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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 98 (1989), S. 0 
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: A previously developed Bottom Shear Modulus Profiler (BSMP) theory (Yamamoto & Torii 1986) allows the seabed shear modulus versus depth profile to be extracted by inverting measurements of seabed motion and water wave-induced pressures at one point on the seafloor. Preliminary BSMP experiments (Trevorrow et al. 1988b; Badiey et al. 1988), compared to existing geologic borehold data at two inner continental shelf sites, showed that this method can accurately predict the magnitude and depth structure of the sediment shear modulus. An improved version of BSMP instrumentation system has been developed and deployed in deeper water at outer continental shelf sites. Gravity water wave-induced bottom pressures are measured in a period band from 7 to 200 s, whereas measurements of gravity water wave-induced ground motion are limited to a period band between 7 and 30 s, due to the limited sensitivity of the seismometers used. It is also found that burial of a BSMP in the seabed improved the seabed seismometer coupling significantly. The BSMP inversions of these data extract the shear modulus versus depth profile of the seabed with a depth resolution of a few meters and penetrating as much as 200 m into the seabed. The shear modulus of a sediment at a given depth of burial is a unique function of the porosity of the sediment. Using this relation, the porosity versus depth profile of the seabed is calculated from the shear modulus profile obtained by the BSMP inversion. Excellent agreements are shown between the porosity profiles obtained from the BSMP inversion and the borehole porosity logs. The pressure data indicate that the potential penetration depth of the BSMP inversion is about 2 km into the continental shelf and 20 km into the deep seafloor.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-0581
    Keywords: ocean bottom seismometer (OBS) ; seabed ; coupling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Sources of very low frequency (0.01 to 1.0 Hz) ambient seismic noise in the shallow (〈100 m) water continental margin sediments are investigated using Ocean Bottom Seismometers (OBS). The predominant seismic motions are found to be due to surface gravity (water) waves and water-sediment interface waves. Actual experimental measurements of seabed acceleration and hydrodynamic pressure are given, including side by side comparisons between buried and plate-mounted OBS units. OBS-sediment resonant effects are found to be negligible at the low frequencies under investigation. Wherever there exists relative motion between the seabed and the water, however, an exposed OBS is subject to ‘added mass’ forces that cause it to move with the water rather than the sediments. Calculations based on measured seabed motions show that a neutral density, buried seismometer has superior sediment coupling charactersitics to any exposed OBS design.
    Type of Medium: Electronic Resource
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  • 3
    Publication Date: 2022-05-25
    Description: Author Posting. © IEEE, 2004. This article is posted here by permission of IEEE for personal use, not for redistribution. The definitive version was published in IEEE Journal of Oceanic Engineering 29 (2004): 1231-1248, doi:10.1109/JOE.2004.834681.
    Description: The inversion of a broad-band "source of opportunity" signal for bottom geoacoustic parameters in the northeastern South China Sea (SCS) is presented, which supplements the towed source and chirp sonar bottom inversions that were performed as part of the Asian Seas International Acoustics Experiment (ASIAEX). This source of opportunity was most likely a "dynamite fishing" signal, which has sufficient low-frequency content (5-500 Hz) to make it complimentary to the somewhat higher frequency J-15-3 towed source (50-260 Hz) signals and the much higher frequency (1-10 kHz) chirp signals. This low frequency content will penetrate deeper into the bottom, thus extending the other inverse results. Localization of the source is discussed, using both a horizontal array for azimuthal steering and the "water wave" part of the pulse arrival for distance estimation. A linear broad-band inverse is performed, and three new variants of the broad-band inverse, based on: 1) the Airy phase; 2) the cutoff frequency; and 3) a range-dependent medium are presented. A multilayer model of the bottom compressional wave speed is obtained, and error estimates for this model are shown, both for the range-independent approximation to the waveguide and for the range-dependent waveguide. Directions for future research are discussed.
    Description: This work was supported by the Office of Naval Research under Grant N0 001 498-1-0413, Grant N00014-00-0931, and Grant N00014-01-0772 and by the National Science Council, Taiwan, R.O.C. under Grant NSC92-2611-E-002-005-CCS.
    Keywords: Broadband geoacoustic inversions ; Shallow water acoustics ; South China Sea
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: 1203211 bytes
    Format: application/pdf
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  • 4
    Publication Date: 2022-05-26
    Description: Author Posting. © Acoustical Society of America, 2020. 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 148(3),(2020): 1663, doi:10.1121/10.0001970.
    Description: The Pacific Arctic Region has experienced decadal changes in atmospheric conditions, seasonal sea-ice coverage, and thermohaline structure that have consequences for underwater sound propagation. To better understand Arctic acoustics, a set of experiments known as the deep-water Canada Basin acoustic propagation experiment and the shallow-water Canada Basin acoustic propagation experiment was conducted in the Canada Basin and on the Chukchi Shelf from summer 2016 to summer 2017. During the experiments, low-frequency signals from five tomographic sources located in the deep basin were recorded by an array of hydrophones located on the shelf. Over the course of the yearlong experiment, the surface conditions transitioned from completely open water to fully ice-covered. The propagation conditions in the deep basin were dominated by a subsurface duct; however, over the slope and shelf, the duct was seen to significantly weaken during the winter and spring. The combination of these surface and subsurface conditions led to changes in the received level of the sources that exceeded 60 dB and showed a distinct spacio-temporal dependence, which was correlated with the locations of the sources in the basin. This paper seeks to quantify the observed variability in the received signals through propagation modeling using spatially sparse environmental measurements.
    Description: This work was supported by the Office of Naval Research Ocean Acoustics Program (ONR OA322) under Grant Nos. N00014-15-1-2144, N00014-15-1-2119, N00014-15-1-2017, N00014-15-1-2068, N00014-15-1-2110, N00014-19-1-2721, N00014-15-1-2898, N00014-15-1-2806, and N00014-18-1-2140. The basin moored environmental data were supported by the ONR Arctic and Global Prediction Program (ONR AG322) under Grant No. N00014-15-1-2782. Mooring and hydrographic data were collected and made available by the Beaufort Gyre Exploration Program based at the Woods Hole Oceanographic Institution (http://www.whoi.edu/beaufortgyre) in collaboration with researchers from Fisheries and Oceans Canada at the Institute of Ocean Sciences. The ITP data were collected and made available by the ITP Program (Krishfield et al., 2008; Toole et al., 2011) based at the Woods Hole Oceanographic Institution (http://www.whoi.edu/itp). We acknowledge the use of imagery from the Worldview Snapshots application (https://wvs.earthdata.nasa.gov), part of the Earth Observing System Data and Information System (EOSDIS).
    Description: 2021-03-23
    Repository Name: Woods Hole Open Access Server
    Type: Article
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