16 



WAVE ACOUSTICS 



5«^ 



UJ 



z*" 8 



UJ 



o: UJ . 

 O UJ O 

 oiz 



100 200 300 400 500 

 DEPTH IN FEET 



32 33 34 35 36 37 



SALINITY IN PARTS PER THOUSAND 



FiGUKE 4. Speed of sound in sea water. 



10 20 30 



SALINITV IN PARTS PER THOUSAND 

 EFFECT OF SALINITY 



u 1.005 



500 1000 1900 



DEPTH OF SEA IN FEET 

 EFFECT OF DEPTH 



Figure 5. Percentage variation of sound velocity with 

 water temperature, salinity, and depth. A. Effect of 

 temperature. B. Effect of salinity. C. Effect of depth. 



simple formula. However, tables have been con- 

 structed which show the velocity of sound as a func- 

 tion of three variables which can be measured di- 

 rectly: the water temperature, pressure, and salin- 

 ity. Although the relationship is not simple, these 

 three variables determine precisely both the bulk 

 modulus and the density, from which the sound 

 velocity can be calculated from equation (26). 



At 32 F, atmospheric pressure, and normal salinity 

 (34 parts per thousand by weight), the velocity of 

 sound in sea water is about 4,740 ft per sec. Increase 

 of either temperature, pressure, or salinity causes the 

 sound velocity to increase. The increase of sound 

 velocity with temperature is about 8.5 ft per sec per 

 degree F at 32 F, and about 4.0 ft per sec per degree F 

 at 90 F. The increase of sound velocity with water 

 depth, caused by the increase in pressure, is 1.82 ft 

 per sec per 100 ft of depth. In the open ocean for the 

 depths of interest in sonar operations the water 

 temperature is the controlling factor in determining 

 the velocity; since sonar gear is usually operated at 



