DEFERRARI: FIXED-SYSTEM MEASUREMENTS OF THE TIME-VARYING MULTIPATH 

 AND DOPPLER SPREADING 



One of the things I wanted to do in the model work was to include 

 all possible scattered arrivals as well as the specular paths and to 

 look at the resulting distribution for a pulse both in time and fre- 

 quency. Figure 28 shows the modeled results for levels as a function 

 of time. The top line represents the RBR rays with their characteris- 

 tic buildup as they stay closer and closer to the bottom. Successive 

 arrivals have one additional bounce. SRBR arrivals (second line) tend 

 to spread out because they are traveling up and down and each order has 

 a significantly greater travel time. They have a little spreading-loss 

 anomaly in the beginning, and then drop in amplitude as a result of 

 the surface interactions. 



The model predicts that the Doppler- shifted energy is going to 

 come in and peak out somewhere behind the main RBR group. The first 

 SRBR doesn't have any arrivals that get there at about the same time. 

 The later ones have one or two. Then they peak out with four or five. 

 The surface bounces then start to take over. 



Figure 29 is a measurement of this process. The Doppler spectrum 

 has been measured for each successive part of the received signal for 

 a transmitted pulse. Repetitive pulses are actually used to obtain 

 these data. They come in just the way the model says at about the 

 right intensity. 



These computations gave me enough confidence in the model to 

 attempt the deep ocean case. Figure 30 corresponds to the 700-nautical- 

 mile case. The bottom line shows the refracted- refracted (RR) rays 

 coming in with various intensities. The top two lines show the RBR 

 rays and SRBR arrivals. The third and fourth lines show the up- and 

 down-Doppler scattered arrivals, respectively. Our model keeps track 

 of all these arrivals, and the Doppler spectrum is predicted to be 

 asymmetric. 



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