Continental Shelf-Scale Passive Acoustic Detection and Characterization of Diesel-Electric Ships Using a Coherent Hydrophone Array

Abstract

The passive ocean acoustic waveguide remote sensing (POAWRS) technique is employed to detect and characterize the underwater sound radiated from three scientific research and fishing vessels received at long ranges on a large-aperture densely-sampled horizontal coherent hydrophone array. The sounds radiated from the research vessel (RV) Delaware II in the Gulf of Maine, and the RV Johan Hjort and the fishing vessel (FV) Artus in the Norwegian Sea are found to be dominated by distinct narrowband tonals and cyclostationary signals in the 150 Hz to 2000 Hz frequency range. The source levels of these signals are estimated by correcting the received pressure levels for transmission losses modeled using a calibrated parabolic equation-based acoustic propagation model for random range-dependent ocean waveguides. The probability of the detection region for the most prominent signal radiated by each ship is estimated and shown to extend over areas spanning roughly 200 km in diameter when employing a coherent hydrophone array. The current standard procedure for quantifying ship-radiated sound source levels via one-third octave bandwidth intensity averaging smoothes over the prominent tonals radiated by a ship that can stand 10 to 30 dB above the local broadband level, which may lead to inaccurate or incorrect assessments of the impact of ship-radiated sound.

Angular Resolution Enhancement Provided by Nonuniformly-Spaced Linear Hydrophone Arrays in Ocean Acoustic Waveguide Remote Sensing

“…In addition to echo returns of the transmitted source signal, vocalizations from more than eight distinct marine mammal species including fin, humpback, sei, minke, orca, pilot, sperm, and other unidentified baleen and toothed whale species were also passively recorded by the coherent hydrophone array [1,4,5,12]. The ecosystem-wide spatial distributions of vocal marine mammals from multiple cetacean species were simultaneously mapped by the POAWRS technique [1,[4][5][6]. Detailed information about the Gulf of Maine 2006 Experiment is provided in Refs.…”

“…In contrast, several of these population centers were previously blurred together when beamformed with the array's uniformly-spaced single subaperture. In passive OAWRS (POAWRS) of marine mammal vocalizations and ship-radiated underwater sound, the nonuniformly-spaced subarrays improve angular resolution, bearing estimation, and provide SNR enhancement for whale call and ship-radiated sound in the beamformed spectrograms when compared to that obtained with the uniformly-spaced subapertures [1,[4][5][6].…”

“…We provide an analysis of the Office of Naval Research Five Octave Research Array (ONR-FORA) [26]. The ONR-FORA is a primary receiver array for long range ocean acoustics research of the US academic community, widely employed in field experiments for ocean acoustic propagation, scattering, remote sensing and communications studies [1][2][3][4][5][6][11][12][13]15,16]. The ONR-FORA is a linear oil-filled array consisting of four nested subapertures, each uniformly spaced, designed for beamforming signals without spatial aliasing over frequencies spanning from below 250 Hz up to 2000 Hz.…”

“…These results are compared to those of the uniformly-spaced single subaperture counterparts. The ONR-FORA has been employed as the primary receiver implementing the ocean acoustic waveguide remote sensing (OAWRS) technology [1][2][3][4][5][6][12][13][14], providing real-time or near real-time instantaneous wide-area sensing of the ocean environment in field experiments. Here, we provide illustrative examples showing enhancements in both passive and active OAWRS achieved via beamforming with the nonuniformly-spaced subarrays of the ONR-FORA over that of its uniformly-spaced individual subaperture counterparts using data acquired during the Gulf of Maine 2006 Experiment (GOME06) [1,2,[4][5][6][7][8][11][12][13]24,50,51].…”

“…Large aperture densely-sampled arrays of sensors are employed in remote sensing and communication applications [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] to enhance signal-to-noise ratio (SNR) via coherent beamforming [17][18][19][20][21][22], which reduces noise coming from directions outside the signal beam. Coherent beamforming also provides an estimate of signal bearing, required for direct spatial localization of a signal [11,12,[23][24][25].…”