To better understand fin whale vocalization behaviour in the Norwegian and Barents Seas, a large-aperture densely sampled coherent hydrophone array was deployed in late winter 2014 to monitor their vocalizations instantaneously over wide areas via passive ocean acoustic waveguide remote sensing (POAWRS). Here, we (i) provide a time-frequency characterization for different call types observed (20 Hz pulses, 130 Hz upsweeps, 30–100 Hz downsweep chirps, and 18–19 Hz backbeats); (ii) compare their relative abundances in three different coastal regions off Alesund, Lofoten, and Northern Finnmark; (iii) estimate the temporal and spatial distributions; (iv) source level distributions; and (v) probability of detection (PoD) regions for the more abundant 20 Hz pulse and 130 Hz upsweep call types. The fin whale vocalizations received over the diel cycle (24 h) were significantly more abundant by a factor of roughly seven off Northern Finnmark than the other two regions, associated with fish feeding activities. The source levels are estimated to be 190.5±7.4 dB for the fin whale 20 Hz pulses and 170.3 ± 5.2 dB for the 130 Hz upsweeps. We find that fin whales are capable of producing each vocalization type either independently or simultaneously with other types, and the 20 Hz sound production in the fin whales involves a mechanism that generates a significantly less-intense second-order harmonic of the fundamental.

Multiple mechanized ocean vessels, including both surface ships and submerged vehicles, can be simultaneously monitored over instantaneous continental-shelf scale regions >10,000 km 2 via passive ocean acoustic waveguide remote sensing. A large-aperture densely-sampled coherent hydrophone array system is employed in the Norwegian Sea in Spring 2014 to provide directional sensing in 360 degree horizontal azimuth and to significantly enhance the signal-to-noise ratio (SNR) of ship-radiated underwater sound, which improves ship detection ranges by roughly two orders of magnitude over that of a single hydrophone. Here, 30 mechanized ocean vessels spanning ranges from nearby to over 150 km from the coherent hydrophone array, are detected, localized and classified. The vessels are comprised of 20 identified commercial ships and 10 unidentified vehicles present in 8 h/day of Passive Ocean Acoustic Waveguide Remote Sensing (POAWRS) observation for two days. The underwater sounds from each of these ocean vessels received by the coherent hydrophone array are dominated by narrowband signals that are either constant frequency tonals or have frequencies that waver or oscillate slightly in time. The estimated bearing-time trajectory of a sequence of detections obtained from coherent beamforming are employed to determine the horizontal location of each vessel using the Moving Array Triangulation (MAT) technique. For commercial ships present in the region, the estimated horizontal positions obtained from passive acoustic sensing are verified by Global Positioning System (GPS) measurements of the ship locations found in a historical Automatic Identification System (AIS) database. We provide time-frequency characterizations of the underwater sounds radiated from the commercial ships and the unidentified vessels. The time-frequency features along with the bearing-time trajectory of the detected signals are applied to simultaneously track and distinguish these vessels.

The passive ocean acoustic waveguide remote sensing technique is employed to detect diesel-electric vehicles at ranges exceeding 100 kilometers. The underwater sounds radiated from these vessels are received at long ranges on a large-aperture densely-sampled horizontal coherent hydrophone array. 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. Here we find spectra of ship-radiated sound that is extremely dynamic containing both broadband signals and narrowband tonals at discrete frequencies with source levels that vary depending on ship conditions. We track a vessel with increasing range to find range dependence on broadband signals at close range and tonal signals at long range. Machinery noise generated from engines, propellers, flow noise and other cavitation sources are found to vary depending on ship conditions and are unique to each vessel. Our analysis indicates these vessels can be instantaneously tracked over wide areas spanning more than 300 kilometers in diameter.

The vocalizations of the fin whale are detected, characterized and localized over instantaneous wide areas of the Norwegian and Barents Seas using a large-aperture densely-sampled coherent hydrohone array via the passive ocean acoustic waveguide remote sensing (POAWRS) technique from observations in late winter to early spring 2014. The fin whale vocalizations are comprised of their characteristic 20 Hz pulses, interspersed by 130 Hz upsweeps, less abundant 30-100 Hz downsweep chirps and 18-19 Hz centered backbeats. The time-frequency characteristics of these vocalization types and their diel occurrence rate time-series are quantified in three distinct regions of the Norwegian Sea, off the coasts of Alesund, Lofoten, and the Northern Finnmark. Their vocalization rates are a factor of roughly 5 times and 17 times larger respectively for the 20 Hz and 130 Hz centered vocalizations off Northern Finnmark than the other regions. The vocalization rate spatial density distributions, source level distributions and probability of detection (PoD) regions are estimated for the 20 Hz and 130 Hz vocalizations. Highly intense 20 Hz pulses from closeby fin whales are received with their first-order harmonics centered at 40 Hz with twice the bandwidth but 30 dB lower source levels, indicating a nonlinear mechanism for their production.