OPTICAL TRANSMISSOMETER-NEPHELOMETER FOR DEEP OCEAN USE David Michael Mosey DUDLEY KNOX USR^ oot NAVAL POSTGRADUATE SCHOOL Monterey, California THESIS OPTICAL TRANSMISSOMETER-NEPHELOMETER EOR DEEP OCEAN USE by David Michael Mosey September 1976 Thesis Advisor: S. P. Tucker Approved for public release; distribution unlimited. T 175026 SECURITY CLASSIFICATION OF THIS PAGE (Whan Dot* Bntorod) REPORT DOCUMENTATION PAGE I REPORT NUMBER READ INSTRUCTIONS BEFORE COMPLETING FORM 2. GOVT ACCESSION NO 3. RECIRIENT'S CATALOG NUMBER 4. TITLE (mnd Submit) Optical Transmissometer-Nephelometer for Deep Ocean Use S. TYRE OF REPORT ft RERIOO COVEREO Master's Thesis; September 19 7 6 • PERFORMING ORG. REPORT NUMBER 7. AUTHORf'J David Michael Mosey ft. CONTRACT OR GRANT NUMBERS >. PERFORMING ORGANIZATION NAME ANO AOORESS Naval Postgraduate School Monterey, California 10. PROGRAM ELEMENT. PROJECT, TASK AREA ft WORK UNIT NUMBERS II. CONTROLLING OFFICE NAME ANO AOORESS Naval Postgraduate School Monterey, California 93940 12. REPORT DATE September 1976 IS. NUMBER OF PAGES 76 IS. SECURITY CLASS. (o( thf roport) Unclassified 14. MONITORING AGENCY NAME ft AOORESSfil dllUrunt horn Controlling Otllco) Naval Postgraduate School Monterey, California 93940 15*. DECLASSIFICATION/ DOWNGRADING SCHEDULE 16. DISTRIBUTION STATEMENT (ol thlc Roport) Approved for public release; distribution unlimited. 17. DISTRIBUTION STATEMENT (ol tho mmotrmct ontorod In Block 20, It dlttoront rromt Roport) 18. SUPPLEMENTARY NOTES 19. KEY WORDS (Confirm* on rorormo ol4o II noeommmrr mnd Idontltr by Mock nummot) 20. ABSTRACT (Contlnuo on rormroo olmm It nocooomtr mnd Immmtlfy by •!••* momoor) A submersible light transmissometer-nephelometer was designed and constructed for the purpose of measuring the beam attenuation and relative volume scattering coefficients at two fixed angles and at depths to 1000 meters. Flexibility, a major design criterion, makes it possible for the unit to be operated in a number of configurations. Addition of an internal battery supply, a filter wheel, light DD .HR, 1473 (Page 1) EDITION OP 1 NOV 61 IS OBSOLETE S/N 0102-014-6601 I SECURITY CLASSIFICATION OF THIS PAOE (Whon Dmtm mntmrotl) 1 tliCumTV CLASSIFICATION OF THIS P»GErW>i»n n»K Enfrmd- stops, a photomultiplier tube and amplifiers is possible. The NPS light transmissometer-nephelometer is not a single purpose instrument but has the capability to be utilized as a submersible optical bench, useful in the development of underwater optical instrumentation. DD Form 1473 , 1 Jan 73 S/N 0102-014-6601 SECURITY CLASSIFICATION OF THIS Wk.Gt.Chf> Dmlm Bnfrmd) Optical Transmissometer-Nephelometer for Deep Ocean Use by David Michael Mosey Lieutenant, United States Navy B.S.E.E., Purdue University, 1971 Submitted in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE IN OCEANOGRAPHY from the NAVAL POSTGRADUATE SCHOOL September 1976 :hoOI MONTEREY, CAi -S40 ABSTRACT A submersible light transmissometer-nephelometer was designed and constructed for the purpose of measuring the beam attenuation and relative volume scattering coefficients at two fixed angles and at depths to 10 00 meters. Flexibility, a major design criterion, makes it possible for the unit to be operated in a number of configurations . Addition of an internal battery supply, a filter wheel, light stops, a photomultiplier tube and amplifiers is possible. The NPS light transmissometer-nephelometer is not a single purpose instrument but has the capability to be utilized as a submersible optical bench, useful in the development of underwater optical instrumentation. TABLE OF CONTENTS I. INTRODUCTION - - _ _ _ _ 9 A. BACKGROUND -- - __________ 9 1. Water Characteristics Instrumentation -----_--____ 9 2 . Scattering and Absorption _______ n B. OTHER TECHNIQUES FOR MEASURING VOLUME ATTENUATION COEFFICIENT --__--- 15 1. Contrast Reduction ______-_--- 15 2. c at High Collimation ------___ 15 3. c from Measurements of Irradiance on Axis _____---_-- 16 4. c from Visual Threshold Range ----- 16 5. c from Telephotometry of an Extended Diffuse Source __---_-- 17 6. c for Laser Light ----------- 17 C. MEASUREMENT OF THE VOLUME SCATTERING FUNCTION - - -------- 17 II. INSTRUMENTATION ----------------20 A. NPS UNDERWATER TRANSMISSOMETER AND SCATTERING METER -------- --20 1. Collimated Source -----------20 2. Receiver/Optical Sampler Section - - - - 22 3. Power Requirements ___________ 33 4. System Operation ____________ 33 5. Output -----------------38 B. RESULTS ------------------38 1. Bench Testing ------------- 38 a. Equipment ---------____ 40 b. Optical Filters ----------41 c. Detector Biasing ---------- 44 2. In-Water Testing ------------44 III. CONCLUSIONS -.46 APPENDIX A: NPS Transmissometer-Nephelometer Drawings and Specifications -------48 APPENDIX B: List of Off-the-Shelf Components Utilized in the NPS Transmissometer- Nephelometer ------_---_-__ 72 BIBLIOGRAPHY __74 INITIAL DISTRIBUTION LIST 75 LIST OF FIGURES Figure 1. Simplified diagram of dual purpose instrument --------------------- 10 2. Basic nephelometer configuration ---------- 12 3. NPS Transmissometer-Nephelometer ---------- 21 4. Arrangement of components on rods --------- 23 5. Transmissometer-nephelometer light source ----- 24 6. Schematic representation of detector inputs - - - - 2 5 7. Ray diagram-mirror position one ---------- 27 8. Ray diagram-mirror positions 2, 3 and 4 ------ 29 9. Detector mounting ----------------- 30 10. Mirror positioning drive motor ----------- 31 11. Photodetector mounting arrangement --------- 32 12. Underwater electrical connector wiring diagram ------------------- 34 13. System operation conceptual diagram -------- 35 14. Scattering sensor arrangement, side view ------ 36 15. Scattering sensor arrangement, top view ------ 37 16. Transmissometer-nephelometer system -------- 39 17. Voltage output, bench operation ---------- 40 18. Experimental set-up for bench tests -------- 41 19. Transmission curves for Corning 1-57 and Wratten 61 filters --------------- 42 20. Transmission curve for Hoya HA- 3 0 filter ------ 43 21. Detector biasing schematic ------------- 414 22. In-water test results --------------- 45 ACKNOWLEDGEMENT I wish to express appreciation to my thesis advisor, Stevens P. Tucker for his interest and patience in oversee- ing the design and construction of the instrument;, to the NPS Machine Facility for their cooperation in fabricating the many components required; to Machinery Repairman First Class Travis Adams for his professionalism in machining several components under a severe time constraint; to Prof (Ret.) Sid Kalmbach of the NPS Physics Department for his professional evaluation and advice concerning the finished product; to the technicians of the Physics Department, especially Bob Moeller and Tom Maris, who supplied many components for the device; and to my wife Kathryn for her understanding and encouragement during times when my work necessitated my absence from home and family. I. INTRODUCTION A. BACKGROUND 1. Water Characteristics Instrumentation A knowledge of certain underwater optical parameters is essential if one wishes to characterize optically a par- ticular type of water in which operations involving light are to be conducted. Such operations may include among others the use of imaging systems, fixed underwater lighting, remote underwater television cameras and external lights for use on deep submergence vehicles, optical detection and communica- tion systems, and near-shore bathymetry. Many instruments have been developed to measure under- water optical characteristics. The instrument which was de- signed and constructed was made in an attempt to combine two meters into one for measuring the volume attenuation coeffi- cient c(A) at visual wavelengths and the scattering coeffi- cient, 3(9). These quantities will be discussed in detail later. A simplified diagram of the dual-purpose instrument is shown in Figure 1. In general a transmissometer or c-meter is used to measure the volume attenuation coefficient at some wavelength, A. A basic transmissometer consists of a light source with a narrow, highly collimated beam and a receiver with a narrow "Frequently this attenuation coefficient has been designated by "a". (U CD o C^ G •H Q) Ph P, /"■^ cd ■P O W M Mh £ •H CD C CD b0 P Ph'H P. •H P*'H P rH O P, CD -P fn P> P> 0) ,C cu rtf O •H -P Ph O O P1 b0> H C XI rd •H P> p * C a) cu (1) p S E p1 ^ CU rd H — 1 O 0 0) CO > 3-* p. o p> o CD P c CD in P CO C •H CD CO O a, p. Ph rd O S rtf P. bO rd •H -X3 T3 CD •H •H H Ph S ■H CO CD H P. rd 3 O P. bO •H 0 •H P P> Ph Ph O 0 0 CD P> T3 CD 10 field of view. The source and detector are separated by a fixed distance, usually one to two meters. Normally, photo- cells are used to measure the radiant output of the source and the irradiance detected at the receiver. From these measurements, the transmissivity , T, over the length of the beam's path can be determined. An instrument used to determine the volume scatter- ing function, 8(6), is the large-angle scattering meter or nephelometer [5], In this instrument the light scattered from an elemental scattering volume is recorded by a photo- detector that rotates in a semicircle at a fixed radius from the scattering volume, 9 being the angle between the optical axis of the detector and the forward direction of the source (see Figure 2 ) . These instruments measure two of the inherent optical properties of seawater. 2 . Scattering and Absorption Attenuation of light is due to the effects of scat- tering and absorption. The attenuation of a beam passing through seawater can thus be considered to be the sum of the effects of (1) scattering by the water, b : (2) scattering w by dissolved material, b , ; (3) scattering by suspended par- ticulates, b ; (4) absorption by the water, a ; (5) absorp- tion by dissolved material, a,; and (6) absorption by sus- pended particulates, a . It is then described by the relation c = a + a, + a^ + b + b , + b^ (1) w d p w d p 11 / / rd 2 TD s cu m A £ ■H -P rH ,C rH bO 0 •H o H 0 a; •M O •H O H W C O •H -H bO •H Mh C O a -p e o rH (U c o •H CO rti CQ OJ •H 12 The volume scattering function, 8(0) describes the angular dependence of the light scattered from a small volume element. 8(0) is defined operationally by the equa- tion: dJ(9) = B(0)HdV (2) where dJ(0) = radiant intensity (power/solid angle) of the light scattered from a colli- mated beam in the volume element dV. 0 = polar angle which describes the direc- tion of the scattered light with res- pect to the axis of the collimated beam. H = irradiance (power/unit area) of the light incident on dV. The scattering coefficient b, is related to the volume scattering function 8(0) as follows: 7T b = 2tt f 8(0) sin0 d0 (3) o b may be considered to be, composed of a forward scat- tering term, bf, and a backscatter term, b, , where b = b^ + b, . Thus b tt/2 bf = 2tt f 8(0) sin0 d0 (4) b, = 2tt /* 8(0) sin0 d0 (5) tt/2 13 An absorption coefficient a, describes the attenuation of light for a particular wavelength by the absorption mecha- nism alone. It strongly depends on the optical wavelength, and is related to the attenuation coefficient, c, and the scattering coefficient, b = b + b , + b , in the following ° w d p ° manner : a = c - b (6) The volume attenuation coefficient c(A), can be de- fined operationally as follows: if a collimated source of radiance Nfi and wavelength X is directed through a medium (such as water), the radiance at distance r down the beam is N . N is smaller than N~ - because of absorption and scattering in the medium - by the ratio: !E = e-cU)r (7) NQ Hence, the volume attenuation coefficient for a collimated light source described is defined as [2]: t N c = -?lnr (8) The measurement of c is, complicated, however, by the necessity to distinguish unscattered light from the light which has been scattered at very small angles. Be- cause some scattered light is always collected at the 14 receiver of even the best instruments, the measured attenua- tion is actually given by: c' = c + gb (9) where g is some number less than one, the value of which de- pends on the instrument. Because the value of the measured attenuation coefficient depends on the design of the instru- mentation as well as the properties of the water, the accu- racy of reported measurements of the attenuation coefficient must be carefully evaluated [5], B. OTHER TECHNIQUES FOR MEASURING VOLUME ATTENUATION COEFFICIENT There are many techniques for measuring the spectral volume attenuation coefficient, c, and no attempt will be made to present all of them. Several significant and quite different types of measurements, which in all cases yield the same numerical result, will be mentioned briefly here. Duntley [1] gives detailed discussions of such measurements. 1. Contrast Reduction Underwater photographs of objects taken in the hori- zontal direction disclose that a simple exponential form of the contrast reduction equation holds for daylight. The value of the attenuation coefficient measured in this way is in fact c [3] . 2 . c at High Collimation By varying the length of the water path and making a semilogarithmic plot of flux received vs. distance from 15 a collimated light source, absolute values of c can be found from the slope of the resulting straight line without requir- ing an air reading. The values of attenuation coefficient are remarkably unaffected by beam and receiver geometry as long as (1) stray light is effectively eliminated and (2) the ratio of beam diameter to length of the water path is small. It is not necessary to have high collimation at both the light source and the receiver, although stray light is easier to suppress when some practical amount of collimation is pro- vided for both source and receiver. Beam divergence and re- ceiver field of view of the order of 1 degree seems to be a good choice for fixed path transmissometers using an air measurement to establish the c=0 reading [1] . Higher colli- mation does not result in an appreciably different value of the volume attenuation coefficient. 3 . c from Measurements of Irradiance on Axis Several ways of measuring c are suggested when the receiver of a transmissometer is an irradiance collector. The curves obtained for various combinations of beam diam- eters, beam divergences and path segments will follow the c-slope [3], In most practical circumstances, however, they are not attractive options from the standpoint of convenience. 4. c from Visual Threshold Range Underwater psychophysical experiments show that laboratory visual threshold data are applicable to valid numerical predictions of visual threshold distances . Such 16 a collimated light source, absolute values of c can be found from the slope of the resulting straight line without requir- ing an air reading. The values of attenuation coefficient are remarkably unaffected by beam and receiver geometry as long as (1) stray light is effectively eliminated and (2) the ratio of beam diameter to length of the water path is small. It is not necessary to have high collimation at both the light source and the receiver, although stray light is easier to suppress when some practical amount of collimation is pro- vided for both source and receiver. Beam divergence and re- ceiver field of view of the order of 1 degree seems to be a good choice for fixed path transmissometers using an air measurement to establish the c=0 reading [1] . Higher colli- mation does not result in an appreciably different value of the volume attenuation coefficient. 3 . c from Measurements of Irradiance on Axis Several ways of measuring c are suggested when the receiver of a transmissometer is an irradiance collector. The curves obtained for various combinations of beam diam- eters, beam divergences and path segments will follow the c-slope [3], In most practical circumstances, however, they are not attractive options from the standpoint of convenience. 4. c from Visual Threshold Range Underwater psychophysical experiments show that laboratory visual threshold data are applicable to valid numerical predictions of visual threshold distances . Such 16 data show that black-suited swimmers having no areas of higher reflectance will, when deployed horizontally , lose sight of each other at a separation of 4 attenuation lengths when there is ample daylight [3], Thus, two swim- mers can determine 1/c simply by separating horizontally while connected by a measuring line. One fourth of their mutual disappearance range equals 1/c. No equipment other than a knotted, measured line is needed. Water clarity may be measured in this way. 5 . c from Telephotometry of an Extended, Diffuse Source Telephotometer measurements of the apparent radiance of the center of a diffusely emitting surface will produce a straight line on a semilogarithmic plot of apparent radiance vs. lamp distance, the slope of which is a measure of c [3], 6 . c for Laser Light Several of the foregoing techniques are applicable to laser sources, which lead to the same values for c [3], C. MEASUREMENT OF THE VOLUME SCATTERING FUNCTION A nephelometer , or large angle scattering meter is used to determine the volume scattering function 3(8). The basic configuration of a nephelometer is shown in Figure 2. In the measurement of 3(8) as a function of 8, scattering volume is recorded by a photodetector that rotates in a semicircle at a fixed radius from the scattering volume. One problem with nephelometers has been a difficulty in defining the elemental scattering volume. Another problem occurs because 17 the instruments normally cannot measure scattering at very small angles. Because the volume scattering function is strongly peaked at small angles, errors occur in attempting to evaluabe b by integrating the volume scattering function that is determined by this type of instrument , [5] . If the complete scattering function is desired the scatterance must be observed at a number of angles from 0° to 180 . A general discussion of the various techniques is given by Jerlov [3]. If b is to be obtained the observations must cover both small and large angles, and they should be carried out in situ Small angle forward scattering is due especially to the presence of suspended particles which in number lead to a significant amount of light scattered at angles less than one degree. Most in vitro measurements are in the angular interval 10 to 165° and given only in relative units. This prevents (1) a calculation of the scattering coefficients by integration, and (2) a separation of molecular and particle scatterance. In the present review, attention has been focused on the observations giving absolute values, and pri- marily those made in situ. The in vitro technique is ham- pered by the risk of contamination and of changes in the particles while sampling and during the time lapse between sampling and measurement [3], The calibration of scattering instruments presents a special problem. The use of standard scatterers or perfect diffusers is not reliable. The technique of Morel (1966) 18 using benzene as a known standard gives very accurate rela- tive - but not absolute - results. Kullenberg (1968, 1969) avoids the use of a reference by measuring the intensity and elemental volume. This is a reliable technique, provided the scattering volume is accurately determined, and the geometry of the system is well defined [3] . 19 II. INSTRUMENTATION A. NPS UNDERWATER TRANSMISSOMETER AND SCATTERING METER The NPS Underwater Transmissometer and Scattering meter was designed and constructed by the author and Stevens P. Tucker. It was an attempt to incorporate off-the-shelf optical components and solid state photodetection devices. The mechanical complexity was minimized by using only one motor with associated gearing to drive the optical sampling mirror. Fiber-optics ("light pipes") were used to minimize the number of prisms and lenses which require critical alignment and positioning. The use of a single, solid- state photodetector provides an output which is always ref- erenced to the same light intensity. The one-meter path for the light beam was chosen to keep the optical system simple and is an acceptable length for measurements in coastal and upwelling areas. Figure 3 is an overall view of the NPS instrument, and the numbers refer to part numbers listed in Appendix A. 1. Collimated Source Originally the NPS instrument was to incorporate a helium-neon laser as a light source. However, difficulties in the high voltage supply of the unit necessitated return to the manufacturer for repair. Unfortunately, the particu- lar laser was no longer in production, and repair was 20 & CD ■M Q) 6 O r-\ CD .c a. bO •H P +-> rd O Pi cu h •n < ,£) O • o CO ft J- ■H Fh 0 +-> cu +J cu rd CO CO Fh S G 3 o cu z. bO Jh -a ft o •H ^ p e J- ft o 0 rd o rd o H • 1 < 1 o 1 1 c/o 23 CD o O M ■H •H U CD -P (D s O H CD ,£ Ph , rd oo Q) P. bO •H 29 Figure 9. Detector mounting 30 ' " ■■ -' £. Figure 10. Mirror positioning drive motor 31 Figure 11. Photodetector mounting arrangement. 32 3 . Power Requirements The instrument requires a low-voltage source capable of providing a maximum of 24 volts and 3 amperes. Figure 12 is a wiring diagram of the underwater electrical connector. Voltages supplied to pins 3,4, 5 and 6 of this connector via a supply cable power the lamp and D.C. motor. The motor requires 24 volts to drive it at 42 rpm. In tests conducted in the laboratory, a supply of 6 volts was sufficient to pro- vide 10 samples per minute. Rotation rates greater than 42 rpm may be obtained by changing the drive gears. Pins 3 and 6 are for the motor supply. The power for the G.E. 1974 lamp is supplied through pins 4 and 5. No polarity need be observed on the lamp supply. There is sufficient room provided in the pressure case that surrounds the detector to install a fixed battery supply should this become necessary. However, the cable to the ship makes it possible to change supply voltages and thus the lamp intensity and motor speed. 4. System Operation Figure 13 is a conceptual diagram depicting the basic operation of the instrument. The rotating diagonal mirror sequentially reflects the light coming from four different sources, into the solid state detector. Three of these sources represent quantities to be measured and the fourth is the lamp reference input. Figures 14 and 15 show the scattering sensor arrangement in side and top views, respec- tively. 33 O P O 6 > en 03 6 ® o +-> o -M rd 0 CO O 4-| rd ' ' Pi C) -M U P O > s—\ /-*N CN J" *-n GO 00 1 PU ^N £ CO ^ ro PU hOGO v_^ bO ~.5£ •5 d k w P-i o § dJ rd < Dh k CQ s rd Pi to rd •H -a rd 3 +J ft a) a c o o c o •H ■P rd Pi . 00 CO 0) Pi •H 35 3 o> •H > •H CO +J C 0) g CD bO G id & id & O CO C 0) CO bO G •H 0) ■P ■P id o c/o CD bC ■H 36 CD •H > P. O +J C 0) 6 CD bO C & id & o CO e CD CO bO C •H & cd -p -p rd O c/o LO CD U bO •H 37 The detector is operated in a biased mode and gives an output voltage proportional to the input light intensity. Although this method of operation increases detection sensi- tivity, a dark current exists which must be dealt with dur- ing data analysis. A Wratten 61 filter was installed in front of the detector for the purpose of restricting the wavelengths of light admitted to a bandwidth of about 6 0 nm having a dominant wavelength of about 5 34 nm. During air calibration the infrared wavelengths must be attenuated, as they are present in the spectrum admitted to the detector, which is sensitive to I.R. Removal of the I.R. wavelengths is best accomplished by using a Schott BG-18 I.R. blocking filter which was unavailable during the initial laboratory set-up. Instead, a Corning 1-57 filter was used in conjunction with a Hoya HA-30. The total system is shown in Figure 16 with the pressure housings removed for clarity. 5 . Output The detector output (Figure 17) is an analog voltage signal representing each property measured: transmission, scattering at angle 0., , reference intensity and scattering at angle G-. The absence of scattering signals is explained by noting that the meter was bench operated and the scatter- ing levels are imperceptible in air. B. RESULTS 1. Bench Testing A Gould Model 110 recorder was used to obtain a laboratory calibration of the instrument. On the 5-mV scale the maximum signal level was 2.2 5 mV. 38 £ CD ■P CO >> to Pi a) +J — — 25 O CO CO o co co O co o — — CN CO O O CO o CO CN O CO CN O 1- CN O ^^ CN CN 1 1 III! 1 1 1 O co U Q) -M H •H to C 0) ■P ■P rtJ U T3 C (d LO I H bO C •H C o o W > o c o •H CO CO •H CO C id 5h Eh CD 3 bO •H p4 o o o o 00 o o to o o co o o CN r- OCN ±N33U3d NOISSIIAISNVdl 42 u CD +J r-\ •H o CO I >> o 5h O Mh 0) > o C o •H CO CO •H e CO C rd in Eh o CM cu bO •H © o o o o o o o o o o> 00 f^ 03 to "* CO OJ {%) eoueuiujsueji 43 c. Detector Biasing The detector biasing arrangement is shown in Figure 21. \ A/W lKfi K- 10 volts incident light Figure 21. Detector biasing schematic. During bench testing, a decade resistor substitu- tion box was used in conjunction with the variable power supply to obtain a suitable signal. A bias of 10 volts (as per manufacturers recommendations) was adequate for satisfac- tory operation. 2 . Environmental Testing On 16 September 1976, the instrument and laboratory apparatus were transported aboard R/V Acania, the Oceanographic research vessel of the Naval Postgraduate School. A 7-meter cast to verify meter operation in an ocean environment was performed. The ship was berthed at the Coast Guard pier in 44 Monterey Harbor, Monterey, California. This location provided good conditions for the observation of scattered light, as the harbor is a biologically active region having an abundance of dissolved and suspended matter. The results are presented in Figure 22. Depth Scale Reading (mV) Transmit tance in water C m"1 on deck 2.250 9 2.50 (in air) 1.0 0.200 8.22 2.42 2.5 0.250 10.28 2.20 3 0.250 10.28 2.20 4 0.200 8.22 2.42 5 0.250 10.28 2.20 6 0.155 6.37 2.68 7 0.100 4.11 3.11 bottom 0 0 100 Figure 22. In-water test results. Scattering of the beam was detectable in the 110 fixed angle sensor, but not measurable, as the recorder sensi- tivity and response were not great enough to provide a useable signal. 45 III. CONCLUSIONS The NPS Transmissometer-Nephelometer performed as ex- pected in the rather turbid harbor water. The scattering signals were anticipated to be extremely low due to the present poor termination of the fiber bundles and the de- crease of light intensity at the detector after the instal- lation of the filters. Several schemes to improve the performance of the in- strument are possible. A. Detector biasing improvements. A circuit arrange- ment that is suitable for exhibiting the ultimate capabili- ties of the detector is given in the manufacturer' s applica- tion notes. It is operated in the biased mode and includes an A.C. amplifier (i.e. UDT FET 100) to increase the detectable output signal. B. Fiber-optic terminations. The transmission of scattered light to the detector is extremely dependent upon the manner in which the light pipes are terminated. Potting the ends of the fiber bundles in epoxy and polishing the tips to reduce reflections is one method to reduce attenua- tion at the input sensor. The sensor ends should also be filled with immersion oil (n=1.515) to match the refractive indexes of glass and the optical fibers. Small negative lenses at the detector end of the sensor input could serve to increase the area of the detector 46 illuminated. The active area of the PIN-10 detector is 2 1.2 50 cm and should be fully utilized to obtain maximum output signal. C. Better fibers. The installation of Bausch and Lomb series 32-01, 02 or 03 light "wires" which have been commer- cially terminated would enhance the light transmission. These non-coherent "wires" have an incident light gathering efficiency of 60% at the receiving end and a transmitting efficiency of 95% per foot. D. Photomultiplier tube. Replacing the PIN-10 detector with a photomultiplier tube and a logarithmic amplifier would provide considerably more output signal. This is especially useful when scattering signals are very low. E. Chopper relays. The addition of a series of chopper relays synchronized with the rotating mirror may be used to separate electrically the signals representing 1(0), 1(1), 3(0,), and 6(e„). These signals may then be recorded on separate channels of a tape recorder to simplify analysis. F. Data processing. Improved results can also be obtained through the use of digital processing technique. The analog signals may be recorded on a magnetic tape recorder, digitized with an A to D converter, and computer analyzed. 47 APPENDIX A NPS TRANSMISSOMETER-NEPHELOMETER DRAWINGS AND SPECIFICATIONS 48 APPENDIX A NPS TRANSMISSOMETER-NEPHELOMETER DRAWINGS AND SPECIFICATIONS 48 SESlS " ' ' ^ \ < I <■ ' ' * r' ' \rv 55 Wi *? 49 X * N l CD 5 * !a i 5 s «>i U: va F ^ ^ k -j \> V X s l § 5 3 Q 50 HCLfS O// 'oia azae L*l t- i_ i i i i i i i i i i i i i i ! + op - 4-010 "!:&% ■ 5" -s£'- PETATNER, WWPOIV %3 3o 3 * 5 5 * k ^ ^ 1 *5 h;%H 58 59 I I 1 W>3 <$ $ ^ IN 60 5? * IP 1 * ;? S! gc " * « ^ ?* 5 3: ^ k ^ 4 3 5 S ^ ^ ^ ^ £ 61 62 *. >l 5 5 if x»* c^ •J 5* j( ^ ^ Q -5"- >/ ' •*- it i_ ■! 63 Ntt o> N A § * > § £ *** f * $ s J s MS V ,f «yz* 9'/ n. i "^T.&f ? ^ .:-.:3 ^r C=D 7T~ L.L I -J 5 I- M >0 . is I* §S 5*5 65 66 ■vl o- s \-z%— \&\ cd: czd: •^ 67 I 68 . x5» «4 «,* 0 3 % 4 * u k ft or ■ S . N» 1 *j*i to 1 1 fin k $ It O * ^ 1 ^ "*I\K J & s I — i 69 i ■*** 70 I V 1 -S fc «0 ^> « .J 3 ^ 3 s v) q 3 ^ • ■« s u n n ii 1 1 n XL -t-"-n 1 I 1 ka?« vfrV) fit > K o qJ 71 APPENDIX B LIST OF OFF-THE-SHELF COMPONENTS UTILIZED IN THE NPS TRANSMISSOMETER-NEPHELOMETER 1. Motor: 2 4 VDC , 42 RPM D.C. motor, Magnatorc, Hansen Mfg. Co., Inc., Princeton, Indiana. 2. Gears: 50 tooth, 2 3/16" O.D. 3. Lens: aspheric condenser, unsymmetrical ; S/N 40339, Dia. 72.5 mm, F.L. 46 mm; Edmund Scientific Co., Barrington, N. J. 08007 (2 required). 4. Lens: achromat , coated; S/N 6246, Dia. 39 mm, F.L. 63 mm; Edmund Scientific. 5. Lens: achromat, Dia. 30 mm, F.L. 55 mm; Edmund Scientific. 6. Fiber optics; 12 feet required; No. 0P736-C, 0.152", 6 foot lengths of jacketed fiber, contains 37 0.017" plastic fibers, 0.119" I.D./0.152" O.D.; International Rectifier Corporation. 7. Terminations: Indicator light for fiber optics; S/N 41232; Edmund Scientific. 3. Glass windows: 3/4" thick Pyrex, 4" Dia.; (2 required) 9. Fittings: Swagelock, 1/4", stainless steel. 10. Bearings: Fafnir F5, (2 required). 11. Lamp: General Electric miniature lamp, #1974, 20W, 6 volt. 72 12. Detector: PIN-10 solid state photoconductor , P/N 2023; United Detector Technology, Santa Monica, California. 13. Waterproof connector: Mecca, #2047 w/o-ring; MECCA, P.O. Box 3693, 519 Jessamine, Houston, Texas 77036. 14. 0-rings : (for pyrex windows), Parker 2-2 3 9 0-ring, (2 required). 73 BIBLIOGRAPHY 1. Duntley, S. Q., Underwater Lighting by Submerged Lasers and Incandescent Sources, S.lTo. Ref 21-1, ppT 2-1 through 2-26, June 1971. 2. Gilbert, G. , Underwater Light Attenuation Data Taken Near San Clemente Island, Naval Weapons Center, China Lake, CA; pp. 1-13, April 196 8. 3. Jerlov, N. G. and E. S. Nielsen, Optical Aspects of Oceanography , Academic Press, London and New York, pp. 28-49, 1974. 4. Nichols, D. A., Block 50 Compilation, Defense Meteoro- logical Satellite Program (DMSP) , Headquarters Space and Missle Systems Organization, Air Force Systems Command, United States Air Force, pp. 44 and 45, July 1975. 5. Underwater Imaging System Design, Ocean Technology Department, Naval Undersea Center, pp. 2-3 through 2-22, July 1972. 74 INITIAL DISTRIBUTION LIST No. Copies 1. Department of Oceanography, Code 6 8 3 Naval Postgraduate School Monterey, California 9 3940 2. Oceanographer of the Navy 1 Hoffman Building No. 2 200 Stovall Street Alexandria, Virginia 22332 3. Office of Naval Research 1 Code 480 Arlington, Virginia 22 217 4. Dr. Robert E. Stevenson 1 Scientific Liaison Office, ONR Scripps Institution of Oceanography La Jolla, California 92037 5. Library, Code 33 30 1 Naval Oceanographic Office Washington, D. C. 20373 6. SIO Library 1 University of California, San Diego P. 0. Box 2367 La Jolla, California 92037 7 . Department of Oceanography Library 1 University of Washington Seattle, Washington 98105 8. Department of Oceanography Library 1 Oregon State University Corvallis, Oregon 97331 9. Commanding Officer 1 Fleet Numerical Weather Central Monterey, California 93940 10. Commanding Officer 1 Navy Environmental Prediction Research Facility Monterey, California 9 3940 75 11. Department of the Navy Commander Oceanographic System Pacific Box 1390 FPO San Francisco 96610 12 . Defense Documentation Center Cameron Station Alexandria, Virginia 2 2 3m 13. Library (Code 0142) Naval Postgraduate School Monterey, California 93940 14. Stevens R. Tucker, Code 6 8Tx Naval Postgraduate School Monterey, California 93940 15. LT. David M. Mosey USN SW0SC0LC0M Class No. 54 Newport, Rhode Island 30465. 76 Thesis 166777 M84075 Mosey c.l Optical transmi sso- meter for deep ocean use. U FEB 79 25HU7 23 DEC 3 12 9 5 Thesis 1SB777 M84075 Mosey c.1 Optical transit sso- meter for deep ocean use. thesM84075 °,m«!i transmissometer-nephelometer for 3 2768 001 91745 3 DUDLEY KNOX LIBRARY