| Popis: |
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. |
