Bottom parameter extraction from long range reverberation measurements

Abstract

From 1996 through 2000 the author participated with the SACLANT Undersea Research Centre in four Rapid Environmental Assessment (REA) trials, including experiments for bottom reverberation. SUS charges were used as sources. The receivers were horizontal arrays (four apertures) spanning a wide frequency range. Sets of nearly monostatic recordings were analyzed in frequency bands from 80 to 4000 Hz. Previous results by the author, [Berlin ASA meeting, 1999] showed polar plots of the beam time series superimposed on bathymetric charts, revealing a number of scattering features not on the charts and that directional reverberation measurements are a useful remote-sensing tool. A manual procedure was used in the first 3 sea trials to obtain bottom parameter estimates that could reproduce the reverberation decay for at-sea results. Recently this inversion scheme has been automated using a constrained simulated annealing (SA) algorithm giving more formal inversion results. In May of 2000 a Scientific REA experiment was conducted with SACLANTCEN, ARL/PSU, DREA and NRL near the Malta Plateau. Reverberation data from 100 Hz-4000 Hz was obtained using SUS. The horizontal array data are compared with the Generic Sonar Model (GSM) predictions for both the manual and automated inverse schemes. Results show a definite improvement using the automated technique.