Angle spreads of broadband high‐frequency signals reflecting from a random surface

Abstract

A simple geometric‐acoustic model (appropriate for high frequencies) has recently been used to compute time and frequency spreading of a broadband acoustic signal reflecting from an ocean bottom [M. H. Brill, X. Zabal, and S. L. Adams, J. Acoust. Soc. Am. Suppl. 1 73, S11 (1983); also 74, S76 (1983)]. In that model, the expected power received from a bottom facet dxdy at (x,y,0) is computed as a function of the x and y coordinates of the reflecting point on the bottom. A ray arriving from any reflecting point has a well‐defined travel time, relative frequency shift (for a given source and receiver motion), polar arrival angle, and azimuthal arrival angle. In the present work, the received power from a grid of facets is histogrammed in the two arrival angles. The resulting histogram, called the angle‐spread function, is a measure of the spatial coherence of the reflected signal. Computed angle‐spread functions will be presented for various source/receiver geometries, and implications for sonar signal processing will be discussed.