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Jan 2010

Volume 127, Issue 1, pp. EL1-611

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Broadband source localization using horizontal-beam acoustic intensity striations

Altan Turgut, Marshall Orr, and Daniel Rouseff

J. Acoust. Soc. Am. Volume 127, Issue 1, pp. 73-83 (2010); (11 pages) | Cited 7 times

Online Publication Date: 05 Jan 2010

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Waveguide invariant theory is applied to horizontal line array (HLA) beamformer output to localize moving broadband noise sources from measured acoustic intensity striation patterns. Acoustic signals emitted by ships of opportunity (merchant ships) were simultaneously recorded on a HLA and three hydrophones separated by 10 km during the RAGS03 (relationship between array gain and shelf-break fluid processes) experiment. Hough transforms are used to estimate both the waveguide invariant parameter “beta” and the ratio of source range at the closest point of approach to source speed from the observed striation patterns. Broadband (50–150-Hz) acoustic data-sets are used to demonstrate source localization capability as well as inversion capability of waveguide invariant parameter beta. Special attention is paid to bathymetric variability since the acoustic intensity striation patterns seem to be influenced by range-dependent bathymetry of the experimental area. The Hough transform method is also applied to the HLA beam-time record data and to the acoustic intensity data from three distant receivers to validate the estimation results from HLA beamformer output. Good agreement of the results from all three approaches suggests the feasibility of locating broadband noise sources and estimating waveguide invariant parameter beta in shallow waters.
Show PACS
43.30.Bp Normal mode propagation of sound in water
43.30.Wi Passive sonar systems and algorithms, matched field processing in underwater acoustics
43.30.Zk Experimental modeling
43.60.Lq Acoustic imaging, displays, pattern recognition, feature extraction

Geoacoustic inversions and localizations with adaptively beamformed data from a surface ship of opportunity source

Steven A. Stotts and Robert A. Koch

J. Acoust. Soc. Am. Volume 127, Issue 1, pp. 84-95 (2010); (12 pages) | Cited 2 times

Online Publication Date: 05 Jan 2010

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A technique has been developed for incorporating adaptively beamformed (ABF) data into geoacoustic inversions and source localizations based on matched-field processing. Rather than adaptively adjusting matched-field weights, for this paper ABF processing is applied to construct subaperture beam data from which the inversions and localizations are derived. This application of ABF processing to inversion and localization is successfully demonstrated with data collected on a horizontal line array from a surface ship of opportunity source (SSOS). When measured data representing noise from one or more interfering sources at various levels are injected into the data collected from the SSOS, the inversion processing with ABF subaperture data is successful at interferer noise levels exceeding the SSOS levels by 10–13 dB and for which the inversion processing with conventionally beamformed data fails.
Show PACS
43.30.Pc Ocean parameter estimation by acoustical methods; remote sensing; imaging, inversion, acoustic tomography
43.60.Kx Matched field processing
43.60.Mn Adaptive processing
43.30.Bp Normal mode propagation of sound in water

Observations and modeling of angular compression and vertical spatial coherence in sea surface forward scattering

Peter H. Dahl

J. Acoust. Soc. Am. Volume 127, Issue 1, pp. 96-103 (2010); (8 pages) | Cited 1 time

Online Publication Date: 05 Jan 2010

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Measurements and modeling of spatial coherence and related angular spreading associated with forward scattering from the sea surface are presented. The measurements were taken in waters 80 m deep off the New Jersey coast in August 2006. Acoustic signals from a source at depth 40 m were recorded on a vertical line array of length 1.4 m, centered at depth 25 m, and at range 200 m. Measurements in the 14–20-kHz frequency range are reported; the rms waveheight H was 0.16 m, setting kH as ∼ 10 where k is acoustic wavenumber. A systematic study of measurements taken over four source–receiver bearing angles separated by 90° suggests a null influence of changing bearing angle or equivalently directional wave effects. Sound speed was characterized by a downward-refracting profile. Refraction modifies the vertical angular spread due to rough sea surface scattering, which can be understood from Snell’s law. The Snell mapping is smooth, so an approximation based on the mean grazing angle provides a functional relation between the angular variance near the surface and that at the receiver. The latter is measurably reduced owing to refraction, the effect called angular compression, and a parameter that quantifies this effect is defined.
Show PACS
43.30.Re Signal coherence or fluctuation due to sound propagation/scattering in the ocean
43.30.Zk Experimental modeling
43.30.Hw Rough interface scattering

Low-frequency target strength and abundance of shoaling Atlantic herring (Clupea harengus) in the Gulf of Maine during the Ocean Acoustic Waveguide Remote Sensing 2006 Experiment

Zheng Gong, Mark Andrews, Srinivasan Jagannathan, Ruben Patel, J. Michael Jech, Nicholas C. Makris, and Purnima Ratilal

J. Acoust. Soc. Am. Volume 127, Issue 1, pp. 104-123 (2010); (20 pages) | Cited 5 times

Online Publication Date: 05 Jan 2010

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The low-frequency target strength of shoaling Atlantic herring (Clupea harengus) in the Gulf of Maine during Autumn 2006 spawning season is estimated from experimental data acquired simultaneously at multiple frequencies in the 300–1200 Hz range using (1) a low-frequency ocean acoustic waveguide remote sensing (OAWRS) system, (2) areal population density calibration with several conventional fish finding sonar (CFFS) systems, and (3) low-frequency transmission loss measurements. The OAWRS system’s instantaneous imaging diameter of 100 km and regular updating enabled unaliased monitoring of fish populations over ecosystem scales including shoals of Atlantic herring containing hundreds of millions of individuals, as confirmed by concurrent trawl and CFFS sampling. High spatial-temporal coregistration was found between herring shoals imaged by OAWRS and concurrent CFFS line-transects, which also provided fish depth distributions. The mean scattering cross-section of an individual shoaling herring is found to consistently exhibit a strong, roughly 20 dB/octave roll-off with decreasing frequency in the range of the OAWRS survey over all days of the roughly 2-week experiment, consistent with the steep roll-offs expected for sub-resonance scattering from fish with air-filled swimbladders.
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43.30.Sf Acoustical detection of marine life; passive and active
43.30.Pc Ocean parameter estimation by acoustical methods; remote sensing; imaging, inversion, acoustic tomography
43.30.Vh Active sonar systems

Spatial and temporal patterns of Risso’s dolphin echolocation in the Southern California Bight

Melissa S. Soldevilla, Sean M. Wiggins, and John A. Hildebrand

J. Acoust. Soc. Am. Volume 127, Issue 1, pp. 124-132 (2010); (9 pages) | Cited 12 times

Online Publication Date: 05 Jan 2010

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Geographical and temporal trends in echolocation clicking activity can lead to insights into the foraging and migratory behaviors of pelagic dolphins. Using autonomous acoustic recording packages, the geographical, diel, and seasonal patterns of Risso’s dolphin (Grampus griseus) echolocation click activity are described for six locations in the Southern California Bight between 2005 and 2007. Risso’s dolphin echolocation click bouts are identified based on their unique spectral characteristics. Click bouts were identified on 739 of 1959 recording days at all 6 sites, with the majority occurring at nearshore sites. A significant diel pattern is evident in which both hourly occurrences of click bouts and click rates are higher at night than during the day. At all nearshore sites, Risso’s dolphin clicks were identified year-round, with the highest daily occurrence at the southern end of Santa Catalina Island. Seasonal and interannual variabilities in occurrence were high across sites with peak occurrence in autumn of most years at most sites. These results suggest that Risso’s dolphins forage at night and that the southern end of Santa Catalina Island represents an important habitat for Risso’s dolphins throughout the year.
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43.30.Sf Acoustical detection of marine life; passive and active
43.80.Ka Sound production by animals: mechanisms, characteristics, populations, biosonar

Localization of sperm whales in a group using clicks received at two separated short baseline arrays

Ryo Hirotsu, Masao Yanagisawa, Tamaki Ura, Masao Sakata, Harumi Sugimatsu, Junichi Kojima, and Rajendar Bahl

J. Acoust. Soc. Am. Volume 127, Issue 1, pp. 133-147 (2010); (15 pages) | Cited 3 times

Online Publication Date: 05 Jan 2010

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In this paper, a sperm whale click analysis scheme is proposed in order to calculate the position of individual sperm whales in a group using data received at two arrays deployed near the surface. The proposed method mainly consists of two parts: short baseline (SBL) with classification and long baseline (LBL) with class matching. In SBL with classification, a click is automatically detected, and its direction of arrival is calculated. The clicks are then classified based on their direction vectors. The class data are then sent together with direction data and matched to the other array’s class data. LBL with class matching is used for localization. The classification algorithm can be used to estimate the number of whales clicking and to list potential candidates for LBL matching. As a result, the proposed method is able to localize the positions of the whales in a group. The performance of the proposed method is evaluated using data recorded off Ogasawara islands with two arrays near the surface. The three-dimensional underwater trajectories of six sperm whales are extracted to demonstrate the capability of the proposed method.
Show PACS
43.30.Wi Passive sonar systems and algorithms, matched field processing in underwater acoustics
43.80.Ev Acoustical measurement methods in biological systems and media
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