Specular Scatter of Underwater Sound From a Wind-Driven Model Sea Surface

Abstract

Underwater sound was scattered from a wind-agitated random rough model sea surface. The surface energy spectral density, the surface rms height, and the surface correlation function were measured. The mean square magnitude and probability distribution of the specularly scattered sound were measured for various angles of incidence between 35 degrees and grazing. The results are compared with the basic theories expressed by Eckart and Beckmann and shadowing corrections derived by Wagner. The frequency spectrum of the scattered sound was studied and found to contain doppler shifted components, contrary to theory which predicts no doppler shifting in the purely specular direction. A detailed analysis of the origin of this doppler shifting is presented, and it is shown that interaction between axial and off-axis radiation is the explanation of the observed frequency broadening.