Shallow water waveguide characterization using the Hankel transform

Abstract

A technique for acoustically characterizing shallow water waveguides is presented. 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. It is shown that, in the context of normal mode theory, the Green’s function contains information about the nature of the discrete and continuous modal spectra as well as the plane-wave reflection coefficients of the waveguide boundaries. Inversions are performed using pressure field data generated synthetically over reasonable experimental apertures (1–5 km) to obtain Green’s functions for the cases of an isovelocity water column overlying both hard and fast isovelocity bottoms (Pekeris waveguide). The Green’s function results show excellent agreement with theory, while the subsequently calculated reflection coefficients of the bottom are of somewhat lower quality. It is shown that features of the Green’s function itself can be used to extract modal properties and characteristics of the bottom. The effects of sediment attenuation and shear in the Pekeris case are discussed, and a comparison of this method with conventional phased array mode resolution techniques is made.