Impact of sub-bottom layers on low-frequency acoustic propagation in the abyssal plain during the New England Seamounts Acoustic experiment

Seabed characteristics play an important role in ocean acoustic propagation, particularly at low frequencies where sound can penetrate far into the sub-bottom and reflect from deep sediment interfaces. As part of the New England Seamount Acoustics (NESMA) experiment, broadband airgun transmissions were recorded on a vertical line array deployed over the abyssal plain south of the Atlantis II Seamount. Low-frequency (f 50 Hz) arrivals were analyzed using an isovelocity, ray-based propagation model, which provides intuitive, physics-based interpretations of the received signals and revealed eigenray paths that interacted with sediment layers as deep as 340 m below the seafloor. These sub-bottom reflections, observed at ranges up to 20 km, arrived at levels comparable to primary bottom-bounce paths and produced significant interference patterns at certain ranges. These results emphasize the importance of deep sediment layering in influencing low-frequency acoustic propagation, with key implications for modeling and geoacoustic inversion. This work was sponsored by the Office of Naval Research (ONR) during 2023–2024 as part of the Task Force Ocean (TFO) Department Research Initiative (DRI).