Real-time instantaneous wide-area ocean acoustic monitoring in the shallow Great South Channel and deep ocean south of Rhode Island with Northeastern University coherent hydrophone array

Abstract

A large-aperture 160-element coherent hydrophone array system, developed in-house at Northeastern University, was deployed and tested at sea in shallow water Great South Channel and deep ocean south of Rhode Island during September 2021. The system implements the passive ocean acoustic waveguide remote sensing technology for real-time instantaneous wide area ocean monitoring. The array data sampled at 100 kHz per element were processed in real-time at sea to provide beamformed spectrogram imagery in multiple frequency subbands from 10 Hz to 50 kHz and spanning 360 degree horizontal azimuths about the receiver array. A wide variety of acoustic detections were made in real time, including marine mammal vocalizations and motion-related signals, fish grunts and other fish-generated signals, tonal and broadband signals from distant ships and own tow ship. Real-time detections of marine mammal vocalizations include fin whale 20 Hz pulses, humpback whale songs and social sounds, minke whale buzz sequences, sperm whale echolocation and social clicks, dolphin whistles and echolocation clicks, as well as calls from unidentified baleen and toothed whale species. A database of automatically detected signals with bearing-time information along with extracted time-frequency characteristics was generated in real-time at sea.