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  • Echo  (4)
  • ENERGY PRODUCTION AND CONVERSION
  • Fisheries
  • Industrial Chemistry
  • Inorganic Chemistry
  • Meteorology and Climatology
  • Seismology
  • Acoustical Society of America  (6)
  • 2005-2009  (6)
  • 1980-1984
  • 1955-1959
  • 1
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    On the acoustic diffraction by the edges of benthic shells (2008)
    Acoustical Society of America
    Details
    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © Acoustical Society of America, 2004. 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 116 (2004): 239-244, doi:10.1121/1.1675813.
    Beschreibung: Recent laboratory measurements of acoustic backscattering by individual benthic shells have isolated the edge-diffracted echo from echoes due to the surface of the main body of the shell. The data indicate that the echo near broadside incidence is generally the strongest for all orientations and is due principally to the surface of the main body. At angles well away from broadside, the echo levels are lower and are due primarily to the diffraction from the edge of the shell. The decrease in echo levels from broadside incidence to well off broadside is shown to be reasonably consistent with the decrease in acoustic backscattering from normal incidence to well off normal incidence by a shell-covered seafloor. The results suggest the importance of the edge of the shell in off-normal-incidence backscattering by a shell-covered seafloor. Furthermore, when considering bistatic diffraction by edges, there are implications that the edge of the shell (lying on the seafloor) can cause significant scattering in many directions, including at subcritical angles.
    Beschreibung: This research was supported by the U.S. Office of Naval Research (Grant No. N00014-02-1-0095) and the Woods Hole Oceanographic Institution (WHOI), Woods Hole, MA.
    Schlagwort(e): Underwater sound ; Acoustic wave diffraction ; Acoustic wave scattering ; Echo
    Repository-Name: Woods Hole Open Access Server
    Materialart: Article
    Format: application/pdf
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  • 2
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    Three-dimensional beam pattern of regular sperm whale clicks confirms bent-horn hypothesis (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): 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
    Materialart: Article
    Format: application/pdf
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  • 3
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    Underwater tunable organ-pipe sound source (2008)
    Acoustical Society of America
    Details
    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © Acoustical Society of America, 2007. 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 122 (2007): 777-785, doi:10.1121/1.2751268.
    Beschreibung: A highly efficient frequency-controlled sound source based on a tunable high-Q underwater acoustic resonator is described. The required spectrum width was achieved by transmitting a linear frequency-modulated signal and simultaneously tuning the resonance frequency, keeping the sound source in resonance at the instantaneous frequency of the signal transmitted. Such sound sources have applications in ocean-acoustic tomography and deep-penetration seismic tomography. Mathematical analysis and numerical simulation show the Helmholtz resonator's ability for instant resonant frequency switching and quick adjustment of its resonant frequency to the instantaneous frequency signal. The concept of a quick frequency adjustment filter is considered. The discussion includes the simplest lumped resonant source as well as the complicated distributed system of a tunable organ pipe. A numerical model of the tunable organ pipe is shown to have a form similar to a transmission line segment. This provides a general form for the principal results, which can be applied to tunable resonators of a different physical nature. The numerical simulation shows that the “state-switched” concept also works in the high-Q tunable organ pipe, and the speed of frequency sweeping in a high-Q tunable organ pipe is analyzed. The simulation results were applied to a projector design for ocean-acoustic tomography.
    Beschreibung: The work was supported by ONR.
    Schlagwort(e): Acoustic generators ; Underwater sound ; Acoustic resonators ; Oceanographic equipment ; Seismology
    Repository-Name: Woods Hole Open Access Server
    Materialart: Article
    Format: application/pdf
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  • 4
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    Calibration of broadband active acoustic systems using a single standard spherical target (2008)
    Acoustical Society of America
    Details
    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © Acoustical Society of America, 2008. 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 124 (2008): 128-136, doi:10.1121/1.2917387.
    Beschreibung: When calibrating a broadband active acoustic system with a single standard target such as a sphere, the inherent resonances associated with the scattering by the sphere pose a significant challenge. In this paper, a method is developed which completely eliminates the source of resonances through isolating and exploiting the echo from the front interface of a sphere. This echo is relatively insensitive to frequency over a wide range of frequencies, lacking resonances, and is relatively insensitive to small changes in material properties and, in the case of spherical shells, shell thickness. The research builds upon the concept of using this echo for calibration in the work of Dragonette et al. [J. Acoust. Soc. Am. 69, 1186–1189 (1981)]. This current work generalizes that of Dragonette by (1) incorporating a pulse compression technique to significantly improve the ability to resolve the echo, and (2) rigorously accounting for the scattering physics of the echo so that the technique is applicable over a wide range of frequencies and material properties of the sphere. The utility of the new approach is illustrated through application to data collected at sea with an air-filled aluminum spherical shell and long broadband chirp signals (30–105 kHz).
    Beschreibung: This work was supported by the U.S. Office of Naval Research Grant Nos. N00014-04-1-0475 and N00014- 04-1-0440 and the J. Seward Johnson Chair at WHOI.
    Schlagwort(e): Acoustic resonance ; Acoustic wave scattering ; Calibration ; Echo ; Pulse compression
    Repository-Name: Woods Hole Open Access Server
    Materialart: Article
    Format: application/pdf
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  • 5
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    Geoacoustic inversion by mode amplitude perturbation (2008)
    Acoustical Society of America
    Details
    Publikationsdatum: 2022-05-26
    Beschreibung: Author Posting. © Acoustical Society of America, 2008. 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 123 (2008): 667-678, doi:10.1121/1.2821975.
    Beschreibung: This paper introduces a perturbative inversion algorithm for determining sea floor acoustic properties, which uses modal amplitudes as input data. Perturbative inverse methods have been used in the past to estimate bottom acoustic properties in sediments, but up to this point these methods have used only the modal eigenvalues as input data. As with previous perturbative inversion methods, the one developed in this paper solves the nonlinear inverse problem using a series of approximate, linear steps. Examples of the method applied to synthetic and experimental data are provided to demonstrate the method's feasibility. Finally, it is shown that modal eigenvalue and amplitude perturbation can be combined into a single inversion algorithm that uses all of the potentially available modal data.
    Beschreibung: Funding for the research presented here was provided by the Office of Naval Research, and the WHOI Academic Programs Office.
    Schlagwort(e): Geophysical techniques ; Inverse problems ; Sediments ; Seismology
    Repository-Name: Woods Hole Open Access Server
    Materialart: Article
    Format: application/pdf
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  • 6
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    Acoustic scattering from double-diffusive microstructure (2008)
    Acoustical Society of America
    Details
    Publikationsdatum: 2022-05-26
    Beschreibung: Author Posting. © Acoustical Society of America, 2007. 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 122 (2007): 1449-1462, doi:10.1121/1.2764475.
    Beschreibung: Laboratory measurements of high-frequency broadband acoustic backscattering (200–600 kHz) from the diffusive regime of double-diffusive microstructure have been performed. This type of microstructure, which was characterized using direct microstructure and optical shadowgraph techniques, is identified by sharp density and sound speed interfaces separating well-mixed layers. Vertical acoustic backscattering measurements were performed for a range of physical parameters controlling the double-diffusive microstructure. The echoes have been analyzed in both the frequency domain, providing information on the spectral response of the scattering, and in the time domain, using pulse compression techniques. High levels of variability were observed, associated with interface oscillations and turbulent plumes, with many echoes showing significant spectral structure. Acoustic estimates of interface thickness (1–3 cm), obtained for the echoes with exactly two peaks in the compressed pulse output, were in good agreement with estimates based on direct microstructure and optical shadowgraph measurements. Predictions based on a one-dimensional weak-scattering model that includes the actual density and sound speed profiles agree reasonably with the measured scattering. A remote-sensing tool for mapping oceanic microstructure, such as high-frequency broadband acoustic scattering, could lead to a better understanding of the extent and evolution of double-diffusive layering, and to the importance of double diffusion to oceanic mixing.
    Beschreibung: Funding for this project was provided by the Ocean Acoustics program at the Office of Naval Research and by the Woods Hole Oceanographic Institution Cecil and Ida Greene Technology Award. Tetjana Ross was supported by the WHOI Postdoctoral Scholarship through the generous support of the Doherty Foundation.
    Schlagwort(e): Acoustic measurement ; Acoustic wave scattering ; Echo ; Oceanographic techniques ; Pulse compression ; Remote sensing ; Underwater sound
    Repository-Name: Woods Hole Open Access Server
    Materialart: Article
    Format: application/pdf
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