Further considerations for approximating a physics-Based model of surface reflection loss

Abstract

Previously, the authors prepared a model of the coherent acoustic reflection loss at the ocean surface by combining an existing model of roughness loss with a description of surface grazing angle which accounted for the near-surface sound speed reductions due to an assumed distribution of wind-driven bubbles. More recently, the authors showed that the full derivation of surface incidence angle, which was based on an analysis by Brekhovskikh, could be approximated by a simple expression in terms of the physical parameters of the assumed model of bubble population, together with wind speed and frequency. In an extension to this work, the practical limits to the application of this approximated solution are examined, in terms of the wind speed-frequency combinations, and the range of grazing angles, for which it is adequate. The adequacy of the approximated model is tested by incorporating it within a Gaussian-beam acoustic propagation code and generating loss values for surface ducted transmission scenarios, to compare against data obtained by Monte Carloruns of Parabolic Equation (PE) transmission calculations for which the sea surface is roughened and the near-surface sound speed reductions from the bubble distribution are included.