LABIANCA/HARPER: A THEORETICAL APPROACH TO THE PREDICTION OF SIGNAL 

 FLUCTUATIONS DUE TO ROUGH-SURFACE SCATTERING 



Figure 20 is a transmission loss plot for g = 0° displaying the 

 total power distribution for a smooth (deep nulls) surface and a 

 random (smooth plot) surface. The source and receiver are located at 

 50 m and 1,000 m, respectively. The redistribution of energy is 

 readily apparent. Figure 21 shows the corrected carrier against the 

 smoothed surface. Of course, the carrier nulls are deeper than for 

 the total transmission loss. Note the two numbers, R = 2,000 m 

 and R = 3,200 m, at which a peak and a null occur because a later 

 figure displays the sideband system function and the acoustic fre- 

 quency spectrum at those points for purposes of comparison. 



Figure 22 shows the spectral breakdown into carrier and side- 

 bands. The sidebands are seen to start out together at short range 

 with the down Doppler- shifted one (IM) falling off more readily at 

 long range. 



The asymmetry in the sidebands is even more readily apparent 

 in plots of the sideband system function as a function of surface 

 frequency. Figure 23 displays this function (QIP and QIM on the 

 plots) at the range 2,000 m, a peak in the transmission loss. For 

 a Pierson-Moskowitz spectrum giving rise to an rms waveheight of 

 2.48 m, as displayed in Figure 24, the acoustic spectrum, normalized 

 to the carrier, appears as in Figure 25. The asymmetry in the side- 

 bands and the fact that the receiver point is at a peak in the 

 surface-image interference is readily apparent. For the same surface 

 spectrum, the system function and the acoustic spectrum at a null in 

 the surface-image interference (R = 3,200 m) are displayed, respec- 

 tively, in Figures 26 and 27. In this last figure, the dominance 

 of the sidebands is apparent. 



The next five figures display the various curves showing the 

 3 = 90° plane of symmetry. Figure 28 shows the spectral breakdown. 



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