Scintillation index of the acoustic field forward scattered by a rough surface for two- and three-dimensional scattering geometries

Abstract

Scintillation indices of acoustic waves forward scattered by a rough surface are obtained from numerical techniques leading to both accurate and approximate results in two-dimensional (2-D) and three-dimensional (3-D) geometries. The Kirchhoff approximation with a Gaussian spectrum and an empirical model for ocean surface height fluctuations is used. It is found that in the case of a Gaussian spectrum, the 3-D accurate values obtained are lower than the 2-D ones when the focusing–defocusing phenomenon does not occur. However when this phenomenon occurs, the 3-D results become higher than the 2-D ones. In the case of the empirical spectrum, both 2-D and 3-D accurate scintillation indices decrease with the wind speed on the ocean surface. The 2-D model predicts larger values than the 3-D model. When an ensonification factor or finite incident beam size is introduced, the scattering moves from the saturation limit into the focusing–defocusing range.