SOUND TRANSMISSION 

 (Continued) 



Sound rays directed at other than 

 normal angles to an undulating thermo- 

 cline are refracted both horizontally and 

 vertically. 



In one series of tests a high- 

 frequency, tower-mounted transducer 

 was trained on target spheres tethered 7 

 feet above the bottom 100 feet from the 

 tower. One target was located southwest, 

 another to the west, and another to the 

 north of the tower. The amplitude of the 

 return ping as a function of time was re- 

 corded simultaneously with, and inde- 

 pendently of, the internal waves. The 

 sound record shows fluctuations in 

 transmission of up to 30 dB. An analysis 

 of the internal-wave and sound- 

 transmission spectra revealed that the 

 two are frequency- coupled at the funda- 

 mental frequency, but that the higher 

 harmonics must be considered when 

 comparing the simultaneous spectra of 

 internal waves with the sound level. 



Results also indicate that changes 

 in the relative angle between sound beams 

 are reflected in the intensity and charac- 

 ter of reflected signals. Internal-wave 

 characteristics are of the utmost im- 

 portance in the operational and experi- 

 mental use of underwater sound. 



Amplitude of a transducer's return ping as a 

 function of time is displayed on a scope and 

 recorded on 35-mm film by the sonar receiver. 

 Analysis reveals the pattern of focusing and 

 defocusing of sound rays caused by internal 



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