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  • Woods Hole Oceanographic Institution  (3)
  • 1
    Publication Date: 2022-05-26
    Description: These notes provide supporting information for a JASA (Journal of the Acoustical Society of America) LttE (Letter to the Editor) manuscript, "Deep seafloor arrivals: A new class of arrivals in long-range ocean acoustic propagation" (Stephen et al., submitted). It addresses five issues raised by the co-authors: 1) incorrect processing for the time-compressed traces at T2300 and T3200 that appeared in an early version of the LttE (T2300, T3200 … refer to transmissions at 2300, 3200km etc from the DVLA (Deep Vertical Line Array)), 2) processing issues, including the trade-offs between coherent and incoherent stacking and corrections for the effects of moving sources and receivers and tidal currents (Doppler), 4) the distinction between "deep shadow zone arrivals", which occur below the turning points in Parabolic Equation (PE) models, and "deep seafloor arrivals", which appear dominantly on the Ocean Bottom Seismometer (OBS) but are either very weak or absent on the deepest element in the DVLA and do not coincide with turning points in the PE model (some of these OBS late arrivals occur after the finale region), 4) the role of surface-reflected bottomreflected (SRBR) paths in explaining the late arriving energy, and 5) generally reconciling the OBS analysis with work by other North Pacific Acoustic Laboratory (NPAL) investigators and Dushaw et al (1999).
    Description: Funding was provided by the Office of Naval Research through Contract No. N00014-06-1-0222.
    Keywords: Ocean bottom seismology ; Ocean acoustic propagation ; Bottom interaction
    Repository Name: Woods Hole Open Access Server
    Type: Technical Report
    Format: application/pdf
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  • 2
    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
    Format: application/pdf
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  • 3
    Publication Date: 2022-05-26
    Description: This report gives an overview of the analysis that was done on Deep Seafloor Arrivals since they were initially presented in Stephen et al (2009). All of the NPAL04/LOAPEX (North Pacific Acoustic Laboratory, 2004/ Long Range Ocean Acoustic Propagation Experiment) data on three ocean bottom seismometers (OBSs) at ~5,000m depth and the deepest element of the deep vertical line array (DVLA) at 4250m depth has been analyzed. A distinctive pattern of late arrivals was observed on the three OBSs for transmissions from T500 to T2300. The delays of these arrivals with respect to the parabolic equation predicted (PEP) path were the same for all ranges from 500 to 2300km, indicating that the delay was introduced near the receivers. At 500km range the same arrival was observed throughout the water column on the DVLA. We show that arrivals in this pattern converted from a PEP path to a bottom-diffracted surface reflected (BDSR) path at an off-geodesic seamount.
    Description: Funding was provided by the Office of Naval Research under Contract No. N00014-10-1-0510.
    Keywords: Underwater acoustics ; Ambient sounds
    Repository Name: Woods Hole Open Access Server
    Type: Technical Report
    Format: application/pdf
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