Environmental influences on low‐frequency, shallow‐water acoustic propagation and inversion.

Abstract

Historically, the seabed has been considered to play the dominant role in shallow‐water acoustic propagation at low frequencies. As a result, propagation models have focused on the incorporation of accurate values of bottom properties, while inversion techniques have concentrated on the determination of geoacoustic properties of the seabed. In recent years, however, the assumption of a benign water column has increasingly come under scrutiny in addressing both the forward and inverse problems. This paper addresses these issues as they relate to a measurement and inversion methodology in which acoustic data are acquired on synthetic radial apertures that are created using a moving source/receiver configuration in concert with precision navigation. These data can be transformed into the horizontal wavenumber domain to obtain an estimate of the propagation characteristics of the waveguide; namely, its modal content. The modal spectra can then be inverted using a variety of techniques to determine estimates of the waveguide parameters, specifically the geoacoustic properties of the seabed. The issues associated with the successful implementation of this modal mapping method in a highly variable shallow‐water environment are discussed. [Work supported by ONR.]