Modeling of broadband time signals in shallow water using environmental inversion

Abstract

A numerical modeling scheme is applied to perform broadband environmental inversion by using explosive data acquired in the Mediterranean Sea in May 1997. The area shows a moderate range dependency, and the received time signals from explosive charges cover a frequency band of several kilohertz. The acoustic propagation model is based on a layered normal mode approach, which is capable of efficiently predicting broadband sound propagation in shallow water [Westwood et al., ‘‘A normal mode model for acoustic–elastic ocean environments,’’ J. Acoust. Soc. Am. 100, 3631–3645 (1996)]. This model has been extended to handle range-dependent environments using the adiabatic approximation. Thus calculation of broadband transfer functions from 0 to 10 kHz of range-dependent, shallow-water waveguides can now be done within a few minutes. The combination of the above propagation model and a state-of-the-art global inversion scheme [Gerstoft, ‘‘SAGA user manual 2.0: An inversion software package,’’ SACLANTCEN SM-333 (1997)], makes it possible to perform environmental focusing by optimizing the correlation between the numerical and experimental received time signal at one or more receiver locations. The broadband inversion scheme is introduced to extract the uncertain acoustic parameters in the waveguide, and to assess how accurate broadband signals can be modeled in complex shallow-water regions.