Surface wave effects on bottom geoacoustic inversions

Abstract

Underwater sound propagation in the ocean can suffer from the scattering, focusing and defocusing effects caused by surface gravity waves. These effects can in fact also influence bottom geoacoustic inversions, which use sound pressure field measurements in the water column to estimate/infer acoustic properties of the seafloor and/or seabed. In our study presented in the paper, analytical, numerical and experimental approaches are taken to investigate how surface gravity waves can affect bottom geoacoustic inversions (the dependencies on acoustic frequency, surface wave spectrum and directivity, and acoustic waveguide parameters.) The analytical approach is based on acoustic mode theory, and the numerical approach is utilizing both the parabolic-equation (PE) model and the ray model. Experimental data were collected from the Seabed Characterization 2017 experiment conducted on the New England shelf in March and April, 2017. During the experiment, several storms passed through the experimental area, and broadband sound transmissions (500 to 1000 Hz) from fixed sources to fixed receivers have shown significant acoustic effects of surface wind waves. These sound transmissions were at 160 dB source level and had two scheduling window types, one with rapidly repeated sampling and one with less-frequent sampling for a long duration. [Work supported by the Office of Naval Research.]