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  • 1
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    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
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    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
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  • 3
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    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
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  • 4
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    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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    detail.hit.zdb_id: 3094197-0
    SSG: 16,13
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  • 5
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    Barotropic currents and vorticity in the central North Pacific Ocean during summer 1987 determined from long‐range reciprocal acoustic transmissions
    American Geophysical Union (AGU) ; 1994
    In:  Journal of Geophysical Research: Oceans Vol. 99, No. C2 ( 1994-02-15), p. 3263-3272
    Details
    In: Journal of Geophysical Research: Oceans, American Geophysical Union (AGU), Vol. 99, No. C2 ( 1994-02-15), p. 3263-3272
    Abstract: Large‐scale depth‐integrated currents and relative vorticity were measured in the central North Pacific Ocean during summer 1987 using long‐range reciprocal acoustic transmissions between transceivers in a triangle approximately 1000 km on a side. Inverse techniques were used to estimate the depth‐averaged (barotropic) current bihourly at 4‐day intervals from differential travel times. Tidal constituent amplitudes and phases found from the acoustically determined currents agree with those found from current meters and with the tidal models of Schwiderski (1980) and Cartwright et al. (1992), providing confirmation that the tomographically derived barotropic currents are correct within the expected uncertainties. The estimated low‐frequency, large‐scale currents are compared with depth‐averaged currents determined by point measurements using current meters and bottom‐mounted electrometers. Meridional and zonal currents are calculated using the topographic Sverdrup balance with the Fleet Numerical Oceanography Center wind field. The measured time derivative of the areally averaged relative vorticity is shown to be insignificant to the Sverdrup balance. Currents and vorticity calculated using the Sverdrup balance are an order of magnitude smaller than the observations. The magnitude and variability of the large‐scale currents and vorticity determined from the Semtner and Chervin (1988) eddy‐resolving model of ocean circulation are similar to the direct measurements.
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/93JC03335
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1994
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    detail.hit.zdb_id: 3094104-0
    detail.hit.zdb_id: 2130824-X
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    detail.hit.zdb_id: 2016810-X
    detail.hit.zdb_id: 2403298-0
    detail.hit.zdb_id: 2016800-7
    detail.hit.zdb_id: 161666-3
    detail.hit.zdb_id: 161667-5
    detail.hit.zdb_id: 2969341-X
    detail.hit.zdb_id: 161665-1
    detail.hit.zdb_id: 3094268-8
    detail.hit.zdb_id: 710256-2
    detail.hit.zdb_id: 2016804-4
    detail.hit.zdb_id: 3094181-7
    detail.hit.zdb_id: 3094219-6
    detail.hit.zdb_id: 3094167-2
    detail.hit.zdb_id: 2220777-6
    detail.hit.zdb_id: 3094197-0
    SSG: 16,13
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  • 6
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    On equations for the speed of sound in seawater.
    Acoustical Society of America (ASA) ; 1992
    In:  The Journal of the Acoustical Society of America Vol. 91, No. 4_Supplement ( 1992-04-01), p. 2391-2391
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 91, No. 4_Supplement ( 1992-04-01), p. 2391-2391
    Abstract: Long-range acoustic transmissions made in conjunction with extensive environmental measurements and accurate mooring position determinations have been used to test the accuracy of equations used to calculate sound speed from pressure, temperature, and salinity. The sound-speed field computed using the Del Grosso equation [V. A. Del Grosso, J. Acoust. Soc. Am. 56, 1084–1091 (1974)] give predictions of acoustic arrival patterns which agree significantly better with the long-range measurements than those computed using the Chen and Millero equation [C. Chen and F. J. Millero, J. Acoust. Soc. Am. 62, 1129–1135 (1977)] . The predicted ray travel times and travel time error have been calculated using objectively mapped sound-speed fields computed from CTD and XBT data. Using the measured and predicted ray travel times, a negligible correction to Del Grosso’s equation of 0.05±0.05 m/s at 4000-m depth is calculated. Small errors of about 50 m in the GPS determination of mooring positions lends a depth-independent error of 0.1 m/s to the sound-speed equation correction. [Work supported by NSF and ONR.]
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.403304
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 1992
    detail.hit.zdb_id: 1461063-2
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  • 7
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    Barotropic currents, vorticity, and tides in the northcentral Pacific in summer 1987 determined from long-range acoustic transmissions
    Acoustical Society of America (ASA) ; 1993
    In:  The Journal of the Acoustical Society of America Vol. 94, No. 3_Supplement ( 1993-09-01), p. 1801-1802
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 94, No. 3_Supplement ( 1993-09-01), p. 1801-1802
    Abstract: Large-scale depth-integrated currents, relative vorticity, and tides were measured in the northcentral Pacific Ocean during summer 1987 using long-range reciprocal acoustic transmissions between transceivers in a triangle approximately 1000 km on a side. Tidal harmonic constants found from the acoustically determined currents agree with those found from current meters and with the tidal models of Schwiderski [E. W. Schwiderski, Mar. Geod. 3, 161–255 (1980)] and Cartwright et al. [D. E. Cartwright et al., NASA Tech. Mem. 104578 (1992)] . Sum travel times were used to calculate the baroclinic tide isotach displacement. A significant part of the derived internal tide is deterministic. Currents are calculated using the topographic Sverdrup balance with the Fleet Numerical Oceanography Center wind field. The measured time derivative of the areal-averaged relative vorticity is insignificant to the Sverdrup balance. Currents and vorticity calculated using the Sverdrup balance are an order of magnitude smaller than the observations. The magnitude and variability of the large-scale currents and vorticity determined from the Semtner–Chervin eddy-resolving model of ocean circulation [A. J. Semtner and R. M. Chervin, J. Geophys. Res. 93, 15 502–15 522 (1988)] are similar to the direct measurements. [Work supported by NSF and ONR.]
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.407907
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 1993
    detail.hit.zdb_id: 1461063-2
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  • 8
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    An engineering test of moving ship tomography in the Greenland Sea
    Acoustical Society of America (ASA) ; 1990
    In:  The Journal of the Acoustical Society of America Vol. 88, No. S1 ( 1990-11-01), p. S140-S141
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 88, No. S1 ( 1990-11-01), p. S140-S141
    Abstract: Moving ship tomography seeks to synthesize a high-resolution three-dimensional snapshot of the ocean sound speed field from a few tomographic instruments by moving them during the survey. A moored array of six acoustic transceivers was deployed in the Greenland Sea from September 1988 to August 1989 as part of the Greenland Sea Tomography Experiment. A prototype ship-deployed array of ten hydrophones was used to receive about 30 transmissions after mooring deployment and about 40 prior to recovery, distributed at locations encircling the moored sources. The positions of the sources and receivers are imperfectly known at this time, but it is possible to compare the observed arrivals with ray theory and identify many of the observed arrivals with numerical ray paths. The second survey yielded enough identified rays to produce estimates of the ocean sound-speed field in spite of the need to solve for the unknown instrument positions. The resolution of the sound-speed maps will improve as the ship and mooring positions are refined using NAVSTAR Global Positioning System data. The tests in the Greenland Sea are preparatory to a trial of moving ship tomography in the western North Atlantic in 1991. The experimental design for that experiment includes simulations examining the effects of ocean dynamics on the reconstruction process. Cases including both linear planetary wave propagation and advection by uniform barotropic currents show that the mapping can proceed in the presence of realistic dynamical evolution. [Work supported by ONR and ONT.]
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.2028631
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 1990
    detail.hit.zdb_id: 1461063-2
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  • 9
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    A comparison of measured and predicted broadband acoustic arrival patterns out to 10-Mm range during the ATOC Acoustic Engineering Test
    Acoustical Society of America (ASA) ; 1995
    In:  The Journal of the Acoustical Society of America Vol. 97, No. 5_Supplement ( 1995-05-01), p. 3233-3233
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 97, No. 5_Supplement ( 1995-05-01), p. 3233-3233
    Abstract: A low-frequency acoustic source suspended from R/P FLIP approximately 340 nautical miles WSW of San Diego transmitted to receivers 90 to 10 000 km distant during the Acoustic Engineering Test of the Acoustic Thermometry of Ocean Climate (ATOC) Program. The source was sus-pended for 7 days during November 1994 near the depth of the sound channel axis (about 650 m) in water over 4000 m deep, in order to avoid near-source bottom interactions. The source transmitted a phase-coded m-sequence with a center frequency of 75 Hz and a digit length of 27 ms [Metzger et al., this meeting]. Measured receptions on five bottom-mounted SOSUS receivers at ranges from 300–4000 km, on two vertical line array receivers at ranges of 90 and 3300 km, and on a sonobuoy modified to have the hydrophone on the sound channel axis at about 10 000-km range, are compared with ray theoretic, adiabatic normal mode, and broadband parabolic equation predictions. [Work supported by the Strategic Environmental Research and Development P rogram through ARPA.]
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.411768
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 1995
    detail.hit.zdb_id: 1461063-2
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  • 10
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    Acoustic thermometry of ocean climate. A description of the acoustic network
    Acoustical Society of America (ASA) ; 1996
    In:  The Journal of the Acoustical Society of America Vol. 100, No. 4_Supplement ( 1996-10-01), p. 2580-2580
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 100, No. 4_Supplement ( 1996-10-01), p. 2580-2580
    Abstract: The ATOC acoustic feasibility network became functional in December 1995 following the installation of an acoustic source on Pioneer Seamount approximately 50 nm off the coast of Northern California. The current effort is part of the Marine Mammal Research Program Pilot Study. This paper describes the acoustic network of sources and receivers, including the augmentations to be made in summer 1996. The network was designed to take advantage of existing hydrophone arrays, while providing for maximum coverage of the North Pacific by the acoustic paths. The acoustical receptions currently being obtained are processed to obtain ‘‘dot plots’’ which show the arrival times and arrival angles of acoustical energy above a chosen signal-to-noise ratio. The ‘‘dot plot’’ histories demonstrate stable ray arrivals (albeit with significant amplitude fluctuations) for even the longest propagation ranges of 5 Mm. [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: 10.1121/1.417518
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 1996
    detail.hit.zdb_id: 1461063-2
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