Acoustic propagation through a biological deep scattering layer at the New England shelf break

The New England Shelf Break is a dynamic ocean environment with strong spatial variability due to complex physical processes and interactions with warm core rings originating from the Gulf Stream. An acoustic autonomous underwater vehicle (AUV) was deployed in the New England Shelf Break Acoustics (NESBA) experiment in May 2021 to investigate environmental variability and its effect on sound propagation. The AUV system was comprised of a modified REMUS 600 vehicle with a hull-mounted 3.5 kHz transducer, a downward-facing EK80 echosounder, and a towed linear hydrophone array. Shipboard EK80 data measured during the AUV mission showed the presence of a biological deep scattering layer. Preliminary analysis of AUV source signals passing through the layer suggested significant attenuation compared to signals not passing through the layer. To investigate this further, a parabolic equation (PE) model with range-dependent attenuation patches in the water column was constructed to replicate the biological attenuation through the scattering layer. The model uses estimates of absorption and scattering derived from shipboard and AUV EK80 data. Through this study we aim to better understand the scattering effects of this deep biological layer on acoustic propagation. Work supported by the Office of Naval Research.