Low‐frequency normal mode propagation in shallow water and its application to the acoustic inverse problem.

Abstract

Acoustic normal mode theory is useful to describe low‐frequency sound propagation in shallow water. In this talk, normal‐mode propagation effects will be reviewed, as well as acoustic inverse approaches based on modal propagation theory. The normal modes of low frequency sound in shallow water are geometrically dispersive due to the presence of surface and bottom boundaries. One can exploit this modal dispersion to solve some acoustic inverse problems, such as passive acoustic localization and geoacoustic inversion. The approaches of matched field processing and backpropagation are commonly used. In addition, the modal wavenumber spectrum contains information on seabed properties that can be used to infer the geoacoustic parameters. Underwater sound propagation is strongly affected by water‐column fluctuations, and internal waves are one of the significant effects in shallow water environment. An overview of internal wave effects on normal mode propagation will be presented here, along with their consequence on acoustic inversions.