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  • Boyd, Janice  (2)
  • Cornuelle, Bruce D.  (2)
  • 1
    Online Resource
    Online Resource
    A comparison of measured and predicted broadband acoustic arrival patterns in travel time–depth coordinates at 1000-km range
    Acoustical Society of America (ASA) ; 1994
    In:  The Journal of the Acoustical Society of America Vol. 95, No. 6 ( 1994-06-01), p. 3118-3128
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 95, No. 6 ( 1994-06-01), p. 3118-3128
    Abstract: Broadband acoustic signals were transmitted from a moored 250-Hz source to a 3-km-long vertical line array of hydrophones 1000 km distant in the eastern North Pacific Ocean during July 1989. The sound-speed field along the great circle path connecting the source and receiver was measured directly by nearly 300 expendable bathythermograph (XBT), conductivity-temperature-depth (CTD), and air-launched expendable bathythermograph (AXBT) casts while the transmissions were in progress. This experiment is unique in combining a vertical receiving array that extends over much of the water column, extensive concurrent environmental measurements, and broadband signals designed to measure acoustic travel times with 1-ms precision. The time-mean travel times of the early raylike arrivals, which are evident as wave fronts sweeping across the receiving array, and the time-mean of the times at which the acoustic reception ends (the final cutoffs) for hydrophones near the sound channel axis, are consistent with ray predictions based on the direct measurements of temperature and salinity, within measurement uncertainty. The comparisons show that subinertial oceanic variability with horizontal wavelengths shorter than 50 km, which is not resolved by the direct measurements, significantly (25 ms peak-to-peak) affects the time-mean ray travel times. The final cutoffs occur significantly later than predicted using ray theory for hydrophones more than 100–200 m off the sound channel axis. Nongeometric effects, such as diffraction at caustics, partially account for this observation.
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.409977
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 1994
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  • 2
    Online Resource
    Online Resource
    Ocean acoustic tomography at 1000‐km range using wavefronts measured with a large‐aperture vertical array
    American Geophysical Union (AGU) ; 1993
    In:  Journal of Geophysical Research: Oceans Vol. 98, No. C9 ( 1993-09-15), p. 16365-16377
    Details
    In: Journal of Geophysical Research: Oceans, American Geophysical Union (AGU), Vol. 98, No. C9 ( 1993-09-15), p. 16365-16377
    Abstract: Broadband acoustic signals transmitted from a moored 250‐Hz source to a 3‐km‐long vertical line array of hydrophones 1000 km distant in the north central Pacific Ocean were used to determine the amount of information available from tomographic techniques used in the vertical plane connecting a source‐receiver pair. A range‐independent, pure acoustic inverse to obtain the sound speed field using travel time data from the array is shown to be possible by iterating from climatological data without using any information from concurrent environmental measurements. Range‐dependent inversions indicate resolution of components of oceanic variability with horizontal wavelengths shorter than 50 km, although the limited spatial resolution of concurrent direct measurements does not provide a strong cross‐validation, since the typical cast spacing of 20–25 km gives a Nyquist wavelength of 40–50 km. The small travel time signals associated with high‐wavenumber ocean variability place stringent but achievable requirements on travel time measurement precision. The forward problem for the high‐wavenumber components of the model is found to be subject to relatively large linearization errors, however, unless the sound speed field at wavelengths greater than about 50 km is known from other measurements or from a two‐dimensional tomographic array. The high‐ocean‐wavenumber resolution that is in principle available from tomographic measurements is therefore achievable only under restricted conditions.
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/93JC01246
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1993
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