Three-dimensional acoustic propagation effect in subaqueous sand dune field

Abstract

Very large subaqueous sand dunes are discovered on the upper continental slope of the northern South China Sea in water depth of 160–600 m, which composed of fine to medium sand. The amplitude and the crest-to-crest wavelength of sand dunes are about 5–15 m and 200–400 m, respectively. This topographic feature could causes strong acoustic scattering, mode coupling, and out-of- plane propagation effects, which consequently result in sound energy redistribution within ocean waveguide. This research focus on the three-dimensional propagation effects (e.g., horizontal refraction) induced by the sand dunes in the South China Sea, which are expected as the angle of propagation relative to the bedform crests decreases. The three-dimensional propagation effects are studied by numerical modeling and model-data comparison. For numerical modeling, the in-situ topographic data of subaqueous sand dune and sound speed profiles were inputted to calculate the acoustic fields, which were further decomposed into mode fields to show the modal horizontal refraction effects. The modeling results were manifested by data observations. [This work is sponsored by the Ministry of Science and Technology of Taiwan.]