Effect of random sea surface and bottom roughness on propagation in shallow water

Abstract

The potential difficulties associated with modeling acoustic propagation in shallow-water environments are well documented. Larger scale deterministic features combine with random fluctuations in the water column, sediment, sea surface, and water–sediment interface to produce an extremely complicated propagation regime. The extent to which each of these factors needs to be included in realistic propagation modeling remains to be quantified. Toward this end, results from a series of detailed simulations generated using the parabolic equation method are presented. Beginning with a deterministic downward refracting sound-speed profile and a known sloping bottom, realizations of the random features are sequentially added to the simulation. Wind-driven surface gravity waves and power-law bottom roughness are considered. The individual and cumulative effects of these scattering mechanisms on the acoustic wavefront are quantified. Successive interactions with the random interfaces are studied. A modal decomposition reveals evidence of significant mode coupling. Temporal fluctuations in the acoustic wave are related to the time evolution of the sea surface.