The Determination of Geoacoustic Models in Shallow Water

Abstract

A technique for determining geoacoustic models in shallow water is described. For a horizontally stratified ocean and bottom, the method consists of measuring the magnitude and phase versus range of the pressure field due to a CW point source and numerically Hankel transforming these data to obtain the depth-dependent Green’s function versus horizontal wavenumber. In shallow water, the Green’s function contains prominent peaks at horizontal wavenumbers corresponding to the eigenvalues for any trapped and virtual modes excited in the waveguide. A geoacoustic model for the bottom is obtained by computing the theoretical Green’s function for various values of the bottom parameters and determining the parameter set which provides the best agreement with the experimental Green’s function, particularly in the positions and relative magnitudes of the modal peaks. Comparisons are also made between the measured and theoretically computed pressure field magnitudes. The technique is demonstrated using experimental data at 140 Hz and 220 Hz.