Geoacoustic inversion of broadband data by matched beam processing

Abstract

This paper describes results of geoacoustic inversion using broadband signals from an experiment carried out at a site near the South Florida Ocean Measurement Centre in the Florida Straits. M-sequence coded pulse trains at different center carrier frequencies from 100to3200Hz were recorded at a vertical line array at a distance around 10km. Geoacoustic inversion was carried out to determine the feasibility of inverting the environmental parameters from this long-range propagation experiment. The received signal at lower frequencies below 400Hz consisted of a dominant water column signal and a secondary arrival delayed by 0.4s. The secondary signal was spatially filtered by beamforming the array data, and the beam data were inverted by matched beam processing in the time domain, combined with an adaptive simplex simulated annealing algorithm. The estimated values of compressional wave speed and density were in good agreement with ground truth values from sediment cores. The inverted shear wave speed appears to be a sensitive parameter and consistent with compressional wave speed. As a cross check, range and water depth were also included as inversion parameters, and the inversion results were close to the known values within small uncertainties.