High resolution geoacoustic inversion in shallow water: a joint time and frequency domain technique

Abstract

High resolution geoacoustic data are quired for accurate predictions of

acoustic propagation and scattering in shallow water. Since direct measurement of geoacoustic data is difficult, time-consuming and expensive, inversion of acoustic data is a promising alternative. However, the main problem encountered in geoacoustic inversion is the problem of uniqueness, i.e., many diverse geoacoustic models can be made to fit the same data set. A key, and perhaps unique, aspect of this approach is the combination of data analysis in both the space-time and the space-fkquency domains. This combination attempts to ameliorate the uniqueness problem by incorporating as much independent data as possible in the analysis. In order to meet the stringent requirements of high spatial resolution and uniqueness, an entire method has been developed including a new measurement technique, processing/analysis technique, and inversion strategy. In this paper we describe each of these techniques and then show how they were applied to a shallow water data set in the Mediterranean Sea. The resulting sound speed gradients in the upper 150 m. sub-bottom appear to be much higher (one order of magnitude) than generally assumed. Inversion results in the upper several meters compare favorably with axe analysis