Effects of sound speed fluctuations in the water column on geoacoustic parameter estimates

Abstract

The effects of environmental variability on acoustic propagation and sonar performance in shallow water has received much attention in recent literature. Of particular interest is the influence of water column variability on acoustic propagation and the subsequent effects on geoacoustic inversion. In this paper, a modal-based inversion method is considered with the inclusion of internal waves in a shallow-water waveguide. The input data to the inversion algorithm are estimates of horizontal wavenumbers corresponding to the propagating modes of a cw point-source field. Often, wavenumber estimation is performed under the assumption that the pressure field can be represented by an adiabatic mode sum. However, it is well known that sound speed fluctuations in the water column due to internal waves promote the coupling of energy between propagating acoustic modes, thus violating the adiabatic assumption. Nevertheless, it was recently demonstrated that sound speed fluctuations in the water column due to a weak deterministic internal wave field can enhance spectral wavenumber estimates [Becker and Frisk, in Impact of Littoral Variability on Acoustic Predictions and Sonar Performance (Kluwer, Dordrecht, 2002)]. That work is extended to compare inversion results for wavenumber estimates obtained both with and without internal waves. [Work supported by ONR Ocean Acoustics.]