DEFERRARI: FIXED-SYSTEM MEASUREMENTS OF TIME-VARYING MULTIPATH 

 AND DOPPLER SPREADING 



different paths so we may be looking at, say, a twentieth convergence 

 zone sliding back and forth relative to the receiver. There are also 

 significant variations ■<20-dB or so) on the order of a day which have 

 been omitted for the time being from the study. I don't think they are 

 multipath either. 



Figure 15 shows the Bermuda phase record again. The phase has 

 long-term trends in it as well as the tidal component. I have chosen 

 to differentiate this record to look at the rate of change of phase as 

 another variable for comparison. Figure 16 shows these results. Long- 

 term trends have very slow rates of change so they don't contribute 

 very much. One thing that stands out is the large tidal component for 

 both the Eleuthera and the Bermuda ranges. They have about the same 

 average rate of change of phase 9, and they have about three or four 

 cycles of change per tidal period. This appears to be a good place to 

 start on some model comparisons. 



The first thing that we do with the bilinear profile (shown at 

 the top of Figure 17) is to take a perturbation which is constant 



with range but varied in time. That is, let the whole profile rise and 

 fall like the first-mode internal tide. The next thing is to adjust 

 the amplitude of the fluctuation so that it gives the right amount of 

 phase shift. However, when we do that, we don't get enough interference. 

 The fades don't come as frequently as they do in the experiment. In 

 fact, there doesn't seem to be any way that you can adjust this profile 

 in this manner to get anything else but the kind of variations shown. 

 The fluctuations that yield large shifts in phase don't give enough 

 amplitude interference, and they decorrelate in about a half hour in- 

 stead of the four minutes typical of the experiment. This also seems 

 to be true for fluctuations which have a scale larger than the cycle dis- 

 tances of the SOFAR rays. We have tried using an internal tide starting 



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