SUMMARY 



Data on the speed of sound in the sea is a prime requirement 

 in Navy operations. Only relative accuracy in the measurements of sound 

 speed as a function of depth is needed in tactical situations because it 

 is the shape of the velocity profile that is of major importance to hull 

 mounted sonar. Absolute accuracy in the measurement of sound speed is 

 desirable, however, in order to exploit longer range propagation in the 

 deep sound channel. 



The sound speed can be measured either indirectly, by computation 

 from temperature and salinity or density data, or directly, by using 

 "velocimeters". In tactical situations, temperature data alone has sufficed 

 for the indirect method except under certain near shore conditions, where 

 skilled guesswork has been required. 



Present velocimeters based on the "sing-around" principle are 

 adequate for oceanographic survey purposes, from the points of view of 

 accuracy and depth capability. However, their connecting cables render 

 them unsuitable for tactical use; in general, the manufacturers of 

 velocimeters are aware of and have been attempting solutions to the problems 

 that arise from this application. 



The value of temperature data alone for defining the presence 

 of a surface duct in shallow water where sharp salinity changes can occur 

 should be studied. We believe that there exists a case for the develop- 

 ment of an expendable instrument or of a synoptic technique for tactical 

 use to supplement the now successful expendable bathythermograph. 



Arthur ZH.3UttIc.3nr. 



