Sea surface scattering using 2‐D perturbation theory

Abstract

Comparisons with exact integral equation results for 1‐D surfaces have shown that perturbation theory, when carried to fourth order in kh for the scattering cross section, gives accurate predictions at low frequencies for low‐grazing‐angle backscattering from the “classical” sea surface. Here, k is the acoustic wave number, h is the rms surface height, and the classical sea surface assumes linear gravity waves with no bubbles. it will be shown that 1‐D perturbation theory is accurate for frequencies up to 800 Hz for a Pierson‐Moskowitz surface spectrum with a wind speed of 20 m/s (39 kn). For this example, kh = 7.1. Perturbation theory has now been extended to 2‐D surfaces, in other words, to surfaces that vary in two horizontal directions. Similar accuracy for perturbation theory can be expected for 2‐D and 1‐D predictions. Examples of 2‐D results for scattering strengths will be presented. [Work supported by ONR.]