Using a coherent hydrophone array for observing sperm whale range, classification, and shallow-water dive profiles

Abstract

Sperm whales in the New England continental shelf and slope were passively localized, in both range and bearing, and classified using a single low-frequency (<2500 Hz), densely sampled, towed horizontal coherent hydrophone array system. Whale bearings were estimated using time-domain beamforming that provided high coherent array gain in sperm whale click signal-to-noise ratio. Whale ranges from the receiver array center were estimated using the moving array triangulation technique from a sequence of whale bearing measurements. Multiple concurrently vocalizing sperm whales, in the far-field of the horizontal receiver array, were distinguished and classified based on their horizontal spatial locations and the inter-pulse intervals of their vocalized click signals. The dive profile was estimated for a sperm whale in the shallow waters of the Gulf of Maine with 160 m water-column depth located close to the array's near-field where depth estimation was feasible by employing time difference of arrival of the direct and multiply reflected click signals received on the horizontal array. By accounting for transmission loss modeled using an ocean waveguide-acoustic propagation model, the sperm whale detection range was found to exceed 60 km in low to moderate sea state conditions after coherent array processing.

Diel and Spatial Dependence of Humpback Song and Non-Song Vocalizations in Fish Spawning Ground

“…Whale vocalizations were detected using a peak detector with 5.6 dB detection threshold and verified by visual inspection. The detection of long-range propagated biological sounds is significantly enhanced by spatial beamforming and spectrogram analysis which filters background noise that is outside of the whale vocalization beam and frequency band [2,3]. The high gain [4,46] of the densely-sampled large aperture coherent POAWRS receiver array used here, up to 10 log 10 n = 18 dB gain where n = 64 hydrophones for each sub-aperture, enabled detection of whale vocalizations either two orders of magnitude more distant in range or lower in SNR than a single hydrophone which has no array gain (see Extended Data Figure 1 of [1] and Figure 13 of [2]).…”

“…The diel vocalization behavior of Northwestern Atlantic humpback whales (Megaptera Novaeangliae) was monitored over vast areas of the Gulf of Maine using the passive ocean acoustic waveguide remote sensing (POAWRS) technique [1][2][3] from 19 September to 6 October 2006. Humpback vocalizations were measured using a large-aperture densely-sampled coherent hydrophone array system at a rate of approximately 1800 ± 1100 calls per day occurring in the 100-1000 Hz frequency range.…”

Vocalization Source Level Distributions and Pulse Compression Gains of Diverse Baleen Whale Species in the Gulf of Maine

“…The vocalization behaviors of diverse marine mammal species [1] have been simultaneously monitored over vast areas of the Gulf of Maine using the Passive Ocean Acoustic Waveguide Remote Sensing (POAWRS) technique [1][2][3] from 19 September-6 October 2006. The marine mammal vocalizations were received on a large-aperture densely-sampled coherent hydrophone array system that provides orders of magnitude higher array gain [4] than a single sensor, enabling whale vocalizations to be detected, localized and classified over an approximately 100,000 km 2 region instantaneously by POAWRS without aliasing in time and space (see the POAWRS detection region for whale vocalizations from diverse species in Figure 3a of [1]).…”

“…Sonar, radar and ultrasonic systems [43,44] often employ pulse compression to enhance signal-to-noise ratios in signal detection and range-resolution in imaging applications. Marine mammal vocalization pulse compression gains are required for determining detection regions in underwater passive single sensor [45][46][47][48] or array sensor systems [1,2,22] that employ match-filter operations to enhance vocalization detection, as well as vocalization arrival time and bearing estimation for localization applications [1,3,22].…”

Continental-shelf scale Passive Ocean Acoustic Waveguide Remote Sensing of marine mammals and other submerged objects including detection, localization, and classification

“…The GOM is among the more diverse, productive, and trophically complex marine temperate areas in the world, with Atlantic herring (Clupea harengus) comprising a keystone prey species, common in the diets of many marine mammals, piscivorous fish and seabirds of the region [12]. Using a large-aperture, densely sampled, coherent hydrophone array with orders of magnitude higher array gain [13] than previously available in acoustic marine mammal sensing, we could detect, localize and classify vocalizing MMs from multiple species instantaneously over roughly 100,000 km 2 region by POAWRS [14,15] without aliasing [13] in time and space. Simultaneous fish distributions were acquired over tens of thousands of square kilometer areas instantaneously by ocean acoustic waveguide imaging (OAWRS) [16][17][18][19], combined with conventional fisheries ultrasonic echosounding [20] and fish trawl sampling [21] to obtain thousands of calibrations at statistically significant locations [18].…”