Underwater Mapping with Photography and Sonar

JOSEPH POLLIO* iJ. S. Naval Oceanographic Ofice Washington, D. C. 20390 Underwater Mapping with Photography and Sonar

Deep-towed vehicles and manned submersibles not only can inspect but also can obtain stereophotos from which investigative mapping can be meaningfully conducted.

(Abstract on next page)

INTRODUCTION vessel was sighted the next morning in the RELEASE issued by the~anishN~~~ stormy Skagerrak Straits with transmitter A on September 13, 1970, informed the problems which caused the failure to report. world of another impending tragedy-the lives were lost and was Okay- Danish submarine MARHVALEN was re- Had there been a casualty 10 years ago ported missing with 20 men onboard. very little could have been done; the available Throughout the world concerned scientists was no match for the great depths wondered if another search would be required of the ocean. Today inspection or retrieval of to locate and map the wreckage while a multi- artifacts placed intentionally and uninten- national research operation was mobolized. tionally on the deep ocean bottom is no longer ~~~~~~~~~l~no search was required as the restricted by depth. Deep-towed vehicles (such as those described by Spiess (1966), * Presented at the Annual Convention of the Buchanan (1968) and Daugherty (1969)) and American Society of Photogrammetry, Washing- manned (which number more ton, D. C., March 1971. than 40) not only can inspect but also can be 955 equipped to obtain stereophotographs from tography from submersibles using the pan and which investigative mapping can be meaning- tilt mechanism (Figure 4) has been developed fully conducted (Figure 1). and tested on BEN FRANKLIN during the Stereophotography from submersibles may Gulf Stream Drift Mission and provides reli- also supplement data for the investigation of able measurements from the pair of calibrated biologic phenomena and dynamic processes in cameras which can be trained and triggered the ocean (Pollio 1969a). Calibrated stereo- together. The constraints imposed by the photography provides a three-dimensional fixed base and the known camera characteris- coordinate system within the photographed tics make the solution of the photographs area from which the size, shape, and spatial simple. Hence, the photogrammetry serves distribution of biologic and other ocean not only to document, but also to bring the phenomena can be derived (Figurk 2). object of interest out of the ocean environ- Photogrammetric documentation and sub- ment into the office where precise measure- sequent mensuration is no less important to ments and review can take place in comfort.

ABSTRACT:An underwater surveying and mapping system has been designed and tested. This system is considered a major elemen6 in the field of underwater cons~ruction,inspection and maintenance of man-made objects, and the investigation of critical wreckage. In a rant underwater mapping test it was found that the data derived from stereophobography takes with the manned submersible ALUMINAUT codd be used to calibrade an acou~tictransponder system and to rectify the side-scan sonar trace. Calibration and rectification were made possible by a special photographic suite of tandem-mounted cameras. A calibrated Pair of 35 mm. cameras was vertica62y mounted on each side of ALUMINAUT with a separation of 2.71 meters (8.89ft.). Control for the strip map formed the control framework to rectqy the side-scan sonar record. The side-scan sonar trace was adjusted to an equal x-y scale ratio by photographic dretching in only one directwn. Variations in the track velocity were also accommodated by Eike variations in ratio change. The geodetic positioning of this strip map was possible because the transponder navigation net was positioned by theodolik? inter- sections relative to shore geodetic poioilzts. The mapped features could thus be described in terms of plane coordinates (Universal Transverse Mercator coordinates) or .In precise iterms of latitude and longitude with respect to the terrestrial datum. the ocean engineer who must devise ways of The Zeiss C-8 stereoplanigraph (Figure 5) recovery or must reconstruct on paper some could discern distances of 0.1 cm. (0.4 in.) of the catastrophic casualties which occur in from the proper photographs exposed 9 the ocean. The photograph of the crabs meters (30 ft.) from an object. (Figure 3) demonstrates the ability, through Although the pan and tilt type of stereo- stereophotography, to orient objects in rela- photography is an invaluable aid to dimen- tion to each other and the ocean floor. A sional interpretation of underwater photog- similar exercise might show the same relation- raphy, the submersible is better used to ob- ship between aircraft, ship, or submarine tain mapping stereophotography. wreckage if it is required for accident investigation purposes. It is emphasized that one camera on a stationary submersible platform The manned submersible's ability to follow provides only an interesting photograph at a predetermined and systematic survey grid best, whereas two properly oriented cameras close to the bottom while permitting the can provide data from which the engineer can surveyor to observe the terrain he is mapping derive dimensions and spatial characteristics greatly facilitates construction of topographic as well. Only if systematically approached maps and provides detail that is virtually im- with survey instrumentation and techniques possible to obtain through conventional can the arduous task of appraisal take place techniques. Minute topographic detail is of with any degree of certainty. vital importance for the installation of any A system of stereophotogrammetric pho- underwater cable or pipeline, or for almost UNDERWATER MAPPING WITH PHOTOGRAPHY AND SONAR

STAR Ill

DEEP QUEST

FIG.1. Submersibles equipped for stereophotographic mapping. PHOTOGRAMMETRIC ENGINEERING, 197 1

manner in which many bottom and biological sampling programs and ocean current studies are pursued. The optimum solution then must combine the rapidity of electro-optical- acoustic techniques with the much more comprehensive human sensor in surveys where precise details of the ocean bottom are required. The three basic survey methods used to measure precise details of bottom relief prior to the production of underwater topographic maps are: Echo Sounding Surveys, Side-Scan Sonar Surveys, and Stereophotographic Sur- veys. Each of these yield maps with different degrees of refinement, but experience has shown that a combination of the above systems to obtain simultaneous data is a significant improvement over the use of any single method.

ECHO SOUNDING SURVEYS Of the three basic submersible survey methods, echo sounding is the least precise because contours must be interpolated be- FIG.2. Photograph coordinate system and spatial tween sounding line profiles. But, unlike its geometry of a fixed-base system. surface counterpart, little loss of definition of any installation on the ocean floor. Figure 6 shows a hydrophone footing in the Bahamas which fortunately escaped being placed on the adjacent outcrop. Had this occurred, the array could have toppled over and been rendered useless. Such small-size topographic details were completely missed in a variety of conventional surveys of the Tongue of the Ocean which preceeded this installation. Viewing this area directly produced an en- tirely different picture of the bottom than was originally deduced. In this age of sophisticated electronics, justification for the use of manned submersibles is necessary if an engineer can assure that remote electronic devices can be built to suit virtually any requirement. It is well-docu- mented fact that, in spite of the availability of sophisticated electronics, the manned submersible has been instrumental in the dis- covery of the extreme roughness, including near-vertical scarps and huge boulders, that is present over vast areas of the ocean floor. This new appreciation is of more than mere academic interest because, as a result, the surveyor has become much more judicious in interpreting remotely obtained data and now knows that the results of such surveys lack detail that could be important. This awareness FIG. 3. Tilted photograph restored to a plan by makes crystal clear the inadequacies of many applying a tilt determination of the stereophoto- conventional instruments and the fortuitous graphs. UNDERWATER MAPPING WITH PHOTOGRAPHY AND SONAR

FIG.4. A pair of 70 mm. cameras mounted on the pan-tilt of the BEN FRANKLIN. the bottom features due to beam spreading record of the features between the sounding occurs on a submersible inasmuch as the lines was provided and, depending on vehicle sounding distance can be kept small by altitude selected, horizontal swaths of 75, 150, changing the depth of the submersible (Figure or 300 meters (250, 500, or 1,000 ft.) on each 7). While monitoring the depth of the sub- side were imaged in one transit along a sound- mersible with either a recording pressure ing line. This technique is more thorough than transducer or upward echo sounder, recon- conventional echo sounding because it allows naissance surveys can be flown at cruising easier and more accurate interpretation and speed because the operation can be conducted less extrapolation between sounding lines by at a safe altitude above bottom obstacles. either locating anomalous topographic features or verifying the similarity between the SIDE SCAN SONAR SURVEYS profiles. Thus, side-scan sonar can serve as a By mounting side-scan sonar transducers qualitative tool to augment conventional on ALUMINA UT (Figure 8) a qualitative sonic mapping. However, if attempts are made to use the side-scan sonar as a quantita- tive tool and to view the record as a true plan, the inherent distortions of the side-scan sonar record must be recognized and removed. Dis- tortions to the side-scan sonar record are in-

FIG.J. L IIC a~e~roplanigraphcan resolve underwater. photogrammetric problems with detailed preclslon. FIG.6. Hydrophone footing. FIG.7. Resolution gained by near-bottom sounding.

m FIG.8. Side-scan sonar on the ALUMINA UT. UNDERWATER MAPPING WITH PHOTOGRAPHY AND SONAR troduced by environmental variations, geo- bottom-mounted transponders has been used metric com~ression.and vehicle velocitv. to rectify the sonar data. A better solution Sound veiocity variations from site to'site might include a servo-recorder which uses may be large and must be considered because information from a Doppler sonar navigation the scale across the record is based on a fixed system to adjust the paper speed of the re- sound velocity of 1,524 meters (5,000 ft.) per corder to correspond with vehicle velocity. In second. A correction to the record must be lieu of a servo-recorder, some measure of made inasmuch as the recorder cannot be ad- rectification can be obtained photographically justed to accommodate the change. by stretching the record in only one dimension Geometric compressions of the record exist to yield equivalent x-y scales as shown in because only those topographic features di- Figure 9. rectly beneath the vehicle are represented in the vertical; all other topography is displayed STEREOPHOTOGRAPHIC SURVEYS with increasing obliqueness. Hence, the record The greatest underwater topographic map- is neither vertical nor horizontal and, worse, ping precision was achieved by stereophoto- the error is not uniform but varies with the grammetric methods. Both vertical and depression angle to the topographic feature. horizontal solutions could be obtained with a For example, in flying 9 meters (30 ft.) above minimum of ground position control because a flat bottom (a typical mapping altitude) all of the ability to relate a photograph to its the detail from directly below the submersible conjugates by triangulation. Using this pro- to 15 meters (50 ft.) horizontally outward is cedure, five position control points were compressed and displayed on the record be- sufficient to orient 380 photographs of a 48.8 tween 9 and 18 meters (30 and 58.5 ft.). This meter (160 ft.)-square test map area (Pollio amounts to compression of about 57 percent 1969b). The photographs for this test were ob- in the first 15 meters (50 ft.). The compres- tained with a calibrated Rebikoff 70 mm. sion, however, becomes less with distance underwater camera mounted on a PEGASUS from the vehicle, so that an interval of 15 wet submersible (Frontispiece). The pilot/ meters (50 ft.) at 61 meters (200 ft.) distance photographer flew parallel tracks tripping is displayed between 61.6 meters (202.2 ft.) the shutter at the correct interval to provide and 76.7 ft., or a one percent compression. the necessary coverage. This distortion could be removed by digitizing The resultant map (Figure 10) is the first images of interest, solving with an analytic known underwater map derived solely from program, and displaying the result on an flown photography and photogrammetric analog plotter, but no requirement for this methods. The most significant finding of the refinement exists at present. test was the vertical precision of the mapped Table 1 is an example of the corrections for environmental variations (4,700 ft/sec) and geometric compression which were applied to the record when the system was used in the Total Horizontal Distance at Recorder Scale fresh water of Lake Champlain. Divisions (Ft.) A serious distortion to the side-scan sonar record results if the paper speed is not syn- 0-50 50-100 100-150 150-200 20&250 chronized with the vehicle's velocity. As the 0 0-47 47-94 9P141 141-188 188-235 EG&G side-scan sonar system employed on 25 0-38 38-90 90-138 138-186 186-232 ALUMINA UT and BEN FRANKLIN had Vehicle 50 0 0-80 80-131 131-182 182-229 Altitude 75 0 0-55 55-119 119-172 172-222 a fixed paper speed of 1 inch per 12 seconds 100 0 0 0-99 99-159 159-213 and 1 inch across the record represented 50 125 0 0 0-65 65-141 141-198 feet (15.25 meters), a correct x-y scale could 150 0 0 0 0-115 115-179 be obtained only when the vehicle speed was about 4.2 feet/second (2.5 kts). If the vehicle Distance Interval Represented between could have maintained this speed uniformly Recorded Scale Divisions (Ft.) along a straight track, then no corrections would have been needed. However, no sub- 1 0-50 50-100 100-150 150-200 200-2.50 mersible we have used has been able to safely fly at a speed of 2.5 kts while only 30 feet (9 meters) off the bottom. Instead, speeds near 1 knot are more the rule, and even at this low speed progress is not always uniform. In past operations, data obtained from FIG.9. Photographic rectification of side-scan sonar.

GRID 20 FOOT INTERVAL I 160 FEET 4 FIG. 10. An underwater planimetric map. Form lines indicate locations and shapes of coral heads. UNDERWATER MAPPING WITH PHOTOGRAPHY AND SONAR

FIG. 11. Detailed underwater topographic map of area shown in inset of Figure 10. The grid interval is 4.5 feet, the contour interval is 2 inches with 1-inch supplements, and the reference level is 32 feet below sea level. detail. It was found that one-inch contours also provided the necessary real-time data to could easily be drawn as elevation differences navigate the survey track. This insured the of about 7.5 mm. (0.3 inch) could be detected correct overlap and side lap, a basic consider- (Figure 11). It is estimated that the area ation in obtaining adequate photographic could be increased by a factor of 10 and still coverage with the least number of pictures. remain within tolerable limits, but if the area The net employs three transponders all of to be mapped is larger than one-half mile, which are interrogated at 18 kHz but reply total photogrammetric mapping with present at different frequencies (14, 15, & 16 kHz). technology becomes cost-prohibitive. To An onboard computer has been developed to cover a one-half mile sauare area with over- square the ranges to two transponders and lapping normal-angle stereophotography fly- take the difference between these squared ing 9 meters (30 ft.) above the bottom would distances. These data define a plane normal require about 48,000 photographs with ac- to the transponder baseline and allow the companying expenditures of unacceptably submersible to follow a series of parallel, large amounts of labor. equally spaced, straight lines in order to completely cover a predetermined survey area or PHOTO-ACOUSTIC SURVEYS to reconstruct the actual track should the Recent tests with ALUMINAUT have submersible be unable to follow the prede- shown that a good compromise exists where termined track. (Figure 12) the continuous photographic coverage along The transponder net also provided the posi- the survey track was supplemented by quali- tion data needed to relate the resultant pho- tative side-scan sonar images. This survey tography to the net which, in turn, wasori- technique required a transponder navigation ented to a geodetic system at the surface. system, tandem-mounted mapping photog- Horizontal coordinates relative to the trans- raphy, and side-scan sonar. ponder net were observed at intervals which A transponder system developed at NAVO- corresponded to photograph exposures. These CEANo (Merrifield 1968) was needed to navi- yielded 10 horizontal position points along gate the survey lines and to derive the posi- the track which were sufficient to orient the tion and orientation of the photographic flight line. As the precision of each point was coveragethe photography in turn served to about f3 meters (10 ft.), the single random calibrate the transponder system. The system position points could not be used individually PHOTOGRAMMETRIC ENGINEERING, 1971

to control the photography. If taken in total along the 300-meter (1,000 ft.) survey track, however, regression analysis of the position data relative to the photogrammetric positions indicated the orientation precision value increased to better than + 1/2 degree. To control the photography, relative distances along the survey track were derived by a photographic suite of tandem-mounted cameras. A calibrated pair of 35 mm. EG&G cameras (Model 207A) was mounted with a separation of 2.71 meters (8.89 ft.) and the optical axes parallel. The lighting arrangement was similar to the fixed-base system employed on the submersible STAR 111 (Pollio 1968), two 250 watt-sec. strobe lights with a fixed time delay (about 1/50 sec) between cameras. The separation of light and camera is achieved by synchronizing the port camera with the starboard strobe and the starboard camera with the port strobe. The parallel camera separation provided the optical base line for each pair of photographs along the track (Figure 13). Each pair of exposures along the track established a base line of approximately 2.70 meters (8.89 ft.), and by photogrammetric triangulation of overlapping conjugate pairs, a dimension and relative track solution was derived (Figure 14). The centers of each photograph along with the detailed contours, annotations, and delineations were compiled into a strip map of the area covered by the photographs. The resultant strip map not only served to portray the detail along the track but plotted photograph centers formed the control framework to rectify the side scan sonar record and to calibrate the transponder systems as well. As described, the side-scan sonar trace was brought to equal scale ratio, but the abun- dance of horizontal control points provided by the photogrammetric solution allowed a more refined rectification. Variations in the track velocity were also accommodated by like variations in ratio change, hence a montage of rectified records which conformed to the equivalent mapped photograph centers was assembled with the photogrammetric

FIG.12. Underwater navigation/position system (after Merrifield). The seven photographs are, from top to bottom: transponder, transducer, transeiver, range counter logic, display unit, converter and computer, and the xy-recorder. The sketch at the bottom depicts the submersible's track consisting of a series of parallel, equally spaced, straight lines. UNDERWATER MAPPING WITH PHOTOGRAPHY AND SONAR ..gTRANSPONDER

FIG.13. The optical baseline. data to form a combination strip map (Figure tions from shore. The features can thus be 15). described in terms of plane coordinates, such The geodetic positioning of this strip map as Universal Transverse Mercator coordi- was possible because the transponder naviga- nates, or in precise terms of latitude and tion net was positioned by theodolite intersec- longitude with respect to the terrestrial datum. A compiled map included rectified side- scan sonar records and topographic contours mapped from stereophotography, and demonstrated the underwater mapping capabil- ity. The total length, 370 meters (1,214 ft.), was controlled by horizontal photogrammetric bridging of 225 exposures (137 photographs from the port camera and 88 photographs from the starboard camera). The topographic features were shown using form lines with about a 1 meter (3 ft.) vertical interval; the remainder of the map consisted of rectified side-scan sonar records brought to the same scale as the topographic strip map. A slight mismatch between the side-scan sonar and the topographic map was caused by distortion of the side-scan sonar record due to flight geometry. Maps of bottom topography made from this kind of comprehensive survey present a continuous overview of the area whereas the topographic detail is displayed in strips along the survey track. Relative heights, FIG.14. The track solution at bottom roughness, and differences in eleva- compilation scale. tion can then be related to and assist in the FIG.15. Rectified side-scan sonar fitted to the track. interpretation of the side-scan sonar data be- the change in the index of refraction of ocean tween survey lines. Although this technique water owing to changes in the density of sea cannot be used to survey extremely rough water. areas, it does lend itself to surveying where most maps are required. Thus, photogram- LIGHTING metric precision is supplemented by the quali- Lighting must be improved to accommo- tative imagery of side-scan sonar. date the compatible wide-angle systems. Non- uniform illumination and back-scatter are great drawbacks to efficient mapping. Also, CAMERAS the long recycle rates, high failure rates, and Although maps such as these can be pro- wattage inefficiency of present underwater duced with present instrumentation, it should electronic flash units all tend to inhibit mis- be noted that the system was improvised sion success. from existing or slightly modified equipment. The cameras used to date are not photogram- CAMERA CONTROL metric: to be photogrammetric the cameras There is no suitable intervalometer (a de- should have a high resolution, calibrated-in- vice which would cycle the cameras at the water lens system with small distortion; focal correct interval) available at present. The lengths (principal distances or nodal-image photograph exposure interval, which varies distances) which are compatible with com- with speed and altitude, must be set from pilation machinery; a flat focal plane with estimated values of average height and speed. fiducial marks or reseau (grid) marks; a film To insure complete stereophotographic cover- flattening device; a rapid and smooth film age, however, the photographs are usually transport; a data chamber and a sturdy, non- taken at an excessively small interval at the distorting construction. expense of area coverage efficiency, increased Of prime importance is the lens system and cost of data processing, and shortened bottom its focal length. This length, or the nodal- excursion time (Pollio, 1968). image distance, once calibrated must not al- Photography for the mapping of the ocean ter under the varying stress conditions of the bottom must be ~erformedat an interval ocean depths. This requires a special camera which produces a precise overlap. A variation construction in which the lens system is not of greater than 10 percent may cause either altered by pressure, such as a lens cone which inefficiency due to excessive photography and is independent of the pressure case. Tests data reduction, or mission failure due to loss must also be made which investigate the of overlap. An automatic system is required alteration of the nodal-image distance due to to trigger the camera at the proper time be- UNDERWATER MAPPING WITH PHOTOGRAPHY AND SONAR

cause the interval for desired overlap will speed of sound as the distance parameter. vary with vehicle velocity and altitude. Because of this, the photogrammetric system The camera control system may be inde- accuracies, both vertical and horizontal, can pendent or it may be tied to existing equip- be verified only to the degree that the mea- ment which senses vehicle velocity and al- surement of this parameter will practically titude. The velocity is recoverable from an allow, about three significant figures or 1 per- acoustic Doppler navigator, an optical image cent of the measured distance. Until these scanner under development, the navigation systems become available, stereophotogram- transponder net, or a rolling wheel device, metry, which can be made reliable to four and the altitude can be recovered from the significant figures, or 0.1 percent of the depth/altitude system. A small, off-the-shelf traversed distance, remains superior as a system then computes the velocity-altitude distance measuring device. Hence, the in- ratio and controls the exposure interval. clusion of stereophotogrammetry in the underwater mapping system helps to make it SUBMERSIBLE ATTITUDE comprehensive in that the stereophotogram- Accurate interpretation of underway sur- metry generates its own dimension control. vey measurements (bottom and sub-bottom profiling, side-looking sonar, photographic documentation, etc.) requires that con- The depth and altitude of the submersible tinuous and retrievable information concern- must be known and recorded at all times during vehicle attitude be obtained during the ing a survey. The pilot and scientists within conduct of the survey. The output of vehicle the submersible require a visual display of attitude sensors should be recorded for cor- altitude/depth in order to make proper relation with simultaneous measurements of operational decisions. Reduction and inter- the ocean environment. Visual display of pretation of survey data are dependent on vehicle attitude would also assist pilot/ reconstruction of the vertical path of the sub- operators in conductinn the survey. mersible in the water column as well as in a A vehicle attitude system should include geographic coordinate system. pitch, roll, yaw and azimuth sensors not un- Altitude/depth systems are considered off- like present aircraft flight indicators and dis- the-shelf items, but some modifications are plays. The sensors must provide electric necessary before these systems will be ac- analog signals which can be recorded. Other ceptable in terms of survey requirements. parameters which should be recorded by this Present systems utilize up- and down-look- system are speed over the bottom and total ing acoustic transducers for altitude/depth distance traveled. Recording will be made on positioning. Recently completed project a multichannel magnetic tape unit. To insure studies (Berger, in preparation) indicate that fully automated data retrieval and process- these systems are sufficiently accurate for ing, sensor output should be sequentially shallow surveys. Deep surveys will require scanned and recorded, with time being the replacement of the upward-looking trans- data entry group. Vehicle attitude data can ducer (depth) by a combination of highly ac- then be automatically used in the correction curate pressure gauges, both the full scale and of data from environmental sensors or naviga- differential pressure types. The replacement tion systems. is recommended because in deep water the Components of this system generally exist error of acoustic systems is greater than that as separate units or parts of other systems. of pressure systems due to the uncertainty of Logic and recorder units which provide multi- the sound velocity profile. Indicated modifica- channel sequential recording are frequently tions are well within the state-of-the-art. Ex- used in oceanographic or other instrumenta- perience has shown that analog displays tion. Developmental costs would consist (continuous-strip chart records) are easier to mainly of interface engineering and com- interpret than digital (numerical) displays ponent integration. A long and costly de- because the rate of change of altitude/depth velopment time is not anticipated. relationships are frequently as useful as the absolute real-time values. SUBMERSIBLE POSITION CONTROL For reconstruction of survey events it is Underwater position control systems must also required that the output of the altitude/ be developed to provide the horizontal and depth device be recorded on magnetic tape vertical control for the finished map. All with date and time in the manner of other known methods of positioning or establishing onboard systems. dimension control under water utilize the Commercial systems generally incorporate graphic analog displays which are suitable for fracture size and sha~e.or other vital details A # survey positioning. It will be necessary to helpful toward arriving at the possible cause interface the altitude/depth record with time of such catastrophies. in a format which allows direct correlation of this and other survey data through a digital computer. Data from this system should be The author expresses his appreciation to combined with that of a vehicle attitude Mr. E. Geary, W. Burrows, R. Haas, and sensor for most efficient data recording and T. Jaskiewicz for ably assisting in the reduc- retrieval; however, a separate digital recorder tion of photogrammetric data. The author with time tags would suffice initially. also acknowledges the efforts of Mr. B. Burke in preparation of the art work and Mrs. THE IMPORTANCE OF mapping and pho- E. Burl in typing the manuscript and pre- tography in underwater research and survey- paring it for publication. ing cannot be overemphasized. Upon surfac- ing, the first question is usually, "What did you see?"; "Did you get any pictures?" Brundage, Jr., W. L. et al. (1967) Search and inevitably follows. Subsequent investigation Serendipity. Deep-Sea Photography, The Johns also has shown that more than merely look- Hopkins Press: Baltimore ing at a photograph is generally desired. This Buchanan, C. I,. and Isaacson R. (1968) A General Purpose, Frequency Multiplex, Telemetry De- appraisal usually involves relative positions, sign For Oceanographic Instrument Systems. and size and height of the photographed ob- Proc. of the Fifth Military Oceanography Sym- ject, and for this type of information stereo- posium, pp. 309-332. photography is invaluable. An example of the Daugherty, Jr. F. M. 1969. Pictures From The Deep. Ocean Echo, Vol. 1, No. 7. pitfalls of deep-ocean photo interpretation, Merrifield, R. and Delort, R. R. 1968. Results where few indications of scale are present, was With U. S. Naval Oceanographic Office Deep demonstrated during the THRESHER search Research Vehicle Transponder Navigation Sys- when a line attached to the towed instrument tem. PIOC.4th ATatl I.S.A. Mar. Sci. Instru. Sym., Cocoa Beach, Fla. Jan. vehicle was accidentally photographed and Pollio, J. 1968. Undersea studies with the Deep later misidentified as the sunken submarine's Research Vehicle STAR 111. U. S. Naval sail. A photograph of THRESHER'S mush- Oceano~.Off. Informal Rent. No. 68-103. room anchor was in turn misidentified as a Pollio, J. 7969a. ~hoto~ramietricapplications to undersea tasks. Jour. Soc. Mot. Pic. & Tel. Eng., railroad wheel (Brundage, et a1 1967). Rec- Vol. 78, pp. 152-157. ognizing the intense pressure under which the Pollio, J. 1969b. Applications of underwater photo- THRESHER search was conducted, such grammetry. Mar. Tech. Soc. Jour., Vol. 3, No. 1, mistakes are understandable. but calibrated pp. 55-72. Spiess, F. N. 1966. Underwater Acoustic Position- stereophotography helps to avoid such errors, ing; Applications. Proc. First Mar. Geod. Sym., and provides precise dimensions of features Columbus, Ohio., U. S. Government Printing such as stress deformation, impact scour, Office, pp. 93-101.

Notice to Contributors 1. Manuscripts should be typed, dou- 4. Tables should be designed to fit into ble-spaced on 83x11 or 8x103 a width no more than five inches. white bond, on one side only. Referen- 5. Illustrations should not be more than ces, footnotes, captions-everything twice the final print size: glossy should be double-spaced. Margins prints of photos should be submitted. should be 13 inches. Lettering should be neat, and de- 2. Two copies (the original and first signed for the reduction anticipated. carbon) of the complete manuscript Please include a separate list of cap- and two sets of illustrations should tions. be submitted. The second set of il- 6. Formulas should be expressed as lustrations need not be prime quality. simply as possible, keeping in mind 3. Each article should include an ab- the difficulties and limitations en- stract, which is a digest of the article. countered in setting type. An abstract should be 100 to 150 words in length.