underwater where suspended matter tends to obliterate the 

 sharp edges of all targets more than a few meters from the 

 camera. Sharpness of definition depends on such factors as 

 lens quality, water transparency, exposure and target dis- 

 tance, type of film, quality of look-through port, and film 

 processing. Since contrast is often poor in bottom photo- 

 graphs, it is necessary to apply indirect methods to decipher 

 unknown and obscure markings. Shadow effects are used 

 extensively for this purpose. 



A knowledge of the agencies that create the micro- 

 relief can help in photo interpretation. For example, 

 scratches, tracks, grooves, trails, impressions, pits, 

 mounds, and holes can normally be related to some form 

 of benthonic organism if enough photos of an area are 

 examined. Obtaining actual specimens makes such identi- 

 fication easier and more reliable. Organisms in shallow 

 environments sometimes can be viewed directly while 

 creating their peculiar marks or disturbances. Patterns 

 of organism distribution can be worked out from photos 

 where scale, target distance, and angular field coverage 

 are known or can be calculated. 



Rock outcrops can usually be detected and delineated 

 easily on photographs by means of contrast, resulting sharp 

 boundaries, and relief with respect to the surrounding 

 sediment. 



Where ripple marks show up, it is safe to assume 

 the presence of sandy materials, and of current or wave 

 motion of sufficient strength to form the ripples. A know- 

 ledge of grain size and density, along with the velocity of 

 water flow present, can be used to supplement the photo- 

 graphic data, furnishing descriptions of wave characteristics, 

 estimations of length, and determinations of symmetry and 

 steepness of ripple marks. 



The firmness of the sediment-water interface can 

 be determined indirectly from photographs. The generation 

 of turbid clouds of fine-grained material by artificial agita- 

 tion of the sea floor usually denotes a soft clay bottom. (On 

 the other hand, such turbid clouds occasionally form over 

 a hard bottom, the fine suspended material coming from 

 elsewhere. ) The presence of silt in clay hardens the 

 bottom, and the effect is intensified when sand is present. 

 Although these bottom materials are subject to movement 



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