VERTICAL NOISE DISTRIBUTION 



V. C. Anderson 



Scripps Institute of Oceanography 

 University of California 

 La .Tolla, California 



A recent experience in attempting to measure the vertical 

 directionality of noise is recounted with the emphasis on 

 several instrumentation pitfalls. Specific problem areas 

 included angular sampling, frequency filtering, data 

 quantization, and common-mode noise. The last problem 

 was the most severe, making data interpretation quite dif- 

 ficult. The filtering problems limited the estimate of 

 noise level to only the high noise directions. Neverthe- 

 less, an estimate of the noise directionality at low fre- 

 quencies was obtained as a function of receiver depth for 

 a deep-water site in the Northeastern Pacific. The results 

 are consistent with energy arriving via sound-channel paths 

 from distant shipping. 



INTRODUCTION 



This paper addresses primarily the problems associated with a 

 recent attempt to measure vertical noise directionality, and 

 secondarily the results of that measurement attempt. The measure- 

 ments were made using FLIP in the Northeastern Pacific. Figure 1 

 illustrates the sound-speed profile at FLIP'S location, and the 

 positions of the 500-meter, 20-element measurement array. These 

 positions were occupied twice, in the time sequences indicated in 

 Figures 2 and 3. Additional noise "events" such as nearby ships and 

 biologies are indicated as well. Note that the array positions span 

 depths from the sound-channel axis to 500 meters below the critical 

 depth of 4380 meters. The C and E designators identify actual data 

 sets analyzed. 



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