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  • 1
    Online Resource
    Online Resource
    A single slice tomography experiment using a long vertical array of receivers
    Acoustical Society of America (ASA) ; 1990
    In:  The Journal of the Acoustical Society of America Vol. 88, No. S1 ( 1990-11-01), p. S117-S117
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 88, No. S1 ( 1990-11-01), p. S117-S117
    Abstract: Broadband signals were transmitted from a near-axial source to a long vertical receiving array 1000 km distant in the North Pacific for 9 days in July 1989. The signals were received at 50 hydrophones spaced 60 m apart in the vertical, starting near the surface. Pulses were recorded at 10-min intervals for two periods, totaling 24 h, while hourly pulses were recorded for the duration, giving a total of about 320 pulses. Individual ray arrivals were resolved and their arrival times measured with a precision of a few milliseconds using phase-coded transmissions centered at 250 Hz with a bandwidth of 83 Hz (12-ms resolution). The pulse arrivals as a function of time and depth correspond well with predictions based on geometric (ray) and physical (WKBJ) optics. In each transmission, 600 to 900 ray arrivals can be identified with rays from numerical analysis, distributed along up to 24 distinct wave fronts. The ray arrivals evolve at the time scales of ocean processes. The longest period travel time changes can be inverted to infer changes in the mean sound-speed field between the source and receiver and in high-wave-number ocean features with wavelengths correspondng to ray loop lengths and their harmonics (70 km and shorter wavelengths). Simultaneous CTD and XBT surveys are available for comparison. Temporal and vertically lagged fluctuation statistics of the individual arrivals quantify internal wave and fine-structure effects. [Work supported by ONT.]
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.2028535
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 1990
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  • 2
    Online Resource
    Online Resource
    Analysis of multipath acoustic field variability and coherence in the finale of broadband basin-scale transmissions in the North Pacific Ocean
    Acoustical Society of America (ASA) ; 2005
    In:  The Journal of the Acoustical Society of America Vol. 117, No. 3 ( 2005-03-01), p. 1538-1564
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 117, No. 3 ( 2005-03-01), p. 1538-1564
    Abstract: The statistics of low-frequency, long-range acoustic transmissions in the North Pacific Ocean are presented. Broadband signals at center frequencies of 28, 75, and 84 Hz are analyzed at propagation ranges of 3252 to 5171 km, and transmissions were received on 700 and 1400 m long vertical receiver arrays with 35 m hydrophone spacing. In the analysis we focus on the energetic “finale” region of the broadband time front arrival pattern, where a multipath interference pattern exists. A Fourier analysis of 1 s regions in the finale provide narrowband data for examination as well. Two-dimensional (depth and time) phase unwrapping is employed to study separately the complex field phase and intensity. Because data sampling occured in 20 or 40 min intervals followed by long gaps, the acoustic fields are analyzed in terms of these 20 and 40 min and multiday observation times. An analysis of phase, intensity, and complex envelope variability as a function of depth and time is presented in terms of mean fields, variances, probability density functions (PDFs), covariance, spectra, and coherence. Observations are compared to a random multipath model of frequency and vertical wave number spectra for phase and log intensity, and the observations are compared to a broadband multipath model of scintillation index and coherence.
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.1854615
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2005
    detail.hit.zdb_id: 1461063-2
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  • 3
    Online Resource
    Online Resource
    Comparisons of measured and predicted acoustic fluctuations for a 3250-km propagation experiment in the eastern North Pacific Ocean
    Acoustical Society of America (ASA) ; 1999
    In:  The Journal of the Acoustical Society of America Vol. 105, No. 6 ( 1999-06-01), p. 3202-3218
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 105, No. 6 ( 1999-06-01), p. 3202-3218
    Abstract: During the Acoustic Engineering Test (AET) of the Acoustic Thermometry of Ocean Climate (ATOC) program, acoustic signals were transmitted from a broadband source with 75-Hz center frequency to a 700-m-long vertical array of 20 hydrophones at a distance of 3252 km; receptions occurred over a period of six days. Each received pulse showed early identifiable timefronts, followed by about 2 s of highly variable energy. For the identifiable timefronts, observations of travel-time variance, average pulse shape, and the probability density function (PDF) of intensity are presented, and calculations of internal-wave contributions to those fluctuations are compared to the observations. Individual timefronts have rms travel time fluctuations of 11 to 19 ms, with time scales of less than 2 h. The pulse time spreads are between 0 and 5.3 ms rms, which suggest that internal-wave-induced travel-time biases are of the same magnitude. The PDFs of intensity for individual ray arrivals are compared to log-normal and exponential distributions. The observed PDFs are closer to the log-normal distribution, and variances of log intensity are between (3.1 dB)2 (with a scintillation index of 0.74) for late-arriving timefronts and (2.0 dB)2 (with a scintillation index of 0.2) for the earliest timefronts. Fluctuations of the pulse termination time of the transmissions are observed to be 22 ms rms. The intensity PDF of nonidentified peaks in the pulse crescendo are closer to a log-normal distribution than an exponential distribution, but a Kolmogorov–Smirnov test rejects both distributions. The variance of the nonidentified peaks is (3.5 dB)2 and the scintillation index is 0.92. As a group, the observations suggest that the propagation is on the border of the unsaturated and partially saturated regimes. After improving the specification of the ray weighting function, predictions of travel-time variance using the Garrett–Munk (GM) internal-wave spectrum at one-half the reference energy are in good agreement with the observations, and the one-half GM energy level compares well with XBT data taken along the transmission path. Predictions of pulse spread and wave propagation regime are in strong disagreement with the observations. Pulse time spread estimates are nearly two orders of magnitude too large, and Λ–Φ methods for predicting the wave propagation regime predict full saturation.
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.424650
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 1999
    detail.hit.zdb_id: 1461063-2
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  • 4
    Online Resource
    Online Resource
    Variability of Heat Content in the Central North Pacific in Summer 1987 Determined from Long-Range Acoustic Transmissions
    American Meteorological Society ; 1993
    In:  Journal of Physical Oceanography Vol. 23, No. 12 ( 1993-12), p. 2650-2666
    Details
    In: Journal of Physical Oceanography, American Meteorological Society, Vol. 23, No. 12 ( 1993-12), p. 2650-2666
    Type of Medium: Online Resource
    ISSN: 0022-3670 , 1520-0485
    URL: Article
    DOI: 10.1175/1520-0485(1993)023〈2650:VOHCIT〉2.0.CO;2
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 1993
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  • 5
    Online Resource
    Online Resource
    Barotropic Rossby wave radiation from a model Gulf Stream : BAROTROPIC ROSSBY WAVE RADIATION
    American Geophysical Union (AGU) ; 2007
    In:  Geophysical Research Letters Vol. 34, No. 23 ( 2007-12-16), p. n/a-n/a
    Details
    In: Geophysical Research Letters, American Geophysical Union (AGU), Vol. 34, No. 23 ( 2007-12-16), p. n/a-n/a
    Type of Medium: Online Resource
    ISSN: 0094-8276
    URL: Article
    DOI: 10.1029/2007GL031937
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2007
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    detail.hit.zdb_id: 7403-2
    SSG: 16,13
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  • 6
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    A TOPEX/POSEIDON global tidal model (TPXO.2) and barotropic tidal currents determined from long-range acoustic transmissions
    Elsevier BV ; 1997
    In:  Progress in Oceanography Vol. 40, No. 1-4 ( 1997-1), p. 337-367
    Details
    In: Progress in Oceanography, Elsevier BV, Vol. 40, No. 1-4 ( 1997-1), p. 337-367
    Type of Medium: Online Resource
    ISSN: 0079-6611
    URL: Article
    DOI: 10.1016/S0079-6611(98)00008-1
    RVK:
    RB 10402
    Language: English
    Publisher: Elsevier BV
    Publication Date: 1997
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    detail.hit.zdb_id: 4062-9
    SSG: 21,3
    SSG: 14
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  • 7
    Online Resource
    Online Resource
    Observation of barotropic-tide relative vorticity in the northwest Atlantic
    Acoustical Society of America (ASA) ; 1996
    In:  The Journal of the Acoustical Society of America Vol. 100, No. 4_Supplement ( 1996-10-01), p. 2565-2565
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 100, No. 4_Supplement ( 1996-10-01), p. 2565-2565
    Abstract: Time series of reciprocal ray travel times were obtained at 350-, 410-, and 670-km ranges in the western North Atlantic during the 1991–1992 Acoustic Mid-Ocean Dynamics Experiment (AMODE). Transmissions were recorded for approximately 300 days between six transceivers in a pentagonal array. Barotropic current along each of the 15 propagation paths is derived from the difference of reciprocal ray travel times, while ten independent estimates of areal-averaged relative vorticity are found by integrating current around triangles in the pentagonal array. The estimated tidal currents are highly accurate, and tidal relative vorticity at the M2 frequency is detected. This vorticity is induced primarily by the stretching of vortex lines by tidal elevation. Harmonic constants (amplitude, phase) of M2 tidal vorticity are about (4–8±2×10−9 s−1, 270°−320° ±20°), while harmonic constants of about (2–3×10−9 s−1, 300°−340°) are predicted using the shallow-water equations. The measured tidal harmonic constants are compared with those derived from a global barotropic tidal model.
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.417379
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 1996
    detail.hit.zdb_id: 1461063-2
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  • 8
    Online Resource
    Online Resource
    North Pacific basin heat content variability determined from long-range acoustic transmissions
    Acoustical Society of America (ASA) ; 1996
    In:  The Journal of the Acoustical Society of America Vol. 100, No. 4_Supplement ( 1996-10-01), p. 2581-2581
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 100, No. 4_Supplement ( 1996-10-01), p. 2581-2581
    Abstract: ATOC signals transmitted from the Pioneer Seamount acoustic source have been received on hydrophone arrays located throughout the North Pacific Basin since the beginning of 1996. Propagation times can be used to infer average temperature (or heat content) variability because the speed of sound changes with temperature. The time series of resolved-ray travel times show both an annual cycle with amplitudes up to 0.5 s, and other higher frequency fluctuations of comparable magnitude caused by natural oceanic variability. The range-averaged temperature is derived from the low-pass filtered ( & lt;1 cpd) resolved-ray travel times by constructing a model for the structure and statistics of oceanic variability, fitting the model to the data using weighted least-squares techniques, and then calculating the range- and depth-averaged quantity including its uncertainty. Because many of the resolved rays reflect off the sea surface, the mixed layer in particular, and the upper ocean in general, must be correctly modeled. The variability of acoustically determined heat content is compared to that determined from the Levitus94 atlas, historical expendable bathythermograph (XBT) data; other concurrent data types are not yet available for direct comparison. [Work supported by the Strategic Environmental Research and Development Program through ARPA.]
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.417522
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 1996
    detail.hit.zdb_id: 1461063-2
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  • 9
    Online Resource
    Online Resource
    A test of basin-scale acoustic thermometry using a large-aperture vertical array at 3250-km range in the eastern North Pacific Ocean
    Acoustical Society of America (ASA) ; 1999
    In:  The Journal of the Acoustical Society of America Vol. 105, No. 6 ( 1999-06-01), p. 3185-3201
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 105, No. 6 ( 1999-06-01), p. 3185-3201
    Abstract: Broadband acoustic signals were transmitted during November 1994 from a 75-Hz source suspended near the depth of the sound-channel axis to a 700-m long vertical receiving array approximately 3250 km distant in the eastern North Pacific Ocean. The early part of the arrival pattern consists of raylike wave fronts that are resolvable, identifiable, and stable. The later part of the arrival pattern does not contain identifiable raylike arrivals, due to scattering from internal-wave-induced sound-speed fluctuations. The observed ray travel times differ from ray predictions based on the sound-speed field constructed using nearly concurrent temperature and salinity measurements by more than a priori variability estimates, suggesting that the equation used to compute sound speed requires refinement. The range-averaged ocean sound speed can be determined with an uncertainty of about 0.05 m/s from the observed ray travel times together with the time at which the near-axial acoustic reception ends, used as a surrogate for the group delay of adiabatic mode 1. The change in temperature over six days can be estimated with an uncertainty of about 0.006 °C. The sensitivity of the travel times to ocean variability is concentrated near the ocean surface and at the corresponding conjugate depths, because all of the resolved ray arrivals have upper turning depths within a few hundred meters of the surface.
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.424649
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 1999
    detail.hit.zdb_id: 1461063-2
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  • 10
    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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