ANDERSON: BOTTOM PROPERTIES FOR LONG-RANGE PROPAGATION PREDICTION 



entirely differently than scattering at angles of incidence much less 

 than the root mean square slope. One region is specular and in 

 another case it is backscattering . Are there similar kinds of con- 

 siderations for sea-floor scattering? 



Dr. M. Schulkin (Naval Oceanographic Office) : Not quite, but 



there is a spectrum of the sea floor bottom that has been proposed — 



-3 

 K . 



Dr. Munk: Is that taken seriously? 



Dr. Schulkin: Well, until there is something to replace it, 

 it is semi-serious. 



Dr. Munk: It goes down to what short wave length? Two hundred 

 meters? 



Dr. Schulkin: Yes. 



Dr. Donald Ross (Tetra Tech, Inc.) : May I make a comment on 

 some model work? We are closely associated with the work that is go- 

 ing on at Naval Undersea Center in which a computer model for propa- 

 gation, FACT model and FACT extended, is being compared with hundreds 

 of experimental measurements in the low-frequency regions and we are 

 finding that the models do well in the region in which you have 

 refracted rays and that they are extremely sensitive to bottom loss 

 in the region in which the bottom is involved, that the bottom loss 

 is apparently averaging of the order of 1 dB, and that a quarter of 

 a dB difference in the loss per bottom bounce makes a significant 

 difference in the results that you get when you are comparing the 

 experiment and the propagation model. 



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