One track, two experiments four years apart: On the repeatability of geoacoustic inversion on the New England Mud Patch

Our current knowledge of the geoacoustic properties of the New England Mud Patch (NEMP) is mostly driven by data collected in 2017 as part of the Seabed Characterization Experiment (SBCEX17). In 2021, a modest geoacoustic inversion experiment was performed on the NEMP using a simple and low-cost pair of experimental assets: a “TOSSIT” passive acoustic mooring and an impulsive “RIUSS” (Rupture Induced, Underwater Sound Source). The TOSSIT/RIUSS data were collected on a track that was studied intensively during SBCEX17, but with fundamental differences in oceanographic conditions: a frontal intrusion was present at the experimental site in 2021, creating a strongly stratified sound speed profile (SSP) in the water column, while the water column was essentially iso-speed in 2017. The 2021 TOSSIT/RIUSS data are used to perform geoacoustic inversion using warping and Bayesian trans-dimensional methods. The geoacoustic properties estimated for the 2021 data compare favorably to results obtained with SBCEX17 data, even when the 2021 data are inverted jointly for water-column SSP and seabed parameters. This study demonstrates inversion repeatability on the NEMP using data sets collected years apart and under different (and potentially unknown) oceanographic conditions. [Work supported by the Office of Naval Research.]