Acoustic propagation through a model of shallow fronts in the deep ocean

Abstract

The effects of sound-speed variations produced by shallow (less than 300 m) deep-ocean fronts on short-range acoustic transmission between surfaced sound source and receiver are investigated using ray theory. A parametric model of such fronts, based on observational data, is constructed via sound-speed profiles which are trilinear with depth. The model is sufficiently general to permit determination of acoustical effects for fronts of varying strengths, vertical extents, and positions within the propagation range. Frontal influences on travel time and geometrical spreading loss are examined, and expressions for per-ray amplitude and phase are developed for cw transmissions with source and receiver near the surface. Then, the dependence of total-field amplitude and phase on frontal strength, vertical extent, and relative location are determined. All these frontal quantities are demonstrated to produce significant acoustical variations, such as total-field transmission-loss changes of more than 6 dB depending on frontal location. Simple and accurate approximations to both per-ray and total-field variations are presented which could predict changes in these quantities due to shallow fronts.