PERTURBATIVE INVERSION OF GEOACOUSTIC PARAMETERS IN A SHALLOW-WATER ENVIRONMENT

In many strategic shallow water areas, the geoacoustic properties of t he sub-bottom are largely unknown. This paper demonstrates that invers e theory and measured data from a single hydrophone can be used to acc urately deduce the geoacoustic properties of the sub-bottom, even when the initial background geoacoustic model is a highly inaccurate estim ate, Since propagation in shallow water is very sensitive to the geoac oustic properties of the sub-bottom, the inverse technique is a vitall y important, practical, and inexpensive means to improve sonar perform ance prediction in a potentially hostile environment. To provide groun d truth for the inverse technique, measured data collected during Proj ect GEMINI were compared to the inverse solutions. Detailed, site-spec ific geoacoustic models were developed for two array locations and the finite-element parabolic equation (FEPE) model was used to estimate t ransmission loss (TL), The model estimates from FEPE compared well wit h the measured data and the detailed geoacoustic models were considere d as ''ground truth.'' To test the efficacy of the technique, initial background geoacoustic models were constructed assuming no a priori in formation of the bottom, The resultant inverse solution was used to pr edict the geoacoustic properties at each of the sites, The final resul ts were in excellent agreement with the measured data and the resultin g TL estimates derived from the inverse technique were as good or bett er than the TL estimates obtained from the detailed, site-specific geo acoustic models.