EWING: ACOUSTIC PROPERTIES OF THE SEA FLOOR 



If I understood you properly, I believe the records showed a 

 pass band from 20 to 40 Hertz or something of that sort. It would 

 seem to me that, just very crudely speaking, the time resolution 

 implied by that pass band might be of the order of tens of milli- 

 seconds. I wonder what possible influence that resolution might have 

 on the scatter of the data that you plotted here. Using your value 

 of 2 for K, this resolution would translate into something like 50 

 or 100 meters per second scatter. 



MR. EWING: I guess the answer comes in two parts. How 

 accurately can we time an arrival? The question I guess then is 

 what does that arrival really mean particularly if you are in a 

 region where you are having an interference of two low frequency 

 signals? I completely agree that this is a possible source of our 

 problem. 



The kind of data we are normally using, a reflection arrival 

 for instance, we usually just pick on the basis of like phase but 

 not precisely like phase. I mean whether it's positive or negative. 

 In very low frequency situations, of course, that gives potentially 

 a rise of big timing errors. I'm aware of that. 



We are trying to stay with arrivals that are separated enough 

 in time. I guess another part of my sidestepping your direct question 

 is the answer I gave to Walter Munk. We do the same thing when we 

 work with the sediments on the continental shelf. We treat that 

 data in exactly the same way. Yet we get a much smaller distribution, 

 much tighter distribution. 



In other words, if we go to a rather localized area and shoot a 

 dozen sonobuoys in this fashion and plot them up this way with diff- 

 erent filter settings, we can pick different levels in the sediment 

 usually because some level will be reflective for one frequency, 

 another level will be more reflective for another frequency. 



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