I. THE MEASUREMENT OF SOUND SPEED IN THE OCEAN : 

 REQUIREMENTS FOR THE NAVY 



A. Introduction 



Knowledge of the local sound velocity field in the ocean is 

 one of the limiting factors in naval operations. Generally, this know- 

 ledge involves the surface velocity (v) and the variation of the velocity 



with depth (t~) • Various factors such as required accuracy, available 

 dz 



time, convenience, and system cost can dictate the choice of measuring 

 instruments used. All systems measure sound speed rather than the vector 

 velocity. 



The speed of sound in sea water is affected by the temperature, 

 the salinity, and the pressure (which depends on the depth) and increases 

 with increase of any of these factors. The composite effect can be well 

 represented by the empirical equation. 



v = 1449 + 4.6t - 0.055t 2 + (139 - 0.012t)(s - 35) + 0.017d (1) 



where 



v is the velocity in meters per second 



t is the water temperature in °C 



s is the salinity expressed in parts per thousand 



d is the depth below the surface in meters 

 This equation is a simplification of more complicated equations obtained 

 by Wilson (Reference 1) and others as a "best fit" to experimentally 

 measured data. Equation (1) is accurate to about one meter per second 

 for those conditions commonly occurring in the various oceans. The 



Arthur ZB.lUttlcIlitr. 



