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  • Biocommunications  (11)
  • Oceanography  (8)
  • Acoustics
  • Antartica
  • Acoustical Society of America  (21)
  • American Association for the Advancement of Science
  • Public Library of Science
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  • 1
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    Annual Acoustic Presence of Fin Whale (Balaenoptera physalus) Offshore Eastern Sicily, Central Mediterranean Sea (2016)
    Public Library of Science
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    Publikationsdatum: 2017-04-04
    Beschreibung: In recent years, an increasing number of surveys have definitively confirmed the seasonal presence of fin whales (Balaenoptera physalus) in highly productive regions of the Mediterranean Sea. Despite this, very little is yet known about the routes that the species seasonally follows within the Mediterranean basin and, particularly, in the Ionian area. The present study assesses for the first time fin whale acoustic presence offshore Eastern Sicily (Ionian Sea), throughout the processing of about 10 months of continuous acoustic monitoring. The recording of fin whale vocalizations was made possible by the cabled deep-sea multidisciplinary observatory, “NEMO-SN1”, deployed 25 km off the Catania harbor at a depth of about 2,100 meters. NEMO-SN1 is an operational node of the European Multidisciplinary Seafloor and water-column Observatory (EMSO) Research Infrastructure. The observatory was equipped with a low-frequency hydrophone (bandwidth: 0.05 Hz–1 kHz, sampling rate: 2 kHz) which continuously acquired data from July 2012 to May 2013. About 7,200 hours of acoustic data were analyzed by means of spectrogram display. Calls with the typical structure and patterns associated to the Mediterranean fin whale population were identified and monitored in the area for the first time. Furthermore, a background noise analysis within the fin whale communication frequency band (17.9–22.5 Hz) was conducted to investigate possible detection-masking effects. The study confirms the hypothesis that fin whales are present in the Ionian Sea throughout all seasons, with peaks in call detection rate during spring and summer months. The analysis also demonstrates that calls were more frequently detected in low background noise conditions. Further analysis will be performed to understand whether observed levels of noise limit the acoustic detection of the fin whales vocalizations, or whether the animals vocalize less in the presence of high background noise.
    Beschreibung: Published
    Beschreibung: e0141838
    Beschreibung: 3A. Ambiente Marino
    Beschreibung: JCR Journal
    Beschreibung: open
    Schlagwort(e): Whales ; Bioacoustics ; Background noise (acoustics) ; Acoustic signals ; Sperm whales ; Vocalization ; Acoustics ; Data acquisition ; 03. Hydrosphere::03.01. General::03.01.08. Instruments and techniques ; 03. Hydrosphere::03.02. Hydrology::03.02.04. Measurements and monitoring ; 03. Hydrosphere::03.02. Hydrology::03.02.07. Instruments and techniques ; 03. Hydrosphere::03.04. Chemical and biological::03.04.99. General or miscellaneous
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 2
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    Predicted scattering of sound by diffuse hydrothermal vent plumes at mid-ocean ridges (2008)
    Acoustical Society of America
    Details
    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © Acoustical Society of America, 1998. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 103 (1998): 330-335, doi:10.1121/1.421092.
    Beschreibung: Amplitude and phase fluctuations of monochromatic acoustic signals traveling through diffuse mid-ocean ridge hydrothermal vent plumes are modeled using existing theory in an attempt to find suitable frequencies and path lengths for plume monitoring. Weak-scattering solutions are evaluated numerically, with model parameters adjusted to match observed plume characteristics. Constraints required for weak-scattering solutions to be valid can be met for transmission ranges of 500–2000 m and frequencies of 20–80 kHz. Therefore, because fluid structure and scattering strength are more closely linked for weak scattering than for stronger scattering, inversion for fluid statistical properties may be possible, enabling diffuse vent monitoring. Such monitoring would be subject to geometric assumptions such as transmission entirely within a statistically homogeneous plume. Performance-limiting phase fluctuations have also been computed for a 13–17 kHz geodetic survey system.
    Beschreibung: This work was supported by the Woods Hole Oceanographic Institution with research funds provided by the Mellon Foundation.
    Schlagwort(e): Underwater sound ; Oceanography ; Acoustic wave scattering ; Seafloor phenomena
    Repository-Name: Woods Hole Open Access Server
    Materialart: Article
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  • 3
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    Manatee (Trichechus manatus) vocalization usage in relation to environmental noise levels (2009)
    Acoustical Society of America
    Details
    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © Acoustical Society of America, 2009. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 125 (2009): 1806-1815, doi:10.1121/1.3068455.
    Beschreibung: Noise can interfere with acoustic communication by masking signals that contain biologically important information. Communication theory recognizes several ways a sender can modify its acoustic signal to compensate for noise, including increasing the source level of a signal, its repetition, its duration, shifting frequency outside that of the noise band, or shifting the timing of signal emission outside of noise periods. The extent to which animals would be expected to use these compensation mechanisms depends on the benefit of successful communication, risk of failure, and the cost of compensation. Here we study whether a coastal marine mammal, the manatee, can modify vocalizations as a function of behavioral context and ambient noise level. To investigate whether and how manatees modify their vocalizations, natural vocalization usage and structure were examined in terms of vocalization rate, duration, frequency, and source level. Vocalizations were classified into two call types, chirps and squeaks, which were analyzed independently. In conditions of elevated noise levels, call rates decreased during feeding and social behaviors, and the duration of each call type was differently influenced by the presence of calves. These results suggest that ambient noise levels do have a detectable effect on manatee communication and that manatees modify their vocalizations as a function of noise in specific behavioral contexts.
    Beschreibung: This research was supported by a P.E.O. Scholar Award and National Defense Science and Engineering Fellowship awarded to Jennifer Miksis.
    Schlagwort(e): Acoustic noise ; Acoustic signal processing ; Biocommunications ; Hearing ; Speech intelligibility
    Repository-Name: Woods Hole Open Access Server
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  • 4
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    Propagation of narrow-band-high-frequency clicks : measured and modeled transmission loss of porpoise-like clicks in porpoise habitats (2010)
    Acoustical Society of America
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    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © Acoustical Society of America, 2010. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 127 (2010): 560-567, doi:10.1121/1.3257203.
    Beschreibung: Estimating the range at which harbor porpoises can detect prey items and environmental objects is integral to understanding their biosonar. Understanding the ranges at which they can use echolocation to detect and avoid obstacles is particularly important for strategies to reduce bycatch. Transmission loss (TL) during acoustic propagation is an important determinant of those detection ranges, and it also influences animal detection functions used in passive acoustic monitoring. However, common assumptions regarding TL have rarely been tested. Here, TL of synthetic porpoise clicks was measured in porpoise habitats in Canada and Denmark, and field data were compared with spherical spreading law and ray-trace (Bellhop) model predictions. Both models matched mean observations quite well in most cases, indicating that a spherical spreading law can usually provide an accurate first-order estimate of TL for porpoise sounds in porpoise habitat. However, TL varied significantly (±10 dB) between sites and over time in response to variability in seafloor characteristics, sound-speed profiles, and other short-timescale environmental fluctuations. Such variability should be taken into account in estimates of the ranges at which porpoises can communicate acoustically, detect echolocation targets, and be detected via passive acoustic monitoring.
    Beschreibung: Field data collection was partially supported by a Student Research Award from the WHOI Ocean Life Institute (Grant No. 25051351). P.T.M. and M.H. were funded by Steno and frame grants from the Danish Natural Science Foundation.
    Schlagwort(e): Bioacoustics ; Biocommunications ; Mechanoception ; Underwater acoustic propagation ; Zoology
    Repository-Name: Woods Hole Open Access Server
    Materialart: Article
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  • 5
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    Coincidence echo statistics (2012)
    Acoustical Society of America
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    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © Acoustical Society of America, 1996. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 99 (1996): 266-271, doi:10.1121/1.414537.
    Beschreibung: Two scatterers at similar range give an echo which may appear to be due to a single scatterer. Methods for determining target strength that depend on resolving single scatterers may fail in this instance. Statistics associated with the described special case of coincidence are derived and illustrated by theoretical computation for the SIMRAD EK500 echo sounder system with the ES38B split‐beam transducer resonant at 38 kHz. Connections to angle measurement in radar and swath bathymetry and to bottom‐scattering‐strength measurement are noted.
    Schlagwort(e): Acoustic resonance ; Acoustic transducers ; Echoes ; Bathymetry ; Beam splitting ; Oceanography ; Scattering ; Sediment−water interfaces ; Sound waves
    Repository-Name: Woods Hole Open Access Server
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  • 6
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    Three-dimensional beam pattern of regular sperm whale clicks confirms bent-horn hypothesis (2008)
    Acoustical Society of America
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    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © Acoustical Society of America, 2005. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 117 (2005): 1473-1485, doi:10.1121/1.1828501.
    Beschreibung: The three-dimensional beam pattern of a sperm whale (Physeter macrocephalus) tagged in the Ligurian Sea was derived using data on regular clicks from the tag and from hydrophones towed behind a ship circling the tagged whale. The tag defined the orientation of the whale, while sightings and beamformer data were used to locate the whale with respect to the ship. The existence of a narrow, forward-directed P1 beam with source levels exceeding 210 dBpeak re: 1 µPa at 1 m is confirmed. A modeled forward-beam pattern, that matches clicks 〉20° off-axis, predicts a directivity index of 26.7 dB and source levels of up to 229 dBpeak re: 1 µPa at 1 m. A broader backward-directed beam is produced by the P0 pulse with source levels near 200 dBpeak re: 1 µPa at 1 m and a directivity index of 7.4 dB. A low-frequency component with source levels near 190 dBpeak re: 1 µPa at 1 m is generated at the onset of the P0 pulse by air resonance. The results support the bent-horn model of sound production in sperm whales. While the sperm whale nose appears primarily adapted to produce an intense forward-directed sonar signal, less-directional click components convey information to conspecifics, and give rise to echoes from the seafloor and the surface, which may be useful for orientation during dives.
    Beschreibung: This work was funded by grants from the Office of Naval Research Grants N00014-99-1-0819 and N00014-01-1-0705, and the Packard Foundation.
    Schlagwort(e): Bioacoustics ; Biocommunications ; Array signal processing ; Echo ; Hydrophones ; Multidimensional signal processing ; Underwater sound ; Sonar signal processing
    Repository-Name: Woods Hole Open Access Server
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  • 7
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    A versatile pitch tracking algorithm : from human speech to killer whale vocalizations (2009)
    Acoustical Society of America
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    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © Acoustical Society of America, 2009. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 126 (2009): 451-459, doi:10.1121/1.3132525.
    Beschreibung: In this article, a pitch tracking algorithm [named discrete logarithmic Fourier transformation-pitch detection algorithm (DLFT-PDA)], originally designed for human telephone speech, was modified for killer whale vocalizations. The multiple frequency components of some of these vocalizations demand a spectral (rather than temporal) approach to pitch tracking. The DLFT-PDA algorithm derives reliable estimations of pitch and the temporal change of pitch from the harmonic structure of the vocal signal. Scores from both estimations are combined in a dynamic programming search to find a smooth pitch track. The algorithm is capable of tracking killer whale calls that contain simultaneous low and high frequency components and compares favorably across most signal to noise ratio ranges to the peak-picking and sidewinder algorithms that have been used for tracking killer whale vocalizations previously.
    Beschreibung: C.W. was supported by DARPA under Contract No. N66001-96-C-8526, monitored through Naval Command, Control, and Ocean Surveillance Center and by the National Science Foundation under Grant No. IRI-9618731. A.D.S. was supported by a National Defense Science and Engineering Graduate Fellowship.
    Schlagwort(e): Acoustic signal detection ; Biocommunications ; Fourier transforms ; Target tracking
    Repository-Name: Woods Hole Open Access Server
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  • 8
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    Common humpback whale (Megaptera novaeangliae) sound types for passive acoustic monitoring (2011)
    Acoustical Society of America
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    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © Acoustical Society of America, 2011. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 129 (2011): 476-482, doi:10.1121/1.3504708.
    Beschreibung: Humpback whales (Megaptera novaeangliae) are one of several baleen whale species in the Northwest Atlantic that coexist with vessel traffic and anthropogenic noise. Passive acoustic monitoring strategies can be used in conservation management, but the first step toward understanding the acoustic behavior of a species is a good description of its acoustic repertoire. Digital acoustic tags (DTAGs) were placed on humpback whales in the Stellwagen Bank National Marine Sanctuary to record and describe the non-song sounds being produced in conjunction with foraging activities. Peak frequencies of sounds were generally less than 1 kHz, but ranged as high as 6 kHz, and sounds were generally less than 1 s in duration. Cluster analysis distilled the dataset into eight groups of sounds with similar acoustic properties. The two most stereotyped and distinctive types (“wops” and “grunts”) were also identified aurally as candidates for use in passive acoustic monitoring. This identification of two of the most common sound types will be useful for moving forward conservation efforts on this Northwest Atlantic feeding ground.
    Beschreibung: This paper was funded by the National Oceanic and Atmospheric Administration (NOAA)’s National Marine Sanctuaries Program. It was also sponsored in part by the University of Hawaii Sea Grant College Program, School of Ocean and Earth Science and Technology, under Institutional Grant No. NA05OAR4171048 from the NOAA Office of Sea Grant, Department of Commerce.
    Schlagwort(e): Bioacoustics ; Biocommunications ; Underwater sound
    Repository-Name: Woods Hole Open Access Server
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  • 9
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    Captive dolphins, Tursiops truncatus, develop signature whistles that match acoustic features of human-made model sounds (2008)
    Acoustical Society of America
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    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © Acoustical Society of America, 2002. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 112 (2002): 728-739, doi:10.1121/1.1496079.
    Beschreibung: This paper presents a cross-sectional study testing whether dolphins that are born in aquarium pools where they hear trainers' whistles develop whistles that are less frequency modulated than those of wild dolphins. Ten pairs of captive and wild dolphins were matched for age and sex. Twenty whistles were sampled from each dolphin. Several traditional acoustic features (total duration, duration minus any silent periods, etc.) were measured for each whistle, in addition to newly defined flatness parameters: total flatness ratio (percentage of whistle scored as unmodulated), and contiguous flatness ratio (duration of longest flat segment divided by total duration). The durations of wild dolphin whistles were found to be significantly longer, and the captive dolphins had whistles that were less frequency modulated and more like the trainers' whistles. Using a standard t-test, the captive dolphin had a significantly higher total flatness ratio in 9/10 matched pairs, and in 8/10 pairs the captive dolphin had significantly higher contiguous flatness ratios. These results suggest that captive-born dolphins can incorporate features of artificial acoustic models made by humans into their signature whistles.
    Beschreibung: J.R.B. gratefully acknowledges the support of the National Science Foundation Ocean Sciences CAREER Award 9733391. P.L.T. acknowledges the support of the Office of Naval Research Grant N00014-87-K-0236 and NIH Grant 5 R29 NS25290 for supporting the collection of the data used in this study and NIH Grant R01 DC04191 for support in preparation of the manuscript.
    Schlagwort(e): Acoustic field ; Acoustic signal processing ; Biocommunications ; Speech ; Acoustic variables measurement
    Repository-Name: Woods Hole Open Access Server
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  • 10
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    Preliminary evidence for signature vocalizations among free-ranging narwhals (Monodon monoceros) (2008)
    Acoustical Society of America
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    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © Acoustical Society of America, 2006. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 120 (2006): 1695-1705, doi:10.1121/1.2226586.
    Beschreibung: Animal signature vocalizations that are distinctive at the individual or group level can facilitate recognition between conspecifics and re-establish contact with an animal that has become separated from its associates. In this study, the vocal behavior of two free-ranging adult male narwhals (Monodon monoceros) in Admiralty Inlet, Baffin Island was recorded using digital archival tags. These recording instruments were deployed when the animals were caught and held onshore to attach satellite tags, a protocol that separated them from their groups. The signature content of two vocal categories was considered: (1) combined tonal/pulsed signals, which contained synchronous pulsatile and tonal content; (2) whistles, or frequency modulated tonal signals with harmonic energy. Nonparametric comparisons of the temporal and spectral features of each vocal class revealed significant differences between the two individuals. A separate, cross-correlation measure conducted on the whistles that accounted for overall contour shape and absolute frequency content confirmed greater interindividual compared to intraindividual differences. These data are consistent with the hypothesis that narwhals produce signature vocalizations that may facilitate their reunion with group members once they become separated, but additional data are required to demonstrate this claim more rigorously.
    Beschreibung: I thank the WHOI Academic Programs office, the National Science Foundation Research Fellowship, and the National Defense Science and Engineering Graduate Fellowship for financial support. This field operation was funded by the Greenland Institute of Natural Resources, the National Environmental Research Institute, Department of Fisheries and Oceans, Nunavut Wildlife Management Board and the Danish Cooperation for the Environment in the Arctic (DANCEA). Additional logistical support was provided by the Polar Continental Shelf Project.
    Schlagwort(e): Biocommunications ; Bioacoustics ; Spectral analysis
    Repository-Name: Woods Hole Open Access Server
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  • 11
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    Field measurements of sonic boom penetration into the ocean (2008)
    Acoustical Society of America
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    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © Acoustical Society of America, 2000. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 107 (2000): 3073-3083, doi:10.1121/1.429336.
    Beschreibung: Six sonic booms, generated by F-4 aircraft under steady flight at a range of altitudes (610–6100 m) and Mach numbers (1.07–1.26), were measured just above the air/sea interface, and at five depths in the water column. The measurements were made with a vertical hydrophone array suspended from a small spar buoy at the sea surface, and telemetered to a nearby research vessel. The sonic boom pressure amplitude decays exponentially with depth, and the signal fades into the ambient noise field by 30–50 m, depending on the strength of the boom at the sea surface. Low-frequency components of the boom waveform penetrate significantly deeper than high frequencies. Frequencies greater than 20 Hz are difficult to observe at depths greater than about 10 m. Underwater sonic boom pressure measurements exhibit excellent agreement with predictions from analytical theory, despite the assumption of a flat air/sea interface. Significant scattering of the sonic boom signal by the rough ocean surface is not detected. Real ocean conditions appear to exert a negligible effect on the penetration of sonic booms into the ocean unless steady vehicle speeds exceed Mach 3, when the boom incidence angle is sufficient to cause scattering on realistic open ocean surfaces.
    Beschreibung: This work was funded by the NASA Langley Research Center (Technical Monitor, Dr. Kevin Shepherd).
    Schlagwort(e): Shock waves ; Oceanography ; Underwater acoustic propagation
    Repository-Name: Woods Hole Open Access Server
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  • 12
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    Simulated tomographic reconstruction of ocean features using drifting acoustic receivers and a navigated source (2008)
    Acoustical Society of America
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    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © Acoustical Society of America, 1995. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 98 (1995): 2270-2279, doi:10.1121/1.413341.
    Beschreibung: Numerically simulated acoustic transmission from a single source of known position (for example, suspended from a ship) to receivers of partially known position (for example, sonobuoys dropped from the air) are used for tomographic mapping of ocean sound speed. The maps are evaluated for accuracy and utility. Grids of 16 receivers are employed, with sizes of 150, 300, and 700 km square. Ordinary statistical measures are used to evaluate the pattern similarity and thus the mapping capability of the system. For an array of 300 km square, quantitative error in the maps grows with receiver position uncertainty. The large and small arrays show lesser mapping capability than the mid-size array. Mapping errors increase with receiver position uncertainty for uncertainties less than 1000-m rms, but uncertainties exceeding that have less systematic effect on the maps. Maps of rms error of the field do not provide a complete view of the utility of the acoustic network. Features of maps are surprisingly reproducible for different navigation error levels, and give comparable information about mesoscale structures despite great variations in those levels.
    Beschreibung: This work was supported by Office of Naval Research grants N00014-9l-J-1138 (Arctic Sciences )and N00014-92-I-1162 (Ocean Acoustics).
    Schlagwort(e): Accuracy ; Errors ; Mapping ; Oceanography ; Remote sensing ; Simulation ; Tomography ; Wave propagation ; Sound sources ; Sound velocity
    Repository-Name: Woods Hole Open Access Server
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  • 13
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    The acoustic field on the forehead of echolocating Atlantic bottlenose dolphins (Tursiops truncatus) (2010)
    Acoustical Society of America
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    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © Acoustical Society of America, 2010. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 128 (2010): 1426-1434, doi:10.1121/1.3372643.
    Beschreibung: Arrays of up to six broadband suction cup hydrophones were placed on the forehead of two bottlenose dolphins to determine the location where the beam axis emerges and to examine how signals in the acoustic near-field relate to signals in the far-field. Four different array geometries were used; a linear one with hydrophones arranged along the midline of the forehead, and two around the front of the melon at 1.4 and 4.2 cm above the rostrum insertion, and one across the melon in certain locations not measured by other configurations. The beam axis was found to be close to the midline of the melon, approximately 5.4 cm above the rostrum insert for both animals. The signal path coincided with the low-density, low-velocity core of the melon; however, the data suggest that the signals are focused mainly by the air sacs. Slight asymmetry in the signals were found with higher amplitudes on the right side of the forehead. Although the signal waveform measured on the melon appeared distorted, when they are mathematically summed in the far-field, taking into account the relative time of arrival of the signals, the resultant waveform matched that measured by the hydrophone located at 1 m.
    Beschreibung: This work was supported by the U.S. Office of Naval Research.
    Schlagwort(e): Acoustic field ; Acoustic signal detection ; Bioacoustics ; Biocommunications ; Hydrophones ; Underwater sound ; Zoology
    Repository-Name: Woods Hole Open Access Server
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  • 14
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    High-frequency acoustic scattering from turbulent oceanic microstructure : the importance of density fluctuations (2008)
    Acoustical Society of America
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    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © Acoustical Society of America, 2003. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 114 (2003): 2685-2697, doi:10.1121/1.1614258.
    Beschreibung: Acoustic scattering techniques provide a unique and powerful tool to remotely investigate the physical properties of the ocean interior over large spatial and temporal scales. With high-frequency acoustic scattering it is possible to probe physical processes that occur at the microstructure scale, spanning submillimeter to centimeter scale processes. An acoustic scattering model for turbulent oceanic microstructure is presented in which the current theory, which only accounts for fluctuations in the sound speed, has been extended to include fluctuations in the density as well. The inclusion of density fluctuations results in an expression for the scattering cross section per unit volume, σv, that is explicitly dependent on the scattering angle. By relating the variability in the density and sound speed to random fluctuations in oceanic temperature and salinity, σv has been expressed in terms of the temperature and salinity wave number spectra, and the temperature-salinity co-spectrum. A Batchelor spectrum for temperature and salinity, which depends on parameters such as the dissipation rates of turbulent kinetic energy and temperature variance, has been used to evaluate σv. Two models for the temperature-salinity co-spectrum have also been used. The predictions indicate that fluctuations in the density could be as important in determining backscattering as fluctuations in the sound speed. Using data obtained in the ocean with a high resolution vertical microstructure profiler, it is predicted that scattering from oceanic microstructure can be as strong as scattering from zooplankton.
    Beschreibung: This work was supported in part by ONR, NSF, and the Woods Hole Oceanographic Institution.
    Schlagwort(e): Acoustic wave scattering ; Underwater acoustic propagation ; Oceanography ; Remote sensing ; Oceanographic techniques
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  • 15
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    Travel-time perturbations due to internal waves : equivalence of modal and ray solutions (2008)
    Acoustical Society of America
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    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © Acoustical Society of America, 1996. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 99 (1996): 822-830, doi:10.1121/1.414563.
    Beschreibung: In a recent paper, Lynch et al. used modal and ray based perturbation techniques to compare predicted variances of acoustic travel times due to internal waves to measured variances in the Barents Sea Polar Front experiment [Lynch et al., J. Acoust. Soc. Am. 99, 803–821 (1996)]. One of the interesting results of this work is that the modal and ray travel-time variances are substantially different for rays and modes with the same grazing angle. Specifically, the maximum modal travel-time variance shows a resonant effect in which the variance increases with increasing frequency. Unlike the modal solution, the ray travel-time variance has a geometrically constrained maximum, independent of frequency. In this paper, the linear first-order solutions for the ray and modal variances due to the internal waves are reviewed, and in an Appendix the effects of the linearizing assumptions are examined. The ray and mode solutions are then shown to be consistent by considering a truncated sum of modes that constructively interfere along a geometric ray path. By defining the travel-time perturbation due to a truncated sum of modes, the travel-time variance of the modal sum is derived. With increasing frequency the maximum value of this variance converges to a frequency-independent result with a similar magnitude to the ray maximum variance.
    Schlagwort(e): Internal waves ; Oceanography ; Sound waves ; Travelling waves ; Underwater ; Wave propagation ; Barents Sea ; Ray trajectories ; Shallow–water equations ; Travel time
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    A beamforming video recorder for integrated observations of dolphin behavior and vocalizations (2008)
    Acoustical Society of America
    Details
    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © Acoustical Society of America, 2005. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 117 (2005): 1005-1008, doi:10.1121/1.1831284.
    Beschreibung: In this Letter we describe a beamforming video recorder consisting of a video camera at the center of a 16 hydrophone array. A broadband frequency-domain beamforming algorithm is used to estimate the azimuth and elevation of each detected sound. These estimates are used to generate a visual cue indicating the location of the sound source within the video recording, which is synchronized to the acoustic data. The system provided accurate results in both lab calibrations and a field test. The system allows researchers to correlate the acoustic and physical behaviors of marine mammals during studies of social interactions.
    Beschreibung: This research was funded by NSF Ocean Sciences CAREER award 9733391.
    Schlagwort(e): Bioacoustics ; Biocommunications ; Array signal processing ; Acoustic correlation ; Video recording ; Frequency-domain analysis ; Acoustic signal detection ; Underwater sound ; Hydrophones
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    Ray-acoustic caustic formation and timing effects from ocean sound-speed relative curvature (2008)
    Acoustical Society of America
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    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © Acoustical Society of America, 1994. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 96 (1994): 1033-1046, doi:10.1121/1.410380.
    Beschreibung: Using deterministic ray-acoustic modeling of 1000-km propagation in the North Pacific, a depth-dependent parameter of ocean sound channels has been found to strongly influence geometrical ray propagation. This parameter is the sound speed times the second vertical derivative of sound speed divided by the square of the first derivative. Ray and wavefront timing and intensity can be influenced within realistic ocean sound channels by unpredictable wavefront triplications and caustics. These triplications are associated with large values of the parameter at ray turning points. The parameter, a relative curvature, behaves as a random variable because of ocean finestructure, causing the unpredictability. The relative curvature has a higher mean value near the sound-speed minimum for both an internal-wave model and actual data, so that this mechanism is a plausible explanation of poor multipath resolution and identifiability late in North Pacific pulse trains.
    Beschreibung: This work was supported by the Office of Naval Technology (N00014-90-C-0098) and the Office of Naval Research, Ocean Acoustics Program (N00014-92-J-1162).
    Schlagwort(e): Pacific Ocean ; Ray-tracing ; Sound waves ; Wave propagation ; Pulses ; Acoustics ; Sound velocity ; Depth profiles ; Wave front ; Fluctuations ; Underwater
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    Estimated communication range and energetic cost of bottlenose dolphin whistles in a tropical habitat (2012)
    Acoustical Society of America
    Details
    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © Acoustical Society of America, 2012. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 131 (2012): 582-592, doi:10.1121/1.3662067.
    Beschreibung: Bottlenose dolphins (Tursiops sp.) depend on frequency-modulated whistles for many aspects of their social behavior, including group cohesion and recognition of familiar individuals. Vocalization amplitude and frequency influences communication range and may be shaped by many ecological and physiological factors including energetic costs. Here, a calibrated GPS-synchronized hydrophone array was used to record the whistles of bottlenose dolphins in a tropical shallow-water environment with high ambient noise levels. Acoustic localization techniques were used to estimate the source levels and energy content of individual whistles. Bottlenose dolphins produced whistles with mean source levels of 146.7±6.2 dB re. 1 μPa(RMS). These were lower than source levels estimated for a population inhabiting the quieter Moray Firth, indicating that dolphins do not necessarily compensate for the high noise levels found in noisy tropical habitats by increasing their source level. Combined with measured transmission loss and noise levels, these source levels provided estimated median communication ranges of 750 m and maximum communication ranges up to 5740 m. Whistles contained less than 17 mJ of acoustic energy, showing that the energetic cost of whistling is small compared to the high metabolic rate of these aquatic mammals, and unlikely to limit the vocal activity of toothed whales.
    Beschreibung: This study received support from the Danish Ph.D. School of Aquatic Sciences (SOAS), Aarhus University, DK, WWF Verdensnaturfonden and Aase & Ejnar Danielsens Foundation, the Siemens Foundation, the Faculty of Science at the University of Aarhus, DK, and the Danish Natural Science Foundation via a Steno scholarship and a logistics grant to PTM.
    Schlagwort(e): Acoustic arrays ; Acoustic noise ; Acoustic radiators ; Acoustic variables measurement ; Acoustic wave transmission ; Biocommunications ; Global Positioning System ; Hydrophones ; Underwater sound
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    Long distance passive localization of vocalizing sei whales using an acoustic normal mode approach (2012)
    Acoustical Society of America
    Details
    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © Acoustical Society of America, 2012. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 131 (2012): 1814-1825, doi:10.1121/1.3666015.
    Beschreibung: During a 2 day period in mid-September 2006, more than 200, unconfirmed but identifiable, sei whale (Balaenoptera borealis) calls were collected as incidental data during a multidisciplinary oceanography and acoustics experiment on the shelf off New Jersey. Using a combined vertical and horizontal acoustic receiving array, sei whale movements were tracked over long distances (up to tens of kilometers) using a normal mode back propagation technique. This approach uses low-frequency, broadband passive sei whale call receptions from a single-station, two-dimensional hydrophone array to perform long distance localization and tracking by exploiting the dispersive nature of propagating normal modes in a shallow water environment. The back propagation approach is examined for accuracy and application to tracking the sei whale vocalizations identified in the vertical and horizontal array signals. This passive whale tracking, combined with the intensive oceanography measurements performed during the experiment, was also used to examine sei whale movements in relation to oceanographic features observed in this region.
    Beschreibung: Office of Naval Research
    Schlagwort(e): Acoustic signal processing ; Bioacoustics ; Oceanography ; Underwater sound
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    On acoustic scattering by a shell-covered seafloor (2008)
    Acoustical Society of America
    Details
    Publikationsdatum: 2022-05-26
    Beschreibung: Author Posting. © Acoustical Society of America, 2000. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 108 (2000): 551-555, doi:10.1121/1.429585.
    Beschreibung: Acoustic scattering by the seafloor is sometimes influenced, if not dominated, by the presence of discrete volumetric objects such as shells. A series of measurements of target strength of a type of benthic shelled animal and associated scattering modeling have recently been completed (Stanton et al., "Acoustic scattering by benthic and planktonic shelled animals," J. Acoust. Soc. Am., this issue). The results of that study are used herein to estimate the scattering by the seafloor with a covering of shells at high acoustic frequencies. A simple formulation is derived that expresses the area scattering strength of the seafloor in terms of the average reduced target strength or material properties of the discrete scatterers and their packing factor (where the reduced target strength is the target strength normalized by the geometric cross section of the scatterers and the averaging is done over orientation and/or a narrow range of size or frequency). The formula shows that, to first order, the backscattering at high acoustic frequencies by a layer of shells (or other discrete bodies such as rocks) depends principally upon material properties of the objects and packing factor and is independent of size and acoustic frequency. Estimates of area scattering strength using this formula and measured values of the target strength of shelled bodies from Stanton et al. (this issue) are close to or consistent with observed area scattering strengths due to shell-covered seafloors published in other papers.
    Beschreibung: This research was supported by the U.S. Office of Naval Research Grant No. N00014-95-1-0287.
    Schlagwort(e): Underwater sound ; Oceanography ; Acoustic wave scattering ; Backscatter
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    Solutions to range-dependent benchmark problems by the finite-difference method (2008)
    Acoustical Society of America
    Details
    Publikationsdatum: 2022-05-26
    Beschreibung: Author Posting. © Acoustical Society of America, 1990. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 87 (1990): 1527-1534, doi:10.1121/1.399452.
    Beschreibung: An explicit second-order finite-difference scheme has been used to solve the elastic-wave equation in the time domain. Solutions are presented for the perfect wedge, the lossless penetrable wedge, and the plane parallel waveguide that have been proposed as benchmarks by the Acoustical Society of America. Good agreement with reference solutions is obtained if the media is discretized at 20 gridpoints per wavelength. There is a major discrepancy (up to 20 dB) in reference-source level because the reference solutions are normalized to the source strength at 1 m in the model, but the finite-difference solutions are normalized to the source strength at 1 m in a homogeneous medium. The finite-difference method requires computational times between 10 and 20 h on a super minicomputer without an array processor. The method has the advantage of providing phase information and, when run for a pulse source, of providing insight into the evolution of the wave field and energy partitioning. More complex models, including velocity gradients and strong lateral heterogeneities, can be solved with no additional computational effort. The method has also been formulated to include shear wave effects.
    Beschreibung: This work was supported by the Office of Naval Research under Contract No. N00014-87-K-0007.
    Schlagwort(e): Finite difference method ; Range ; Benchmarks ; Wave equations ; Sound levels ; Shear waves ; Acoustics
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    Off-axis effects on the multipulse structure of sperm whale usual clicks with implications for sound production (2008)
    Acoustical Society of America
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    Publikationsdatum: 2022-05-26
    Beschreibung: Author Posting. © Acoustical Society of America, 2005. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 118 (2005): 3337-3345, doi:10.1121/1.2082707.
    Beschreibung: Sperm whales (Physeter macrocephalus) produce multipulsed clicks with their hypertrophied nasal complex. The currently accepted view of the sound generation process is based on the click structure measured directly in front of, or behind, the whale where regular interpulse intervals (IPIs) are found between successive pulses in the click. Most sperm whales, however, are recorded with the whale in an unknown orientation with respect to the hydrophone where the multipulse structure and the IPI do not conform to a regular pulse pattern. By combining far-field recordings of usual clicks with acoustic and orientation information measured by a tag on the clicking whale, we analyzed clicks from known aspects to the whale. We show that a geometric model based on the bent horn theory for sound production can explain the varying off-axis multipulse structure. Some of the sound energy that is reflected off the frontal sac radiates directly into the water creating an intermediate pulse p1/2 seen in off-axis recordings. The powerful p1 sonar pulse exits the front of the junk as predicted by the bent-horn model, showing that the junk of the sperm whale nasal complex is both anatomically and functionally homologous to the melon of smaller toothed whales.
    Beschreibung: This work was funded by grants to from the Office of Naval Research Grant Nos. N00014-99-1-0819 and No. N00014-01-1-0705, and the Packard Foundation.
    Schlagwort(e): Bioacoustics ; Underwater sound ; Biocommunications
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    Accelerated freshening of Antarctic Bottom Water over the last decade in the Southern Indian Ocean (2017)
    American Association for the Advancement of Science
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    Publikationsdatum: 2022-05-26
    Beschreibung: © The Author(s), 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Science Advances 3 (2017): e1601426, doi:10.1126/sciadv.1601426.
    Beschreibung: Southern Ocean abyssal waters, in contact with the atmosphere at their formation sites around Antarctica, not only bring signals of a changing climate with them as they move around the globe but also contribute to that change through heat uptake and sea level rise. A repeat hydrographic line in the Indian sector of the Southern Ocean, occupied three times in the last two decades (1994, 2007, and, most recently, 2016), reveals that Antarctic Bottom Water (AABW) continues to become fresher (0.004 ± 0.001 kg/g decade−1), warmer (0.06° ± 0.01°C decade−1), and less dense (0.011 ± 0.002 kg/m3 decade−1). The most recent observations in the Australian-Antarctic Basin show a particularly striking acceleration in AABW freshening between 2007 and 2016 (0.008 ± 0.001 kg/g decade−1) compared to the 0.002 ± 0.001 kg/g decade−1 seen between 1994 and 2007. Freshening is, in part, responsible for an overall shift of the mean temperature-salinity curve toward lower densities. The marked freshening may be linked to an abrupt iceberg-glacier collision and calving event that occurred in 2010 on the George V/Adélie Land Coast, the main source region of bottom waters for the Australian-Antarctic Basin. Because AABW is a key component of the global overturning circulation, the persistent decrease in bottom water density and the associated increase in steric height that result from continued warming and freshening have important consequences beyond the Southern Indian Ocean.
    Beschreibung: The 2016 I08S cruise and the analysis and science performed at sea, as well as the individual principal investigators were funded through multiple National Oceanic and Atmospheric Administration (NOAA) and NSF grants including NSF grant OCE-1437015. The research for this article was mainly completed at sea. For land-based work, V.V.M. relied on her postdoctoral funding through NSF grant OCE-1435665, and A.M.M. was supported in part by NSF grant OCE-1356630 and NOAA grant NA11OAR4310063.
    Schlagwort(e): Salinity ; AABW ; Changes ; Water masses ; T-S properties ; Iceberg ; Calving ; Antartica ; Abyss ; Climate change
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