CAVANAGH: AMBIENT-NOISE MODELS 



DR. DONALD ROSS (Tetra Tech, Inc.) : Adding to that, I think we 

 have to recognize that there is a dominant tonal structure in ship 

 noise below about 60 Hz, and this means that even if I know exactly 

 where the ship is and what its name is, it doesn't tell me the spectrum 

 within 5, 10, 15 dB. So what is the use in knowing what the ship is? 



DR. MARSHALL: I was not suggesting that knowing where the ship 

 was all that important, really. But it would be nice to have more 

 confidence in the numbers than we now do. 



DR. ROSS: There is no way of getting this. Because the ships 

 do not follow the same tracks from one voyage to another. The weather, 

 for example, plays a major role in ship traffic across the ocean. 



816 



