Ambient sound levels, directionality, and transport velocity around a seamount measured by a deep-drifting acoustic vector sensor

Abstract

In September 2022 an opto-acoustic drifter was deployed several times in the vicinity of the Kelvin seamount (38°49’N, 64°2’W) in the North Atlantic Ocean, which rises to a depth of 1500 m from a 5 km deep abyssal plain. The “SQUALL-E” drifter incorporates stereo video cameras, vertical (1.75 m aperture) and tetrahedral hydrophone arrays, and a 2-D Geospectrum M35 acoustic vector sensor. One overnight deployment descended to 250 m depth, and a another to 400 m depth, which resulted in highly different drift rates. The M35 sensor demonstrated the ability to estimate the directionality of ambient sounds between 1 and nearly 30 kHz. Sperm whales, delphinids, various vessels, and other discrete and distributed sources were detected. For both deployments we present distributions of ambient sound levels, azimuthal and elevation angles, and transport velocity. We discuss how these distributions evolved throughout the deployments. [Work sponsored by ONR TFO program.]