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  • 1
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    Array design considerations for exploitation of stable weakly dispersive modal pulses in the deep ocean (2017)
    Elsevier
    Details
    Publication Date: 2017-07-01
    Print ISSN: 0022-460X
    Electronic ISSN: 1095-8568
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Published by Elsevier
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  • 2
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    Array design considerations for exploitation of stable weakly dispersive modal pulses in the deep ocean (2017)
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    Publication Date: 2022-05-25
    Description: © The Author(s), 2017. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Journal of Sound and Vibration 400 (2017): 402-416, doi:10.1016/j.jsv.2017.03.035.
    Description: Modal pulses are broadband contributions to an acoustic wave field with fixed mode number. Stable weakly dispersive modal pulses (SWDMPs) are special modal pulses that are characterized by weak dispersion and weak scattering-induced broadening and are thus suitable for communications applications. This paper investigates, using numerical simulations, receiver array requirements for recovering information carried by SWDMPs under various signal-to-noise ratio conditions without performing channel equalization. Two groups of weakly dispersive modal pulses are common in typical mid-latitude deep ocean environments: the lowest order modes (typically modes 1–3 at 75 Hz), and intermediate order modes whose waveguide invariant is near-zero (often around mode 20 at 75 Hz). Information loss is quantified by the bit error rate (BER) of a recovered binary phase-coded signal. With fixed receiver depths, low BERs (less than 1%) are achieved at ranges up to 400 km with three hydrophones for mode 1 with 90% probability and with 34 hydrophones for mode 20 with 80% probability. With optimal receiver depths, depending on propagation range, only a few, sometimes only two, hydrophones are often sufficient for low BERs, even with intermediate mode numbers. Full modal resolution is unnecessary to achieve low BERs. Thus, a flexible receiver array of autonomous vehicles can outperform a cabled array.
    Keywords: Ocean acoustics ; Weakly dispersive modal pulses ; Long-range sound propagation ; Underwater communications
    Repository Name: Woods Hole Open Access Server
    Type: Preprint
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  • 3
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    Three-dimensional numerical modeling of bottom-diffracted surface-reflected arrivals in the North Pacific [poster] (2016)
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    Publication Date: 2022-05-25
    Description: Poster presented AGU Fall Meeting, San Francisco, Californai USA, December 14-18, 2015
    Description: Bottom-diffracted surface-reflected (BDSR) arrivals were first identified in the 2004 Long-range Ocean Acoustic Propagation Experiment (Stephen et al, 2013, JASA, v.134, p.3307-3317). The BDSR mechanism provides a means for acoustic signals and noise from distant sources to appear with significant strength on the deep seafloor. At depths deeper than the conjugate depth ambient noise and PE- predicted arrivals are sufficiently quiet that BDSR paths, scattered from small seamounts, can be the largest amplitude arrivals observed. The Ocean Bottom Seismometer Augmentation in the North Pacific (OBSANP) Experiment in June-July 2013 was designed to further define the characteristics of the BDSRs and to understand the conditions under which BDSRs are excited and propagate. The reciprocal of the BDSR mechanism also plays a role in T-phase excitation. To further understand the BDSR mechanism, the SPECFEM3D code was extended to handle high-frequency, deep water bottom scattering problems with actual bathymetry and a typical sound speed profile in the water column. The model size is 38km x 27km x 6.5km. The source is centered at 10Hz with a 5Hz bandwidth. Work supported by NSF and ONR.
    Description: The data acquisition was funded by the Office of Naval Research and the computer modeling using SPECFEM3D was supported by the National Science Foundation.
    Repository Name: Woods Hole Open Access Server
    Type: Presentation
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  • 4
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    Three-dimensional bottom diffraction in the North Pacific (2019)
    Acoustical Society of America
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    Publication Date: 2022-05-25
    Description: Author Posting. © Acoustical Society of America, 2019. 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 146(3), (2019): 1913-1922, doi:10.1121/1.5125427.
    Description: A significant aspect of bottom-interaction in deep water acoustic propagation, from point sources to point receivers, is the diffraction (or scattering) of energy from discrete seafloor locations along repeatable, deterministic paths in three-dimensions. These bottom-diffracted surface-reflected (BDSR) paths were first identified on the North Pacific acoustic laboratory experiment in 2004 (NPAL04) for a diffractor located on the side of a small seamount. On the adjacent deep seafloor, ambient noise and propagation in the ocean sound channel were sufficiently quiet that the BDSRs were the dominant arrival. The ocean bottom seismometer augmentation in the North Pacific (OBSANP) experiment in June–July 2013 studied BDSRs at the NPAL04 site in more detail. BDSRs are most readily identified by the arrival time of pulses as a function of range to the receiver for a line of transmissions. The diffraction points for BDSRs occur on the relatively featureless deep seafloor as well as on the sides of small seamounts. Although the NPAL04 and OBSANP experiments had very different geometries the same diffractor location is consistent with observed arrivals in both experiments within the resolution of the analysis. On OBSANP the same location excites BDSRs for 77.5, 155, and 310 Hz transmissions.
    Description: We greatly appreciate the support from Captain Curl, the officers, and crew of the R/V Melville (MV1308). The OBS data used in this research was acquired on instruments from the ocean bottom seismograph instrument pool (OBSIP) at Scripps Institution of Oceanography. Ernie Aaron (SIO) was responsible for shipboard OBS operations. The multi-beam data was processed using the MB-System (Caress and Chayes, 1996). Figure 1 was prepared using the generic mapping tool (Wessel and Smith, 1998). Feedback and reviews from an anonymous reviewer and the editorial staff of JASA are also greatly appreciated. The OBSANP experiment was funded by the ONR Ocean Acoustics Program (Code 322 OA) under Grant Nos. N00014-10-1-0987 and N00014-10-1-0510. Analysis was carried out under ONR Grant Nos. N00014-14-1-0324, N00014-16-1-2337, and N00014-17-C-7043.
    Description: 2020-03-30
    Repository Name: Woods Hole Open Access Server
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  • 5
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    Three-dimensional numerical modeling of sound propagation and scattering in the deep ocean with elastic bottoms [poster] (2015)
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    Publication Date: 2022-05-26
    Description: Poster presented AGU Ocean Sciences Meeting, Honolulu, Hawaii USA, February 23-28, 2014
    Description: A challenging problem in bottom-interacting ocean acoustics and marine seismology is to accurately describe environmental variability in a computationally feasible model. Wave field predictions are often difficult in environments with strong range dependence, with rapid bathymetric variations, with multiple scattering regions, with interface waves at fluid/solid boundaries, and/or with shear waves in the bottom. In this presentation, we are using an existing three-dimensional spectral-finite-element code (SPECFEM3D, distributed and supported by the NSF funded program, Computational Infrastructure for Geodynamics), originally developed for simulations of seismic wave propagation at the local or regional scale, to bottom interaction problems in underwater acoustics. Recent developments of the SPECFEM3D model include full compressional attenuation in elastic media and improved transparent boundary conditions. Numerical results from SPECFEM3D are compared with wave fields simulated using acoustic propagation model based on the parabolic equation (PE) method, for a 10 Hz broadband acoustic pulse propagating in the deep ocean. The importance of out-of-plane scattering and bottom shear properties on resulting wave fields are investigated.
    Description: Work supported by the National Science Foundation in the U. S. and L'Agence Nationale de la Recherche and Le Centre National de la Recherche Scientifique in France
    Repository Name: Woods Hole Open Access Server
    Type: Presentation
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  • 6
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    Ocean Bottom Seismometer Augmentation in the North Pacific (OBSANP) - cruise report (2015)
    Woods Hole Oceanographic Institution
    Details
    Publication Date: 2022-05-26
    Description: The Ocean Bottom Seismometer Augmentation in the North Pacific Experiment (OBSANP, June-July, 2013, R/V Melville) addresses the coherence and depth dependence of deep-water ambient noise and signals. During the 2004 NPAL Experiment in the North Pacific Ocean, in addition to predicted ocean acoustic arrivals and deep shadow zone arrivals, we observed "deep seafloor arrivals" (DSFA) that were dominant on the seafloor Ocean Bottom Seismometer (OBS) (at about 5000m depth) but were absent or very weak on the Distributed Vertical Line Array (DVLA) (above 4250m depth). At least a subset of these arrivals correspond to bottomdiffracted surface-reflected (BDSR) paths from an out-of-plane seamount. BDSR arrivals are present throughout the water column, but at depths above the conjugate depth are obscured by ambient noise and PE predicted arrivals. On the 2004 NPAL/LOAPEX experiment BDSR paths yielded the largest amplitude seafloor arrivals for ranges from 500 to 3200km. The OBSANP experiment tests the hypothesis that BDSR paths contribute to the arrival structure on the deep seafloor even at short ranges (from near zero to 4-1/2CZ). The OBSANP cruise had three major research goals: a) identification and analysis of DSFA and BDSR arrivals occurring at short (1/2CZ) ranges in the 50 to 400Hz band, b) analysis of deep sea ambient noise in the band 0.03 to 80Hz, and c) analysis of the frequency dependence of BR and SRBR paths. On OBSANP we deployed a 32 element VLA from 12 to 1000m above the seafloor, eight short-period OBSs and four long-period OBSs and carried out a 15day transmission program using a J15-3 acoustic source.
    Description: Funding was provided by the Office of Naval Research under contract #'s N00014-10-1-0987 and N00014-10-1-0510
    Keywords: Melville (Ship) Cruise MV1308 ; Underwater acoustics ; Oceanographic instruments
    Repository Name: Woods Hole Open Access Server
    Type: Technical Report
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