EWING: ACOUSTIC PROPERTIES OF THE SEA FLOOR 



DISCUSSION 



DR. W. H. MUNK (Institute of Geophysics and Planetary Physics, 

 University of California at San Diego) : Is the scatter on Figure 1 

 oceanographic or geological? Also, are there any measurements on 

 land in sediments that could give a clue as to whether the order of 

 scattering there is consistent or not with geologic inhomogeneities? 



MR. EWING: We have some data that really made me suspect most 

 strongly that it was the water column that was causing this. For 

 example, in the Hatteras abyssal plain which our seismic data indi- 

 cates to be a nicely layered section of sediment, the individual 

 reflectors can be followed for hundreds of miles. The bottom seems 

 to be just a beautiful cake of sediment. The data scatter represents 

 a standard deviation of a hundred meters per second. 



We can move up onto the continental shelf where from a geologi- 

 cal point of view I would expect a bigger variation in geology, and 

 there we get maybe half of that standard deviation. I think that is 

 because we removed a lot of the water problem by going to shallow 

 water. 



DR. H. WEINBERG (New London Laboratory, Naval Underwater Systems 

 Center) : It seems to me that you are using ray theory at low fre- 

 quencies and shallow grazing angles, and we have seen that this is 

 one case when ray theory can really get you into a lot of trouble. 

 Have you every tried to incorporate a better theory than regular ray 

 theory; what would happen if you treated the propagation loss 

 directly? 



MR. EWING: We are concentrating primarily at the moment on 

 developing the best model we can for velocity gradient. Working at 

 appropriate incidence angles keeps you away from ray theory problems. 



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