EWING: ACOUSTIC PROPERTIES OF THE SEA FLOOR 



us to suspect that we do have to worry quite a lot more about the 

 horiziontal changes. 



DR. FLATTE: Right. And my question is a quantitative one. 

 What horizontal difference does there have to be in order for you to 

 get the scatter you observed? 



MR. EWING: I'm not sure I can answer you without a little 

 thinking. 



DR. FLATTE: If it's a hundred meters — If it's a fifteenth of 

 a second — I'm not really sure that it is though because you have to 

 determine velocity and depth of layer at the same time. But if it is 

 a fifteenth of a second — what model could you make of the water 



column that would do that? Because internal waves can't do it I'm 



-4 

 sure, at the expected level of 10 for 6c/c. 



MR. EWING: It does not take a very big change. You see, the 

 derivative of the reflection curves gives us the angle of the ray at 

 the sea surface. If this ray has encountered very much of a perturba- 

 tion anywhere near the surface it works on an awful long lever to 

 change the angle of incidence on the bottom, and the angle of inci- 

 dence on the bottom in our kind of analysis is very critical. A 

 rather small angle change near the surface makes a big change in 

 AX versus AT in the bottom layer. 



DR. FLATTE: Might it be milliseconds' difference in travel time 

 that could be the effect? 



MR. EWING: It's more the effect of changing the direction of 

 the ray, of course, than it is of anything else. 



DR. FLATTE: Yes, but your experimental data are just travel time, 



MR. EWING: Yes. 



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