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SUMMARY 

 OBJECTIVE 



Determine the high-frequency acoustic scattering cliaracteristics of a random set of ice 

 keels. 



APPROACH 



Parabolic sections were used to represent ; ce keels that are random in size and spacing. 

 A large number of rays were computed to model the interaction of a plane wave with the 

 random sec 



RESULTS 



The principal results of this work are diagrams of scattering strength versus angle as 

 functions of incident angle. Reflection lo«_s data in the specular direction are also given. 



CONCLUSIONS 



1. Plane wave reflection coefficients strongly control the scattering action of the set 

 of keels. 



2 At grazing angles below 20 degrees, transmission through the keels as shear waves 

 is the dominant energy path. 



3. Specular reflection is determined predominantly by the extent of unshadowed 

 surface. 



4. The parabolic-shaped keels underestimate backscatter from the keels. 



RECOMMENDATIONS 



1. Determine and paramaterize the shapes and internal structure of real keels, and if 

 substantial variation is observed, determine probability distributions for these 

 parameters. 



2. Use compound figures to model realistic keel shapes and their acoustic properties. 



3. Include internal structure and attenuation in models. 



4. Seek experimental verification for acoustic results reported here. 



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