SURVEYING THE OCEANS (OCEANOGRAPHIC) 



GEOLOGICAL FORMATIONS 



The shape and character of the sea bed affect the conduct of 

 naval operations in many ways. The performance of long range 

 sonars is degraded if bottom reflected echoes are absorbed in 

 sediments at great depths. The risk to minesweepers detonating 

 enemy magnetic mines in shallow water increases and the efficiency 

 of sweeping decreases where the electrical resistivity of the bottom 

 forces the magnetic sweeps to be brought closer to the mines. 

 Mine-laying activities must take into account the likelihood of 

 mines sinking into the bottom or being covered by shifting sedi- 

 ments. Emplacement of cables and equipment on the ocean floor 

 requires knowledge of bottom topography and of sediment bearing 

 strength. Finally, search and rescue operations for submarines 

 or other lost objects are affected profoundly by the kinds of 

 bottom features in the search area and by the tendency of 

 sediments to cloud bottom waters when disturbed, or to bury 

 objects and resist their extraction. Observations of properties 

 of the sea floor determining these operational conditions are 

 included in the survey programs of the Oceanographic Office. 



Surveys to support mine warfare operations are carried out in 

 bays and estuaries, extending outward from the coast to depths 

 of some thirty fathoms. Working either from survey ships or 

 from Fleet mine craft, the oceanographers collect sample cores 

 of the bottom and make laboratory analyses of them to deduce 

 sediment strength and stability. Suitability of the ocean floor 

 for sweeping magnetic mines is determined by measuring electrical 

 current flow between towed conductors. 



Features that are further offshore, those of the continental 

 slopes and the offlying plains, are increasingly difficult to survey 

 as depths increase. The slopes are now understood to be regions 

 where rugged topography may be the rule rather than the excep- 

 tion, but means of mapping details of their hills and canyons fifty 

 or even a hundred feet across are not yet operational. To provide 

 increased readiness for search and salvage operations, and to 



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