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PROBLEM 



Specify and procure a portable, general -purpose, 

 underwater-sound measuring system, primarily, but not 

 exclusively, for the investigation of ambient noise in the 

 ocean. 



RESULTS 



1. A portable underwater sound-pressure measuring 

 system has been developed, and in a variety of situations 

 has demonstrated the capability of measuring very low 

 ambient -noise levels. 



2. High self-noise levels at frequencies less than 50 to 

 63 Hz are quite likely to be present if measurements are 

 made from a drifting" ship and the cable is towed at the drift 

 velocity. These high self-noise levels are believed to be 

 due to a combination of flow noise and noise arising from 

 cable vibrations. 



3. These high self-noise levels can be satisfactorily 

 eliminated by using a slack cable system as described in 

 this report. 



RECOMMENDATIONS 



1. Use a slack cable system if a tethered system is 

 used; and use an all -buoyant in preference to a nonbuoyant 

 cable for a simple system to be used for measurements from 

 a ship on the open ocean. 



