PLANE 

 PARALLEL 

 TO WAVE CREST 



SEA FLOOR 



FIELD OF 

 HIGH 

 INTENSITY 



As the sound beam is directed through internal waves in a direction parallel to their 

 crests, it is refracted both horizontally and vertically by the moving thermocline. As a 

 result, the higher intensity cones of sound tend to subscribe an ellipse on the sea floor 

 with each passing internal wave. 



TARGET TO WEST 



Typical sonar transmission recordings in three directions show short-period (less than 

 1-second) changes in sound-reflection intensity. Some larger intensity changes occur 

 within several seconds; others, related to the character of internal waves, have periods 

 of around 7 to 10 minutes and show fluctuations of as much as 30 dB. Sound rays traveling 

 parallel or nearly parallel to internal wave crests (to N) show greater variation in in- 

 tensity than do sound rays traveling at right angles to internal wave crests. 



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