SOUND TRANSMISSION 



The transmission of sound through 

 the water is greatly affected by internal 

 waves. This is especially true of high- 

 frequency sound. The greatest influence 

 is refraction by the vertical (and horizon- 

 tal) sound-velocity gradients. These, in 

 turn, depend on the strength of the 

 thermocline and the angle at which the 

 sound rays intersect it. 



Sound rays directed normal to an 

 undulating thermocline intersect it at 

 different angles. The refraction and 

 sound-focusing effects can be calculated 

 by applying Snell's Law. This was done, sec" 



using a Univac computer. The calcula- 20-foot layer of -0.6 ft sec - -'- ft - -*- . 



tions were based on a common transducer The internal wave had a normal amplitude 

 pattern and the normal velocity structure of ~9 feet and a wave length of 300 feet, 



observed at the tower during summer. The focusing effects computed by the 



This structure is a mixed layer for the Univac were later verified experimentally 



upper 30 feet: a thermocline of -4. 8 ft at the tower. 



"1 ft - * for 10 feet; and a deeper 



One and two-way sound transmission studies are 

 conducted with a 175-kc/s sonar transducer mounted 

 on the west track at varying depths below the sur- 

 face. The orientation and depth of the transducer are 

 maintained by the rigid tracks. Signals are trans- 

 mitted through internal waves to hydrophones and 

 acoustic targets consisting of 1 -foot-diameter alumi- 

 num spheres, buoyed 7 feet from the sea floor. 

 Hemispheres are also used as targets. They are 

 built with windows ■ which produce stronger and more 

 distinct echoes than the complete spheres. 



TARGET 



TARGET SPHERE 



HEMISPHERE 



-7 



