Model for the frequency spread of backscattered underwater sound based on the facet model of the rough sea surface

Abstract

A theoretical model for the doppler spread of backscattered acoustic waves from the rough sea surface is described on the basis of the decomposition of the continuous sea-surface spectrum that leads to the concept of facets. The facet statistics are derived for a gaussian sea surface. The results are evaluated for a Pierson-Moskowitz spectrum. A procedure for choosing the facet length is developed. Approximate, simple formulas for the Pierson-Moskowitz case are given. The general result for the doppler spread of the backscattered acoustic wave is evaluated for sea-surface spectrum due to Scott, and examples for doppler spectra are given for different windspeeds, wind directions, grazing angles, and acoustic frequencies.