work. The present solid multilayer program models the variable sediment properties with 

 many layers (up to 1000 layers or more, if necessary) and maintains the accuracy needed 

 for efficient computer calculation. Important physical parameters used in the model are 

 the speed and attenuation of both the compressional and shear waves that travel in the 

 sediment. The many constant layers are used to approximate the results of a linear 

 gradient concept. 



The solid multilayer model should be satisfactory as the coupling mechanism 

 between the sediment parameters and the calculations of the acoustic field. The model 

 includes all physical factors except for roughness which usually is not important at low 

 frequencies. This model, based on wave theory, is interfaced very easily with most sound 

 propagation normal mode programs. 



In addition, a so-called equivalent bottom concept has been developed for the 

 Parabohc Equation propagation program. This technique should enable the P.E. program 

 to be used for bottom limited areas. 



The geoacoustic model discussed in Part I, which presents sediment properties, is 

 an essential input to the bottom loss model. We recommend that when geoacoustic in- 

 formation is available, the principal method of analyzing bottom interaction and making 

 predictions should be through the sediment models. The predictions should be supple- 

 mented when possible by careful direct measurements of bottom loss. 



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