2. Will future systems benefit from or require such data? 



The first question should be considered from the point of view 

 of both deep and shallow water conditions. In some shallow water condi- 

 tions such as deltas where there are strong salinity changes and the 

 possibility of fresh water overlying sea water, BT data may be inadequate 

 to predict sound velocity. Here a need for reasonably accurate data 

 implies direct measurement of sound speed. It is possible that there 

 may be horizontal changes in velocity in shallow water and that ranging 

 will be in error. Nevertheless, the shape and variability of the vertical 

 profile is required to determine operating mode. In particular in tactical 

 situations a knowledge of the existence of a surface duct is the most 

 important requirement. 



In deep water, the knowledge of velocity to greater depth 

 would be of value now if it indicated the occurrence of a convergence 

 zone which current sonars could exploit. Generally we can state that the 

 accuracy required for current active sonar operation is rather in the 

 profile shape than in absolute value of the velocity. The accuracy to 

 which the profile should be known depends entirely on the sophistication 

 which is employed for shipboard prediction in tactical situations. 



The exception to this requirement for only relative accuracy 

 is in the use of the deep sound channel for passive location. 



C. Requirements for Oceanographic Survey 



There is considerable value to the Navy in surveys of large 

 areas of the oceans. The ideal from the point of view of naval operations 

 is long term mapping of velocity profiles and surface duct depths and deep 

 sound channels as regards occurrence and short-time and seasonal persistence. 



12 



Srtliur aUitttlcilnr. 



