Time domain geoacoustic inversion using back-propagation on an L-shaped array.

Abstract

This paper presents inversion of Shallow Water 06 experimental data measured on an L‐shaped array (SWAMI 32). The array was deployed in 70‐m water depth and consists of an equally spaced 10‐element vertical line array (VLA) and a 256‐m‐long bottom moored 20‐element horizontal line array (HLA). A mid‐frequency (1100–2900‐Hz) chirp source was towed at 35‐m depth along a circular track around the VLA with radius 190 m. Time domain inversions using VLA, HLA, and both arrays were carried out and results compared. For the inversions, a multi‐step optimization scheme is applied to the data using very fast simulated reannealing. The objective function is defined by the power of the back‐propagated signal from the array to the source. At each step, water column sound speed profile, experimental geometry, and geoacoustic parameters are inverted successively. Accurate HLA positions were essential for the HLA and the HLA+VLA inversions. Finally, the inversion results were compared with other results near the site. [Work supported by ONR.]