EWING: ACOUSTIC PROPERTIES OF THE SEA FLOOR 



DR. J. S. HANNA (Office of Naval Research, AESD) : I didn't want 

 to say too much right at this point about these problems with negative 

 reflectivity because I had some comments I was expecting to give this 

 evening in my discussion which are germane to some of the shortcomings 

 or deficiencies in the transmission loss model used to reduce these 

 data. 



There are several effects one needs to worry about — the kinds 

 that were mentioned here earlier as well as the implications of third- 

 octave band processing with regard to whether you are adding these 

 arrivals coherently or incoherently. 



The particular model that was used here assumed that the four 

 arrivals added without regard to phase. This is not strictly speaking 

 true at low frequencies with third-octave processing. 



DR. S. M. FLATTE (University of California, College at Santa 

 Cruz) : I wanted to ask Ewing a question. When you are comparing two 

 paths where you try to cancel out the effect of the water column, 

 there are of necessity still two paths which go through different 

 parts of the water column. What is the typical difference in travel 

 time that would have been assumed equal that would cause your 

 scatter in points on the velocity determination? 



DR. EWING: Which are the other two paths, Stan, that you are 

 talking about? 



DR. FLATTE: The direct path goes through a different part of 

 the water than the one which has traversed the bottom layer. 



MR. EWING: It goes through a different part of the water, yes, 

 and our only assumption was that if there is no horizontal variation, 

 then we should have eliminated most of the problems with the water 

 column. The fact that we did not eliminate most of the problems led 



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