Murray James J.

No Thumbnail Available
Last Name
Murray
First Name
James J.
ORCID

Filters

2013 2
2
2
Reset filters

Settings

Search Results

Now showing 1 - 2 of 2
  • Article
    Estimating the horizontal and vertical direction-of-arrival of water-borne seismic signals in the northern Philippine Sea
    (Acoustical Society of America, 2013-10) Freeman, Simon E. ; D'Spain, Gerald L. ; Lynch, Stephen D. ; Stephen, Ralph A. ; Heaney, Kevin D. ; Murray, James J. ; Baggeroer, Arthur B. ; Worcester, Peter F. ; Dzieciuch, Matthew A. ; Mercer, James A.
    Conventional and adaptive plane-wave beamforming with simultaneous recordings by large-aperture horizontal and vertical line arrays during the 2009 Philippine Sea Engineering Test (PhilSea09) reveal the rate of occurrence and the two-dimensional arrival structure of seismic phases that couple into the deep ocean. A ship-deployed, controlled acoustic source was used to evaluate performance of the horizontal array for a range of beamformer adaptiveness levels. Ninety T-phases from unique azimuths were recorded between Yeardays 107 to 119. T-phase azimuth and S-minus-P-phase time-of-arrival range estimates were validated using United States Geological Survey seismic monitoring network data. Analysis of phases from a seismic event that occurred on Yearday 112 near the east coast of Taiwan approximately 450 km from the arrays revealed a 22° clockwise evolution of T-phase azimuth over 90 s. Two hypotheses to explain such evolution—body wave excitation of multiple sources or in-water scattering—are presented based on T-phase origin sites at the intersection of azimuthal great circle paths and ridge/coastal bathymetry. Propagation timing between the source, scattering region, and array position suggests the mechanism behind the evolution involved scattering of the T-phase from the Ryukyu Ridge and a T-phase formation/scattering location estimation error of approximately 3.2 km.
  • Article
    Deep water towed array measurements at close range
    (Acoustical Society of America, 2013-10) Heaney, Kevin D. ; Campbell, Richard L. ; Murray, James J. ; Baggeroer, Arthur B. ; Scheer, Edward K. ; Stephen, Ralph A. ; D'Spain, Gerald L. ; Mercer, James A.
    During the North Pacific Acoustic Laboratory Philippine Sea 2009 experiment, towed array receptions were made from a towed source as the two ships transited from a separation of several Convergence Zones through a Closest Point of Approach at 3 km. A combination of narrowband tones and broadband pulses were transmitted covering the frequency band 79–535 Hz. The received energy arrives from two general paths—direct path and bottom bounce. Bearing-time records of the narrowband arrivals at times show a 35° spread in the angle of arrival of the bottom bounce energy. Doppler processing of the tones shows significant frequency spread of the bottom bounce energy. Two-dimensional modeling using measured bathymetry, a geoacoustic parameterization based upon the geological record, and measured sound-speed field was performed. Inclusion of the effects of seafloor roughness and surface waves shows that in-plane scattering from rough interfaces can explain much of the observed spread in the arrivals. Evidence of out-of-plane scattering does exist, however, at short ranges. The amount of out-of-plane scattering is best observed in the broadband impulse-beam response analysis, which in-plane surface roughness modeling cannot explain.