EWING: ACOUSTIC PROPERTIES OF THE SEA FLOOR 



DR. FLATTE: And so the question is whether it is difference in 

 travel time you might have observed. 



MR. EWING: I would need to do a little arithmetic before I 

 could answer you for sure. I don't know what the scale is. 



MR. R. L. MARTIN (New London Laboratory, Naval Underwater 

 Systems Center) : Santanello and Berstein at NUSC have also done 

 several measurements of bottom loss, and they have observed this 

 negative bottom loss below 10 degrees grazing. They approach the 

 analysis quite differently. They took the broadband signal and 

 isolated the direct and the first bottom-reflected pulse, and then 

 ran the filtering after that; rather than taking the propagation 

 model over the entire path, they just took the differences in the 

 propagation over the path increment differences of the direct and 

 bottom-reflected arrivals. 



I would guess that this illuminates two questions that arise 

 in processing these data and coming up with negative bottom loss. 

 One is sensitivity of it to the particular propagation model used, 

 and the other is the coherent effect through narrowband filters. So 

 negative bottom loss has been observed using different analysis 

 methods . 



DR. A. 0. SYKES (Office of Naval Research) : Does sedi- 

 mentary ooze act more like a fluid or like a solid? 



MR. EWING: More like a fluid. 



DR. HANNA: Referring to the comment that was just made here by 

 Bob Martin, if you are taking the difference in transmission loss 

 along those two paths it still presumes that your model for trans- 

 mission loss in the water is sufficiently good to get both of those 

 right. If the path interacts with either boundary, there are still 

 the influences of caustic shadows on the field and things of that 



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