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  • Underwater acoustic propagation  (10)
  • Astronomy
  • Fisheries
  • Seismology
  • Industrial Chemistry
  • Inorganic Chemistry
  • Acoustical Society of America  (12)
  • 2005-2009  (12)
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  • 1
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    Performance analysis of adaptive equalization for coherent acoustic communications in the time-varying ocean environment (2009)
    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 118 (2005): 263-278, doi:10.1121/1.1907106.
    Beschreibung: Equations are derived for analyzing the performance of channel estimate based equalizers. The performance is characterized in terms of the mean squared soft decision error of each equalizer. This error is decomposed into two components. These are the minimum achievable error and the excess error. The former is the soft decision error that would be realized by the equalizer if the filter coefficient calculation were based upon perfect knowledge of the channel impulse response and statistics of the interfering noise field. The latter is the additional soft decision error that is realized due to errors in the estimates of these channel parameters. These expressions accurately predict the equalizer errors observed in the processing of experimental data by a channel estimate based decision feedback equalizer (DFE) and a passive time-reversal equalizer. Further expressions are presented that allow equalizer performance to be predicted given the scattering function of the acoustic channel. The analysis using these expressions yields insights into the features of surface scattering that most significantly impact equalizer performance in shallow water environments and motivates the implementation of a DFE that is robust with respect to channel estimation errors
    Beschreibung: This work has been supported by ONR Grant Nos. N00014-00-1-0048 and N00014-02-C-0201.
    Schlagwort(e): Underwater acoustic communication ; Adaptive equalisers ; Channel estimation ; Acoustic signal processing ; Adaptive signal processing ; Underwater acoustic propagation
    Repository-Name: Woods Hole Open Access Server
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  • 2
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    Surface wave focusing and acoustic communications in the surf zone (2009)
    Acoustical Society of America
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    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): 2067-2080, doi:10.1121/1.1771591.
    Beschreibung: The forward scattering of acoustic signals off of shoaling surface gravity waves in the surf zone results in a time-varying channel impulse response that is characterized by intense, rapidly fluctuating arrivals. In some cases, the acoustic focusing by the curvature of the wave crest results in the formation of caustics at or near a receiver location. This focusing and the resulting caustics present challenges to the reliable operation of phase coherent underwater acoustic communications systems that must implicitly or explicitly track the fluctuations in the impulse response. The propagation physics leading to focusing are studied with both experimental data and a propagation model using surface wave profiles measured during the collection of the experimental data. The deterministic experimental and modeled data show good agreement and demonstrate the stages of the focusing event and the impact of the high intensity arrivals and rapid fluctuations on the ability of an algorithm to accurately estimate the impulse response. The statistical characterization of experimental data shows that the focusing by surface gravity waves results in focused surface reflected arrivals whose intensity often exceeds that of the direct arrival and the focusing and caustic formation adversely impacts the performance of an impulse response estimation algorithm.
    Beschreibung: This work has been supported by ONR Grant Nos. N00014-96-1-0120, N00014-00-1-0303, N00014-99-1-0274, and N00014-00-1-0048.
    Schlagwort(e): Underwater acoustic communication ; Underwater acoustic propagation ; Acoustic focusing ; Acoustic wave refraction ; Direction-of-arrival estimation ; Acoustic signal processing
    Repository-Name: Woods Hole Open Access Server
    Materialart: Article
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  • 3
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    Deep seafloor arrivals : an unexplained set of arrivals in long-range ocean acoustic propagation (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): 599-606, doi:10.1121/1.3158826.
    Beschreibung: Receptions, from a ship-suspended source (in the band 50–100 Hz) to an ocean bottom seismometer (about 5000 m depth) and the deepest element on a vertical hydrophone array (about 750 m above the seafloor) that were acquired on the 2004 Long-Range Ocean Acoustic Propagation Experiment in the North Pacific Ocean, are described. The ranges varied from 50 to 3200 km. In addition to predicted ocean acoustic arrivals and deep shadow zone arrivals (leaking below turning points), “deep seafloor arrivals,” that are dominant on the seafloor geophone but are absent or very weak on the hydrophone array, are observed. These deep seafloor arrivals are an unexplained set of arrivals in ocean acoustics possibly associated with seafloor interface waves.
    Beschreibung: The LOAPEX source deployments, the moored DVLA receiver deployments, and some post-cruise data reduction and analysis were funded by the Office of Naval Research under Award Nos. N00014-1403-1-0181, N00014-03-1-0182, and N00014-06-1-0222. Additional post-cruise analysis support was provided to RAS through the Edward W. and Betty J. Scripps Chair for Excellence in Oceanography. The OBS/Hs used in the experiment were provided by Scripps Institution of Oceanography under the U.S. National Ocean Bottom Seismic Instrumentation Pool (SIO-OBSIP—http://www.obsip.org). To cover the costs of the OBS/H deployments funds were paid to SIO-OBSIP from the National Science Foundation and from the Woods Hole Oceanographic Institution Deep Ocean Exploration Institute.
    Schlagwort(e): Hydrophones ; Ocean waves ; Oceanographic equipment ; Sonar ; Underwater acoustic propagation
    Repository-Name: Woods Hole Open Access Server
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  • 4
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    Statistics of normal mode amplitudes in an ocean with random sound-speed perturbations : cross-mode coherence and mean intensity (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 126 (2009): 1026-1035, doi:10.1121/1.3158818.
    Beschreibung: In this paper Creamer's [(1996). J. Acoust. Soc. Am. 99, 2825–2838] transport equation for the mode amplitude coherence matrix resulting from coupled mode propagation through random fields of internal waves is examined in more detail. It is shown that the mode energy equations are approximately independent of the cross mode coherences, and that cross mode coherences and mode energy can evolve over very similar range scales. The decay of cross mode coherence depends on the relative mode phase randomization caused by coupling and adiabatic effects, each of which can be quantified by the theory. This behavior has a dramatic effect on the acoustic field second moments like mean intensity. Comparing estimates of the coherence matrix and mean intensity from Monte Carlo simulation, and the transport equations, good agreement is demonstrated for a 100-Hz deep-water example.
    Beschreibung: This work was supported by the Office of Naval Research and the Naval Undersea Warfare Center’s (NUWC) Under- Sea Warfare (USW) chair at the Naval Postgraduate School.
    Schlagwort(e): Acoustic field ; Acoustic intensity ; Matrix algebra ; Monte Carlo methods ; Underwater acoustic propagation
    Repository-Name: Woods Hole Open Access Server
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  • 5
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    Analysis and modeling of broadband airgun data influenced by nonlinear internal waves (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): 3404-3422, doi:10.1121/1.1819499.
    Beschreibung: To investigate acoustic effects of nonlinear internal waves, the two southwest tracks of the SWARM 95 experiment are considered. An airgun source produced broadband acoustic signals while a packet of large nonlinear internal waves passed between the source and two vertical linear arrays. The broadband data and its frequency range (10–180 Hz) distinguish this study from previous work. Models are developed for the internal wave environment, the geoacoustic parameters, and the airgun source signature. Parabolic equation simulations demonstrate that observed variations in intensity and wavelet time–frequency plots can be attributed to nonlinear internal waves. Empirical tests are provided of the internal wave-acoustic resonance condition that is the apparent theoretical mechanism responsible for the variations. Peaks of the effective internal wave spectrum are shown to coincide with differences in dominant acoustic wavenumbers comprising the airgun signal. The robustness of these relationships is investigated by simulations for a variety of geoacoustic and nonlinear internal wave model parameters.
    Beschreibung: This work was supported by an ONR Ocean Acoustics Graduate Traineeship Award and by ONR grants to Rensselaer, the University of Delaware, and Woods Hole Oceanographic Institution.
    Schlagwort(e): Acoustic resonance ; Nonlinear acoustics ; Underwater acoustic propagation ; Parabolic equations ; Acoustic intensity
    Repository-Name: Woods Hole Open Access Server
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  • 6
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    Entropy and scintillation analysis of acoustical beam propagation through ocean internal waves (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): 1611-1623, doi:10.1121/1.1854571.
    Beschreibung: Parabolic equation numerical simulations of waveguide acoustical beam propagation in an ocean of Garrett–Munk internal waves are used to examine the range evolution of beam properties such as beamwidth (both spectral and spatial), Shannon entropy, and scintillation index, as a function of beam angle. Simulations are carried out at 250- and 125-Hz acoustic frequencies. The ray trajectories associated with these beams are predominantly chaotic or exponentially sensitive to initial conditions and/or medium perturbations. At long range near saturation, the finite-frequency beams show a constant rate of change of Shannon entropy with range, independent of acoustic frequency. This full-wave rate of entropy is of the same order of magnitude as the average rate of entropy for the ray trajectories associated with this beam. Finite-range Lyapunov exponents provide the estimates of ray entropy rate or Kolmogorov–Siani entropy. The correspondence between full-wave and ray entropies suggests a full-wave manifestation of ray chaos, but only once statistical saturation is obtained. In spite of this correspondence, the simulated acoustical beams expand diffusively not exponentially (or explosively).
    Schlagwort(e): Underwater acoustic propagation ; Acoustic signal processing ; Parabolic equations ; Entropy ; Ocean waves ; Chaos
    Repository-Name: Woods Hole Open Access Server
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  • 7
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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
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  • 8
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    Acoustic detection and quantification of benthic egg beds of the squid Loligo opalescens in Monterey Bay, California (2008)
    Acoustical Society of America
    Details
    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 119 (2006): 844-856, doi:10.1121/1.2149840.
    Beschreibung: The squid Loligo opalescens is a key species in the nearshore pelagic community of California, supporting the most valuable state marine fishery, yet the stock biomass is unknown. In southern Monterey Bay, extensive beds occur on a flat, sandy bottom, water depths 20–60 m, thus sidescan sonar is a prima-facie candidate for use in rapid, synoptic, and noninvasive surveying. The present study describes development of an acoustic method to detect, identify, and quantify squid egg beds by means of high-frequency sidescan-sonar imagery. Verification of the method has been undertaken with a video camera carried on a remotely operated vehicle. It has been established that sidescan sonar images can be used to predict the presence or absence of squid egg beds. The lower size limit of detectability of an isolated egg bed is about 0.5 m with a 400-kHz sidescan sonar used with a 50-m range when towed at 3 knots. It is possible to estimate the abundance of eggs in a region of interest by computing the cumulative area covered by the egg beds according to the sidescan sonar image. In a selected quadrat one arc second on each side, the estimated number of eggs was 36.5 million.
    Beschreibung: funding from the National Sea Grant, Essential Fish Habitat Program, Sea Grant Project No. NA16RG2273.
    Schlagwort(e): Acoustic measurement ; Acoustic devices ; Sonar imaging ; Underwater acoustic propagation
    Repository-Name: Woods Hole Open Access Server
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  • 9
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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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  • 10
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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
    Repository-Name: Woods Hole Open Access Server
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  • 11
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    Observed limiting cases of horizontal field coherence and array performance in a time-varying internal wavefield (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): EL97-EL103, doi:10.1121/1.2947630.
    Beschreibung: Using a moored source and horizontal/vertical line array combination, horizontal coherence properties of high signal to noise ratio (〉=20 dB) 100–1600 Hz signals have been measured. Internal waves in the area of the measurement created moving episodic sound-speed anomaly structures, influencing coherence length. Measured horizontal coherence scales for 100 Hz ranged from 5 to 20 acoustic wavelengths, and were inversely related to the sound-speed anomaly strength. Horizontal field properties were compared with fields computed using modal decompositions of the vertical signals. The comparison allows azimuthal field coherence properties to be studied apart from normal-mode interference effects.
    Beschreibung: This work was funded by grants to Boston University and the Woods Hole Oceanographic Institution from the Ocean Acoustics Program at the U.S. Office of Naval Research, including an ONR Postdoctoral Fellowship award to the first author.
    Schlagwort(e): Acoustic arrays ; Acoustic signal processing ; Acoustic wave velocity ; Ocean waves ; Underwater acoustic propagation
    Repository-Name: Woods Hole Open Access Server
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  • 12
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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
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