DIRECT MEASUREMENT OF BOTTOM SLOPE 



SEDIMENT SOUND VELOCITY AND ATTENUATION 



AND SEDIMENT SHEAR STRENGTH FROM 



DEEPSTAR 4000 



Edwin C. Buffington, 



Edwin L, Hamilton, 



David G. Moore 



U. S. Navy Electronics Laboratory- 

 San Diego, California 



GENERAL 



Among the capabilities of deep submersibles which are especially- 

 useful, but poorly known, are those permitting types of measurements 

 which set up, or complement, remote data customarily taken from sur- 

 face ships. So much emphasis in the employment of submersibles has 

 been toward those things which the submersible can do uniquely that 

 frequently overlooked or, at least underpublicized, are those contri- 

 butions which upgrade, calibrate, or give added significance to those 

 data taken by wire-lowered or acoustic sensors. It is the purpose of 

 this paper to briefly describe and discuss the significance of three 

 such types of measurements which have been made with a high degree 

 of success from the DEEPSTAR 4000. 



DIRECT MEASUREMENT OF BOTTOM SLOPE 



The sources of error inherent in echo sounding have been identi- 

 fied almost from the beginning, but their correction has not always 

 been a simple matter. The two principal causes are the speed of sound 

 in water, and the shape or character of the sound cone produced by the 

 echo-sounder transducer. While the first cause applies at all times, 

 and is particularly significant in deep water, whether over a flat or 

 rugged bottom, the second applies only on slopes. And the steeper the 

 slope and the shallower the water, the more complicated and sizable 

 the error. Only the second cause will be discussed in this paper. 



The determination of a true slope may be approached by utiliz- 

 ing narrow-beam echo sounders, by taking lead line soundings, or by 

 attempting a correction of the errors inherent in a slope measured 

 with a wide-beam echo sounder. To date, the determination of these 

 errors has been attacked by assuming given, apical angles for the 



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