£00 FT. 


RANGE 


17 NM 


PAY LOAD CAPACITY 


1CU.FT.,100LB 


OPERATING- CYCLES 


4 



y^^A^a^ ^/yff/Z!f7yC!^/t^ 



LIQUID PROPELLANT 

14° lOS KNOTS 



ETHYLENE OXIDE 



z 

§100 




< 



HYDRAZINE 



PAYLOAP PERCENT OF 

TOTAL VEHICLE PISPLACEMENT y67. 

'107. 

.15% 

-207. 

•257. 




VEHICLE LENGTH -FEET 



VEHICLE LENGTH-FEET 



306 



3 feet to insure that the vehicle will remain 
afloat even if any of the various flood and 
vent valves leak. hIso, the flotation bag will 
be painted a highly visible color and perhaps 
have a radar reflective surface . 

Fig. 2 shows In tabular form the physical 
and performance characteristics of the first 
Porpoise vehicle. It is emphasized that the 
performance data is for a vehicle equipped 
with a 3)000 psi gas storage cylinder. With 
a solid or liquid fueled hot gas generator, 
which is proposed as the system for the opera- 
tional vehicle, the performance will be greatly 
increased. For example, with a hydrazine or 
ethylene oxide gas generator system, this 12 
foot long vehicle would have a range of about 
26 nautical miles and a depth capability of 
at least 1,000 feet. Also, use of a hot gas 
generator in a 12 foot vehicle will allow 
increasing the instrumentation payload to 
about 2.5 cubic feet. 



miles with a 10 cubic foot payload. Operating 
this vehicle at a maximum depth of 1,000 feet, 
the distance traveled per cycle is about I.33 
nautical miles, requiring about 1+2 cycles for 
the mission. If the maximum depth is changed 
from 1,000 feet to 2,000 feet, then the dis- 
tance traveled per cycle is about 2.6? nautical 
miles requiring only 21 cycles for a 56 nautical 
mile range. However, since the pressure against 
which the gas generator must expel the ballast 
is doubled, then the fuel requirement is ap- 
proximately doubled for each cycle. Therefore, 
total range will not change. Depth of operation 
is limited by the amount of fuel required for 
one cycle to that depth and by the pressure at 
which the decomposition of the ethylene oxide 
or hydrazine can be made to take place . 

The curves for various payload volumes as a 
percentage of total vehicle displacement simply 
indicate the effect of reducing fuel volume 
and increasing instrumentation payload volume. 



PROGRAM PLAH 

Under the present contract with the Office 
of Naval Research, Chance Vought will design 
and fabricate one twelve foot long vehicle 
configured with a compressed gas system. The 
vehicle will be delivered to the Navy in early 
1962. Proposals for follow on work including 
additional vehicles, a hot gas generator de- 
velopment program, and a field test program 
are currently being evaluated by the Office 
of Naval Research. The test program proposed 
consists primarily of feasibility demonstra- 
tions in the Dabob Bay test facility of the 
U. S. Naval Torpedo Station, Keyport, 
Washington. The instrumented test range of 
the Dabob Bay facility is considered to be 
ideal for the initial demonstration since 
tracking accuracy of about ± 1 foot is ob- 
tainable. Water depth is about 60O feet and 
total available range at the facility is 
several miles. Therefore, for demonstration 
of the full capabilities of the hot gas 
generator configured Porpoise, it will be 
necessary to move to the open ocean. 



FUTURE CAPABILITIES 

Fig. 3 shows the range performance which 
is expected from Porpoise vehicles of various 
sizes with two types of liquid monopropellant 
fueled gas generator systems . Vehicle length 
is plotted eigainst range since range remains 
practically constant for a given amount of 
fuel regardless of the maximum depth of opera- 
tion. For example, a 20 foot vehicle con- 
figured with an ethylene oxide gas generator 
system would have a range of about 56 nautical 



The use of hydrazine fuel in the vehicle 
will result in a 10^ or 155^" greater performance 
than that obtainable with the ethylene oxide 
fuel. However, hydrazine costs about $3.00 
per pound whereas ethylene oxide costs only 
about $0.25 per pound. The difference in cost 
may well Justify selection of the ethylene 
oxide for most applications. 

Similar performance curves are shown in 
Fig. h for a soxid propellant fueled gas genera- 
tor and a water reactant fueled gas generator. 
An obvious disadvantage of the solid propellant 
system is that a separate propellant cartridge 
or chajTge must be provided for each cycle de- 
sired, and each cartridge must be sized to 
expel the water ballast at a specific maximum 
operational depth. If it is desired to go to 
a greater depth, two or more charges must be 
fired simultaneously. Therefore, maximum 
range can be obtained only at the cartridge 
design depth and even multiples of that depth. 

The water reactant curve shown indicates 
that lithium hydride as a fuel could provide 
more than twice the performance of the solid 
or liquid fuels. However, lithium hydride as 
a fuel for Porpoise may be further in the 
future than the other fuels because of avail- 
ability, cost, and the difficulties that may 
be encountered in controlling the lithium 
hydride gas generation reaction. 

Fig. 5 illustrates some profile variations 
attainable with future Porpoise vehicles. 
Since the vehicle is a glider, the limits on 
flight path angle and velocity are relatively 
small. By simply providing a wing Incidence 
adjustment, it will be possible to obtain a 
velocity of about 15 knots at a 20° glide 
angle. This, of course, reduces the horizontal 
distance traveled per cycle for the same 



307 



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SOLIP PF?OPELLANT GAS 
<S-ENERATOR 

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ABOUT 15 KNOTS 10.5 KNOTS 
SHORT RAN&E 



^10°&LIDE 
ABOUT 5 KNOTS 
LONG- RAN&E 



WITH SIMPLE CONTROL SYSTEM 




308 



maximum depth. Conversely, range and endurance 
can be increased by changing to a glide angie 
of about 10 degrees which will result in a 
velocity of about 5 knots. 

Variations in mission profile could be ob- 
tained in future vehicles by addition of a 
simple heading control system. Before launch, 
the desired mission profile could be programmed 
into the heading control system, allowing the 
vehicle to perform circular, zigzag, or other 
maneuvers while gathering oceanographic data. 



COHCLUSIOHS 

It is believed that the Porpoise concept 
offers a unique and effective method of ob- 
taining oceanographic data. The vehicle size 
for most instrumentation payloads is small 
enough to be operated from existing oceanograpliic 
vessels. A vessel operating several Porpoise 
vehicles while also taking oceanographic data 
using the shipboard equipment would be able to 
collect data from large areas of the ocean 
simultaneously. In addition, utilizing a fuel 
such as ethylene oxide should make operating 
costs reasonable, and the simplicity of the 
vehicle inherently should provide high relia- 
bility and long life. 



309 



SCUBA AS A TOOL FOR SCIENTISTS 

by EUGENE K. PARKER 
General Engineering Laboratory 
General Electric Company 
Schenectady, New York 



ABSTRACT 

Scientists opportunity to observe under- 
water environment "in situ" by use of scuba 
(self contained underwater breathing apparatus). 
The "Scuba Zone" encompasses: Air-water barrier 
through hyperbenthal, mesobenthal, hypobenthal 
to parahypobenthal stratas to a depth of 150 
feet. Description of scuba. Comparison with 
some other underwater observation and sampling 
devices. The Use of scuba by scientists. 



THE PAPER 

From the shoreline out to a depth of 50 
meters lies an area called the scuba zone. This 
is the zone accessible to the scuba (self- 
contained underwater breathing apparatus) diver. 

(Fig. 1 The Scuba Zone) 

For centuries man has waded the tidal pools 
and shallows. He has sailed the surface. He 
has probed into the water; raking, scratching, 
netting, and dredging up samples of underwater 
life and bottom. More recently he has invaded 
this domain in diving bells, suit and helmet 
rigs and underwater vehicles. None of these 
have permitted man to comfortably study the 
underwater ecology with an appreciable degree 
of ease or continuity. 

The advent of workable scuba has changed 
this picture. Instead of trudging on the 
bottom, or hanging suspended, man has almost 
attained the freedom of a fish. As yet his 
free diving range is limited to relatively 
shallow waters. Recent experiments with special 
scuba indicate that this range may someday 
extend to a thousand feet deep. (Hans 
Keller experiments) 

In this discussion we are concerned 
principally with diving at depths of twenty to 
fifty feet, occasionally to one hundred feet, 
and rarely to one hundred and fifty. 

Although sklndiving has become as socially 
acceptable as golf. Its acceptance by some 
scientists as a legitimate scientific medium 
has not grown proportionately. Many men of 
science have been deprived of the opportunity 
to make "in situ" examination and study of 
subjects within the "scuba zone". Sometimes 



this deprivation is because of real or assumed 
physical or psychological inability to use scuba. 
Occasionally it is because they feel scuba has 
little to offer. The purpose of this paper is 
to demonstrate the usefulness of this medium 
for underwater scientific study. 

That the scuba zone is still a fertile area 
for scientific exploration is becoming more 
apparent . 

Willis Pequegnat, in his article "New World 
for Marine Biologists" (April 1961 Natural 
History) states: "During each descent into these 
shallow waters, we encountered more and more un- 
familiar species, especially among the rock 
inhabiting faunas. It soon became clear that 
we were investigating an almost untouched domain 
of the sea: untouched, not from lack of interest, 
but simply because of its previous inaccessi- 
bility." 

In underwater ecological problems many 
aspects of lymnology and similarly, of oceanog- 
riphy meet. The biology, geology, physics and 
chemistry are interrelated. Scuba permits 
otherwise land- and deck-bound scientists to 
study this interrelation. Studies of the inter- 
relation of currents, salinity, temperatures, 
subsurface topography, sedimentary deposits, 
fossils, and animal life are enhanced by 
personal underwater study. It may not be too 
far fetched to suggest that by actually insinu- 
ating oneself into this environment a better 
sympathy with these factors can be achieved. 
This could be likened to the entymologist 
observing insects in their natural habitat. 

At this juncture a capsule sketch of scuba 
diving equipment is helpful. 

There are two basic classifications of 
scuba: closed circuit and open circuit. The 
diver wearing closed circuit literally rebreathes 
a major part of his own exhalaticms. Exhaled 
breath is reconstituted by a chemical filter, a 
small amount of oxygen is added and the revital- 
ized mixture is rebreathed. A very small amount 
of excess exhausted air is dissipated into the 
water. Very little bubble trace can be discerned 
on the surface. This is one reason why under- 
water demolition teams use closed circuit scuba. 
The other reason is that several hours of 



310 




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311 



immersion may be achieved on one unit. 

Amateur use of closed circuit scuba can be 
dangerous. The diver may be poisoned by faulty 
chemical filtering. He may suffer from anoxia 
or from oxygen poisoning. 

Use of closed circuit scuba in scientific 
diving is unnecessary since there is no need to 
extend submerged time or to conceal bubbles. 

Open circuit is recommended for scientific 
diving. The diver wears a high pressure air 
cylinder on his back. An automatic demand 
regulator mounted on the valve of the tank 
provides air through a hose to the mouthpiece or 
to the mask. The diver breathes air at ambient 
pressure. The exhaled air bubbles out into the 
water, hence the name open circuit. 

About an hour of submerged time is achieved 
with the most common size of scuba tank. This 
varies with depth and with the individual's 
respiratory rate. 

(Fig. 2 The Scuba Diver) 

Basic sklndiving (breath holding diving) 
equipment is the mask, snorkel and fins. 

In addition to the basic equipment the 
scuba diver will need his breathing apparatus. 
He may also need a suit to protect him from cold, 
a weight belt, knife, compass, depth gauge, 
watch, and an inflatable flotation device. In 
some cases he might tow a surface float in which 
samples or tools can be carried. 

Iteny new pieces of accessory equipment are 
now available: 

Metal detectors, underwater prospecting 
and mining equipment, underwater lights, self- 
powered sleds and towing devices, smell salvage 
equipment, underwater cameras, communication 
devices, diver sonar, and a host of others. 

(Fig. 3 Accessory Equipment) 

Scuba diving has to be experienced to be 
believed. The diver can hover almost effort- 
lessly over most scuba zone underwater locations 
while making continuous observations. He can 
rapidly change vantage points, pursue specimens, 
and handle objects. It is even possible to 
make notes or sketches, using special materials, 
underwater. 

Scuba is unparalleled for efficient 
shallow water search of an area. In fresh 
waters two divers on towed planes can cover a 
swath fifteen feet wide and mile long in less 
than a half hour. They will expend little 
energy compared to free divers. Using diving 
planes In depths to l)-0 feet, it is possible to 



double the air duration time of scuba. 

(rig. k Use of Diving Planes) 

Unfortunately, most salt water areas do not 
lend themselves to the diving plane type of 
scuba search. The towed diver feels entirely 
too much like a trolled bait when in shark 
waters. 

Compare the diving ease of scuba with the 
difficulties of the traditional "hard hat" 
diver as he trudges slowly over the ocean floor 
in heavy gear, stirring up the mud. He is 
tethered to the surface by lines. A large boat 
or barge, a line tender, and usually a crew is 
necessary. His gear is expensive. Ee requires 
a great deal of training. 

(Fig. 5 "Hard Hat" Diver) 

These factors preclude the use of "hard hat" 
rigs by most scientists. He traditionally had 
an advantage over scuba divers. This was 
constant telephone communication with the 
surface which increased work efficiency and 
safety. Now the scuba diver can obtain under- 
water wire or wireless communications. 



The same inflexible ruler, regardint; the 
physics end physiologj"" of hard hat diving apply 
to the scuba diver. Proper training and 
adherence to the rules will minimize the danj^er 
of decompression sickness (bends) , diving 
induced embolism, nitrogen narcosis, and other 
diving diseases. 

Before delving into the individual's 
physical and psychological ability to use scuba, 
let us compare scuba observation with other 
contemporary observation or sampling media. Ve 
must, of course, bear in mind that we are 
discussing only depths readily accessible to 
scuba divers. 

One type of observation medium is the 
reproduction of an underwater environment such 
as an aquarium. 

Let us begin by admitting that there is no 
completely satisfactory artificial environment 
in which to reproduce actual underwater condi- 
tions. Indeed, to make an authentic artificial 
reef of (for Instance) underwater biological 
life would require that we reproduce conditions 
of current, depth, animal interdependence, and 
many other factors. 

A sampling medium such as trawling or 
dredging may bring up some undamaged marine 
specimens. This method gives scant information 
regarding the specimen's relationship to its 
environment • 



312 




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Figure 2. The Scuba Diver. 



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Attempting to dredge or grab specimens 
from rocky regions Is obviously even more un- 
satisfactory. This is compounded by the fact 
that marine environments vary according to 
reef, shoal, or bottom type. It is difficult 
to correlate marine fauna or flora with geolog- 
ical structures when blindly groping the bottom. 

(Fig. 7 Travis and Grabs) 

Naturally, it is not valid to state that 
scuba is a substitute for plankton nets, under- 
way samplers, or some electronic devices. How- 
ever, a surprising number of conventional 
oceanographic equipments can be used by a scuba 
diver. Among these are small sampling equip- 
ments like slurp guns, water bottles, traps, 
acjme samplers, some corers, small electronic 
gear, and of course still, movie and TV cameras. 

(Fig. 6 Cameras Used by Scuba Diver) 

Lymnology also contains fertile fields for 
the scuba diver. Most fish are surprisingly 
unafraid of divers. Possibly this is because 
their limited mental capacities have geared 
them to fear only instinctively recognized 
predators. A scuba diver sitting on the bottom 
of a pond becomes the focal point for curious 
fish. It is even possible to catch some species 
in one's bare hands. 

In lake or ocean the relationship of the 
bloraass and geology ranging from the hyper- 
benthal down through mesobenthal,hypobenthal 
to the parahypobenthal zones can be convenient- 
ly studied by the scuba diver. He can chip 
materials and organisms from rock or reef. He 
can sit on a reef to make pelagic fish counts. 
He can even spear or catch selected fish. 

The naturalist finds skin and scuba diving 
excellent for observation of shallow water life 
of denizens of the air-water barrier. 



(Fig. 7 Underwater Archeology) 



Other very gratifying pursuits can be 
underwater archeology and underwater 
photography. There is almost no limit of 
uses which an active mind can find for scuba 
diving. 

Let us turn now to the physiological 
aspects of scuba diving. Scuba diving is not 
the peculiar province of the young, healthy 
athlete. This statement needs qualification. 
True, if the diver is participating in a spear- 
fishing contest, is attempting to combat strong 
adverse currents, or is flirting with decom- 
pression sickness, then robust, good health is 
a great asset. However, we are discussing the 
scientist that drops overside into, relatively 



calm waters, swims down to a reef, and stays in 
the Immediate vicinity of the boat and another 
qualified diver. 

A major portion of the exertion expended in 
most skin and scuba diving is actually encounter- 
ed above the water. It is no easy chore to lug 
from fifty to over a hundred pounds of cumber- 
some equipment to the diving location.... 
Especially when this may Involve unloading a 
vehicle, climbing down slippery cliffs, 
clamborlng into a wave-tossed small boat, 
fighting the boat through breakers, struggling 
into the snug fitting suit and equipment straps, 
and finally plunging overside. It is then 
actually a relief to be underwater and neutrally 
buoyant. This feeling of relief may be somewhat 
marred by the thought that after diving he must 
go through the above water ordeal again, in 
reverse order. No wonder physical fitness is 
stressed.' 

In most cases the underwater scientist will 
be able to obviate much of the above water 
exertion by diving directly from a larger 
vessel. 

Youth itself is not a criterion of diving. 
There are many divers over 60 years of age, some 
over seventy and even a few diving octogenarians. 
Conversely, there are also a lot of healthy 
younger persons for whom diving is contra- 
indicated. A sound respiratory and circulatory 
system is required. 

The underwater depths which can be tolerated 
vary with the Individual. This is not to say 
that the basic laws of underwater physics and 
physiology do not apply to all of us. Some 
people become distinctly unhappy in the gloom of 
deeper water. Others find themselves quite at 
ease In scuba at greater depths. This is a very 
cogent factor in diving, and because of its 
abstruse nature is seldom mentioned in books on 
diving. It is perhaps related to the most common 
sentiment expressed by non-divers: "You wouldn't 
catch me diving around down there.'" Many of 
these people discover, to their delight, that 
their fears evaporate as soon as they gain 
confidence in their scuba. These same persons 
may never venture more than thirty feet deep. 
This is perfectly acceptable. A lot of research 
can be done in less than thirty feet of water. 

A good instruction course in skin and scuba 
diving is essential. The neophyte diver can 
then decide whether diving is for him. A 
physical examination is required before taking a 
diving course. Most courses are from 12 to 30 
hours duration. This includes classroom and 
pool work. One of the first, and still one of 
the best, books on scuba diving was written by 
David Owen of Woods Hole Oceanographic Institu- 
tion. There are several other books on diving 
available. None of these books are a substitute 
for a good instruction course. 



317 



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A fully outfitted scuba diver may vear from 
a hundred dollars to three or four hundred 
dollars worth of gear. This compares very 
favorably with the price of "hard hat" rigs 
which may cost in the thousEinds of dollars. 

Scuba diving as a sport is safer than 
skiing, or even driving a car. But, like these 
other avocations can be as dangerous as you 
make it. 

As an adjunct to your vocation it can be 
considered even safer since the best of equip- 
ment and safeguards should be available. 

It might be well worthwhile to use It as a 
tool In your profession. 



REFERENCE : Natural History Magazine 
April 1961 



320 



EQUIPMENT FOR OBSERVATION OF THE NATURAL ELECTRO- 
MAGNETIC BACKGROUND IN THE FREQUENCY RANGE 0.01-30 
CYCLES PER SECOND 



by W.N. ENGLISH, D.J. EVANS, J. E. LOKKEN, 

and C. S. WRIGHT 

Pacific Naval Laboratory 

Defense Research Board of Canada 

Esquimau, British Columbia 



, A. SHAND, 



ABSTRACT 

The instruments designed and con- 
structed for measuring the geomagnetic 
background between 0.01 and 30 cps, 
which has a great dynamic range in fre- 
quency and time, are described. Large 
effective area detector loops combined 
with high gain, very low noise ampli- 
fiers form an effective receiving sys- 
tem. Methods of absolute calibration 
are discussed. 



INTRODUCTION 

Because sea water is an electrical 
conductor, electromagnetic radiation Is 
attenuated appreciably as it penetrates 
the water. The attenuation is a func- 
tion of frequency and is about 55 db per 
wavelength. Figure 1 shows the wave- 
length as a function of frequency in sea 
water. At 100 cps the wavelength is 
150 meters, and the skin depth about 
23 meters. At 1 cps the wavelength is 
1500 meters and the skin depth 250 
meters, a very useful penetration. 
Since PNL is primarily "interested in 
frequencies which penetrate sea water 



to an appreciable extent, we have chosen 
100 cps as the upper limit of our region 
of interest and have so far made measure- 
ments up to 30 cps. Our lower limit is 
set by convenience and probable appli- 
cation at about 0.01 cps. The magnetic 
disturbances at lower frequencies have 
been extensively studied by magnetic 
observatories and many of their proper- 
ties are known. The upper end of our 
region of interest overlaps the lower end 
of the ELF range. 

Antenna and noise problems at very 
low frequencies make the magnetic com- 
ponent of an electromagnetic wave much 
more accessible to measurement than the 
electric component, hence we have res- 
tricted our observations to the former. 
Furthermore, possible applications tend 
to use the magnetic rather than the 
electric field. The naturally occurring 
geomagnetic fluctuations are often 
referred to as background noise, but 
their character is very different from 
that usually associated with "noise"; for 
example, the distribution of energy with 
frequency is not random over any con- 
venient time interval. The prominent 



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10 100 1000 10000 

FREQUENCY CYCLES/ SEC 



1000000 



1. 



THE FREaUENCY DEPEMDENCE OP WAVELENGTH AM) VELOCITY 
OF AN ELECTROMAGNETIC WAVE IN SEA WATER* 



322 



signals displayed by Figure 2(b) and (o) 
having periods of the order of 15 to 30 
seconds are characteristic of a recog- 
nized type whose occurrence and frequency 
distribution are decidedly not random. 

PROBLEMS IN MEASUREMENT 



1, The small perc 
A large disturbance 
is only about 10-"^ 
field while small s 
per second may be a 
amplitudes of some 
tlons are shown by 
levels such as thos 
dictate the use of 
systems. 



entage fluctuation: 

at 100 seconds period 
of the earth's main 
ignals at a few cycles 
3 low as 10~1". The 
typical mlcropulsa- 
Figure 2. Signal 
e recorded in part (a) 
sensitive detecting 



2. The amplitude-frequency relation; 
As a general rule the mean amplitude 
level Increases with increasing signal 
period. Figure 2 also illustrates this 
point. Part (a) shows a typical signal 
of about 1 cps while parts (b) and (c) 
show that much greater amplitudes char- 
acterize the lower frequencies. Further, 
the longest period signals of part (c), 
technically outside the scope of this 
discussion, are of even greater ampli- 
tude because they have been attenuated 

by 20 to 30 db below the indicated scale. 
Until recently little has been known 
about the continuous background between 
0,1 and 3 cps because of the low signal 
levels and the Inadequate receiving 
equipment In this frequency range. Even 
with the detector systems wliich are 
sensitive to rate of change of flux it 
is normally necessary to filter out the 
low frequencies sharply in order to 
receive these elusive signals. 

3, Wide dynamic range: The received 
signal levels may change abruptly by 
orders of magnitude. Thus, as Figure 2 
shows, the amplifiers and recording 
system must have a wide dynamic range. 

4, Man-made interference: The 
receiving site must be chosen to mini- 
mize power line, radio and especially 
teletype interference. Surprisingly low 
frequencies can occur in such interfer- 
ence and in populated areas these signals 
can be larger than the geomagnetic 
activity even when care is taken to 
choose a site as far removed from power 
lines, radio transmitters, roads, etc. 
as possible. Filters must be used to 
reduce the level of this interference. 
Moving vehicles within several hundred 
feet are of course Intolerable. 

5. Effects of the site: The noise 
observed is greatly influenced by the 
conductivity and permeability structure 
near the site and it will be different 



at sea and on land. Structural discon- 
tinuities can determine the total signal 
strength and its partition among field 
components. It will also materially 
affect the region of coherence of the 
signals. The site must be removed from 
trees or other objects likely to cause 
wind interference. 

DETECTORS 

It has been established that al- 
though the flux density of mlcropulsation 
activity is low compared to the earth's 
main field it is coherent over a large 
area, especially over regions of uniform 
sub-surface conductivity. Thus antennas 
which gather signal energy over a large 
area can do so without an appreciable 
loss of resolution, and therefore possess 
an inherent advantage over devices which 
utilize only a small area or volume for 
their activation. Tliis paper is res- 
tricted to discuss equipment which 
utilizes large effective area fixed loop 
antennas. Witliln limits set by other 
considerations the most economical 
method of Increasing sensitivity is to 
Increase the effective area of the 
antenna. It can be shown that for a 
circular air-core coil of constant avail- 
able power the Inductance-to-resistance 
ratio Is approximately inversely pro- 
portional to the cube of the diameter of 
the coil, and the mass of tii e copper con- 
ductor to the inverse square. Hence 
large diameter colls such as those to 
be described are desirable. 

On a two-station operation near 
Ralston, Alberta, low impedance air- 
cored colls were used to detect the 
vertical component, which in that region 
is considerably smaller than the horiz- 
ontal components. The two coils were 
wound 30 miles apart, on level ground, 
electrostatically shielded and burled. 
Each was 400 feet in diameter and con- 
tained 40 turns of PVC-insulated No. 12 
wire giving a resistance of 80 ohms and 
an inductance of 1.1 henries. Another 
air-cored antenna which has been suc- 
cessfully used consists of two-conductor 
No. 16 shielded cable arrayed in a circle 
4000 feet in circumference. One advan- 
tage in such a configuration is apparent 
in that for 32 ohms resistance, with the 
conductors in series, the inductive reac- 
tance at 40 cps is only 2.8 ohms. On 
the other hand detectors which depend on 
a much smaller jproportion of the avail- 
able flux for their activation possess 
great advantages in portability and con- 
venience. Thus coils with high permea- 
bility cores have been used in lieu of 
large rigid air-core colls for detecting 
the horizontal components. 



323 



(a) 


"■•■ 1 r- 








TYPICAL MICROPULSATION RECOPDS. THE FULL-SCALE 
NOTATIONS OF PEAK TO PEAK FLUX LEVELS ARE APPROXIMATE 
ONLY FOR THE MORE PROMINENT SIGNALS. All are X 
(NORTH-SOOTH) COMPONENTS, 



324 



The most recent type conalsts of 
20,732 turns of No. 18 HF-insulated wire 
taper wound on a core consisting of 35 
Telcon 79 strips, each 0.015" x 0.75" x 
72", about one-half square inch in cross- 
section. All wire splices are welded. 
A copper shield with an insulated lap 
encloses the winding while this in turn 
is enclosed in a section of plastic pipe 
with watertight end fittings and cable 
connectors. The resulting resistance is 
47 ohms and the inductance about 210 
henries. In service these colls and 
their connecting cables are burled. 

AMPLIFIER SYSTEMS 

Two types of amplifier designed and 
built at PNL have been successfully used; 
a DC amplifier for frequencies below 
3 cps and an AC amplifier for frequencies 
above 2 cps. Each type together with its 
auxiliary equipment is described. 

1. DC System ^*'^ 

(1) Input filter - The input filter 
contains two bridged-T, 60 cycle re- 
jtsCtion sections having a total DC 
resistance of 18 ohms inserted between 
the antenna and amplifier. In some 
locations an RF filter is also re- 
quired. Since the frequencies below 
1 cps have much larger amplitudes 
than higher frequencies, and a 
chopper amplifier is used, a low pass 
section is not required. The input 
filter includes the capacitors for 
series tuning the detectors and a set 
of resistors which, if required, 
could reduce the "4" of the detector 
circuit. A line-balance potentio- 
meter is incorporated. The filter 
chassis also incorporates a 1 ohm 
precision copper resistor in series 
with the detector circuit for cali- 
bration when an air-cored antenna is 
used. Low thermal solder is used in 
the filter and DC amplifier input 
staee. 

(ii) DC amplifier - The low frequency 
system uses a chopper type DC ampli- 
fier operating at 60 cps. An elec- 
trostatically shielded, specially 
built input transformer is used to 
match the chopper to the first stage 
of the amplifier. The chopper noise 
has been materially reduced by lower- 
ing the chopper-drive voltage and 
using a "bucking coil", fed by cui — 
rent which can be adjusted in phase 
and amplitude, to cancel out pick-up 
in the contacts introduced by the 
drive coil. Each chopper is care- 
fully adjusted in the laboratory for 
minimum noise. With a source imped- 
ance of 40 ohms the maximum DC 



Superior numbers refer to similarly 
of this paper. 395 



voltage gain is about 10 . An atten- 
uator allows the gain to be reduced 
in 10 db steps to -80 db. A properly 
adjusted instrument has a noise level 
of about 0.005 microvolts rms in the 
frequency band 0.02 to 3 cps with a 
40 ohm source resistance. 

Figure 3 depicts the amplifier 
chassis. Figure 4 the block diagram 
of a three component-two station 
installation, and Figure 5 shows a 
family of frequency response curves. 

A monitor point for the amplified 
60 cycle signal is provided in the 
circuit before demodulation. The 
signal at this point can be displayed 
on an oscilloscope to determine if 
unwanted 60 cycle pick-up is entering 
the amplifier through the detector 
circuit or if a steady DC bias such 
as would be produced by a thermal EMF 
is present. The latter may be coun- 
teracted by an adjustable bias in the 
amplifier whereas the former cannot 
be balanced out in the amplifier. 

Experience has shown that the ampli- 
fier is exceedingly sensitive to cer- 
tain environmental conditions and 
surprisingly tolerant toward others. 
A few of the precautions which seem 
to be well worth observing are 
detailed as follows: 

(a) Installation - Heaters of the 
tubes must be supplied from a DC 
source. The amplifier should be kept 
as far as possible from electrical 
apparatus that might produce 60 cps 
magnetic fields (minimum distance 

5 ft). The amplifiers in a multiple 
Installatl on should be spaced at 
least 2 ft apart. 

(b) The Grounding System - It is 
desirable to obtain a grounding 
system such that there is no appre- 
ciable pick-up of unwanted signals. 
The line balance potentiometer in the 
input filter will have no effect if 
the pick-up is negligible. Exper- 
ience has shown that the interference 
pick-up is very much reduced if a 
high resistance, at least 20 megohms, 
is maintained between coll and shield, 
and between shield and ground. The 
ground connection should be made only 
at the amplifier with the detector 
connected as a balanced input. 

(c) Thermal EMF's - An Inspection 
of the signal at the AC monitor point 

Tav show a constant carrier signal 
60 cps; which cannot be eliminated 
with the line balance potentiometer. 
This may be due to thermal EMF's In 
the input circuit, and can be 

numbered references at the end 





3. THE DC AMPLIFIER CHASSIS, TOP AND FRONT VIEWS. 



326 



BATTERY 
CHARGER 



6V 
—\ STORAGE 
BATTERY 




INPUT 
FILTER 



REGULATED 
PS 




AMP 



BAND PASS 
FILTER 



FM. 
SIGNAL 



DETECTOR 



F M. 
SIGNAL 



FM 
SIGNAL 



MIXER 

a 

FILTERS 




TELEPHONE 
LINE 



REGULATED 
PS. 



BATTERY 
CHARGER 



6V 

STORAGE 

BATTERY 



INPUT 
FILTER 



FILTER 



FM 
DEMOD 



FILTER 



F M 
DEMOD 



r- FILTER 



F M 
DEMOD 




DETECTOR 



F. M. 

7 CHANNEL 

TAPE 

RECORDER 



•—I 6 CHANNEL 
PAPER 
RECORDER 



TIMER 



4. THE ARRANGEMENT OF UNITS IN A TWO-STATION, THREE- 
COMPONENT DC DETECTOR, A^IPLIFIER AND RECORDER SYSTEM. 
THE THREE COMPONENTS X, Y, Z, SPECIFY THE CONVENTIONAL 
ORTHOGONAL COMPONENTS ARRAYED ON GEOGRAPHIC AXES. 
X^ AND Xg WERE SEPARATED IN DISTANCE BY 30 MILES. 



327 



90 



70 



-0 



50 



o 
a. 

3 



30 




DETECTOR NO. IS 
FtLTEIR "aT 

AkhAPLiFlE-R NO 14-2.5 

FORT CHURCHll_U,(VVAN. OCT.!, l9fcO 



10 



I 



oo\ 01 10 

Fr»e<^uervcy Cycles par second 



10 



TYPICAL RESPONSE CURVES FOR THE DC SYSTEM. THE 
NOTATIONS CI to C4 REFER TO VARIOUS SERIES 
CAPACITORS USED IN THE DETECTOR SYSTEM. THE CURVE 
MARKED "BROAD BAND" SHOWS THE RESPONSE WITHOUT 
TUNING CAPACITORS. 



328 



eliminated with 
on the front pa 
amplifier which 
signal in serie 
cult. Wlien the 
tlometer and th 
control are pro 
should be no st 
AC monitor poln 
tuating signal, 
must be made at 
signal level to 
of the amplifie 



the balan 
nel of the 

inserts a 
s with the 

line bala 
e thermal 
perly adju 
eady AC si 
t but only 
These ad 

the lowes 

prevent o 
r at high 



ce control 

chopper 

small DC 

input cir- 
nce poten- 
EMF balance 
sted, there 
gnal at the 

a fluc- 
justments 
t detector 
verloading 
gain settings 



(ill) Outputs - Two outputs are pro- 
vided on the amplifier, a low imped- 
ence balanced output for directly 
driving the millianuneter movement of 
a strip chart recorder, and a high 
impedance single-ended output for 
driving another amplifier or an active 
bandpass filter. 

2. AC System ^' "^ 

The AC amplifier system, cap- 
able of accepting signals in the 2 
to 40 cps range, was designed to 
operate on the 4000 foot circumfer- 
ence air-cored detector coil which 
has been described. Such a detector 
should yield 14.8 millivolts per 
gamma RMS at 10 cps. Because the 
signal level at this frequency is 
likely to approximate 10~* gamma, or 
less, a sensitive amplifier is re- 
quired. 

(i) Input filter - The input filter 
is designed to pass frequencies from 
DC to 40 cps and to reject all higher 
frequencies. In addition to a 60 cps 
rejection section and line balance 
potentiometer similar to that used in 
the DC system, a low-pass section is 
required to reduce power line har- 
monics and RF interference which is 
usually of comparable amplitude to 
the geomagnetic activity between 2 
and 40 cps. The line balance poten- 
tiometer is used to check for a satis- 
factory ground in the same way as 
with the DC system. The filter also 
incorporates a one ohm precision 
resistor for injection of a calibra- 
ting voltage. 

A separate 30 cps rejection filter 
has been found necessary in the 
vicinity of Victoria but has not 
been required at remote sites. 

(ii) Preamplifier - The preamplifier 
has two stages of amplification 
separated by a 60 cps rejection 
filter. The input stage is a vacuum 
tube amplifier, and a special low- 
level high step-up ratio input trans- 
former matches the detector to the 



grid of the first tube of the Input 
stage. The second stage is a tran- 
sistor amplifier. The B+ and tran- 
sistor stages are supplied from 
self-contained batteries. A 6-volt 
storage battery is used to supply 
the heater voltage. Both stages 
are plug-in units. 

With an input transformer primary 
Impedance of 40 ohms and a generator 
of internal impedance of 40 ohms, 
the amplifier gain from generator to 
output is 270,000 times. If the 
input signal should be large enough 
to overload the second amplifier 
stage this can be removed and re- 
placed by a unit having no amplifi- 
cation. 

The preamplifier noise depends to 
a large extent on the characteristics 
of the input tube, which operates 
under special low-noise conditions. 
It has been found on test to be as 
low as 0.004 microvolt for an input 
impedance of 40 ohms and a bandwidth 
of 2 to 30 cps, which is approxi- 
mately the thermal noise level. A 
noisy tube can easily raise this 
value by a factor of ten to 0.04 
microvolt which is still acceptable 
although regular checks should be 
made to avoid a further increase in 
noise. This is accomplished by 
removing the detector from the input 
filter and plugging in instead a 
dummy source which contains the resis- 
tive input impedance plus a calibra- 
tion attenuator. The system noise is 
then compared with a small known 
signal . 

(ill) Postamplifier - The transistor 
postamplifier provides the extra gain 
necessary to amplify small signals to 
the level required by the recorders. 
The maximum gain is about 35 db and 
can be reduced to zero db in a db 
steps. The maximum overall gain f»m 
a 40 ohm source to the postamplifier 
output is now about 1.6 x 10^, times 
or 144 db. The postamplifier power 
supply is run from the 115V, 60 cps 
supply. 

(iv) Output - The postamplifier is 
followed by a commercial active band- 
pass filter which serves to attenuate 
the frequencies persisting above 40 
cps. primarily 60 cps, and its har- 
monics. The bandpass filter output 
can be monitored on an oscilloscope 
or recorded on a high-speed paper 
recorder or tape recorder. 

In order to record the average 
level of activity in this frequency 
range continuously a rectified and 
integrated signal can be fed to a 



329 



slow-speed paper recorder. A recti- 
fier-Integrator whose time constant 
can be varied from zero to 25 seconds 
In five steps has been used. 

Figure 6 shows the block diagram 
of an AC amplifier installation and 
Figure 7 shows a typical system fre- 
quency response curve. 



CALIBRATION 

Two methods of system calibration 
are in current use. In one the cali- 
bration signal is induced into the 
detector circuit from an auxiliary 
winding of a few turns. In the other a 
small measured voltage is injected into 
the detector circuit by means of a 
series precision resistor and dividing 
network. The former is conveniently 
applied to compact metal-cored colls 
and the latter to large air-cored coils 
of known area-turns. Obviously the two 
methods behave differently because a 
constant current in the calibrating 
coll introduces a corresponding constant 
change of flux yielding a frequency- 
dependent detector voltage output, while 
a constant injected sinusoidal voltage 
is independent of frequency. 

When the induction system is used 
the effectiveness of the calibrating 
current must be determined by comparison 
with a known flux density. This is 
accomplished by placing the detector 
under test concentric and coaxial with 
a multi-turn coil 200 feet in diameter 
which, in turn, is fed with a measured 
sinusoidal current over the range of 
frequencies desired. A single, large 
diameter coll was selected because it 
was simple to construct, is capable of 
accommodating detectors having a con- 
siderable range of size and configuration, 
and is not critical with respect to 
positioning the coll under test. Both 
axial and radial deviations from the 
(axial) flux density within 20 feet of 
the coll centre are small (less than 2%) 
and known, Vozoff has shown theoret- 
ically that the error due to the under- 
lying earth is less than 1?& if normal 
conductivities, frequencies below 100 
cps and a coil radius of less than 100 
meters are assumed. This has been 
experimentally verified by noting that 
the effectiveness of the calibration 
current in the auxiliary winding is 
essentially independent of frequency 
and detector orientation. Thus neither 
the effect of proximity to the ground 
nor possible core saturation materially 
invalidate the calibrations. 



It has been standard practice to 
measure the calibration voltage (or 
current) on the DC scale of a calibrated 
dual-beam oscilloscope. Hence it is 
practical to compare the amplifier out- 
put with the input voltage and phase over 
the desired frequency range. 

In order to avoid the simultaneous 
effect of natural signals it is desir- 
able to attenuate the amplifiers by 30 db 
or more during calibration. Their effect 
is further reduced by choosing, for 
routine checks, a calibration frequency 
where the natural signals are usually 
small. 

The calibration signal is applied 
to all of the components at once thus 
affording a convenient check on detector 
polarities. In spite of care, inad- 
vertent transpositions occasionally 
occur. Detailed calibrations are made 
every few days at a time when the back- 
ground is uninteresting, but single fre- 
quency gain checks are made every few 
hours. 

The following precautions have been 

found effective in reducing interference 

Introduced through the calibration cir- 
cuitry: 

(I) When a voltage is injected for 
calibration it may be necessary to 
power the signal generator through an 
Isolation transformer or to use a 
battery operated model. It may help 
to isolate the oscilloscope too. 

(II) An induction calibration circuit 
must use its own shielded leads, 
separated from the signal cables, 
(ill) An RF filter has been required 
on some calibration circuits. 

(iv) When not actually in use the 
calibration circuit is completely 
disconnected from the signal gener- 
ator, oscilloscope and other compo- 
nents. 

TIMING 

A rated chronometer with electrical 
contacts Is used to actuate timing pens 
on the paper charts and to provide 
minute and/or seconds pips on the mag- 
netic tape. Crystal chronometers have 
been obtained and will be used in the 
future. The absolute accuracy required 
depends upon the signal frequencies and 
the resolution of the chart or magnetic 
tape. Radio time signals are often 
applied directly to one of the tape 
channels. All records are kept in 
Greenwich or Universal time. 

A primary problem in timing is one 
of determining when an event commences. 



330 





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331 



FREQUENCY RESPONSE OF 
2-30 C.PS. SYSTEM WITH 
30 C.RS. REJECTION FILTER 
IN CIRCUIT 



CD 
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Q. 



-10 



-20 



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FREQUENCY 



20 
IN C.RS. 



25 



30 



A FREQUENCY RESPONSE CURVE FOR THE AC SYSTEM. THE 
INCLUSION OF A 30 CPS REJECTION FILTER IS NOTED. 



332 



For example, a given excursion or event 
will appear to arrive at different times 
at each of the components on one station. 
On another station the time displace- 
ments will usually be distributed quite 
differently among components. These 
displacements are often a significant 
proportion of the signal period. Hence 
It is difficult to determine the absolute 
time of the commencement or peak of an 
event. Correlation techniques on the 
total "pulsating magnetic field" may be 
used in some cases to minimize the un- 
certainty. 

REFERENCES 

1. "The Low Frequency Electromagnetic 
Detector-Arapllfler System Used During 
PNL Field Operation at S.E.S., June, 
1960", by D.J. Evans, PNL Laboratory 
Note 60-11, July 1960. 

2. "The Pacific Naval Laboratory - 
Stanford University Conjugate Point 
Experiment", by D.J. Evans, S. Horner, 
J.B. Lokken, J. A. Shand and 

C.S. Wright, PNL Laboratory Note 
60-41, December 1960. 

3. "Measurement of the Vertical Com- 
ponent of Magnetic Mlcropulsations 
in the 2 to 40 cps Band", by 

D.J. Evans, PNL Laboratory Note 
60-34, November 1960. 

4. Private communication from K. Vozoff, 
University of Alberta. 



333 



OXYGEN AND CARBON DIOXIDE INSTRUMENTATION 



by JOHN W. KANWISHER, Research Associate 
Woods Hole Oceanographic Institution 
Woods Hole, Massachusetts 



The sum of the biological processes going on 
in the oceans is frequently considered in terms 
of the opposing processes of photosynthesis and 
respiration. In most cases we can consider these 
phenomena as reciprocally exchanging equivalent 
amounts of oxygen and carbon dioxide (0„ and CO,), 
with the environment. For every C0» molecule 
removed from solution in sea water during the 
ph tosynthetic production of carbohydrate an 0, 
molecule is released. An opposite exchange oc- 
curs when this carbohydrate is later oxidized in 
the respiration of some plant or animal. We can 
represent this schematically as: 



I . OXYGEN ELECTRODE RECORDING 



Recent references describe a polarographic 



LIGHT 



PHOTOSYNTHES IS 



\ 



CO2 + H2O 




SUGAR 



RESPIRATION 



A quantitative knowledge of this gas exchange in 
a water mass is basic to any estimation of the 
overall biology taking place. The resulting vari- 
ation of these gases in the water is also 
frequently of hydrographic interest because of the 
way biological activity types a water mass. In 
fact, content probably follows temperature and 
salinity as the most measured hydrographic vari- 
able . 

One would of course like to have as complete 
a picture as possible of the distribution of any 
variable being studied. With 0. we must current- 
ly be satisfied with a relatively few points in 
the vastness of the oceans. Most of these points 
have been determined only once or twice, so our 
knowledge of time variations is equally hazy. 
In addition, the only method currently in use 
involves a chemical titration and is surrounded 
by considerable uncertainty. Direct measure- 
ments of C0_ are nearly nonexistent. Some new 
techniques which allow continuous recording of the 
0, and C0„ dissolved in sea or fresh water will 
be described. 0„ has been determined polaro- 
graphically and C0„ has been monitored by infra- 
red absorption of a gas phase which has been 
equilibrated with the water. The methods are 
applicable to both laboratory and field studies. 
Some of both will be covered. 



1,2 



electrode suitable for recording dissolved 0„ 
It consists of a platinum electrode separated from 
the medium being measured by a layer of polyethy- 
lene or teflon, both of which are markedly perme- 
able to molecular . As this gas diffuses 
through the surface, it reacts immediately at the 
platinum surface to form OH" ions. The 0H~ ions 
diffuse through the film of electrolyte behind the 
membrane and react at the Ag surface to form Ag„0, 
which appear as a dark coating. Thus the eventual 
fate of the dissolved oxygen is to appear as Ag„0 . 
Although the Ag is actually being consumed, in 
practice it will last semi-indef initely . The cur- 
rent passing through the electrode is proportional 
to the rate of diffusion, and this in turn depends 
on the external tension (partial pressure) . We thus 
have in essense a device for measuring the quantity 
of dissolved 0„ since it varies directly with the 
tension (Henri s law). 

The electrode assembly is shown in Figure lA. 
A Ag-Ag„0 electrode is concentric around the center 
platinum electrode. A plastic film is stretched 
over this and traps a small amount of alkali behind 
it. The platinum is kept at -.7 volts. When there 
is no the electrode current is very close to 
zero. It increases linearly with increasing 0. 
tension in the external medium. A more complete 
treatment of the electrode occurs in the original 
references cited. 

It should be kept in mind that the electrode is 
a tension-measuring device. It will read the same 
in fresh or salt water if they are equilibrated 
with the same gas mixture, although the 3-1/2 per 
cent salt content reduces the gas solubility by 
25 per cent. Thus its reading must be referred to 
the solubility of the liquid being measured. The 
extremes of salinity in the open sea, however, 
cause less than a 2 per cent error. It is worth 
noting that the electrode will work in any liquid 
which does not attack the plastic membrane, even 
gasoline . 

Such an electrode has been operated for as long 
as 6 weeks with less than 25% change in current. 
Since no abrupt changes occur, it is sufficient to 
calibrate only once per day to provide values good 
to a few per cent. If there is any doubt about the 
condition of the electrode it can be quickly remade 
with new plastic and KOH . Operation for a long 



Superior numbers refer to similarly numbered references at the end of this paper. 



334 



period of time is aided by placing a disc of fil- 
ter paper over the end of the electrode under the 
plastic. However, this increased the time constant, 
at least several-fold. 

It has been found empirically that the 
reference electrode must "see" the solution 
directly through the plastic film and so should 
not be covered by the retaining ring. This obser- 
vation is inconsistent with the view that the OH" 
ions diffuse only through the layer of electrolyte, 
and it is not yet understood. 

Such electrodes are easy to make. The silver 
and platinum parts are cast in some plastic such 
as an epoxy. Electrical connections are made to 
the back of the electrodes. Care must be taken 
that only silver and platinum are exposed on the 
outside. Any polyethylene can be used. Thick- 
nesses of .001 to .002 inches give convenient 
diffusion rates and response times. 

This polarographic technique is a valuable 
tool in experimental physiology. I have used 
electrodes to follow oxygen changes in a 1 ml . 
chamber containing a bit of seaweed or a single 
copepod. It has also been just as readily applied 
in a 55 gallon oil drum, following the respiration 
of a 30 kg. shark. In one instance it was used to 
measure the oxygen in the expired breath of a 
whale. These indicate to some degree the versa- 
tility of such electrodes. Here, however, I will 
only describe their use for jji situ recording in 
the ocean. 

This is probably the most difficult and also 
the most desired oceanographic task to which they 
might be applied. To accomplish it one must over- 
come several inherent shortcomings in the electrode. 
These will be discussed in turn. 

A. Stirring 



be below saturation as long as it is constant. 
A synchronous motor rotating a large magnet (from 
a magnetron) can be used to induce rotation in a 
small teflon corrected magnet over a considerable 
distance. I have used such a method to stir small 
containers deep inside a water bath. The constant 
speed of the motor insures a steady record. 

Figure IB shows an electrode holder for line 
monitoring. The stream is directed against the 
plastic film directly over the Pt electrode. This 
creates a maximum of effective stirring with a 
minimum of flow. If the incoming tube is brought 
very close to the electrode a flow of 10 ml/min. 
may give a saturation (maximum) electrode current. 

Thinner and more diffusible membranes (i.e. 
teflon as compared to polyethylene) present less 
diffusion resistance. This produces a larger 
electrode current as well as making its response 
faster. But it accentuates stirring difficulties 
since the diffusion resistance in the liquid must 
be likewise reduced. Thus a compromise must be 
struck between sensitivity, speed, and stirring 
difficulties . 

B. Speed of response 

An electrode with a .001" thick polyethylene 
layer will show a 90 per cent response in about 15 
seconds. If the silver area is large (more than 
10 times) compared to the platinum, the response 
to a step function will be very closely exponen- 
tial. With much less silver area, there is a long 
slow component in the current. This presumably 
represents some polarization phenomena at the 
silver surface. 

One would like a faster electrode for vertical 
recording in the sea since with a fast winch the 
electrode can cover more than 100 meters in the 90 
per cent response time. 



The electrode current represents an actual 
consumption of molecular 0. from the solution 
being measured. This depletes the thin layer of 
liquid immediately in front of the plastic mem- 
brane. Stirring the solution renews this depleted 
surface layer. If the solution is not stirred 
this layer will progressively lose more of its 0, 
and a gradient will be set up in the liquid. In 
such a situation the flux of 0~ reaching the 
platinum will be limited by a combination of the 
diffusion resistance through the solution as well 
as through the plastic. Since anything that 
changes this resistance will alter the electrode 
current it is necessary to maintain constant dif- 
fusion conditions. The most direct way of realiz- 
ing this is to mix the solution so strongly that 
it contributes a negligible fraction to the over- 
all 0„ diffusion resistance. This can be accom- 
plished in over- the-side work by running the winch 
fast or accentuating the current past the electrode 
by funnel arrangements or small stirring motors. 

In laboratory applications the stirring may 



From diffusion theory it can be shown that the 
time to reach diffusion equilibrium across a bar- 
rier of thickness t is proportional to 
^2 

This suggests the dual approach 



dif fusibil ity 

of thinner and more diffusible films to lessen the 
time. Teflon is better than polyethylene by this 
criterion since O2 diffuses through it about 3 
times faster. It is also tougher in thin films. 
1 have recently used electrodes in the laboratory 
with .00025" teflon which showed a 90 per cent 
response in 3 seconds. As already indicated, how- 
ever, the stirring problem then is more severe. 

C. Pressure response 



When the electrode is exposed to a constant 0„ 
tension, its current decreases with increasing 
hydrostatic pressure. This dependence is shown in 
Figure 2 for pressures up to 15000 Ib/in'^. (which 
equals about 30,000 ft. in depth). Over the first 
5000 pounds the curve is approximately linear. For 



335 



each 1000 feet increase in depth (500 pounds in 
hydrostatic pressure) the current decreases about 
3 per cent. Beyond 5000 pounds the rate decreases. 
At 15000 pounds only 30 per cent of the initial 
electrode response is left. 

The decreasing electrode current represents 
a decrease in the permeability of the plastic 
film to the diffusion of 0.. The shape of the 
curve indicates that diffusion through the plastic 
is more of a pore-type phenomenon than one of the 
gas being in solid solution. The first part of 
the curve is the same for teflon and polyethylene 
so there seems little chance of decreasing this 
undesirable pressure dependence by using a dif- 
ferent plastic. The only approach at this time 
seems to be to compute it out of the raw signal. 
Fortunately much of the most interesting 0„ vari- 
ations are close to the surface where the 
pressure dependence can either be neglected or 
assumed linear. 

P. In situ recording 



thermistor temperature correction, with light 
battery-operated apparatus. 

II C02 MEASUREMENT 

The measurement of C0„ requires a different 
approach from that used for 0^. It occurs in only 
1/600 the concentration in air (.03 as compared 
with 21 per cent) . But its chemical and physical 
properties result in its being nearly 10 times as 
concentrated in sea water (45 ml/1 vs 5 ml/1 0-) . 
We can summarize this chemistry by the following 
equations : 



AIR CO^ 



v^^>Ls^Ja>^ 



CO2 + H2O 



H^COj 



HCO^ ~ — r CO^ 



SEA WATER 



u 

COMPLEXES 



The electrode has been tested twice for 
recording vertical profiles in the ocean. The 
first measurements were done by Dr. Richardson 
with his ingenious free-falling instruments. The 
electrode current was recorded in the instrument 
along with temperature. Depth was determined by 
time and the rate of fall. The current was then 
corrected for temperature and pressure to obtain 
O2 concentration. The location off Bermuda is 
one where frequent chemical determinations of O2 
are made. The two curves in Figure 3 show essen- 
tial agreement. The electrode showed interesting 
detail below the minimum. These would ordinar- 
ily not be seen from the usual spot measurements 
made from Nansen bottle samples. 

I later lowered an electrode along with a 
pressure transducer on the end of a 3-mile length 
of well-logging cable. No amplification was 
needed. This allowed direct x-y recording of 
vs depth during the lowering. The curve in 
Figure 4 shows a well mixed surface layer with a 
sharp drop in 0, at 125 meters. This drop did not 
come at a thermocline. The temperature actually 
increased .7° C. In such a case , more clearly 
than temperature or salinity, shows two water 
types. A regular hydrographic station was made at 
this time. The Nansen bottles were placed at the 
standard depths and the chemical determinations 
from these are included on the plot. One can 
easily see the difficulty of accurately determin- 
ing the shape of the curve from such spot values. 
If the electrode does not replace the chemical 
method it can at least be used to determine the 
best depths at which to place the Nansen bottles. 

I have also lowered the electrode from row- 
boats for continuous 0„ profiles in lakes. 
Initially an uncorrected electrode was used and 
temperature was simultaneously recorded. The 
advent of solid state choppers has allowed me to 
record the corrected 0~ value directly, using 



Any change in the amount of C0„ in this system 



will, through these reversible equilibria, alter 
the values of pCO^ 
use the former as 
of such changes -* . 



the values of pCO~ and pH. I have been able to 
use the former as a convenient and sensitive index 



The measurement of C0„ is accomplished by equi- 
librating sea water with a gas phase and then 
measuring the C0„ concentration in the gas. The 
partial pressure in the gas is then equal to that 
in the water, if equilibration is gentle and 
complete. It is an attractive approach since C0„ 
in gas mixtures can be determined to better than 
1 part per million by means of a modern infrared 
analyzer . 

We can expect surface sea water to be more or 
less equilibrated with the atmosphere above the 
surface. Since air contains 300 ppm COo, the 
values of pCO, in the water will center about this 
value. With the infrared analyzer technique out- 
lined it is possible to determine pC0„ in this 
range to 1 per cent (± 3 ppm) . 

The chemistry of CO, outlined in the above 
equations results in pCO, being non-linearly 
related to the total amount of the gas in sea 
water. This makes it necessary to calibrate the 
apparatus by introducing known changes in total 
C0„ and measuring the resulting partial pressure. 
Figure 5 shows the result of such a procedure. It 
can be seen that there are very large changes in 
the partial pressure for the variations in total 
CO- we know to exist in the deep ocean waters. 
When such water is anaerobic^ or nearly so, its 
pCO„ may be 10 times that of equilibrated surface 
water. I have tested this in Eel Pond^ a small bay 
here in Woods Hole. It has a sill at its entrance 
which prevents free exchange of the bottom water. 
Sewage from the surrounding houses creates a large 
biological 0„ demand (C0„ production) . The bottom 



336 




Ag Ag 



POLV ETHYLENE OR 
TEFLON MEMBRANE 



RETAINING 

RING 




Ed 

d 

o 

i 



\ 



\ PRESSURE RESPONSE 

•. OF O3 ELECTRODE 



V 



5 10 15 

PRESSURE IN THOUSANDS OF LB/ IN' 





■ 




1 ' 1 ' y 1 ' I 

- ELECTRODE C >/ 






^ 


■ 




- WINKLER \ \/ 


Ul 


- 




/ ^ ' 


K 
^ . 


. 




y^^ INITIAL ELECTRODE - 


_ 




^y^" EQUILIBRATION 


U. 






/^ 





' 




V 


CO 


- 




/^ 


Q 






(\ 


Uj 








a: 






^\^ 


Q 


- 




^^>-^_^ 


I'O 


- 




^^^^^^^ 


3: 


- 




>^ 


5 






^^^ 


£ 






^\""^*1 


- 


32= 


lO'N \ v_, - 


0. 




64 


30' W \ ,-' 


U] 




DEC. 


7,1959 \ C^ 


Q 15 


- 








" 




\ '*' 








1 . 1 , 1 , 1 1 'n 



0; IN ml /I 

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337 



Uj 

to 

i 

a: 



£ 
§ 



ELECTRODE 
WINKLER 




40 

Q, IN mi/t 



2500 


" • 




\ WOODS HOLE SEA WATER 


2000 


\ SALINITY= 31.5% 




\ 


1500 


\ 


1000 


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500 


1 ^ 

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-MOLES CO, ADDED/LITER 



ML. OF CO, GAS 



0, IN ml/L I TER 




5 00 1000 1500 2000 2500 

pCO^ IN ATMOSPHERES X 10^ 



338 



layers go anaerobic in mid-summer. I have 
measured the profiles of pO and pCO- (Figure 6) . 
The surface waters support a large algal popula- 
tion due to the supply of nutrients from the 
sewage. This results in a diurnal variation in 
both gases due to photosynthesis during the day 
and respiration at night. The variation is many- 
fold greater than in the unfertilized ocean 
immediately outside. 

Continuous- track measurements of surface water 
pCOp have recently been made between Woods Hole 
and the equator. This showed interesting latitude 
variations in the tropics. The changes occur at 
points where we have some evidence that there are 
major east-west currents. I feel that such pCO» 
variations are due to different amounts of upwell- 
ing of the high C0„ intermediate water. 

In local waters along this coast there are 
variations in pCO„ during the year. The spring 
plankton bloom is a time of rapid photosynthesis. 
This removal of CO^ may drop the pCO. to below 
200 ppm. In the middle of the summer much of the 
spring growth is decaying and the partial pressure 
may then be as high as 550 ppm. 

CO- is better than as an index of recent 
biological change because it exchanges with the 
atmosphere some 15 times slower. In the spring 
and summer^ weather conditions tend to be gentle 
and the gas exchange across the sea surface is 
slow. pCO„ can then be used to tell the time- 
integrated amount of photosynthesis and respira- 
tion. Storms during the winter tend to more 
quickly bring the oceans and the atmosphere back 
into equilibrium whenever biological events change 
the amount of C0„ in the water. 

SUMMARY 

These techniques of and CO- recording 
represent my answers to problems that arose in 
my own research. It has been necessary for me to 
develop them because there has been no one else 
to fill the need. There may be more suitable 
means when real engineering skill is applied. 
However^ I feel that most useful new instruments 
result from a current research need. 

REFERENCES 

1. Bolin, B., and Eriksson, E., 1959. Rossby 
Memorial Volume (Rockefeller Institute Press, 

New York), pp. 130-142. 

2. Carritt, Dayton E. and Kanwisher, John W. 
1959. Analytical Chem. 31: 5-9. 

3. Kanwisher, John, 1960. Tellus XII(2) : 209- 
215. 



WHOI Contribution No. 1229 



339 



AN ANALYSIS OF A CLASS OF PATTERN RECOGNITION NETWORKS 

by LAVEEN KANAL 

General Dynamics /Electronics 

Rochester, New York 



ABSTHACT 



Recent articles show that considerable 
research is currently being devoted to the 
realization of Pattern recognition by a 
class of adaptive networks. This paper 
presents a few results of studies aimed at 
finding the relationships between work in 
this area and various classification 
procedures, and seeing how efforts in 
machine recognition of patterns can be 
reconciled with some formal principles in 
decision making. 



INTRODUCTION 

Research in classification procedures 
has been largely concerned with two 
situations. One, where an individual 
(pattern, sound) is to be assigned to one 
of k groups, with the numerical value of 
k known but information on the probability 
distributions of observables ranging from 
complete ignorance of the functional form 
of the distribution to the case where the 
functional form and all parameters are known. 
The other situation is similar except that 
the value of k is unknown. The first case is 
typical of many simple pattern and limited 
vocsbulary speech recognition situations. 
Thus for example, it may be desired to 



recognize a soiond as being one of k known 
sounds. The second situation may be en- 
countered for example, in the identification 
of targets from underwater return patterns 
vrtien only limited information is available. 
Only the first situation is considered here. 
Let a pattern be specified by the results 

of a number of measurements or tests , x. , 

1 

i"l,2,...N. In any given instance, the results 
of the tests or measurements may be represented 
by x= (x,, Xp,,..x^). The case where the x^ 

are either or 1 is considered here. This 
situation would obtain for instance when a 
pattern is placed on an "artificial retina" 
with the outputs of the retina elements being 
quantized in this manner. The cases 
where the x^, i-1, 2,..N can take on a 

number of discrete values and where the x. 

a 

are continuous are considered elsewhere . 
Let p (x^, Xg Xfj) denote the joint 

probability distribution of the x^ in a given 
group. In section 1 a parametric representation 
for this distribution is presented. In this 
context the classification cabsbilities of 
some proposed pattern recognition networks are 



"Superior numbers refer to similarly numbered 
references at the end of this paper." 



340 



examined in section 2. Comments on a few 
iterative teohniquea and some experimental work 
conclude the paper. 

1. A representation of the .joint digtri- 
bution. Let X denote the set of all points 



X^^ X-. , Xp f 



x^j) with each x.=0 or 1. Since 



there are 2" points in X any parametric descrip- 
tion of arbitrary probability distribution will, 
in general, require (2'^-l) independent para- 
meters. The particular parametric represen- 
tation considered here is due to Bahadur^. 

Using Ep to denote the expected value when 
the underlying distribution is p(x), define for 
each i=l, 2. . .N, 

mi = pWj^ = Ij =E (x^), o<mi<l: 



Zi = (x.-mi)/y m^d-mi) : 
T^. = Ep(ziZj), i<j ; 

5p(ziZ2., 



"12. .N ^n(2l^2---^^- 



Further define 

N 
p 1 (xi,X2,...x^) = TT^fi (l-mi)l-'^i. 
i = l 

so that p( x^.Xp,. . .Xj^j) denotes the joint 
probability distribution of the x- when 

(1) the x^s are independently distributed and 

(2) they have the same marginal distributions 
as under the distribution p(x) . It is shown 
by Bahadur that for every x={xj[_,X2, . . .x-,) in X, 



p(x) =» p j^j.f(x) 



where 



f(x)»l + 



KJ 



r. .z. z * ^:— - r , z. z z 
ij 1 : i<j<k ijk 1 j k 



.* r. 



12'"N^1^2---^- 
The 2'^-N-l correlations and the N marginal 

frequencies mj_ are the parameters which 
determine the probability distribution p(x). 
In order that an arbitrary set of 2 -N-1 real 
numbers r serve as the correlation parameters 
of a probability distribution p(x) for any 
set of numbers m^ with o<mj[^<l, it is neces- 
sary and sufficient that f(x) be non-negative 
for each x. 

The distribution p(x) can now be approxi- 
mated by distributions of lower order. Thus 
p(x) is a first order approximation to p{x), 



P2(^) = Px(^)-1 1 



1 <i 



r,jz 



i^.l 



is a second order approximation to p(x), 

and so on. For 14 m < N, the approximation 

Pj^](x) has the interesting and useful property 

that it is the only distribution of order not 

exceeding m, under which any set ( Xni ,x -t, . . .x . ^ 

L J-L' j2' jmj 

of m variables has the same joint distribution 
as under the given p(x). Of course, approxima- 
tions to p(x) may also be obtained by retaining 
various selected terms in the expansion for f (x) 
and dropping the remaining terms. Becauss any 
approximation to p{x) is obtained by dropping 
terms of f(x) a classification procedure based 
on it will not do as well as the same procedure 
when p(x) is used. 

2. Application to the analysis of some 
pattern recognition networks . The represen- 
tation for the joint distribution p{x) can now 
be used to examine the capabilities of various 
pattern recognition networks which have been 
proposed. Typically^ these are linear sunmation 
networks with thresholds (see Fig.l), which 
operate on the weighted outputs of selected 
groups of "retina" elements, the selection being 
usually random. Variations on this scheme are 
reported by Hawkins^J from whose article Fig. 2 
is taken. 

Consider Fig. 1 first. Of the total 
x=(x]^, xg, ...Xjg) each sunmation unit gets some 
subset, with the x^'s multiplied by variable 
weights. Let a^^i denote the weights between 
the retina elements and the suinrriation units, 
where a^ • can take on the value o, and let Ti^ 
be the thresholds for the response iinits. Then 
for a given response unit, say No. 1 the oper- 
ation for producing an output is described in 
general by 



(a^^x^ + aj^xj > ... * ajj^Xjj) 
+ (ai2Xi + 322X2 + ... + ^n?^' 



> Ti 



or :^a.x. >T. 

i=l 



Consequently a weighted sura of input variables 
is used to perform classification for the type 
of network described. Rather than obtain the 
coefficients {a-j_,S2> ■■■3^) from assumption 
concerning the functional forms of the proba- 
bility distributions or from a program of 
estimation, interest has centered on starting 
from an arbitrary initial state (a|, ai,...a^) 
and using iteration based on experience, i-e. , 
some learning procedure, to go from the initial 
state to a desired final state. 

The evaluation of the classification 
capabilities of the network in its final state 
is considered here. The problem of using ex- 
perience to go from an initial state to a final 
desired state is commented on in the next section. 



341 



VARIABLE 
WEIGHTS 



SENSORY 
INPUTS 



SUMMATION 
UNITS 



RESPONSE 
UNITS 



FIGURE I A VARIABLE NETWORK D.S.R. MODEL 
(FEEDBACK CONNECTIONS NOT SHOWN) 



342 



The cla33if ication criterion used by the 
pattern recognition network is evaluated by 
comparing the resulting error carve with those 
obtained fron likelihood ratio classification 
functions resulting when different approxi- 
mations to the joint distribution are used. It 
is also compared with some well known intuitive 
classification procedures based on linear 
functions of the variables xj_. To simplify 
the exposition only the case of two groups is 
treated here. 

Let p(x/i), i=l,2., denote respectively 
the probability distribution for x under group 
1 and group 2. Then the likelihood ratio 
regions for classification are defined by: 



%=^(-^^=4^>^ = 



Rg: L(x:) ^t. 

Thus if L(x)'>t, the pattern is classified 
as belonging to grot^j 1, otherwise the pattern 
is classified into group 2. The error curve 
can be obtained by computing the probabilities 
of misclassif ication for different choices of 
the threshold t. For a given threshold, the 
probability of incorrectly classifying a pattern 
from group 1 into group 2 is given by 



> P(x/1) 



^ 



x:L(x) •.< t 



and the probability of 



incorrectly classifying a pattern from group 2 

y p(x/2) 
into group 1 is v^ = ^ — . The classifi- 
x:L(x) > t 

cation functions and corresponding networks which 
result when various approximations to p(x)are 
used in a likelihood ratio procedure can now be 
derived. 

If a first order approximation is used, 
p(x) is replaced by p.,(x). This implies an 

assumption of independence of x^. Letting 

"i " ^p(x/l)(^i) and n. - Ep('^/2)(xi), the 
likelihood ratio 



1-x, 



Tfm. i(l-mi) ^-'^i 



L(x) 



i-1 



Tfni'^i (1-ni) 1-^i 



i=l 



N 



taking the logarithn gives "^ (a-x- +c-; 

i=l ■"■ ■^ 
where a^ =iog '± ^^'"i^ and o^ = log [^^SL- 
n^ (1-m^) (l-n^) 



The summation over c^ can be absorbed in the 
threshold and a particular weighted sum is 
obtained for the classification function. If 
a priori probabilities are included, one gets 
the cognitive nets suggested by Minsky 5 , 

The second order approximation Pj- 'A''^) 
neglects all correlations except those of the 
second order, thus implying that the joint 
distribution for the Xj_ is a multivariate 
normal distribution. If the further assumption 
is made that the groups have equal covariance 
matrices (no assumption of statistical inde- 
pendence of the X- is made) then it can be 
shown6,7 that the likelihood ratio, which is 
now the ratio of two multivariate normal density 
functions which differ only in their means, leads 
to a linear function of the x^, called the dis- 
criminant function, given by 



N 



i=l 



iCj^, where a-- 



= (qiidi«52id2*.. 



■*<\^lS 



where qjj^ are elements of Q the inverse of the 
com.iion covariance matrix, and d-=m.-n. 

( j=l,2, . . .N). This function, which according 
to the likelihood ratio is optimum for the case 
of continuous variables with multivariate normal 
distributions and equal covariance matrices 
in the group is, for the case of arbitrary 
distributions the linear function intro- 
duced by Fisher". The sense in which 
maximum discrimination between the two 
groups is provided by Fisher's discriminant 
function is to choose the coefficients aj_; 
such as to maximizes the ratio 



(>-a,d,)' 



N N 

=51 Za a q^J 

i=l j=l J 

where q-'-J are elements of the covariance matrix 
Q"l. It is the linear function which maximizes 
the variance between samples relative to the 
variance within samples^-'?. 

Without the assumption of equal covariance 
matrices in the groups, even the second order 
approximation would result in a network in- 
volving multipliers. So would higher order 
approximations of the form fj,j„,(x) or other 
approximations which neglect all terms in the 
expansion of f(x) except for the first terra 
and a particular higher order correlation. 

If the total distributions p(x/i) are used 
along with a priori probabilities and costs, 
the networks which result are those derived by 
Chow°. The best error curve is of course 
obtained when the complete joint distributions 
are used. 



343 



13 




z 
o 



1° 

en H 

<^ 
UJ O 

± Ld — 

_i q: </7 

z 

iij u. S. 
o 

a: ^ 
iij a: 
Q. o 

UJ z 
a: 



344 



For gome given classes of patterns the 
classification provided by functions based on 
approximations to p(x) majr be quite acceptable. 
In view of their simple implementation, a 
weighted sum of the x-^, or even a unweighted 
sum or score of the xi are attractive candi- 
dates for classification functions. However, 
their worth as classification functions in a 
given context can only be evaluated to the 
extent that the deterioration in the error 
curve or risk curve with respect to the optimum 
is assessed. 

It is known that when using procedures 
which are not optimum, a classification pro- 
cedure based on a subset of the x^ may do better 
than a procedure based on all the x^- this hag 
been found, for example in a slightly different 
context, in the application of discriminant 
functions to speech patterns. It is also 
known that for some situations, when using 
approximate procedures , dividing the xi into 
a number of (mutually exclusive) subsets Sa, 
deriving classification functions f i based 
separately on the sj and using f j to obtain 
a final classification function F can be better 
than a similar function based directly on all 
the Xj^. This is accomplished to some degree 
by learning networks such as those of Fig. 1 
and Fig. 2, in which subsets of the x^. are 
selectively connected to summation units. 
However, the x^ have usually been selected by 
a random method. Tailoring the grouping of 
the Xj^'s to given classes of patterns will 
generally give better results. 

In the network of Fig. 2, subsets of the 
x^, selected in a random manner, are connected 
tlirough fixed weights to summation units with 
with thresholds, the outputs of a number of 
these summation units being then multiplied 
by weighting coefficients, summed and compared 
against a threshold in the response unit. Let 
bj^j be the fixed weights between the retina 
elements and the summation units, where bjj 
can be 0. Let Tj be the thresholds for the 
summation units, Wjj^ the variable weights 
between summation units and response units, 
and Ty- the thresholds for the response units. 
Also, let yj be the outputs from the summation 
units with yj being when the threshold Tj 
is not exceeded, and a constant otherwise. 
Then the classification functions used by the 
network are 

N 



i=l 



bijXi > Tj 



J = 1,2,. 



^yj«jk>Tk : !<= 1,2,. 



since independently he knows to which group a 
given pattern belongs. The easy availability of 
additional samples from each group makes it 
possible to introduce an iterative or "adaptive" 
procedure to improve the performance of the 
classification function. 

An evaluation of the worth of the classifi- 
cation function resulting when iteration based 
on experience is used to modify the state of a 
learning network, is provided by comparing its 
error curve with error curves obtained from a 
likelihood ratio procedure using p(x) and 
various approximations to it, with the error 
curve resulting when the a. are obtained accord- 
ing to Fisher's discriminant function, and with 
the curve obtained when an unweighted acore of 
the Xj is usedlf^. 

3 . Iterative procedures for learning . The 
problem of using experience to go from some 
arbitrary initial state (aj^, a^.-.-afj) to a 
final state (a^, a2,...aj^) which will produce 
a desired result can be approached in many ways. 
Typical of a number of efforts is the approach 
used by Gaborll of minimizing a mean square 
error criterion. The problem may be also stated 
as one of applying a set of transformations T to 
the state vector. In this form, varying degrees 
of complexity can be introduced into the formu- 
lation of the problem, as is illustrated by the 
work in Dynamic Programming. Useful iteration 
procedures can be derived from the simple point 
of view provided by the techniques used in 
stochastic models for learning 12, 13, lit, 15 gnd 
from the point of view orovided by Stochastic 
approximation methods 16, 

h. Discussion . The operation of some 
proposed networks for pattern recognition has 
been examined in the context of classification 
theory, and related to a class of classification 
procedures. It is clear that the classification 
properties of the networks are acceptable for 
many pattern recognition situations of interest. 

Experimental work on pattern recognition 
and iterative procedures is being carried out 
by the author and his associates C. F. Fey, 
N. J. Kolgaard, D. F. Smith and D. F. Parkhill. 
When using various iteration procedures, a 
number of learning nets have produced-learning 
curves similar to those shown in Fig. 3 and h. 
Fig. 5 shows a device, suggested by 
D. F. Parkhill and designed by D. F. Smith 
to facilitate experimentation on pattern 
recognition networks using simple iterative 
techniques . 



Unlike applications of classification theory 
in many fields, in many pattern recognition 
situations it is possible for the experimenter 
to check how well a particular procedure performs 



REFERENCES 

1. Kanal, L. , "Pattern Recognition Studies". 
I. Use of discriminant functions, distance 
functions and clustering transformations 
in pattern recognition. 



345 



1. II. Evaluation of a class of pattern 

recognition networks. 

III. Iterative procedui'es for learning: 
stochastic approximation and random 
search. 

NOTES : General Dynamics/Electronccs 
1961. 

2. Bahadur, R. R. . "A Representation of the 

Joint Distribution of Responses to 
n Dichotonious Items". U5AF SAM series 
in statistics. Report N'o. 59-142. 
RandoK AFB, Texas, 1959. 

3. Parkhill. D. F. , "Distributed State 

Response Pattern Recognition Systems", 
Proc. Rochester Conference on Data 
= Acqui3:ltion and Processing in Biology 

and Medicine. July 1961. 

h. Hawkins, J. K., "Self-organizing Systens- 
A Review and Commentary". Prod. IRE 
Jan. 1961, p. Bl-W. 

5. Minsky, K. . "Steps Toward Artificial 

Intelligence", Proc. IRE. Jan. 1561, 
p. ?-3C.' 

6. Rao, C.R., "Advanced Statistical Method 

in Bioraetric Research". New York, 
John Wiley, 1952. 

7. Anderson, T.W. , "An Introduction to Kulti- 

variate Statistical Analysis". New 
York, John Wiley, 195*^. 

^. Fisher, R. A , "The Use of Multiple Meas- 
urements in Taxononic Problems ". in 
Contributions to Mathematical 
Statistics. New York. John Wiley. 

p. Chow, C.K., "An Optimum Character 

Recognition System Using Decision 
Functions". IRE Trans, on Electronics 
Computers, Vol. SC-6 p. 2)4 7-251i. 
Dec. 1957. 

10. Solomon, H. , "Classification Procedures 

Based On Dichotomous Response Vectors". 
Contributions to probability and 
Statistics, Olkin: Stanford University 
Press, I960. 

11. Gabor, D. , Wilby, W. , Woodcock, R. , "A 

Universal Nonlinear Filter, Predictor 
and Simulator which Optimizes Itself 
by a Learning Process." Proc. Inst, 
of Electrical Engrs. Vol. lOR, Part B. 
1961. 

12 Bush, R. R. and Hosteller, F. , "Stochastic 
Models for Learning". New York, John 
Wiley, 1955. 



13. Luce, R. D. , 
New York, 



'Individual Choice Behaviour," 
1959. 



Ih. Kanal. L. , "Analysis of Some Stochastic 

Processes Arising From A Learning Model". 
Ph.D. Thesis, University of Fenn. June, 
I960. 

15. Kanal, L. , "On a Random Walk Related to a 

Nonlinear Learning Model", IRE, March 
1961, National Convention Record. 

16. Dvoretzky, A., "On Stochastic Approximation" 

Third Berkely Symposium on Mathematical 
Statistics and Probability, University 
of California, Press, 1956. 



ACKNOtvXEDGSMENTS 

I am indebted to C . F. Fey. N. J. Molgaard 
D. F. Parkhill, and especially D. F. Smith for 
helpful discussions and comments. 

I am also grateful to K K. Kaitra, J. Dietz 
and A. Wolf for their comments and encouragement. 



346 



AN ADAPTIVE CORRELATOR FOR UNDERWATER MEASUREMENTS 



by DR. ALFRED A. WOLF, Director of Research 

and J. H. DIETZ, Fellow Engineer 

Emertron, Inc. 

Silver Spring, Mai-yland 



ABSTRACT 



The measurement and display of the correla- 
tion functions of quasi-stationary random proc- 
esses containing energy in the frequency range 
0.01-100,000 cps have hecome increasing ijiipor- 
tant in oceanography and underwater acoustics. 
Correlation techniques yield useful statistical 
descriptions of sea state, ocean bacliground 
noise, and the acoustical properties of bodies 
of water. In addition, since the correlation 
functions of periodic processes are also peri- 
odic, correlation may be used to separate weaJk 
signals from noise. 



INTRODUCTION 

At present correlation functions are usually 
determined by means of a digital computer, ■'- 
which employs sampled records of the processes 
to compute approximating sums for the time inte- 
grals that define the correlation functions. 
Disadvantages of this method are (l) the need 
for the computer itself, (2) the fact that the 
required number of samples must be determined 
experimentally, (3) the bandwidth limitation 
imposed by sampling, and (4) the discrete dis- 
play of the correlation functions. 

The defining time integral may also be ap- 
proximated by analogue techniques . The re- 
quired time delays are introduced by means of 
tapped delay lines; analogue mirltipliers are 



used to obtain the products of the delayed and 
undelayed signals; and averaging is accomplished 
in a low-pass filter. Like the digital method, 
this scheme gives discrete values of the correla- 
tion functions. The bandnrldths of the signals to 
be correlated are restricted by the pass band of 
the signal multiplier. The principal disadvan- 
tage of this method is the need for low-distor- 
tion delay lines capable of producing delays of 
order of seconds and in some cases minutes. 

In this paper an analogue method requiring no 
delay lines and yielding a continuous approxima- 
tion of the correlation function is considered. 
An outgrowth of the work of Wolf and Dietz in 
system identification, the method consists in ex- 
panding the correlation function in a series of 
orthonormal functions the coefficients of which 
are determined by analogue techniques. A simi- 
lar but less general method was independently 
developed by Lampard.3 Since in practice the 
series must always contain a finite number of 
terms, the problem of an optimum approximation 
to the correlation function is treated. The 
filters that generate the orthonormal functions 
automatically adjust their transmission charac- 
teristics to give an optimum approximation in the 
minimum- integral-square-error sense. 



347 



ORTHONORMAl EXPANSION OF A COKRELATION FUNCTION 
— ... . , . — fcj-^ 



In Fig. 1 a stationary random process g3_(t) 
is applied to the inputs of a set of time-in- 
variant linear filters the impulse responses of 
which form a set of orthonormal fxmctions 
£ hn(t)}- over the interval (0,oo), i.e., 

/oo 1, n = m 

h (t) h^{t) dt = (1) 

0, n / m 

The response of the nth filter to g-]_(t) applied 
at t = is the random process Vjj(t), given hy 



00 

^n('t) =/" gl("t-r) \{Z) d^ 



(2) 



Multiplying the response Vjj(t) hy a second sta- 
tionary random process g2("t) a^^ time-averaging 
the product leads to 

oo 

A^ = g2(t) vn(t) =/ g2(t) g^(t-r) hj^(r) ar (3) 



Since 



the cross-correlation function of g-i(t) and 
g2(''')> (3) may he written: 



U) 



A^=y ^i2(r)h^(z) d. 



(5) 



an integral equation of the first kind, a solu- 
tion of which is 



00 



n=l 



(6) 



That (6) is a solution can be verified hy sub- 
stituting (6) in (5), interchanging the order 
of summation and integration, and invo]ri.ng (l). 
Hence averaging the products of 82^'^) ^^'^ "the 
responses of the filters to g-i(t) leads to the 
coefficients, Ajj, of the orthonormal expansion 
of the correlation function for fiO. 

A second set of identical filters are ex- 
cited by a unit step, to give the indicial 
responses a (t): 



t 
a^(t) = r h^( 



r) dr 



(7) 



d 
dT 



E A^f V'n af = 2J A^ h„(t) (8) 
n=l n=l 



which is the correlation function displayed in 
real time. 



A CLASS OF ORTHONORmL FUNCTIONS AND FILTERS 

A class of orthonormal functions suitable for 
the expansion of correlation functions are defined 
by the following theorem: 

Theorem , ■j^g gg.^ ^f sqiiare-integrable time 
fimotions {hj^(t)J- fonn an ortho- 
normal set over the interval (0,oo) 
if each member possesses a Laplace 
transform H^(s) with 



B (s) 



(9) 



and 



C (-s) 

n-1 



(10) 

in vfcich B-,(s) and the terms Cjj(s) 
are polynominals in s, and if 
the constants IC are such that 



1 

2nJ 



/ H (-s) H^(s) ds = 1 

n = 1, 2, ... (11) 



in which Br denotes an appropriate 
Bromwich contour in the s-plane 
enclosing the poles of H (s). 

(a proof of this theorem appears in the 
Appendix . ) 

Examples of members of this class of ortho- 
normal functions are the Laguerre functions, 
for which 

n-1 
(s -s) 

H (s) =^. — i 



=1 , 

(s^+s, 



n = 1, 2,, 



(12) 



with multiple poles at s = -s-^ and multiple 
zeroes at s = S]_; and the Kautz fimctions for 

which . 

/2s 

^ (13) 



H-j_(s) 



S+Sn 



Each ap)(t) is then multiplied by the correspond- 
ing coefficient A^, all such products are summed, 
and the resulting sum is differentiated, yielding 



348 



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c 


> 




' 


-S 


c 




c 
< „ 




H 


II 

c 





^ 



-€^ 



r<^ 



r<£H 



o 



0) 

;< 
u 
o 
U 

(U 
3 
tJD 
O 

1— I 

c 

< 



4> 



4y 



S^ 






349 



and 



V^ 




^ -i^ Hn-l(s) r,>2 (U) 



n-1 



The physical realization of a set of filters 
with inpulse responses h]_(t), h2(t),,., is 
readily accomplished by analogue -coinputer 
techniques . Denoting the input to the first 
filter by g(t) and the output by x-]_(t), one sees 
from (9) that these quantities are related by 
the linear differential equation 



CJD) x(t) = Ki Bi(D) g(t) 



(15) 



in which D = ■^. Similarly, from (10) it is 
seen that the outputs of the succeeding filters 
are recursively related by the linear differen- 
tial equations 

Kn-1 Cn(0) ^(t) = K^ C^.j_{-D) x^_^(t) n > 2 

(16) 

Operational amplifiers connected to solve (15) 
and (16) are the physical realization of the 
orthonormal filters. 

oftdjIUM orthonormal expansion 

In practice it is desirable to truncate the 
series expansion of the correlation function 
after as few terms as possible. Denoting the 
exact correlation function by 



oo 

^^"^^ = S ^ '"n(^) 

and the N-term approximation by 
N 

n=l 



(17) 



(18) 



one may write the integral-square error of the 
approximation : 



2 r 2 



(19) 



Squaring the integrand of (19), substituting 
(17) and (18) therein, interchanging the orders 
of integration and stuumation, and invoking (1) 
in evaluating the resulting integrals leads to 



The orthonormal time functions hpj(t) are 
also functions of a set of real parameters ■{o< .} , 
e.g., the poles and zeros of the Laplace trans- 
forms of the Laguerre and Kautz functions. Hence 

2 
from (6), (20), and (21) so, too, are A^, S^, 

and £ ^. The optimum expansion of fiiT) for a 
given N and a particular set of orthonormal 
functions is defined as the expansion obtained 
when theo<;^ are selected to minimi ze€f^. Since 

the right member of (20) is always nonnegative, 
the optimum expansion occurs when the dj are 
selected to give 



Max S,, = Max /■ A„ 



(22) 



Hence the determination of the optimum ortho- 
normal expansion is the multivariate majcimization 
of the sxm of the squares of the coefficients of 
the orthonormal series over a set of parameters 

If the orthonormal functions employed to ex- 
pand the correlation function yield Sfj that are 
well-behaved functions of parameters {ci ;^ J , the 
gradient method may be \:ised to reduce the multi- 
variate maximization to a convergent iterative 
procedure involving a single variable 0, This is 
accomplished by transforming the initial set of 

parameterslWi } to a new set{<X ^}by setting 

1 o/'*n\ 1 = 1, 2, ... 

e( =01+1 I e 

"•i i Uo^i/ e>o 

^ (23) 

in which the subscript on the partial derivS' 
tive indicate s that it is evaluated at ee 



.0 



<^' 



0^2 =^2' ' • ' -^^^^ ^23) represents the equa- 
tions of a straight line in a hyperplane tangent 

to Sj, at the point ^ (/ , . . .). Since in 
the neighborhood of triis point one may approxi- 
mate the function S^ by the straight line, in 
this region 



s^(.^^,ot^, ...)^s2( e ) 

Maximizing the right member of (24) yields 



(S, 



N'l 



ufax s;: ( e ) 



(24) 



(25) 



2 r 2 



in Triiich 



N 



^=?1 "- 



(20) 



(21) 



The value of 6 that satisfies (25) is substituted 
in (23) to give the new set of parameter values 

{.^ if . Repeating the procedure by letting 
2 1 / 9s2\ i = 1, 2, ... 
c<i =0<. . (5^ 1 9 (26) 



350 



2 2 
leads to (S,,) > (S.,) and to a set of parameters 
N 2 - Ml 

I C* . / . Continuing the process yields the mono- 
tone nondecreasing sequence 



parameter is therety iteratively adjusted to its 
optimum value , The optimization computer and 
parameter controller is amenable to mechaniza- 
tion by hybrid-computer and step-servo 
techniques . 



(s') <■ (S^) < 
n'i - ^ N 2- 



~ N j 



(27) 



which converges to Max S... The values of the 



i^J 



N* 



parameters that yield this maximum form an 
optimum set of parameter values . 

IMPLEMENTATION OF THE ADAPTIVE CORRELATOR 

The block diagram implementation of the cor- 
relation principle discussed above is shown in 
Fig. 1. Random process g-i(t) is applied to the 
input of the first set of orthogonal filters . 
The resulting outputs — v-]_(t), V2(t),..., V[^(t) 
— are multiplied by the second random process, 
g2(t), by means of analogue multipliers; and the 
respective products are passed through low-pass 
filters, to give the averages A-,, Ap,,.., A^,, 
At the same time a second set of identical 
orthogonal filters receives a repetitive square- 
wave input, producing outputs a]_(t),..., a[vj(t) , 
Each of these responses is multiplied by the cor- 
responding average, and the products are summed. 
Finally, the suia is differentiated to obtain 
'i^ui'^) , the approximate expansion of the correla- 
tion function. 

Fig. 2 shows the block diagram of the 
mechanization of a correlator capable of self- 
adjustment to achieve an optimum orthogonal ex- 
pansion in the mlnimum-lntegral-square-error 
sense. The quantity S^, obtained by squaring 
each of the averages A]_, . , . , A^ and summing the 
sqiiares, is applied as an input to an optimiza- 
tion computer and parameter controller, which 
Iteratively determines the optimum settings of 
the parameters of the orthogonal filters by the 
rflutlne of Fig, 3. After storing the set of 

initial parameter values, (_oi a / , and the initial 
value of the sum of the squares of the averages, 

(Sxj)(-,, the computer determines the set of ap- 
proximate initial parameter sensitivities, 

{ N I . It then normalizes these sensitivities 

by dividing each by the absolute value of the 
largest, Pq, Each parameter is then varied 
over its range in steps proportional to its 
normalized sensitivity. The set of parameter 

values io<-- f , yielding the largest value of Sm 

f 7 
IS compared to the initial setfOL^/. If all 

corresponding members of the two sets differ 

by less than preasslgned amounts, the process 

is temilnated; if not, the initial parameter 

values are replaced by the values giving the 

2 
greatest S^, and the process is repeated. Each 



CONCLUSIONS 

In this paper we have considered certain theo- 
retical and practical aspects of a correlator 
that approximates correlation functions by series 
of orthogonal time fxmctions and iteratively 
adjusts itself to minimize the approximation 
error. Since operational-amplifier methods are 
employed to synthesize the orthogonal filters 
and analogue multipliers are used to obtain the 
required signal products, the device is re- 
stricted to the correlation of signals contain- 
ing no significant energy at frequencies greater 
than 100 kc . With amplifiers and multipliers 
capable of operating at higher frequencies , how- 
ever, the range could be increased. 

A method for synthesizing a class of linear 
orthogonal filters has been presented. Typical 
members of this class are the well-known 
Laguerre and Kautz filters. Other members are 
filters with transfer functions 



Hi(S) = 



s2+2 



(28) 



1 1 



and 



H (S) 
n^ ' 






■1 



S -2^ CO S*(J- 

n-1 n-1 n-1 

s^. ar^^^s.^,^ 



Hn-l^S) 



(29) 

The impulse responses of such filters contain 
exponentially damped cosinusoids and are there- 
fore applicable to the expansion of correlation 
functions with periodic components. 

REFERENCES 

1. Y. W. Lee, Statistical Theory of Communica- 
tion . John Wiley & Sons, Inc., New York, 
1960. 

2. A. A. Wolf and J. H. Dietz, "A Device for 
Measuring Correlation Functions and 
Spectral Density Functions," Technical 
Report No. 1, and "A Study of White-Noise 
Fault Diagnosis in Linear Passive Systems," 
Technical Report No. 2, Stromberg-Carlson 
Company (now General Dynamics/Electronics) 
Applied Mathematical Studies Department, 
Rochester, N.Y., Nov., I960. 



351 




u 
o 



u 
o 

u 

> 

a 

03 






352 







a 



o 
U 

c 
o 

+-> 



a 
O 



s: 
U 

o 

QJ 



a 
6 

•r-l 

CO 



•r-l 



353 



3. D. G. Lanrpaird, "A New Method of Determining 
Correlation Functions of Stationary Time 
Series," J- Inst. Elec. Eng .. part III, 

No. 73, PP. 343 f., Sept., 1954. 

4. W. H. Kautz, "Transient Synthesis in the 
Time Domain," Trans. IKE PGCT . vol. CT-1, 
No. 3, PP. 29-39, 1954. 

5. T. L. Saaty, Mathematical Methods of Opera - 
tions Research . McGraw-Hill Book Co., Inc., 
New York, 1959 

APPENDIX 



Proof of Theorem 



Since each hj^(t) is square-integrahle, it 
follows that 

.00 

\it) hj^(t) dt < oo (30) 





/: 



for all n,m 1. Since in the Laplace trans- 
forms Hj^(s) the terms Cj^(s) are polynomials in 

s, the transforms contain only poles in the left 
half -plane. One may therefore write: 
oo 

J h^(t) h^it) dt = ^y Hm(-s) Hn(s) ds 

in which Br and Br' denote Brorawioh contours in 
the s-plane enclosing the poles of It,(s) and 
Hjjj(s), respectively. 

Noting that the repeated application of 
(10) leads to 

n-1 

Tf cj-s) 



Ms) = K^ Bi(s) ^ 



-, n > 2 (32) 



IT ^s) 

k=l 



we consider the following three cases in which 
n / m: 

(1) n = 1, m > 2 

Substituting (9) and (32) in (31) gives 
m-1 

r TT V^) 



TT S(-^) 

k=l 



1 ds = 



Ci(s) 



(33) 



because the denominator term C-|(s) is cancelled 

by C-|_(s) in the numerator, leaving no terms in 
the denominator with zeros in the left half- 
plane. 



(2) n > 2, m < n 



Br' 



n-1 

Tf C (s) 
' ' k 



k = l 



m-1 



77 -k 

k^l 



Cv(-s) 



TT y^^ 

k = l 



ds = 



(34) 



because the denominator terms Ci(s) C2(s) ... 
C_(s) are cancelled, again leaving no terms in 
the denominator with zeros in the LHP . 



(3) m > 2, n< m 



ij/ Km'^B,(-s)l^ 



m-1 



TT 'k^-) 

k=l 



n-1 



n'^^-'^ 



k = l 



ds = 



(35) 



k=l 

because the denominator terms C-,(s) Cp(s) ... 
C (s) having zeros in the LHPj are cancelled. 

For n = m, (11) applies. Hence 



00 



t) hjt) dt 



LO, n 



/ m 



(36) 



and the theorem is proved. 



354 



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