Broad-band geoacoustic inversion in shallow water from waveguide impulse response measurements on a single hydrophone: Theory and experimental results

The paper discusses an inversion method that allows the rapid determination of in situ geoacoustic properties of the ocean bottom without resorting to large acoustic receiving apertures, synthetic or real. The method is based on broad-band waterborne measurements and modeling of the waveguide impuls e response between a controlled source and a single hydrophone, Results fro m Yellow Shark '94 experiments in Mediterranean shallow waters using single elements of a vertical array are reviewed. Inversion of the bottom paramet ers is performed with an objective function that includes the processing ga in of a model-based matched filter (MBMF) receiver relative to the conventi onal matched filter. The MBMF reference signals incorporate waveguide Green 's functions for known geometry and water column acoustic model and hypothe sized bottom geoacoustic models. The experimental inversion results demonst rated that, even for complex environmental conditions, a single transmissio n of a broad-band (200-800 Hz) coded signal received at a single depth and a few hundred forward modeling runs were sufficient to correctly resolve th e bottom features. These included the sound speed profile, attenuation, den sity, and thickness of the top clay sediment layer, and sound speed and att enuation of the silty clay bottom. Exhaustive parameter search proved unequ ivocally the low-ambiguity and high-resolution properties of the MBMF-deriv ed objective. The single-hydrophone results compare well with those obtaine d under identical conditions from matched held processing of multitone: pre ssure fields sampled on the vertical array. Both of these results agree wit h expectations from geophysical ground truth. The MBMF has been applied suc cessfully to a field of advanced drifting acoustic buoys on the Western Sic ilian shelf, demonstrating the general applicability of the inversion metho d presented in this paper.