all parts of each photo. With the proper grid, measure- 

 ments of ripple marks, benthonic organisms, nodules, 

 rocks, and other relief features were made on each photo 

 when such were distinguishable. Composition of sediment 

 samples and the water clarity were correlated with photo 

 interpretation and measurements whenever possible. With 

 all three camera systems, target distance seldom exceeded 

 12 feet (3. 7 meters). 



INTERPRETATION OF BOTTOM PHOTOGRAPHS 



Value and Limitations of Bottom Photography 



While the human eye has the ability to see and inter- 

 pret, it is unreliable and it cannot retain accurate images 

 for future use. In contrast to the eye, the camera faithfully 

 records everything in its field of view. The image is sub- 

 stantially permanent, and variations can occur only when 

 the photographic prints are being measured and interpreted. 

 As a consequence, the development and application of the 

 underwater camera have shed new light on the nature of the 

 sediment-water interface. 



Fortunately, many techniques used for measurement 

 and interpretation in engineering photography can be, and 

 are being, used in the study of underwater microrelief. 

 Photography as applied to underwater surficial relief does 

 not differ basically from subaerial photography, but the 

 submarine environment is much more difficult to work in. 

 Because of refraction, the angular coverage of the usual 

 lens is restricted in water, and corrections must be made 

 to get normal, undistorted views. Seawater also scatters 

 and absorbs light much more than does dry, clear air. 

 Except in the clearest of deep oceanic waters, target dis- 

 tances for underwater photography are limited to less than 

 12 feet (3. 7 meters) for maximum resolution and detail. 

 Photo coverage is thereby confined to relatively small 

 areas. Electronic flash at 5000° Kelvin temperature gives 

 the greatest light penetration under water. 



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