Estimation of seafloor properties using sources of opportunity in the 2023 NESMA Pilot experiment

Naval Postgraduate School operated a network of Moored Autonomous Noise Recorders (MANRs) in the vicinity of the Atlantis II Seamounts during the 2023 New England Seamounts Acoustics (NESMA) Pilot experiment. Each MANR had a single hydrophone located a few meters above the seafloor. Acoustic pressure was recorded continuously by three MANRs for about 2 months. Two of the MANRs were located on steep flanks of the Atlantis II Seamounts and the other MANR was deployed in a deep trench. In addition to ambient sound, MANRs recorded signals from various compact sources of opportunity, including passing ships, chirp signals from tomographic moorings SIO-E and SIO-N of the Scripps Institution of Oceanography, and the powerful impulsive sound generated by the catastrophic demise of the SIO-E mooring. In this work, arrival patterns from SIO-E chirps and the impulsive sound are analyzed to determine time-dependent source depth. Frequency and angular dependence of the amplitudes of identified ray arrivals are employed to estimate roughness and constrain geoacoustic parameters of the seafloor on SIO-E—MANR propagation paths. Additional constraints on seafloor roughness and reflectivity are derived from the observed Lloyd’s mirror-type interference pattern of broadband noise of the R/V Neil Armstrong. [Work supported by ONR.]