Tit snal ba:k< caiier is in unnaJiStic res i)t because of the limited slope angles of the 

 oaiabolic '-eels "his wil 1 be discussed .11 liter sec ions, which give detailed analyses of the 

 mechanic creJuin.] tie;* curves 1 1 gen:r.i , the f f.dominance of forward scatter over 

 Dactscatnr re. Its frcrn the waer ice r .'flection 1 oefficients. One set of plane wave reflection 

 ,ir.d trans niss t 1 coef,itien! i is shown in F ig. 5. There are siniilir sets of reflection coefficients 

 for the shear and cotr'prcssi:inal v/.iv ::s .'Tip ingii.g en the ice-'»£.ter interface. The sea ice shear 

 sound st"irci of 16(C in s from Tatk I gives a i;ntiial gia:inj. sngie of 26 degrees. Below this 

 angle, pTert reflection occu 5. for .c ..'less ired.i Abovi: ihis aigle, the reflection loss increases 

 rapid V Sirrii.ltar.efj jsly the '. arum ss on less into s.iear wavs decreases rapidly. The ice 

 tecores ven tnt*s v irent tc Ihe sot n<; Th s tanspi ren:> at high grazing angles is a major 

 cauw of tie prefceStial lorv.ard sc« ft :r of th: ra\s. 



GranrfAf.rigie d'eg) 



u 10 - 



S transmission 

 lcompfes*oi( 



2C0O 3000 4000 



R«v V (flexing Soead (m/sl 



Figura 5 'lane wave refection and transmission coefficients at 

 a wate'-ice interface for a compressional wave in th-s water 



Figure 6 shows angular scattering diagrams for three anglei for the three keel sets of 

 Fig. 3. Set A has a considerably higher roughness factor, or sigma, than sets B or C. However, 

 no distinctly different characteristics are apparent in set A. 



Figu»~ 7 gives an idea of what part of the scattered energy is contributed by reflection 

 and what pan by refraction through the keels. Figure 7 is equivalent to panel A in Fig. 6, but 

 only the reflected rays are included As can be seen, the refracted energy accounts for a 

 predominant part of 'he scattered field. This refracted energy tends to remain closer to the 

 specular direction, with the reflected energy accounting for much of the higher angle scatter. 



The specular reflection coefficient is the product of this investigation that is most 

 immediately usable in propagation loss programs. It essentially measures the energy that 

 remains coherent upon reflection from the rough surface. Figure 8 shows this reflection 

 coefficient as a function of grazing angle for the three keel sets Below a grazing angie of 6 

 degrees, the larger roughness of set A seems to produce a larger siatienr.g loss. At larger 



