Mid-frequency geoacoustic inversion using bottom loss in shallow water with constrasting surficial sediment thickness

This study investigates mid-frequency bottom loss at two shallow water sites with contrasting sediment thicknesses. Site 1 and Site 2, located in similar bathymetric conditions, were selected to examine how surficial sediment layer thickness influences acoustic bottom interaction. Continuous wave pulses in the 3–10 kHz frequency range were transmitted at multiple source depths and received by a vertical hydrophone array. Measured bottom loss was derived using a simplified sonar equation, based on the received levels of the direct and bottom paths and ray-based transmission loss differences. Modeled bottom loss was computed using a forward loss model incorporating geoacoustic parameters from both empirical values and inversion. At Site 1, which featured a thick, homogeneous surficial layer, both empirical and inversion based bottom loss closely matched measured bottom loss. In contrast, Site 2, characterized by a thin surficial layer, exhibited pronounced frequency dependent behavior. To accurately retrieve the geoacoustic properties of the thin surficial sediment layer, frequency dependence inversion was performed, enabling improved resolution of fine-scale layering across the mid-frequency band. Additional analysis of sub-bottom reflection was conducted to further support the inversion-based interpretations. [Work supported by the Korea Institute of Marine Science & Technology Promotion (KIMST), funded by the Ministry of Oceans and Fisheries, Korea (20210696).]