EWING: ACOUSTIC PROPERTIES OF THE SEA FLOOR 



DR. WEINBERG: I found that the grazing angle can be 10 degrees. 

 For example, if you go to the extreme case, the ray that grazes the 

 ocean bottom has an infinite propagation loss, and that would tell 

 you that you had a negative infinity bottom loss. 



DR. M. SCHULKIN (Naval Oceanographic Office) : If you 

 consider the bottom in terms of velocity gradient and absorption, 

 that is, consider it was an extension of the water medium, you do get 

 convergence zone type propagation from very steep velocity gradients. 

 It is possible to get an effect of negative bottom loss in the first 

 bottom bounce region. Of course, beyond that it goes off as 3 dB per 

 distance doubled as far as the loss goes. So that you only get this 

 apparent gain in that first zone. But the rays penetrate the bottom 

 and you just carry the ray tracing procedure through with the 

 correction for the convergence effects. 



DR. WEINBERG: That is a possible explanation, but there is 

 another one. If you just take the velocity gradient in deep water 

 and you have a positive velocity gradient going down, instead of 

 using plane waves use Airy function solutions and you may do away 

 with the negative bottom loss. 



MR. VJ. H. GEDDES (Naval Oceanographic Office) : There are a 

 number of alternative explanations. I wouldn't want to hold out for 

 the ray trace solution without saying that the negative loss is a 

 flag indicating that the model (used in this way) is going to produce 

 some strange answers. What I really want to hold out for is an 

 appreciable amount of energy being refracted through the bottom and 

 that it may not be a reflection arrival at all. I don't hold for 

 the negative losses is what I'm saying. 



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