THE PROBLEM 



Investigate the probability density distribution of the ampli- 

 tude of ocean ambient noise and ship noise; determine any 

 differences in the distributions which might lead to the 

 identification of ship noise masked by a high background- 

 noise level. Also, determine, by standard statistical 

 methods, whether the distributions are gaussian or non- 

 gaussian. 



RESULTS 



1. Ambient ocean noise was found to have a gaussian 

 distribution of amplitudes (in the sense that the moments of 

 the distribution satisfied specific tests) only when the am- 

 bient noise was relatively clean, i.e., the noise did not 

 contain high-level ship noise, biological noise, ice noise or 

 any of the other extraneous noises discussed in the text. 



2. The group of ship-noise samples recorded at 

 close range contained a large number of samples that had a 

 non-gaussian distribution. However the other types of ex- 

 traneous noises were found to cause the same kind of de- 

 viation from a gaussian distribution, so that it was not 

 possible by these tests to distinguish between a sample 

 with ship noise and a sample with the other types of ex- 

 traneous noises (such as biological and ice noise). 



MBL/WHOI 



D 03D1 00M0503 1 



