Geoacoustic inversion of broadband data in the Florida Straits

Abstract

Acoustic propagation experiments have been carried out in the Florida Straits with a multi-frequency broadband source that transmitted m-sequence pulses over a range of 10 km to a sparse-filled vertical line array. This paper presents results of matched field inversions of the acoustic field data at low frequencies to estimate geoacoustic model parameters for the experimental site. Two approaches were taken for the inversions. The first was a conventional matched field inversion using multi-frequency data centered at 200 and at 400 Hz from the vertical array. The second approach was designed to model the low frequency waveform at a single hydrophone. For the very long range experimental geometry, the waveform was modeled in terms of modes. Each inversion was cast as an optimization problem using the adaptive simplex simulated annealing algorithm. The inversions provide a comparison between approaches that take advantage of the spatial coherence in one case, and the time coherence in the received signal in the other case. Both inversions give similar results for the parameters of a simple geoacoustic bottom model, and the sensitivities and relative uncertainties of the model parameters are consistent for the two approaches. Notably, the inversions are sensitive to compressional wave attenuation.