Perturbative inversion of geoacoustic parameters in a shallow water environment

Abstract

In many strategic shallow water areas the geoacoustic properties of the sub-bottom are largely unknown. In this thesis it is demonstrated that inverse theory and measured data from a single hydrophone can be used to accurately deduce the geoacoustic properties of the sub-bottom, even when the initial background geoacoustic model is a highly inaccurate guess. Since propagation in shallow water is very sensitive to the geoacoustic properties of the sub-bottom, the inverse technique developed in this thesis presents the Navy with a vitally important, practical, and inexpensive means to improve sonar performance prediction in a potentially hostile environment. To provide ground truth for the inverse technique, measured data collected during Project GEMINI were compared to the inverse solutions. Detailed, site-specific geoacoustic models were developed for two array locations and the Finite Element Parabolic Equation (FEPE) model was used to estimate transmission loss (TL). The model estimates from FEPE compared well with the measured data and the detailed geoacoustic models were considered as ground truth. To test the efficacy of the technique, initial background geoacoustic models were constructed assuming no a priori information of the bottom. The resultant inverse solution was used to predict the geoacoustic properties at each of the sites. The final results were in excellent agreement with the measured data and the resulting inverse technique TL estimates were as good or better than the Th estimates obtained from the detailed, site-specific geoacoustic models. (AN)