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Gassmann, M, Henderson EE, Wiggins SM, Roch MA, Hildebrand JA.  2013.  Offshore killer whale tracking using multiple hydrophone arrays. Journal of the Acoustical Society of America. 134:3513-3521.   10.1121/1.4824162   AbstractWebsite

To study delphinid near surface movements and behavior, two L-shaped hydrophone arrays and one vertical hydrophone line array were deployed at shallow depths (<125 m) from the floating instrument platform R/P FLIP, moored northwest of San Clemente Island in the Southern California Bight. A three-dimensional propagation-model based passive acoustic tracking method was developed and used to track a group of five offshore killer whales (Orcinus orca) using their emitted clicks. In addition, killer whale pulsed calls and high-frequency modulated (HFM) signals were localized using other standard techniques. Based on these tracks sound source levels for the killer whales were estimated. The peak to peak source levels for echolocation clicks vary between 170-205 dB re 1 mu Pa @ 1 m, for HFM calls between 185-193 dB re 1 mu Pa @ 1 m, and for pulsed calls between 146-158 dB re 1 mu Pa @ 1 m. (C) 2013 Acoustical Society of America.

Gassmann, M, Wiggins SM, Hildebrand JA.  2015.  Three-dimensional tracking of Cuvier's beaked whales' echolocation sounds using nested hydrophone arrays. Journal of the Acoustical Society of America. 138:2483-2494.   10.1121/1.4927417   AbstractWebsite

Cuvier's beaked whales (Ziphius cavirostris) were tracked using two volumetric small-aperture (similar to 1 m element spacing) hydrophone arrays, embedded into a large-aperture (similar to 1 km element spacing) seafloor hydrophone array of five nodes. This array design can reduce the minimum number of nodes that are needed to record the arrival of a strongly directional echolocation sound from 5 to 2, while providing enough time-differences of arrivals for a three-dimensional localization without depending on any additional information such as multipath arrivals. To illustrate the capabilities of this technique, six encounters of up to three Cuvier's beaked whales were tracked over a two-month recording period within an area of 20 km(2) in the Southern California Bight. Encounter periods ranged from 11 min to 33 min. Cuvier's beaked whales were found to reduce the time interval between echolocation clicks while alternating between two inter-click-interval regimes during their descent towards the seafloor. Maximum peak-to-peak source levels of 179 and 224 dB re 1 mu Pa @ 1 m were estimated for buzz sounds and on-axis echolocation clicks (directivity index = 30 dB), respectively. Source energy spectra of the on-axis clicks show significant frequency components between 70 and 90 kHz, in addition to their typically noted FM upsweep at 40-60 kHz. (C) 2015 Acoustical Society of America.

Gassmann, M, Wiggins SM, Hildebrand JA.  2017.  Deep-water measurements of container ship radiated noise signatures and directionality. Journal of the Acoustical Society of America. 142:1563-1574.   10.1121/1.5001063   AbstractWebsite

Underwater radiated noise from merchant ships was measured opportunistically from multiple spatial aspects to estimate signature source levels and directionality. Transiting ships were tracked via the Automatic Identification System in a shipping lane while acoustic pressure was measured at the ships' keel and beam aspects. Port and starboard beam aspects were 15 degrees, 30 degrees, and 45 degrees in compliance with ship noise measurements standards [ANSI/ASA S12.64 (2009) and ISO 17208-1 (2016)]. Additional recordings were made at a 10 degrees starboard aspect. Source levels were derived with a spherical propagation (surface-affected) or a modified Lloyd's mirror model to account for interference from surface reflections (surface-corrected). Ship source depths were estimated from spectral differences between measurements at different beam aspects. Results were exemplified with a 4870 and a 10 036 twenty-foot equivalent unit container ship at 40%-56% and 87% of service speeds, respectively. For the larger ship, opportunistic ANSI/ISO broadband levels were 195 (surface-affected) and 209 (surface-corrected) dB re 1 mu Pa-2 1 m. Directionality at a propeller blade rate of 8 Hz exhibited asymmetries in stern-bow (< 6 dB) and port-starboard (< 9 dB) direction. Previously reported broadband levels at 10 degrees aspect from McKenna, Ross, Wiggins, and Hildebrand [(2012b). J. Acoust. Soc. Am. 131, 92-103] may be similar to 12 dB lower than respective surface-affected ANSI/ISO standard derived levels. (C) 2017 Acoustical Society of America.

Guazzo, RA, Helble TA, D’Spain GL, Weller DW, Wiggins SM, Hildebrand JA.  2017.  Migratory behavior of eastern North Pacific gray whales tracked using a hydrophone array. PLOS ONE. 12:e0185585.: Public Library of Science   10.1371/journal.pone.0185585   Abstract

Eastern North Pacific gray whales make one of the longest annual migrations of any mammal, traveling from their summer feeding areas in the Bering and Chukchi Seas to their wintering areas in the lagoons of Baja California, Mexico. Although a significant body of knowledge on gray whale biology and behavior exists, little is known about their vocal behavior while migrating. In this study, we used a sparse hydrophone array deployed offshore of central California to investigate how gray whales behave and use sound while migrating. We detected, localized, and tracked whales for one full migration season, a first for gray whales. We verified and localized 10,644 gray whale M3 calls and grouped them into 280 tracks. Results confirm that gray whales are acoustically active while migrating and their swimming and acoustic behavior changes on daily and seasonal time scales. The seasonal timing of the calls verifies the gray whale migration timing determined using other methods such as counts conducted by visual observers. The total number of calls and the percentage of calls that were part of a track changed significantly over both seasonal and daily time scales. An average calling rate of 5.7 calls/whale/day was observed, which is significantly greater than previously reported migration calling rates. We measured a mean speed of 1.6 m/s and quantified heading, direction, and water depth where tracks were located. Mean speed and water depth remained constant between night and day, but these quantities had greater variation at night. Gray whales produce M3 calls with a root mean square source level of 156.9 dB re 1 μPa at 1 m. Quantities describing call characteristics were variable and dependent on site-specific propagation characteristics.