tog om on . at 3 r if EPG E Ta d Le prat Aes THE U. S. NAVY _—______— ELECTRONICS LABORATORY’S OCEANOGRAPHIC_-———— RESEARCH TOWER a | | : ke 2 = THIS IMITED E. C. LaFond : THE PROBLEM RESULTS i Develop an oceanographic research tower and evaluate its use for studying the shallow water oceanographic environment. The Navy Electronics Laboratory (NEL) has constructed a unique oceanographic research tower for the study of a broad range of marine environmental problems. The tower is readily accessible from NEL. It provides labora- tory-like conditions (stability, quietness, extensive instrumen- tation) for shallow water research in the open sea. It is adapted to a wide diversity of studies. It is also more economical to operate than a ship anchored in the same location. The tower is being successfully used to study water motion, underwater acoustics, electromagnetic propagation, marine chemistry, marine biology, and marine geology. It also serves to test and evaluate newly developed techniques and equipment, and to furnish assistance to other Navy laboratories working on oceanographic problems. eee NOR: Expand facilities on the NEL Oceanographic Research Tower to meet the need for a larger work area. Initiate new research, including investigations with radar, infrared, laser, and at the air-sea interface. Build a new similar tower west of the present one in water 100 feet deep. This deeper tower will: (a) Permit study of water-structure features at greater depths and allow for investigating the seasonal thermocline for longer periods of time. (b) Facilitate joint research projects with ships, submarines, and other submersible vehicles requiring deep water. (c) Serve as a secondplatform for intertower acoustic studies. ADMINISTRATIVE INFORMATION Work was performed under Problem L40461, SR 004 04 01, Task 0580 by members of the Marine Environment Division. This report covers the period June 1955 through December 1965. Acknowledgment is made to a large number of devoted engineers and scientists who have made the tower a great success. The original structure and instrumentation were formulated mainly by A. L. Nelson and W.H. Armstrong. Special contribu- tions to the installation and equipment were made by L.C. Thompson, D.A. Baldwin, W.C. McSparron, J.M. Prince, R.F. Kimball and J.V. Pflaum. Since 1962, D.E. Good has assumed responsibility for the tower and has expanded equipments and facilities. He has been assisted by P.A. Hanson, D.L. Jackson and K.E. Titland. Able assistance is also acknowledged of marine services personnel, including H.G. Kiner, G.B. Ryan, L.L. Jones, H.E. Sprekelmeyer, A.M. Huehn, andC.T. Bell. The scientific divers J.A. Beagles, J.R. Houchen, and W.J. Bunton have been most helpful for under- water installations and repairs, and have developed new equip- ments and techniques for underwater operations. The NEL Operations Officer and the personnel boat crew have provided transportation to the tower. A large part of the research reported here was the work of the following scientists: J.R. Olson, P.G. Hansen, E.G. Barham, R.F. Dill, J.C. Thompson, R.K. Logan, F. Watenpaugh, H.L. Heibeck, D.G. Moore, N. Malley, T. Abe (Tokyo, Japan), H. De Lauze (Marseilles, France), and J. Armstrong (Plymouth, England). The work of these and many others is listed in the Bibliography at the end of this report. I am also indebted to G.H. Curl, O.S. Lee, D.E. Good, E.G. Barham, A.L. Nelson, and K.G. LaFond for reviewing this report. CONTENTS INTRODUCTION... page 7 PART I. TOWER ADVANTAGES... 9 Accessibility . . . 10 Stability. . . 12 Permanence... 14 Economy. . . 16 Laboratory- Like Conditions. . . 18 Versatility . . . 20 PART II. TOWER STUDIES AND INSTRUMENTATION . Water Motion Studies. . . 25 Internal Waves. .. 26 Thermal Structure Measurement... 28 Thermal Structure Prediction. . . 30 Horizontal Currents... 32 Vertical Currents and Turbulence. . . 34 Speed, Height, and Propagation Direction. . . Coherence... 38 Sea-Surface Slicks. .. 40 Surface Temperatures ... 42 Swell and Wind Waves... 44 Acoustic Studies. . . 47 Biological Factors... 48 Ambient Sound, . . 48 Target Identification. . . 50 Acoustic Seattering. . . 52 Sound Attenuation (Plankton)... 54 36 23 CONTENTS (Cont) Physical Factors. . . 56 Sound Attenuation (Bubbles). . . 56 Sound Velocity. . . 58 Sound Transmission . . . 60 Electromagnetic Wage Propagation Studies , . . 65 VLF Transmission . . . 66 Chemical Studies. . . 69 Salinity and Oxygen. . . 70 Plant Nutrients... 72 Foaming Properties . . . 74 Radioactivity. . . 76 Biological Studies . . . 79 Water Turbidity . .. 80 Plankton Distribution . . . 82 Fish Distribution . . . 84 Geological Studies . . . 87 Sea-Floor Topography and Sediment Distribution . . . 88 Subbottom Structure. . . 90 Mine Scour. . . 92 Materials Research Studies . . . 95 Studies with the Diving Saucer . . . 99 Service to Other Organizations . . . 103 PART III. TOWER DESIGN, CONSTRUCTION, INSTALLATION, AND FACILITIES . . . 107 Conception, Design, and Site Criteria . . . 108 Construction and Installation. . . 110 Facilities . . . 112 Lower Catwalk (Level 1). - - 112 Upper Catwalk (Level 2)... 114 Main Deck (Level 3) - . . 116 Exterior . .:. 116 North Room. . . 118 Central Room. . . 120 CONTENTS (Cont) South Room. . . 122 Upper Deck (Level 4)... 124 Equipment Railways and Underwater TV... 126 Scuba and Hookah Diving . . . 128 Underwater Communication . . . 130 Cabling. . . 132 Safety. . . 134 Protection . . . 136 Sea Gull Deterrent... 136 Fouling and Metal Protection . . . 136 PART IV. FUTURE PLANS AND SUMMARY... 139 The Need for Deeper Research... 141 Summary... 145 Recommendations ... 147 BIBLIOGRAPHY... 149 REVERSE SIDE BLANK INTRODUCTION The need for research in oceanography is expanding more rapidly than can be accommodated with present laboratory and float- ing facilities. To meet this demand many new types of installations are being developed. One example is the U.S. Navy Electronics Laboratory Oceanographic Research Tower, located in 60 feet of water off Mission Beach, San Diego, California. This tower is the first stationary sea-based-facility designed andused exclusively for investigating a wide variety of shallow marine environmental features. Knowledge of the physical, chemical, biological, and geolog- ical characteristics of the shallow-water zone is essential to the Navy for the development of improved methods of underwater detec- tion, navigation, and communications. After 6 years of operation, an analysis of the oceanographic data collected has demonstrated the tower's capability in fulfilling its assigned mission. Much of the information has been reported in scientific and technical publications. Other material has been published in appropriate laboratory reports and memorandums. Part I of this report outlines the tower's principal advantages over other methods for conducting intensive shallow marine research. Part II briefly describes selected tower studies. The space given to each study does not reflect its relative importance or the effort expended. Instead, the treatment illustrates the diversity of investigations, the specialized techniques and instrumentation em- ployed, and the results achieved. More detailed information on particular studies may be found in the reports and papers listed in the Bibliography (page 149). Part III traces the tower's development from idea through construction and modifications to the present. In addition, it surveys level-by-level the unique facilities that have contributed to the overall success of the research program. Part IV delineates the need for a new oceanographic tower to conduct studies at a greater depth (100 feet) and in an acoustic range between the present and new towers. This section also summarizes results of the oceanographic tower program and presents specific recommendations for improvement. PART I. TOWER ADVANTAGES of advantages. It provides: _ Accessibility — _ Stability _ Permanence ACCESSIBILITY The tower is about a mile from shore and is within easy commuting dis- tance of the Navy Electronics Laboratory. It is also accessible by radio. A 140.43 Mc/s communications network links the tower with the NEL communications office, the oceanographic division office, and all small assigned boats. The network can also be connected with other frequencies used by the Laboratory's larger ocean- ographic vessels. 10 Personnel, laboratory equipment, and operating supplies travel cone veniently between dock and tower on a 34-foot Navy personnel boat (LCPL). This boat makes four scheduled trips a day. It is also available for operations around the tower between trips, and at off hours. Equipment is also transe ported by the boat and brought aboard by means of boom and nylon webbed basket. 2 HOP BAY Y a i} at 9 RESEARCH FACILITY The tower is only 30 minutes from NEL — 15 minutes by car to the dock facilities at Quivira Basin, Mission Bay, and another 15 minutes by boat to the tower. Yet it is far enough from shore and populated areas to provide a natural undisturbed open-sea en- vironment. Because it is outside lanes of heavy commercial ship traffic, the tower presents a minimum navigational hazard. 11 STABILITY Another asset of the tower is its stability (and high safety factor) under strong winds, waves, and current. It has withstood storm waves up to 18 feet high. The main reason for the tower's steadiness (and the way it differs from practically all other offshore towers) lies in the positioning of the legs. Instead of being perpendicular to the bottom, the legs slant out from the tower platform at a 5-degree angle from the vertical, form- ing a broad base on the sea floor. In addition, the tower is structurally rigid, and is firmly anchored to the sea floor by 12. 75-inch steel pins driven a distance of 63 feet through the bottom sediment to the hard substrata. Since the tower does not move, it provides a fixed reference point for all types of water motion studies (waves, cur- rents, turbulence, and tides). The tower's stability also permits the use of instru- ments such as television and motion- picture cameras and sound transducers. These latter require constancy in depth and orientation for optimum efficiency. 12 63 FT $$ i — 40-FT MAST Laan 16 IN ANCHORING PINS \ \ \\ The angled legs, reinforced heavy steel con- struction, and use of anchoring pins driven in the sea floor give the tower great stability. PERMANENCE The stability and fixed location of the tower make it useful for studies that could not be accomplished economically or efficiently from surface craft. An ex- ample is the making of long-term mea- surements. Many of the instruments mounted on or adjacent to the tower struc- ture are capable of continuously recording oceanographic variables. Examples are shown on this and the following page. These instruments can operate unattended day and night under all weather conditions. The long-term data recordings obtained, covering weeks and months, are used to identify and measure cycles not registered by short-period observations. Because of its permanency, fixed location, and continuous operation year in and year out, the tower permits opera- tions to be scheduled and planned more easily and efficiently than would be possi- ble with movable surface craft. PERT eeceoeeeoe ee Time vs depth recording from iso- therm follower. 14 Data system that records and prints on punched tape temperature sensed by thermally lagged thermistor beads on tower leg. Anemometer. WAVE HEIGHT Swell recorder. Installing tide gauge. PIRSA. 15 ECONOMY The tower is far more economical than a ship for shallow-water oceano- graphic investigations. Although direct comparisons are not entirely valid, some generalities may be made. The initial cost of the tower was only about 1/15 that of an average oceanographic ship. Maintenance costs, such as painting, cathodic protection, utilities, and replacement of worn parts and cables, are only about 1/8 as much asaship. Also, manpower utilization is more efficient. Whereas aboard ship most personnel are concerned with ship- handling, on the tower practically all the human effort goes to the scientific projects on hand. In only one year, the savings real- ized between the cost of operating the tower and the cost of operating an average oceanographic ship could easily amount to the original cost of the tower. Further- more, the operational costs of the tower may be kept within stringent budgetary requirements. Here a working party arrives at the tower. The facility is used by an average of four or five persons per day throughout the year. But it can accommodate several more if the research requires. On the other hand, many measurements are carried out while the tower is completely unattended. 16 ORIGINAL COST $ Sooo sce T SSR GS SS TOWER SHIP OPERATING COST $ Sooo 55 3S TOWER SHIP PERSONNEL 10 00000000000000000000 SCIENTISTS TECHNICIANS CREW TOWER SHIP LABORATORY-LIKE CONDITIONS Tower facilities duplicate in many respects those found in the laboratory, and therefore permit a wide spectrum of controlled studies. Because of the absence of motion, sensitive instruments such as resonant cavity chambers. microscopes, and other optical equipment can be operated. Acoustic studies benefit from the low underwater ambient noise level and from the low self-noise level. There is neither generator noise nor electrical interfer- ence because power is supplied from shore. Other laboratory-like conditions are: the ability to maintain nearly con- stant room temperature; the convenient access to compressed-air and constant- vacuum systems; the stable power sup- ply (voltage, frequency), which permits operation of recording equipment at con- stant speeds and known outputs; and the ready availability of a wide variety of Filtering microorganisms from freshly collected p sea-water samples, through millipore filters, under measurement and test instruments. conditions of constant vacuum. Subjecting planktonic organisms to magnetic fields. 18 Pen rer 7 7 7 7 oe (Ds CAUSES a ce ee Determining the foaming properties of sea water with a water sample shaker. Electronic recording instruments requiring a stable power supply are located in a thermally controlled room. Measuring the sound attenuation caused by plankton with a resonant cavity chamber and recorder. 19 VERSATILITY The tower is versatile. It is well suited for studies of the atmosphere, the shallow-water oceanic environment, and the sea floor. Several investigations -- related or unrelated -- can be conducted simultaneously from its stable platform. It is adapted not only for work on NEL's problems but those of other activities as well. And it has unique value for ocean- ographic research in three dimensions (depth, distance, time) when it is coupled with remote instrumentation, such as sensors anchored on the sea floor, or linked with a moving vessel, such as a ship or diving saucer. 20 The tower's versatility is demonstrated by the wide variety of sensors and instruments located above the water, throughout the water column, and on or under the sea floor adjacent to the tower. Tower studies emphasize factors affecting propagation, transmis- sion, and reception of underwater-sound signals. § WATER MOTION © ACOUSTICS © ELECTROMAGNETICS %* CHEMISTRY © BloLocy @ GEOLOGY she | a ee \ a1 22 PART Il. TOWER STUDIES = AND INSTRUMENTATION — 23 24 WATER MOTION STUDIES Water movement throughout the entire water column is the most intensively studied variable at the tower, for it affects sur- face and subsurface navigation, acoustic transmission, and the permanence of equipment placed on the sea floor. The water motions most studied are the large subsurface slow-motion undulations called internal waves. Other slow motions are related to tide and seiches. The more rapid motions are caused by swell and wind waves. All of these influence the physical, chemical, acoustic, and biological structure of the marine environment. INTERNAL WAVES Thermal structure Horizontal currents Vertical currents and turbulence Speed, height, and direction of propagation Coherence Sea-surface slicks SURFACE TEMPERATURE SWELL AND WIND WAVES 295 Internal Waves Internal waves are found between density layers in the sea. They can be caused by flow over an irregular bottom, atmospheric disturbances, tidal forces, and/or shear flow. They have amplitudes considerably larger than ordinary surface gravity waves and propagate at a much slower velocity. The internal wave peri- ods at the tower range from a few minutes to long diurnal oscillations. At the relatively shallow tower site, the vertical density structure may normally be considered as a two-layer system of warmer and colder water sepa- rated by a thermocline. Under these con- ditions, only one mode of oscillation can exist. The internal waves at different levels are usually in phase with each other, and the greatest vertical displace- ment of water particles takes place at the thermocline. In rare cases a double thermocline may resonate. { A \ Yun jeoeeecer Internal wave trains in deep water coming from different directions combine to reinforce or cancel out individual waves. This results in irregular domes and depressions. As the waves propagate shoreward over the continental shelf, they tend to form into long crests. 26 DEPTH (FT) : 1200 1300 1400 TIME The presence and movement of internal waves at the tower are charted by the continuous measurement of the thermal structure. During the summer there are many small internal waves which have periods of 7 to 10 minutes. These waves are all nearly in phase throughout the water column. This recording also shows the usual afternoon lowering of the thermocline. 27 Thermal Structure Measurement The vertical thermal structure is measured by means of bathythermographs, isotherm followers, and thermistor bead sensors. The thermistor beads are per- manently affixed to the tower, floated down from buoys, or suspended at 2-foot intervals in a vertical string from a taut- wire buoy system. Long-period thermal structure data are obtained from thermistor beads mounted at 6-foot intervals down one tower leg. These are thermally lagged so that the response time (r) is equal to 20 minutes. Temperatures are printed on a digitized recorder, which is pro- grammed for sequential interrogation of each sensor every 10 minutes. For special heat flow and insulation studies, four similarly lagged beads extend into the sea floor. The closely spaced, more rapid response beads ( 7 = 20 seconds) in a taut-wire buoy arrangement record the most detailed thermal structure. Here the temperature is referenced to the bottom rather than to the surface. This method shows the structure near the sea floor in more detail, since sampling is less influenced by surface action. The data are recorded in analog form as well as on punched tape. structure is one of the objectives of these studies. 28 Prediction of thermal DEPTH (FT) 20 30 40 50 60 50° \ohealapl scales 60° 70° TEMPERATURE (°F) The temperature structure of the water at the tower in summer contains a strong thermocline, while in winter the water is nearly isothermal. The near- bottom water is colder in summer than in winter because of up- welling. DEPTH (FT) DEPTH (FT) SEA SURFACE BEAD * SAMPLING > DEPTHS io . 3 \ ee ee y UoR ar ale , oo" aN iv A i ae a g. i ) Be ue Ise ISOTHERMS SEA FLOOR 1600 1700 1800 TIME Thermistor bead sensors are suspended vertically 2 feet apart. The signals from the sensors are interpolated electronically and recorded as whole degree centigrade isotherms. The thermal structure (above) is in a time-depth analog presentation 9 inches wide and recorded at 10 minutes per inch. The internal waves are almost always present. SEA SURFACE 0 0) Pose WATER MASS SAMPLING BOUNDARY ‘DEPTHS 20+ - 30 40h. Cae OS 50h. ise 2 SEA FLOOR eS PS ls ag Vi ee HO el IRL Ae ARE et Yi RA a a 0700 0800 0900 TIME Abrupt changes in depth occurring in some isotherms are caused by water mass boundaries moving past the tower. The depth of the isotherms com- prising the thermocline is a principal study. 29 THERMAL STRUCTURE PREDIC TION The Navy needs to predict therm- ocline depth and strength to make efficient use of sonar equipment. Tower studies have established that these predictions can be successfully made in the summer months by using wind speed and direction and tide height data. The interrelationships between wind, tide, and thermocline were estab- lished by continuously recording these parameters throughout one summer. From this study, empirical equations have been developed. It was established that the nearly semidiurnal tide height is of pri- mary importance and that the diurnal wind speed and direction (nearly parallel to the coast in accordance with the Ekman effect) is of secondary importance. Since the thermocline response is 4 hours later for tide and 15 hours for wind, it is possible to predict in advance the thermocline change at the tower within accuracies of practical limits. The thermocline goes through cyclic variations in strength that corre- spond with the tide. The descending thermocline is stronger than the ascending one. The temperature gradient in descent is approximately 0.3 degree C/ft, and in ascent it is approximately 0.1 degree C/ft. WIND Diurnal cycles in sea breezes normally cause a shoreward (left) and offshoreward (right) displacement of surface water, in accordance with the Ekman effect. The surface-water displacement is such that the thermocline reaches a maximum depth about 1800 hours and a minimum depth in the early morning. Such fluctuations in the thermocline level may amount to as much as 30 feet in 2 hours. WIND The semidiurnal cycle in tide height and the diurnal cycle in wind direction and speed are both reflected in the depth of the thermocline. The graphs show a 3-day com- parison. Vertical lines are 4 hours apart. The power spectra reveal peaks at 4.5- and_ 1-day cycles in both wind-predicted thermocline and measured thermocline depths. The tide is solely responsible for the half lunar cycle peak in the observed thermocline depth. The tide-wind-thermocline re- lationship makes it possible to predict thermocline depths from wind speed and direction and semidiurnal tide level. A plot of the measured thermo- cline depths averaged over 30 days shows a close agree- ment with predicted thermo- cline depths. (Standard devia- tion of hourly values is + 13 feet, standard deviation of daily values is + 6 feet). (FT) aA Oonon a CO (KTS) THERMOCLINE WIND SPEED TIDE HEIGHT DEPTH (FT) (AMPLITUDE) 2(FT) 2 POWER THERMOCLINE DEPTH (FT) OFFSHORE — oO ONSHORE 00 04 08 12 16 20 24 04 08 12 16 20 24 04 08 12 16 20 24 TIME 30 WIND-PREDICTED 25 Pei x SIbANS MEASURED THERMOCLINE DEPTH 15 10 %» LUNAR DAY 5 0 100. 40 30) 90 1s 138d 9 PERIOD (HRS) 14 16 WIND. AND TIDE __ PREDICTED 18 DEPTH CYCLE 20 22 ve MEASURED DEPTH 24 CYCLE 26 28. 30 0000 0600 1200 1800 2400 TIME ol HORIZONTAL CURRENTS The dominant horizontal current in a shallow sea is produced by the short- period, high-speed orbital motion of surface waves. These currents are mod- ified by the prevailing coastal, geostro- phic, tidal, and wind-driven currents. An important low-speed current pattern is produced by the orbital motion of long-period internal waves. The re- sulting horizontal current patterns are detected and measured at the tower with standard oceanographic current meters and tracking floats which suspend vaned drogues at various depths. One type of water flow is caused by the daytime coastal winds which pro- duce a shoreward-moving surface cur- rent. Asa result, the subsurface water flows offshore during the day and a re- verse flow takes place at night. Horizontal currents are measured with several types of current meters. This one from BuShips charts current direction and speed. It is being lowered from the tower boom ona single support wire. For direc- tional orientation, other types of meters utilize twin guide wires extending from the ocean floor to the top of the instrument house. The greatest problem, yet unresolved, is the inability to separate short period, rapid, irregular wave motions from slow coastal drift. Horizontal currents are also de- termined by measuring the movement of float-suspended vaned drogues (above). The drogues are positioned at predetermined depths, usually above and below the thermocline. The surface float is tracked by transit and camera from the tower’s upper deck. Cameras mounted on kites have also been used to photo- graph the sea surface. Time-lapse photography of current effects is ac- complished with this motion-picture camera. It is mounted beneath a convex mirror which reflects the sea surface to the horizon in a 360-degree arc. The camera unit is raised to the top of the 40-foot mast for operation. It takes photographs at 3- to 5-second intervals. For viewing, these films are shown at about 100 times normal speed. Beside drogue-tracking, the pictures are also used to study the motion of sea-surface slicks. Drogue movement measurements by time-lapse photography show that the horizontal current flow is strongest near the surface (5 feet deep),in the water column above the thermocline. Speeds to 0.7 knot were recorded. Other readings at 40 feet (below the thermocline) were around 0.2 knot. The 360-degree surface photographs used in this study also showed that the di- rection of water flow was variable and was mainly related to wind and tide. 33 VERTICAL CURRENTS AND TURBULENCE The tower's TV installation has shown that the dominant motion of water particles is orbital. The nearly circular motion near the surface is modified with depth until along the sea floor it becomes a horizontal surge. The measurement technique for vertical motion is to attach nylon stream- ers to the TV's reference grid. The streamers rotate in circular patterns as surface and/or internal waves move past the grid. This permits the study of orbital motion and turbulence. The movement of the streamers is not continuous. Intermittent pauses at an upward or a downward position re- veal the zones of divergence and conver- gence caused by passing internal waves. Downward motion can be observed be- tween the crest and the following trough; upward motion takes place between the trough and the following crest. Vertical motion caused by internal waves (up to 15 feet per minute) is found in the thermocline. The displacement of clouds of dye dropped vertically through the thermocline demonstrates the orbital circulation associated with internal waves. 60 FEET ae =" REFERENCE GRID Current direction is measured with a reference grid having nylon streamers. The streamers, which have nearly neutral buoyancy, are used as inclinometers. The grid is oriented normal to the direction of Propagation of surface and internal waves, in order to detect orbital motion in the vertical plane. Opera- tion is monitored by TV and recorded on motion- picture film. WAVE PROPAGATION (SHORE WARD) ———> | SEA FLOOR Analysis of streamer The central member of the reference grid is a tube which contains dye. The dye extrudes through small openings. The flow patterns produced are used to study turbulence in the thermocline. Under the divergent circulation conditions shown, even fish must swim down to maintain the same depth. SURFACE WAVE INTERNAL WAVE and dye movement produces this schematic of water particle flow. White advancing lines surface wave. streamlines in an Black lines are streamlines in a progressive internal wave. Wave propagation is from left to right. 35 SPEED, HEIGHT, AND PROPAGATION DIRECTION The speed, height, and direction ~~ of propagation of internal waves at the tower are determined by three NEL- developed isotherm follower units. As the depth of an isotherm changes, sig- nals from a sensor suspended in the thermocline create an imbalance in the we. bridge circuit. The circuit in turn causes a winch to raise or lower the sensor. Thus the vertical oscillation is followed Simultaneous depth-time recordings as the isotherm passes the tower. of the same isotherm are made by . isotherm followers suspended on Approximately 90 percent of the 40-to-50-foot booms out from three internal waves measured propagated in a corners of the tower. The stream- E 5 lined sensing units of the followers westerly and southwesterly direction. move vertically with the depth of The speed of the progressive internal Gnypsolectediiscshe rm: waves, c, varies directly with the thick- ness of the two layers and their density. For internal waves that are long com- pared with the water depth 2 _ ghh' — p-p' INTERNAL Where h' is the thickness of the upper layer, h is the thickness of the lower water layer, and p' and p are the respec- tive water densities. In summer, the speed is about 0.3 knot. Thus as internal waves approach The short-period waves described by an the shore, they decelerate, become more f J isotherm in the middle of a summer thermo- cline show a median height of 5.4 feet, a closely SIAC retract, develop long period of 7.3 minutes, and a speed of about crests, and finally move onshore. 0.3 knot. 36 ee erat The speed and direction of internal waves are also determined visually and photographically by observing the movements of sea-surface slicks. The long slick lines are found at the surface above the convergence zone, which is behind the crest of the internal waves. When the internal wave crests are near the sea surface, the surface becomes rougher, thus identifying the orientation and phase of the internal wave. AB SEA SURFACE fre O Ob bee Ee clece eng, 1 0 | 0 MIN DEPTH (FT) Isotherms outlining the shape of internal waves 3 a change as the thermocline approaches either the sea weed e Fitsnant "60 > floor or the surface. These are three typical record- ings of isotherm depths when the thermocline is: (A) near the surface; (B) at mid-depth around 30 feet; and (C) near the sea floor. | SEA FLOOR | et a Va Oe 37 COHERENCE To study the spatial coherence of internal waves, two-dimensional hori- zontal thermal measurements are made as the waves move shoreward in the vicinity of the tower. This is done with a circular thermistor array 450 feet in diameter. The temperature signals from the array are recorded on the tower in analog and digital form. Several long periods of continuous coherence data have been compiled, to- gether with simultaneous recordings of acoustic transmission loss information. Preliminary analysis indicates that the beam width of the direction of internal wave propagation is about 0.4 radian. Other information reveals that internal waves of high frequency are coherent for distances of over half a wavelength. Observation and measurement of the orientation and movement of sea- surface slicks also provide information on the coherence of internal waves. 700 FT Internal wave coherence is investigated with this circular array of 48 sensors. The array is installed in a horizontal plane at mid-depth, 30 feet from the sea floor and 700 feet southwest of the tower. At this location the tower is too far away to affect the internal wave structure. Each sensor is cable- connected to the tower. @ WARMEST WATER O COLDEST WATER ORDER OF WAVE PROGRESSION TIME WAVE ACTIVATES ARRAY SURFAC BOTTOM Progressive temperature oscilla- tions across the horizontal array provide data for wave-coherence studies. The sensor first activated is the one nearest the oncoming wave. Successive sensors activated indicate the direction of propaga- tion. Cross-spectral analysis be- tween sensors reveals the speed, PROPAGATION DIRECTION direction, and coherence of the OF INTERNAL WAVES internal wave. ~ = te PNT! arms Ree 2 s @ 2 e ® cy e e 2 © ° s Py e ° e 8 ° ° 2 ° cs a bh * fe. e 2 fe te Analog recording of the temperature data from the array. Data are presented as isotherms on a space-time plot. Since the internal waves propagate from a west-southwest direction, the isothermal curves on the analog recording bulge to the left, or earlier position with respect to time. Analyses are made from parallel recorded digital data. 39 SEA-SURFACE SLICKS Sea-surface slicks are character- ized by capillary waves that are smaller than those in adjacent waters. The slicks appear glassy because they reflect the sky better than does the rougher water outside the area. Slick bands. occurring where lighter-than-water film is concentrated. are related to the downward motion of internal waves. These bands signal the presence of active sinking zones. Sea-surface film from near the tower has been collected. It appears to be composed of organic compounds, probably derived from decomposed or- ganisms. The surface tension of sea- water samples from outside a slick area was found to range between 70.5 and 73.5 dynes per centimeter at 20 degrees centigrade. while specimens collected in slick areas gave lower surface tension values of from 49.2 to 68.8 dynes per centimeter. The orientation, speed, and direc- tion of internal wave movement may be determined from time-lapse photographs of slick bands. This information gives a three-dimensional perspective of sub- surface thermal structure and movement. However, under conditions of high wind speeds the internal wave slicks are broken up. The slicks then orient a little to the right of the wind direction. 40 ie & a as ane et The film on the slick reduces both surface tension and the small capillary waves, thus making the area smoother and increasing its ability to reflect light. Ragged bands and patches of a surface slick give the sea around the tower a glassy appearance. Covering as much as 10 percent of the surface, slicks usually orient them- selves in lines parallel to the shore. The time of the slick’s arrival at the tower is noted and correlated with recordings of the thermal structure and other phenomena. The slick film collected from the tower appears oily and frequently contains pieces of seaweed, foam, and other debris. ON-SHORE WIND ———————> 1 SLICK FILM aes) ° nN aS SE PRESSURE (DYNES/CM) Surface pressure across slicks was studied by dropping various concentrations of oil and alcohol on the surface and noting the spreading effect. In this example the greatest surface pressure is skewed in the upwind direction toward the trailing edge of the slick. 41 SURFACE TEMPERATURES Surface-film temperature ina slick has been successfully determined by an infrared sensor at the tower. The sensing equipment consists of an infrared temperature detector, signal-processing electronics, and strip-chart recorder. This noncontact instrument remotely senses radiation in a spectral region (8 to 138 microns) where water is highly emissive but is not reflective. The in- vestigation showed that it is possible to establish water structures and processes in the sea from continuous surface- temperature recordings with an infrared radiometer. Surface temperatures from the tower are also measured by the bucket- thermometer and other sensors. Cue PD aibarnsoseanspi The infrared detector consists of an optical system and thermistor bolometer located 20 feet above the mean tide level. The beam, which is 5 degrees wide, senses 2.4 square feet of the sea surface. 42 Temperature measurements by _ the processed by electronic fed to the strip chart house. circuitry, recorder in detector amplified, are then the instrument —|1 MIN |— SURFACE WAVE ane INTERNAL WAVE FFFECUS Surface temperature variations from such diverse causes as ship's wake, divers working below the thermocline, or passive sea-surface slicks may be measured with the infrared sensor. Other temperature changes have periods corresponding to those of surface and internal waves. Variations as small as 0.1 degree centigrade are detected. This tracing from a recorder chart shows typical fluctuations. INFRARED RECORDING OF SURFACE TEMPERATURE —| 1 MIN \— SUBSURF ACE THERMAL FRONT Swell and Wind Waves The heights and periods of swell and wind waves are used to establish the sea-surface roughness. This is es- pecially important during sound- transmission studies, as these waves reflect and scatter acoustic energy. For the measurement of swell, a permanent tower-mounted swell recorder is monitored 15 minutes daily. This provides information on seasonal variation in swell. Information on wind waves is pro- vided by a vertically directed acoustic transducer which is mounted in a gimbaled tripod on the sea floor. Tower recordings of the strong sound reflections received from the sea surface delineate all types of waves as well as any midwater reflec- tors. The higher surface waves are associated with local and distant storms. The highest wave observed was 18 feet and occurred during a local storm. These waves travel shoreward and are refracted by the shoaling continental shelf. The average swell period is about 12.5 sec- onds in summer and 11.5 seconds in winter. The average height of significant waves is greater in the summer than in winter. To measure the height of swells, a Snod- grass Mark IX pressure sensor is housed 2 feet out from the NW tower leg, 37 feet below the mean sea surface. Pressure is electrically transmitted to a_ specially adapted recorder in the instrument house. The mounting provides a favorite habitat for marine organisms. 44 Ss & ze SWELLS a (LARGER aw WAVES) MID WATER a SCATTERERS Figo sine eons cmt ranean tee arses egaon nse ccrncee acatiy Seeeen eee 53 0 2 4 6 8 TIME (MIN) Surface roughness, with small wind waves superimposed on the swell, is recorded by a bottom-mounted transducer. Most detail of the sea surface is obtained by this acoustic method. My a o 2 Wave recorder has pressure and wave-period factors incorporated in the electronics, so that wave heights can be recorded directly on 0- to 5-, O- to 10-, or 0- to 20-foot scales, at chart speeds of 12 or 60 inches per hour. TIME (MIN) TIME (MIN) SWELL HEIGHT —————- —| 1FT -— SUMMER SWELL There is a seasonal variation in swell height and period. Such information on sea-surface roughness is needed to interpret variations in acoustic scattering from the upper boundary. 45 ACOUSTIC STUDIES Research in acoustics from the tower is concerned with the propagation of subsurface sound signals, and especially with bio- logical and physical factors that interfere with propagation, trans- mission, and reception. The investigations are centered in seven primary areas: 47 Biological Factors AMBIENT SOUND Biological and other sounds which contribute to the total ambient noise are identified and measured from the tower. The low background noise permits the study of a wide variety of sounds of biological origin, and is favorable for high-frequency acoustic tests. There is, however, some low-level water noise be- low 10 ke/s which is caused by waves surging against the tower framework. Two distinct periodic variations in underwater noise level are observed. The first has a semidiurnal period in the band between 200 and 1200 c/s. Higher a\ |. CAMERA intensities are noted around sunrise and i sunset in summer. The second variation has a period of 25 to 40 seconds and is observed only at night and only in the late spring and summer. It is commonly 3 to 6 dB above the background, but a maxi- mum of 16 dB has been recorded. It occurs in the limited 300- to 800-c/s band, with a peak amplitude at 450 c/s. Both ambient sounds are apparently biological in origin and are related to sandy bottoms. Two members of the croaker family; spotfin, Romcador «,, stearnsi; and yellowfin, Umbrina roncador, Listening hydrophone is placed in view of the tele- v ¢ vision camera in an attempt to identify the organisms are believed to be largely responsible. which produce sounds in the sea around the tower. View looking down rail track. Cyclic fluctuations, frequency, and levels of biological sounds are investigated with sound amplifying and recording equipment (Noise Measuring Set AN/PQM-IA). Since the tower has a low noise level (it contains no generators and all small motors can be stopped during critical experiments), the weak biological sounds can be distinguished from the background. YELLOWFIN CROAKER Umbrina roncador : —2 =] SUNRISE The long period (25- to 1 40- second) variations in ai ambient noise observed in ny 42 the 300- to 800-c/s band = increase in intensity dur- {e)} ing the late spring and rm -2 summer months (contoured =] in 1, 5, and 10 dB above normal background). Inten- SUNSET sities reach a maximum just after sunrise and at sal sunset. a9) SPOTFIN CROAKER Roncador Stearnsi Wf 1dB MONTHS TD “= 49 TARGET IDENTIFICATION The varied fish population that lives and feeds around the tower affords an unusual opportunity to observe and measure the sonar target characteristics of individual species. Identification of fish types by acoustic means has value not only to the Navy but also to commer- cial fishermen. One target identification study was conducted by using a diver-held sonar. Sonar reflections from the fish were transmitted by wire to a tape re- corder on the tower. The tapes were analyzed for frequency and relative intensity of echoes from individual species and groups. Analysis of these tapes revealed a variation in signal pattern that depended upon the charac- teristic shape and structure of the in- dividual fish and other objects, the fre- quency of the sound, and the range of the sonar target. Studies of the identification of biological organisms by underwater sounds are not limited to the larger animals. Schools of small fish and masses of zooplankton organisms have been observed to cause extensive acoustic scattering. Divers train NEL-developed hand-held sonar (AN/PQS-1B) on various species of fish to record the characteristics of echoes produced. The sonar sweeps from 85 to 55 kc/s in a linear, sawtoothed manner. An air-filled aluminum sphere is suspended in the water and used as a reference target. 50 SHEEP-HEAD Acoustic intensity contours provide a frequency-time plot of signals reflected from a large sheep-head, Pimelometopon pulchrum. The analysis shows intri- cate patterns which differentiate this fish from other targets. FREQUENCY (kc/s) a SS Uv i > 25 O FL WW > Go lu o~ ie TIME 1 lace. Sse 3 —_ i ea SSS ee ie = oe Fie tS ie ee C- eee 0.5 ; z aN ‘im am > \ [es eo spe al TIME JACK MACKEREL Similar acoustic intensity contours were recorded and analyzed from a school of jack mackerel, Trachurus symmetricus. Other fish studied were: halfmoon, Medzaluna californiensis; grunion, leuresthes tenuis; jacksmelt, Atherinopsis californiensis; and topsmelt, Atherinops affinis. un SS 15) as > 1 O Zz ua) =) G Ww ~ Ww Even individual targets as large as scuba divers may be identified from analysis of echo intensity contours and frequency. Contours left are for a female scuba diver 10 feet away. ol ACOUSTIC SCATTERING Plankton and other suspended matter which cause echoes when high- frequency sound is directed through water may also produce turbidity. To investigate these acoustic scatterers, an echo sounder was gimbaled in a tripod on the sea floor and the sound beam was directed upward. The echograms thus produced show the scattering caused by various organisms in the water column. Some acoustic scatterers around the tower have a negative reaction to both natural and artificial illumination. They dive or disperse when an underwater light is turned on. After the light is turned off they return, but not as quickly as they dispersed. They are normally absent during daylight. These scatterers occur in patches which move toward the coastline from deeper water, or rise from the bottom, at night. The maximum concentrations of scatterers follow the depth of the thermocline. This behavior is similar to that of light scatterers. However. their phototropic behavior is different. It is thought that one type of acoustic scatterer around the tower is the shrimp-like mysid that character- istically feeds at night. Other types, including fish. are also present. DEPTH (FT) An _upward-directed NK-7 transducer is installed on the sea floor to determine the distribution, behavior, and nature of sound-scattering layers. This transducer oper- ates at 21 kc/s with a beam- width of 20 degrees at the 6-dB down points. ‘NIGHT TIME (MIN) Sea floor-to-surface echograms recorded at the tower show that summer scatterers are absent during the day and abound at night throughout the water column. Shrimp-like, phototropic mysids were photographed swarming at night. Since they are not present in the water during the day, they are suspected of con- tributing to the observed acoustic nighttime scattering. r--- I--- = Ww 2 I oe i I L ! a Lu a 60 0 2 4 6 8 TIME (MIN) Echogram compared with a recording of an Isotherm movement, shows that the maximum biological acoustic scattering moves vertically with the thermocline. The scatterers undergo 5- to 10-minute periods of oscillation corresponding with the movement of internal waves. 53 SOUND ATTENUATION (PLANKTON) Attenuation of sound by plankton organisms and other particulate matter is being investigated with resonant cavity equipment. The cavity resonators have acoustically soft side walls. They are capable of measuring excess attenuation in the 10- to 200-dB/kyd range, at dis- crete frequencies of 5 and 8 kc/s. Distilled water or sea water with- out particulate matter shows no mea- surable attenuation. However, natural sea water with particulate matter and medium to high oxygen saturation shows excess attenuation throughout the entire range of instrumentation (i.e., 10 to 200 dB/kyd). The excess attenuation is defined as: a =e = )dB/kyd ex T To where T, and T, are the reverberation times of distilled and plankton filled water, respectively. One investigation was carried out during the "red tide" bloom, a condition caused by an extremely high concentra- tion of the plankton organism, Gonyaulax polyedra. The tower measurements during this ''red tide'' were supplemented by observations at sea made with a com- pliant-tube resonant cavity. The seagoing cavity was constructed as a cage, with the bars made of flattened and therefore compliant tubes. These structures act as _ pressure-release surfaces in a limited frequency band, but are neither as efficient nor as sensitive as the laboratory equip- ment used on the tower. The results from both the tower and ships did, however, confirm high acoustic attenuation where the plankton concentration is high. 54 a > : = 70 : = > ®,6 : Sy Ge 2) apt 5 oF" 5 Q 409 RED WATER a a DRIFTING c Zz = 3 es Oe Ss NOS ae CAVITY LOWERED 4 ee AT THIS TIME TO > 10 5 METERS a DEPTH | od 0 © ed 10 20 30.40 50 ( 60 70 TIME (SEC) READING AT 5 METERS A heavy bloom of Gonyaulax plankton (‘red tide’’) drifting through the resonanf cavity suspended in the sea caused excess sound attenuation of up to 64 dB/kyd. 200 150 . AREA = OF HIGH > ATTEN= = UATION oa} a ‘ Z © 100 = Z <= eS é Z ty = Scientist monitors resonant cavity equipment to Seas : measure sound attenuation caused by plankton : de AREA organisms. Resonant cavity measurements Se : OF LOW of require the tower’s stable platform and proximity cS a0 ; : ATTENUATION <— Ser % to fresh, live marine organisms. se ' : & i Data collected by means of the resonant cavity Se nat e 5s y é : chamber also show the relationship of oxygen epee 0s ——_— - $$ $_$______ saturation of sea water to excess attenuation. Bee ae 90 100 150 When the oxygen saturation is greater than 100 eterna. : OXYGEN (% SATURATION) percent, the attenuation is markedly increased. ay) Physical Factors SOUND ATTENUATION (BUBBLES) Sound attenuation by bubbles is studied at the tower with a bottom- mounted bubble screen, multiple hydro- phones, and a sound source. The attenuation is influenced by sound fre- quency, size and number of bubbles, and other factors. Attenuation as great as 90 percent was found when using a bubble screen 10-feet long which emitted air at 200 cubic feet per minute against a head of 382 pounds per square inch. In addition to greatly attenuating the sound, the bubble screen also caused the colder water near the bottom to up- well. forcing the thermocline in the immediate area to rise. Natural bubbles caused by the breaking white caps (and probably by plankton and fish) are recorded by other acoustic means. The bubble screen (left on facing page) is created by connecting a hose from the air compressor on the tower to a long multiple-hole pipe (perforations 0.8 mm diameter every 13 mm) mounted on the sea floor. The air released causes a bubble screen which extends from bottom to surface. The bubbles expand and sometime coalesce as they approach the surface. Sound intensity is measured before and after the sound waves pass through the bubble screen. In one test series, explosive charges (shown to the right) were used as the sound source. The bubble screen greatly reduced the sound intensity. 56 HYDROPHONE 2 PRESSURE GAUGE FILTER FOR HOOK AH HOSE TO | HOOKAH BUBBLE SCREEN AIR FROM TOWER Compressed air for bubble attenuation work, hookah, and other applications is available on the lower deck. It is valved for single or multiple use. Bubble screen air and hammer hoses are connected to these valves. The bubble screen air flow of 200 cubic feet per minute is valved off. HYDROPHONE 1 SEA FLOOR, EXPLOSIVE | CHARGE 57 SOUND VELOCITY The speed of sound at intervals throughout the water column is computed from measurements of temperature, A salinity, and pressure. In addition, various sound velocity meters have been ofl tested and used. Some meters were mounted on tower carts for vertical sound-velocity structure measurements, while others were attached to a tripod out from the tower for long-period re- cording. The meters normally utilize sing- around circuits which produce a fre- quency proportional to the sound velocity. The frequency is recorded digitally and later converted to sound velocity. The data are used for acoustic transmission studies when precise values are required. In other studies, sound velocity is ob- tained indirectly. Variable-depth sound velocity meter transmits a pulse of sound. When the pulse is received it triggers a new pulse. This process is continuously repeated over asygiven path. The pulse repetition frequency is a direct measure of the sound velocity. The signals are carried to digital recorders in the instrument house and the recordings are later converted by machine to correct sound velocity. 58 DEPTH (FT) DEPTH (FT) SEA SURFACE 0 10 SOUND 7S VELOCITY ae OS PD Wr? OWp \\p D a cae ' Hoy 50 1500 1600 1700 1800 1900 2000 TIME Small scale time fluctuations in sound velocity may be approximatedfrom detailed thermal structure, such as shown in this recording made in the summer of 1965. Since the salinity range from surface to bottom is very small, the principal controlling factor is temperature. Thus, from the detailed recordings of thermal structure and depth, the sound velocity corresponding to each isotherm may be computed from the known temperature-salinity- depth relationship. Such sound velocity detail is useful in the study of fluctuations in acoustic transmission. 0 10 20 30 40 50 The vertical sound velocity structure, like tempera- ture, changes greatly from summer to winter. Thus different acoustic transmission programs are sched- uled to take advantage of the desired sound velocity 60 condition. 4900 4950 5000 SOUND VELOCITY (FT/SEC) 59 SOUND TRANSMISSION The transmission of sound through the water is greatly affected by internal waves. This is especially true of high- frequency sound. The greatest influence is refraction by the vertical (and horizon- tal) sound-velocity gradients. These, in turn, depend on the strength of the thermocline and the angle at which the sound rays intersect it. Sound rays directed normal to an undulating thermocline intersect it at different angles. The refraction and sound-focusing effects can be calculated by applying Snell's Law. This was done, using a Univac computer. The calcula- tions were based on a common transducer pattern and the normal velocity structure observed at the tower during summer. This structure is a mixed layer for the upper 30 feet: a thermocline of -4. 8 ft sec! ft7! for 10 feet; and a deeper 20-foot layer of -0.6 ft sect ftl, The internal wave had a normal amplitude of ~9 feet and a wave length of 300 feet. The focusing effects computed by the Univac were later verified experimentally at the tower. One and two-way sound transmission studies are conducted with a 175-kc/s sonar transducer mounted on the west track at varying depths below the sur- face. The orientation and depth of the transducer are maintained by the rigid tracks. Signals are trans- mitted through internal waves to hydrophones and acoustic targets consisting of 1-foot-diameter alumi- num spheres, buoyed 7 feet from the sea floor. Hemispheres are also used as targets. They are built with windows-which produce stronger and more distinct echoes than the complete spheres. TARGET SPHERE if TARGET 4 HEMISPHERE DEPTH (FT) (Z) DEPTH (FT) (Z) 0 100 200 300 400 500 600 700 DISTANCE (FT) The rays from a directional transducer (1/10 full strength at + 8 degrees) mounted 10 feet below the sea surface will refract when passing through the average summer internal wave structure. The re- fraction depends upon the angle of approach of the sound rays. Note how the ray paths converge and diverge as a result of the internal wave effects. \ \\ Z, = 40-9.1 sin Ra = ee | ee 0 ‘ ONS 0 100 200 300 400 500 600 700 800 900 1000 1100 (x) INTERNAL 800 900 1000 1100 DISTANCE (FT) (X) Above the thermocline the sound-level intensity decreases approximately as the square of the dis- tance, but below the thermocline there are regions of high and low intensity. As the internal wave proceeds past the tower the zones of high and low intensity move in accordance with the refraction pattern. The dB values given refer to a sound level of 60 dB 1 foot from the directional source. x x . “aN \ 0 ‘ RNS \ \ v \ \ ‘ \ \ YN \ \\ 1200 1300 1400 1200 1300 1400 > iISee 10 — 15 dB 5 — 10 dB 0- 5dB 61 SOUND TRANSMISSION (Continued) Sound rays directed at other than normal angles to an undulating thermo- cline are refracted both horizontally and vertically. In one series of tests a high- frequency, tower-mounted transducer was trained on target spheres tethered 7 feet above the bottom 100 feet from the tower. One target was located southwest, another to the west, and another to the north of the tower. The amplitude of the return ping as a function of time was re- corded simultaneously with, and inde- pendently of, the internal waves. The sound record shows fluctuations in transmission of up to 30 dB. An analysis of the internal-wave and sound- transmission spectra revealed that the two are frequency-coupled at the funda- mental frequency, but that the higher harmonics must be considered when comparing the simultaneous spectra of internal waves with the sound level. Results also indicate that changes in the relative angle between sound beams are reflected in the intensity and charac- ter of reflected signals. Internal-wave characteristics are of the utmost im- portance in the operational and experi- mental use of underwater sound. 62 Amplitude of a transducer’s return ping as a function of time is displayed on a scope and recorded on 35-mm film by the sonar receiver. Analysis reveals the pattern of focusing and defocusing of sound rays caused by internal waves. PLANE PARALLEL TO WAVE CREST INTERNAL : WAVE PROGRESSION SEA FLOOR INTENSITY As the sound beam is directed through internal waves in a direction parallel to their crests, it is refracted both horizontally and vertically by the moving thermocline. As a result, the higher intensity cones of sound tend to subscribe an ellipse on the sea floor with each passing internal wave. TARGET TO WEST 1 | ) | La il) Hl Kal i | | " Ml Lh AA | TARGET TO SOUTHWEST Typical sonar transmission recordings in three directions show short-period (less than l-second) changes in sound-reflection intensity. Some larger intensity changes occur within several seconds; others, related to the character of internal waves, have periods of around 7 to 10 minutes and show fluctuations of as much as 30 dB. Sound rays traveling parallel or nearly parallel to internal wave crests (to N) show greater variation in in- tensity than do sound rays traveling at right angles to internal wave crests. 63 64 ELECTROMAGNETIC WAVE PROPAGATION STUDIES The propagation and reception of very low frequency (vlf) electromagnetic waves underwater have been investigated utilizing the tower's vertical railway system to achieve preselected depths. Measurements of subsurface signal attenuation made dur- ing this period revealed that the tower structure has a negligible effect on wave reception to a depth of 35 feet. The tower also provided the requirements of open-sea, natural-wave conditions and unsheltered exposure. An additional advantage was the tower's stability. which permitted the collection of more data at less cost than could have been obtained by use of a relatively unstable submersible. 65 VLF Transmission Undersea reception of very low frequency signals suffers from large amplitude attenuation and severe phase perturbations. The latter result from waves which cause variations in the distance from the sea surface to the point of reception. Experiments utilizing a frequency of 17.2 ke/s show that the change in phase amounts to 8.2 degrees per foot of sea water path. This is of major concern in a phase-coherent sig- naling system. Signal attenuation, on the order of 1.3 dB per foot of immersion, is also observed. Studies at the tower are aimed at establishing adequate control for a phase- compensating system. Pressure mea- surements are made which are known to correlate with the length of the subsurface transmission path. Other factors such as temperature, salinity, antenna orientation, antenna motion, and the relative orienta- tion of water wave to electromagnetic wave are also related to the overall problem of vif propagation. An underwater-loop antenna and pressure transducer are extended 12 feet out from the tower rail before being lowered to varying depths for studies of transmission. With the subsurface wooden extensions, the tower had negligible effect on vif attenuation measurements down to a depth of 35 feet (over half- way to the bottom). 66 LOOP ANTENNA A UNDERWATER SIGNAL PHASE-PERTURBATION B PRESSURE-SENSED SUBMERSION DEPTH APPROX. REL. PHASE REL. PHASE SHIFT DEGREES DEPTH (FT) SHIFT DEGREES 67 A scientist simultaneously records vlf signals under- water andabove the surface. The continuous 17.2-kc/s unmodulated signals were received from Chollas Heights Navy Transmitter approximately 13 miles distant. A phase comparator produces de signals representing the relative phase of ‘‘air’’ and ‘‘under- water’’ signals, which is charted as the ‘‘uncorrected phase.’’’ The vIf underwater signal is electronically modified, by compensating for the changing pressure (depth) caused by sea-surface waves, to give a more constant or corrected signal phase. See ea + . eee == NE UNCORRECTED CORRECTED SIGNAL PHASE 4 SIGNAL PHASE = Bf : : ===: i a =———— + - SSS ee =========552==: — — = ==——====— =a =i} 44 == ——— x == s 10 SEC Comparison of recorded (A) underwater observed signal phase, (B) pressure at the receiver depth, and (C) the more usable signal phase, corrected for pressure (depth) at the receiver. 67 68 CHEMICAL STUDIES — Chemical research at the tower is concerned with several phases of the oceanographic program. Salinity, in conjunction with temperature. is determined for use in computing sound velocity and water density. Oxygen content and foaming properties are studied in connection with sound propagation and attenuation. Plant nutrients are investigated for their influence on phytoplankton production, which largely controls underwater visibility. Radio- activity of marine organisms is studied for biological absorption research. 69 Salinity and Oxygen Periodic determinations of salinity throughout the 60-foot water column, made during spring and summer, indicate that there is rarely a variation of over 0. 24%ofrom the surface to the bottom, and the average maximum vertical range is only 0.19%. Values are usually higher at the sea floor and decrease towards the surface. However, when stronger sum- mer temperature gradients are present a slight inversion in salinity structure usually occurs. For the study of internal waves, the vertical density and Vaisala frequency (stability frequency) can be computed from measurements of the salinity and temperature structure. Sea-water samples collected at the tower are analyzed to find dissolved oxygen content. During spring and summer, dissolved oxygen values range between 4 and 8 ml/l. Higher values include oxygen supplied by photosynthetic action. Oxygen saturation may exceed 100 percent because of biological action and changes in pressure and temperature. In this supersaturated condition, internal waves, turbulent motion, water heating, or the further generation of gas by phyto- plankton causes the release of oxygen bubbles. These bubbles rise to the sur- face or adhere to organisms. They can attenuate underwater sound. Other studies of gas bubbles in the water were made from samples collected in situ by means of a large suspended inverted funnel. Analyses revealed this gas to be composed of: 0, 14 to 18 percent; CO? 1 to 2 percent; CO 0 to 1 percent; CH, 0 to 1 percent; N2 78 to 85 percent. 70 To determine salinity, oxygen, and water density, water samples and temperatures are collected with Nansen bottles at intervals from surface to bottom. Water samples, taken during the summer and analyzed with a laboratory salinometer, show nearly uniform values from surface to bottom. For long-period variations in salinity, an 7” situ salinometer is mounted on a tripod out from the tower. Water sam- ples, collected in water bottles, are analyzed for oxygen by the Winkler method. N 30 60 90 120 150 180 RAD/HR 1,12 14 16 18 20 mM AE This graph, based on a series of water samples collected at the tower in summer, shows tempera- ture (T) and salinity (S) decrease with depth, whereas density (0,) increases. The Vaisala fre- quency (N) fluctuates, with the highest values being found in the thermocline. In summer, the sa- linity ranges from 33.75% to eh tt \ 14 Soo eae average year around S Sebo be) 33.80 33.85 33.90 Too Oo, 23.3 23.8 24.3 24.8 25.3 DEPTH (FT) 71 Plant Nutrients Plant nutrients, together with sunlight, facilitate organic production, especially that of phytoplankton. This lowers visibility underwater. At the tower, the plant nutrient concentrations are determined with an Auto Analyzer. This apparatus mechan- ically mixes the sea water sample with chemical reagents and introduces the mixture into a continuously recording colorimeter. The various plant nutrients such as phosphate, silicate, and nitrate have been continuously recorded with respect to both space and time. Silicon was determined by a modification of a molybdenum blue method, using stannous chloride as a reductant; nitrate was de- termined by reduction to nitrite with a copper-cadmium couple, followed by an adaptation of a standard nitrite deter- mination. At the shallow-water tower site, the nitrate and silicate recordings in the vertical water column vary widely. In spring, the nutrient content in the upper layer of the sea is normally low. A strong thermocline separates this layer from the high values in the deeper layer. A continuous recording at a constant depth (30 feet) from the bottom shows the changes in temperature and concentration of silicate caused by internal waves as they move the nutrient boundary vertically past the sampling level. 72 A continuous supply of sea water from the submersi- ble pump on the north track is automatically mixed with reagents by an Auto Analyzer pump and fed into the colorimeter. Proportioning SiOz (ug atom/L) SEA SURFACE DEPTH (FT) 30 NITRATE (pg atom/L) SILICATE (Ug atom/L) 0 5 10 ; 7 13 19 25 ) 0 oe TRANSPARENCY 10 : | TEMPERATURE NITRATE J. 20 6 ‘Ss TRANSPARENCY Bx HL = & SILICATE = = 30 9 i AL oa Ww lu a a 40 2 an 15 a 18 70 80 90 100 70 80 90 100 TRANSPARENCY (%) TRANSPARENCY (%) 17 15 13 11 16 14 12 10 TEMPERATURE (°C) TEMPERATURE (°C) Simultaneous nitrate, water transparency, and temperature records (left) show abrupt changes at the same depth. At this level and above, the low transparency water has a decreased nutrient concentration, since the nitrate has been used up by plankton. A similar abrupt change may be observed in the water transparency, temperature, and silicate relationship (right). NITRATE (ug atoms/1) 0 1810 TIME TIME 1930 Nitrate values rise and fall in direct relation to the oscillation of an internal wave (in the thermocline). Whenever the thermocline barrier is raised to or near the surface by upwelling or large internal waves, the deeper, colder water, which contains a higher concentration of nitrate, may induce plankton blooms to occur. The nitrate values (right) were recorded at 30 feet simultaneously with temperature (left). 1930 Foaming Properties The ability of sea water to produce and maintain bubbles can be measured through a study of foaming properties. The tower's site enables foam to be col- lected for immediate analysis. Foam is concentrated by the convergence circulation created by in- ternal waves - the foam persists longer in slicks because the accumulated organic film reduces the surface tension. Samples of water collected ad- jacent to and beneath sea surface slicks are studied. The samples are shaken to produce foam and then photographed at short intervals. The photographs estab- lish the size of bubbles in the foam; the maximum foam height, Hg ; and the half-life, or time required for the foam layer to decrease to half its height, T. The product H,T is called the foaming factor, (*), which is useful in character- izing water types. 74 Foam occurs naturally in the sea as a result of strong winds, ship wakes, or breaking waves (white caps). It may persist from 4 to 20 seconds, depending on the foaming factor of the water. i oe Sea-water samples collec- ted adjacent to and be- neath slicks are shaken at known speed and time. After this, the foam layer is photographed every 2 seconds. The initial mean diameter of bubbles in a normal foam layer is about 0.5 mm. This diameter in- creases to around 0.8 mm after 10 seconds due to coalescence. The mean maximum diameter in- creases from 1.8 to 2.7 mm in the same time interval. FOAM HEIGHT (MM) DEPTH (FT) FOAMING FACTOR (F) Water samples collected in slick areas produce higher foaming factor values than samples col- lected from outside the convergence area under slicks. These samples were collected from near and 4 feet below the surface during July. TIME (SEC) Foam produced in water collected outside slicks decays three times as rapidly as foam from nearby slick areas. This indicates that water in and under the slick zone contains more organic material, has a higher foaming factor, and produces more stable foam. Radioactivity Continuous monitoring of sea water for gamma rays is carried out with a scintillation meter system to establish a background level and to relate any changes to biological or other causes. The background is normally very low, running 0.007 to 0.017 mR/hr. This level is maintained for long periods of time. However, occasional increases in radioactivity over normal background have been observed, especially in sum- mer. Further investigation correlated this significant intensification in radiation with occasional blooming of the phyto- plankton Gonyaulax polyedra. Thus, increased radioactivity can usually be correlated with high water turbidity. 76 Heart of the radiation detection system is this gamma ray sensor, mounted 10 feet below mean tide level. Amplified signals of radiation intensity are trans- mitted through electric cables to a recorder in the instrument house. Instrumentation sensitivity ranges are 0 to 0.05, 0 to 0.5, 0 to 5.0, and 0 to 500 mR/hr. Because of the normally low background count, the recorder is usually set on the 0- to 0.5- mR/hr scale. RADIOACTIVITY (MR/HR) RADIOACTIVITY (MR/HR) 1105 1110 1115 TIME A strip-chart recording of the normal background radiation count shows small oscillations (0.01 mR/hr), and wave periods of about 2 minutes. Normal background count fluctuates between 0.0007 and 0.017 mR/hr. No appreciable diurnal nor tidal cycle variation in radioactivity has been detected. 1135 1140 1145 1150 As the patches of Gonyaulax polyedra pass the sensor unit during a ‘‘red tide,’’ readings of 2.0, 3.5, 5.0, and in some instances greater than 5.0 mR/hr have been observed. They last from 1 to 10 minutes. The high count is attributed to the apparent ability of certain phytoplankton to concentrate radioactive phosphorus from sea water. The highest rises in radioactivity occur in the summer. Ct 78 BIOLOGICAL STUDIES The abundance of shallow and (in some seasons) deep-water fauna and flora around the tower offers an ideal opportunity for systematic investigation of biological organisms related to under- sea problems. Studies of marine plants and animals living on and adjacent to the tower cover a wide range, from fouling to feeding habits. The examples presented here are concerned with plankton and its effect on water turbidity, and with the vertical and horizontal distribution of fish that reflect acoustic waves. Water turbidity Plankton distribution Fish distribution 79 Water Turbidity Summer studies of the trans- parency of water adjacent to the tower have been made using a hydrophotometer. The studies record light-transmission values ranging from 20 to 80 percent, based on a distilled water standard of 100 percent. Throughout the winter months the clearer water readings approach 100 percent. Water turbidity is caused by in- organic, dissolved matter and various forms of biological material. However, most turbidity in the water column is related to the phytoplankton population. During summer, plankton blooms fre- quently develop just below the surface, with a low transparency reading (less than 20 percent). Patchiness is caused in part by vertical circulation which brings clearer water upward, creating zones of high transparency within the general turbid region. Following the heavy surface blooms, the lower levels of the water column become more turbid and the upper level clears. The area of maximum turbidity frequently coincides with the maximum vertical thermal gradient. Because the thermocline oscillates vertically with internal waves, the associated turbid layer also oscillates. In some cases, water visibility changes with the tide, with periods of high waves, and with vertical or horizontal water mass boundaries. As irregular turbid zones move past the tower, changes in light transmission as great as 50 percent may occur in 2 minutes. 80 Water transparency tometer (alpha meter). The device measures light scattering and absorption by particles in the water at varying levels. Temperature and biological speci- mens are taken concurrently and at the same level. is determined by a_ hydropho- DEPTH (FT) DEPTH (FT) 2000 TIME G0 “id V 0400 0800 Sample time-depth plots of water transparency at the tower during a 27-hour period show (A) the early stages of a Gonyaulax plankton bloom with maximum concentration just below the surface, and (B) the corresponding water temperature structure (heavy lines) in degrees F, Transparency less than 30 percent is grey. The greatest plankton concentra- tion occurs at the level of maximum temperature gradient. Red water with maximum turbidity slightly below the surface is separated by bands of relatively clear water beneath the sea-surface slick. This patchiness in turbidity is caused by vertical currents associated with a passing internal weve. 20 SEA S URFACE SLICK DEPTH OF THERMOCLINE I=— 1 MIN 81 Plankton Distribution The water at the tower contains numerous species of both phyto- and zooplankton, but frequently one organism dominates. During one investigation plankton populations and movements were studied. Over 200 samples were collec- ted at 3-meter intervals throughout the water column. These repeated samplings were made at 2-hour intervals for more than 24 hours. At this time the main organism in the bloom was a naked dinoflagellate, Gymnodinium flavum (yellow water). It was present in concentrations up to 3.2 x 10 © cells per liter. The bloom corre- lated closely in space, time, and inten- sity with a highly turbid layer (30- to 50- percent transparency), which was resting on a strong thermocline. Pigmented- cell zooplankton and organic detritus, present in significantly lesser volume, showed little correlation with the turbid area. Two weeks later the turbid zone was ill-defined. Gymnodinium had abated to maximum concentrations of 4.8 x 10 ® cells per liter, while another dinoflagellate, Ceratium, Was associated with patchy turbid areas. However, the most domi- nant organism in recent years has been Gonyaulax polyedra. Thus, the principal organisms causing turbidity differ with time and changing environmental conditions. A submersible pump collects planktonic material that causes water turbidity in the tower area. The pump brings fresh sea water by hose from a predetermined (or continuously changing) depth up to a catwalk, where a known volume is filtered with a plankton net. Other sea-water samples are passed through millipore filters to obtain microscopic organisms. Larger plant and animal plankton, many of which are biolumines- cent, are occasionally collected with fine-meshed fishing nets lowered from the tower booms. DEPTH (FT) 1800 TIME 1400 A time-depth plot of the observed relationship be- tween the percent water transparency (black lines) and the total count of all plankton organisms (white lines) is shown on this composite chart. Over a period of about a day the depth and time of low water transparency zones closely coincides with that of the high microorganism count. 83 Fish Distribution Te The tower environment attracts and maintains certain varieties of fish. Studies of fish behavior under- neath and adjacent to the structure are facilitated by the remotely monitored and controlled television system attached to the south rail track. The cameras, with their automated pan and tilt mounts, fol- low both horizontal and vertical animal movements. A technique and a graphic guide for identification of the fourteen common species of fish viewed on the television monitor have been developed and used successfully. The method utilizes a series of binomial choices based on physi- cal appearance and movement. For ex- ample, a fish is initially classified by body shape, then by fin location or swim pattern, and finally by body markings. Television observations of fish over several days at regular time and depth intervals have revealed: The vertical layering of various species during the day. Changes in vertical distribution patterns at night. Avoidance and attraction of vari- ous species by camera lights and TV tilt-train noise. Changes in schooling and behavior traits at various times of day. Schools of pelagic mackerel are common visitors around the tower during the winter months but are relatively rare at other times of the year. 84 DEPTH (FT) 4 tay : : 227 4A 1%4N\M 1600 2000 0000 0400 0800 1200 1600 2000 0000 0400 0800 1200 #41600 TIME Different species of fish have characteristic and predictable time and depth habits. Kelp bass, Paralabrax Clathratus, (solid lines) show extensive vertical distribution at night. During the day, however, they remain above the thermocline. (Curves based on 24-hour summer TV observations taken on 2-minute counts at 5-foot intervals throughout the water column.) Pile perch, Rhacochilus vacca, (dashed lines) observed over the same period reveal a diurnal distribution opposite to that of kelp bass. The perch show a wide vertical daytime range, although the main population mass remains near the bottom. They are rarely observed during the evening hours. RESIDENTS (PELAGIC) . : HAL FMOON KELP BASS PILE PERCH BLACK PERCH STRIPED PERCH Medialuna californiensis Paralabrax clathratus Rhacochilus vacca Embiotoca jacksoni Hypsurus caryt RESIDENTS (BENTHIC) qe KELPFISH CABEZON SCULPIN MUSSEL BLENNY Heterostichus rostratus Scorpaenichthys marmoratus Scorpaena guttata _ Hypsoblennius VISITORS (PELAGIC) : Sr és SHINER SEAPERCH SAND BASS WHITE SEA PERCH CALIFORNIA SARGO Cymatogaster aggregata Paralabrax nebulifer Phanerodon furcatus Anisotremus davidsonti VISITORS (BENTHIC) SHEEP-HEAD LEFTEYED FLOUNDER GOPHER ROCKFISH Pimelometopon pulchrum Bothidae Sebastodes carnatus Some species of fish are permanent residents around the tower while others are occasion- al visitors. 85 oo Pes ee gh FEDS aM eases Ry: 86 GEOLOGICAL STUDIES Geological investigations from the tower utilize the under- water TV system as well as scuba and hookah diving equipment for in situ. sea-floor ovservations and samplings. General topography, microrelief, subsurface structure, sediment distribution, and associated erosional and depositional process studies are carried out in support of acoustic and bottom stability research. In addition to employment of scuba and hookah for in situ work, the Cousteau diving saucer SP 300 has been used to provide additional information on geological features seaward of the tower. The subbottom was investigated with high-power acoustic reflection equipment and by coring. 87 Sea-Floor Topography and Sediment Distribution fe Detailed geological mapping of the SHORE sea floor around the tower shows,recent vay, marine sands overlying older deltic 4 sedimentary fill of the San Diego River. a % The sea-floor surface from ie a Mission Beach to the tower is composed i ‘ va of well-sorted. fine-grained gray sand, i en oe \ with a median particle diameter of 0.09 i i millimeter, and ripple marks approxi- i i i 4 mately 3 to 4 inches high. At the tower, ; y \ 4 sediments change abruptly. Ripple marks i " increase to an average height of 6 inches. ; y and sand grain size increases to around 0.31 millimeter. About 1 mile west of the tower the bottom sediment again be- comes finer, ripple marks disappear, and the bottom slope steepens. \ \ Long-term sea-floor observations around the tower using scuba and televi- sion have identified cyclic variations in ripple mark heights corresponding to seasonal variations in waves, currents, and animal populations. In winter, ripple marks reach a height of approximately 8 inches (with wavelengths up to 40 inches). In summer. they gradually reduce to 2 or 3 inches high due to decreasing water motion and increased activity of marine organisms. Some 900 feet west of the tower, at a depth of 66 feet, coarse sand ripples measuring 36 inches from crest to crest are in evidence. Their 6-inch high peaks show irregular erosion by sand dollars, heart urchins, and sea urchins. Scattered broken shells and a thin layer of organic matter have collected in the troughs. 88 DEPTH (FT) Bae.) D A [faa 1 MILE = —120 — 240 CONTINENTAL SHELF OUTCROP — 36 CONTINENTAL v SLOPE — 480 — 600 The sea-floor topography slopes gently from shore, past the tower, to the edge of the continental shelf 6.5 miles from shore. At this point LOMA the water is 330 feet deep. The break in slope of the sea floor at the SEA —720 continental slope is gradual, as shown in this detailed PDR record. Some outcrops occur on the outer shelf. VALLEY 840 960 Proceeding west a distance of 4400 feet from the tower at a depth of 100 feet, there are sharp-crested medium sand ripples 24 inches long and 5 inches high. Medium sand ripples give way 5300 feet out to Jl-inch high rounded ripples composed of fine sand. Depth here is 128 feet. Organic matter, forming a thin layer on the surface, is again noticeable. Gradation of the fine sand ripples into fine silt takes place 7000 feet from the tower in water 164 deep. The smooth bottom, pockmarked with occasional small depressions, is also mantled with organic de- tritus. 89 Subbottom Structure Information on subbottom structure near the tower site and along a traverse from near shore to approximately a mile and a half seaward of the tower was ob- tained. This was done by using a con- tinuous reflection profiler with a pneu- matic acoustic repeating source fired at a rapid rate (1/4 of a second) and a high- resolution graphic recorder. The re- flection of the transmitted sound is the result of sound velocity, density, and porosity contrasts along subbottom stratified layers or surfaces of uncon- formity. These reflections may be in- terpreted as lithologic or structural units, and, with the aid of core samples. may be correlated with actual sediment units. Prior to the installations of the tower, a core boring was made at the proposed site which shows uncon- solidated sedimentary layers to 63 feet. Superimposed color shows the close relation of core hole data and the sub-bottom structure as defined from later acoustic reflection profiles. 90 DEPTH (FT) i SEA FLOOR 20 30 40 50 60 BROWNISH-GRAY MEDIUM TO COARSE SAND WITH MANY SHELL FRAGMENTS TOWER LOCATION SEA SURFACE SAND [an as era | SAND-SILT-CLAY BEDROCK This reflection profile shows an erosional bedrock surface (dark green) situated about 60 feet beneath the sea floor at the tower. This surface slopes gently seaward with a subbottom high approximately 1/2 mile west of the tower. The bedrock is probably cretaceous sandstone, conglomerates, and shales like those cropping out on nearby Point Loma. The records show deep reflecting structures, indicating that the bedding is nearly horizontal in the vicinity of the tower. Overlying the bedrock is sand-silt-clay (loam) 30 to 70 feet thick. This section has layers of shells interbedded with sandier zones, which probably represents an ancient low sea level deltaic or bay deposit. Overlying this section of ancient bay or deltaic deposits of the San DiegoRiver is a zone of transgressive marine sands (light green). This occurred during the Holocene period as the glaciers melted. The uppermost parts have been modified by present-day currents and wave action. In the subbottom profile (above) the depth to subbottom reflectors is approximate due to variations in sound travel time through sediments. 60 120 180 APPROX. DEPTH (FT) 91 MINE SCOUR Some effects of current-borne sediments and bottom erosion on objects on the sea floor have been determined through the use of plaster-filled mine cases. One case was placed on the bottom 8 feet from the tower and oriented in an east-west direction. Later, another case was placed on the bottom and oriented north-south. Continued observation by television and scuba disclosed any movement or burial of the mines. For the mine with the north-south oriented position the on- shore, off-shore surge was restricted around the obstruction. An anaerobic area developed on the sea floor, with worm tubes projecting from the black subsurface sediment. Divers made repeated visual inspections and measure- ments of the environment around the mines. (A) During winter, large sand ripples were observed moving shoreward past the mine cases. Ripple crests tended to orient parallel to the north-south mine case and to incorporate the case within the ripple symmetry. (B) Initially, the white cases were coded with stripes. Within 2 months the epoxy paint became fouled with algae and small balinoid barnacles. (C) The small, white sea urchin, Hytechinus ana- meSus, migrated periodically through the area and covered the cases for several days each time. Spiny sand star, Astropecten armatus, attached to the casings. The heart urchin, Lowenia cordiformis, was found burrowing and feeding in adjacent sand ripples. 92 —T WHITE SEA URCHIN Hytechinus anamesus HEART URCHIN Lovenia cordiformis < Spel Sree eypnena WERENT SPINY SAND STAR Astropecten armatus 93 94 MATERIALS RESEARCH STUDIES The tower is used for materials research studies in such fields as: Organic coatings (organic resins, acrylics, vinyls, epoxies, polyurethanes, etc.) Surface treatments (anodizing or alodizing of alumi- num, HAE or Dow 17 for magnes- ium alloys) Cathodic protection Metal alloys (nickel or cupronickel) Antifouling techniques and toxicants (organometallic compounds, tinbutyltinoxide, chlorination) Phosphorescent and fluorescent coatings of different colors were tested on the tower under varied lighting conditions. The fluorescent yellow and red colors (F and G) were more visible against the sea during the day and the bright blue coatings (H, |, L and M) Shannon No. 20 or 22 were more effective at night. Because much Navy equipment (including hydrophones) must be sub- a ae merged in the sea for long periods, the protection of materials from corrosion and fouling has grown increasingly criti- cal. The tower offers a favorable site for studies in these fields. Samples of materials have been placed underwater on the tower and inspected periodically by divers. This | work has been supplemented by research on materials suspended in the bay and on racks in a salt-air environment. | Syntactic foam spheres were tested at the tower as Booms and above-water metal structures were test- K instrumentation floats. Alternate floats were coated coated with a polyurethane (Laminar X500) which U with a silicone coating (RTV 60) which reduced the resists corrosion from salt air for a 5-year period. marine growth. a | 96 Do hee | Epoxy resin (EPON) was experimentally applied in the intertidal and splash zones (—2.5 to 14.5 feet) to test its effectiveness in preserving the tower from corrosion and fouling. Here a diver pours water over the dry pilings (dolphins) before applying the EPON coating. Instrument cables are periodically examined and tested for corrosion. A urethane coating has proved useful in preventing corrosion and fouling of running and bearing surfaces in and out of the water. 97 98 ee . STUDIES WITH THE DIVING SAUCER A new research technique developed at NEL consisted of simultaneous investigations from the Cousteau diving saucer and at the tower. This technique extended geographically the area available for oceanographic research. Joint tower-saucer studies included current speed and direction, water transparency, and temperature. Another purpose of the tower-saucer work was to study the sea floor westward of the tower. The detailed features observed and photographed were sediments, bottom roughness, shell dis- tribution, organic matter, benthic organisms, and fish in the water column and on the sea floor. Each of these factors has an influence on acoustic reflection. It was also desirable to find out if there were any unusual features which would influence internal waves propagating shore- ward up the shelf. Finally, a search was made to determine whether or not the location was suitable for the installation of acoustic arrays and a new tower. It was found to be excellently suited for additional installations. Tower-saucer joint operations proved highly success- ful. They extended oceanographic investigations outward from the tower and showed that the area to the west was well suited for additional installations. 99 About 200 feet west of the tower, the saucer de- scended to the bottom and proceeded westward at 0.4 knot. Studies were made of visibility, current, sediments, bottom roughness, calcareous materials, organic matter, benthic organisms, and fish. Nearly two hundred 35-mm colored still pictures and 200 feet of 16-mm movie film were taken. It was found that the sea floor was divided in zones of differing characteristics, and that the area west of the tower affords. an excellent environment for the study of a variety of sea floor and acoustic problems. 100 8000 DISTANCE (FT) BENTHIC ORGANISMS SEA PEN SAND DOLLAR BRITTLE STAR BOTTOM CALCAREOUS ROUGH- MATERIAL ORGANIC SEA URCHINS NESS (SHELL) GAST ROPODS FISH SCATTERED, BROKEN LARGE RIPPLES (CRESTS ERODED) “Saar (CRESTS PRANTL ERODED) vy (SHARP CREST) FLOUNDER SCATTERED (LOW, SMOOTH) MALLEST) VIRTUALLY SURF PERCH NONE a< NEARLY ) FLAT = BOTTOM i iL a, (WITH OCCASIONAL THICK Rained FISH LAYER ANCHOVIES DEPRES- SIONS) 1 PILE PERCH 101 102 SERVICE TO OTHER ORGANIZATIONS In its continuing effort to be of assistance to other naval organizations and Government agencies working on related ocean problems, NEL encourages the use (as time and space permit) of tower facilities and equipment. The following activities have used the tower: Tower leg brackets con- structed and installed for the testing of radioactive ma- terials. The tests were con- ducted for the Naval Radio- logical Defense Laboratory, San Francisco, as an inter- laboratory assistance project. Naval Radiological Defense Laboratory Effect of open-sea environment on radioactive samples Navy Antisubmarine Warfare School Testing and evaluation of sonar transducers Navy Postgraduate School High-frequency sonar research Naval Research Laboratory Study of sea-slick surface film Contractors of the Bureau of Ships Buoy and equipment tests U.S. Fish and Wild Life Service Infrared aerial surveys 103 Navy Radiological Defense Laboratory experiments showed that specimens of strontium titanate containing trace quantities of strontium 85 yielded low amounts of radio-strontium after having been immersed in sea water. The specimens were mounted in special holders on the tower legs. 104 Research in acoustic scattering was carried out at the tower by officer stu- dents of the Navy Postgraduate School, Monterey. Measurements at varying depths, frequencies, and times provided data on the size and distribution of scattering particles in the water. These data were used for thesis material. Postgraduate School students employed a variable- depth electrostatic transducer which transmitted signals over a 3-octave band (24 to 192 kc/s). It determined the presence and distribution of scatterers in the water column. 105 — yl A VAN wa IN SSS Sse Ss Ss SS SS SP FI | a JNA i \pae 10 it it It \ I i i II ee | ORIGINAL TOWER if i II \\ lI \\ I i een LATER ADDITIONS Ht \\ I \\ a \\ im} \\ I] \\ i] \\ I \\ I] i) 1] \\ i] \\ '] \\ f ‘ I \\ y V 106 PART Ill CONSTRUCTION, TOWER DESIGN, a tal — ed > The topside unit of the Towercom consists of speaker, amplifier, and associated electronics. The~ unit is placed near the temperature-recording system in the tower so the engineer may observe the behavior of the sensors being repaired and communicate instructions to the divers. When leaks develop at a thermistor station, divers descend, disconnect the faulty sensor, repair or replace it, and check for proper operation with an engineer monitoring both the temperature sensing and Towercom system. Communication is facilitated by plugging the divers’ leads into the electrical system of the array. Divers can use either scuba or hookah with Towercom equipment. THERMISTOR BEAD ON 30-FOOT PIP SEA FLOOR S| 60 FEET TO SURFACE CABLING The handling of underwater cables is of primary importance to the tower program, since leakage in either power or signal cable leads to faulty or no data transmission. Special clamps and new techniques are used to prevent abrasion of these cables. The cable is laid on the sea floor. In deep water it soon becomes partially buried by sand ripples. 1382 Heavy double-armored cable from a Mission Beach utility line carries electrical power for the tower (background). The cable is being jetted 8 feet below the surf and beach level in this 1959 installation photograph. Protective bell-shaped clamp starts power cable up tower leg(A) through strong permanent clamps (B). The instruments are grounded by another cable which leads to a large copper plate buried in the sand near the tower. Signal cables require chang- ing as sensors are installed, re- moved, and repaired. They are encased in old fire hose to avoid abrasion against the tower by the surging water. They are then clamped with single-channel brack- ets (C) held out from the tower leg. These brackets have been modified to allow additional cables of any size to be attached underwater. Rubber bands made of surgical tubing hold the cables in place. Within the instrument house signal cables are connected to 98 terminals on patch panels. This bundle of signal cables leads through conduit to re- corders in the various rooms. Underwater signal cables may become tangled by water motion unless they are carefully attached to a fixed support by clamps or brackets. 133 SAFETY The safety of personnel working on and around the tower is of primary importance. All necessary safety pre- cautions are therefore taken. The Safety Officer of the Laboratory issues safety glasses, shoes, hard hats, and first aid supplies. Other equipments such as lights and foghorn are approved and in- spected by the Coast Guard. The tower has had a perfect accident-free record. Navigation safety is maintained by remotely con- trolled foghorn. Lights at the masthead are for warning planes, and those on the NW and SE rails are for ships. The lights and radio are powered by the city power supply. Should a power failure occur lights are automatically shifted to a battery source. The tower is equipped with a back-up, battery- operated walkie-talkie on the same frequency as the usual radios. 134 First aid supplies and a stretcher are available. Also, although nearly all the tower is of fireproof construction, extinguishers are available in strategic locations for any possible equipment or paint fire. Life rings are conveniently placed on the rails of the upper three decks. The tower also has a lightweight life and workboat provided with Mae West life jackets. When landing personnel on the tower, the personnel boat ap- proaches the east (or leeside) landing ladder stern first. Heavy double-level rubber airfilled fenders provide a soft landing against the wooden dolphins (A). The person disembarking stands on the unobstructed stern, holding a safety line for balance (B). As the boat eases up to the ladder, the passenger steps a distance of about one foot from the boat to the rungs of the ladder which is recessed between the dolphins (C). On rough days the transfer to the tower takes place as the crest of the wave is under the boat. When disembarking from the tower, the person steps from the ladder to the boat, with boat personnel standing by and holding the safety line for the disembarking person. All equipment (even small arti- cles) is brought aboard in the basket. Thus boarding personnel are unincumbered. For very large equipment, the basket is re- moved anda sling is attached. 135 PROTECTION Sea Gull Deterrent When the tower was originally in- stalled, sea gulls lined the rails and littered the decks. To rid the installation of these pests, a covey of imitation owls was posted at strategic points around the tower. Initially, the owls were success- ful in scaring the birds away. Later they became accustomed to the owls and re- turned. Periodic broadcasts of tape- recorded gull distress calls were then introduced. The cries of anguish take place every hour. As a result the tower is now nearly free of sea gulls. Fouling and Metal Protection Corrosion protection below the water level was originally provided by a cathodic system consisting of four bat- teries of zinc anodes charged with low voltage. The voltage balances the elec- trical potential created by the steel framework in salt water. After 5 years, the underwater portion of the tower shows no appreciable damage due to corrosion. A more permanent system consisting of platinum anodes has now been installed to replace the zinc. 156 Mounted owl acts as a sea gull deterrent. Another deterrent is 3-minute herring gull distress calls broadcast from speakers mounted on upper deck rail. Meters and controls for cathodic mounted in the instrument house. protection are Fouling of the tower's underwater structure by barnacles, mussels, and other sessile marine organ- isms is controlled by an annual scraping. The work is done by hookah (A) and scuba (B) equipped divers using scraping irons and hydraulic hammers. The scraped-off animals and their shells are removed from the area so as to keep the sea floor in a natural state. In fact nothing is thrown over the side that may litter the bottom. Metal protection overlapping the tidal and splash zone (—2.5 to 14.5 feet) is provided by a 3/16-inch neoprene coating. Other metal areas are painted periodically with epoxy paint. 137 L PART IV. FUTURE PLANS AND SUMMARY 139 140 THE NEED FOR DEEPER RESEARCH As studies of the inshore marine environment progress, it becomes necessary to extend oceanographic research into the next deeper stage -- the 100-foot level. An oceanographic tower located west of the present tower is required to supply essential data on this deeper region. Utilizing the techniques developed and the instrumentation employed in present tower studies, a tower at the 100-foot depth would: 1. Permit extensive studies of the relationship between the marine environment and the operation of ships, submarines, and deep-submersible vehicles. These studies are not prac- tical with the present tower. 2. Enable studies of motion, acoustics, chemistry, biology, and geology to be continued in the new deeper water area. 3. Make possible the study of thermocline characteristics for a season up to 50 percent longer than is possible at the present location. 4. Create a stable, fixed-path range for sound and radar transmission experiments between the present and new tower. 5. Allow study of the modification in characteristics of sur- face and internal waves as they progress shoreward. 6. Efficiently support the complex requirements of a sea- bottom laboratory and provide an ideal base for develop- ment of man-in-sea type studies. 141 Proposed acoustic range between towers would be used in the study of short-term and seasonal varia- tions in sound transmission. Surface craft and sub- mersibles could participate in research and opera- tional studies in conjunction with the deeper-water tower. 142 2 hala RER RN! pre odd SUMMER 143 ei eee —_ fh a i a +h : } i a = an I f hye ee 1 . Cm : cs Ut Te a mee © Itai iis he wos | pers ae i — Cae en Bb irae ‘Piven Teas