Experimental verification of the theory for sound propagation in a wedge with a shear supporting bottom

Abstract

Laboratory experiments have been carried out to investigate underwater sound propagation over a sloping bottom that can support shear. The sound field was measured in both the across slope and down slope direction for many different frequencies and bottom slopes. The experimental results have been compared with the source image theory for sound propagation in a penetrable wedge [G. B. Deane, J. Acoust. Soc. Am. 91, 2390 (A) (1992)] and have shown very good agreement for both down slope and across slope propagation. In particular the effect of shear waves on across slope propagation has been demonstrated both theoretically and experimentally. Further the effect of a sediment layer has been successfully incorporated into the source image theory for comparison with the experimental measurements at low frequencies. One of the problems with laboratory scale measurements of underwater sound propagation is the determination of the bottom parameters with sufficient accuracy for acoustic calculations. In this case the model of the sea floor consisted of a sediment layer (modeled experimentally by epoxy) over a hard basement made of concrete requiring 11 variables to describe the geo-acoustic features of the bottom. These were obtained by inverting measurements of the acoustic field in water of constant depth over the same model. The results are therefore geo-acoustically calibrated. [Work supported by ONR.]