CAVANAGH: AMBIENT-NOISE MODELS 



DISCUSSION 



DR. S. W. MARSHALL (Naval Research Laboratory): Ray, I'd like 

 to take issue with you on the question of ambient noise modeling and 

 what is really required. You said that you felt that it was adequate 

 to range -average the transmission loss, and certainly we would all 

 like to have the shipping data in smaller geographical bins than we 

 now have available, whether the numbers are real or perhaps imaginary. 



I think what is really required — and I derive this not from my 

 own opinion but from the people I talk to who use the results we have 

 gotten — is the statistics of the noise. And if you really want the 

 statistics of the noise, then you have to retain not only the structure 

 of the transmission losj but also — and this is my opinion — I think 

 that you need to do some type of statistical calculation to establish 

 what a reasonable distribution would be and that a single calculation 

 is not sufficient to do this. 



DR. R. C. CAVANAGH: I didn't want to give the impression that we 

 are not interested in the other characteristics of ambient noise aside 

 from an average over days or months . 



From a practical point of view in doing production modeling, it 

 is very expensive, as you know, to execute detailed transmission 

 models on 72 or 180 bearings. So, since we typically do have average 

 shipping density inputs, it is practical to use an average transmission. 



Good treatments for doing statistics are available. And, of 

 course, we can take realizations of shipping locations and do some 

 statistics on that in selected cases. But for the general practical, 

 production predictions, I think we have to stick to some average 

 transmission for the moment. 



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