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  • 1
    Online Resource
    Online Resource
    Forward scattering from the Kermit-Roosvelt Seamount complex during the SPICEX-LOAPEX-BASSEX experiments
    Acoustical Society of America (ASA) ; 2005
    In:  The Journal of the Acoustical Society of America Vol. 117, No. 4_Supplement ( 2005-04-01), p. 2549-2549
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 117, No. 4_Supplement ( 2005-04-01), p. 2549-2549
    Abstract: The SPICEX-LOAPEX-BASSEX expermiments were executed in the Northeast Pacific to examine several long range, low frequency propagation phenomena. Low frequency sources centered at 68 and 75 Hz with nominal bandwidth of 30 Hz and a source at 250 Hz with 100 Hz bandwidth were deployed transmitting orthogonal M seqeunces and FM chirps. A 64 element towed array cut for 250 Hz from Penn State Univ. was the primary multichannel receiving system. This presentation concerns the BASSEX study of low frequency scattering around the Kermit-Roosevelt Seamount complex which shoals to 900 m near 39 N and 145 W. We examine (i) the forward scattering shadow, (ii) any patterns of horizontal refraction as a function of source and receiver range from the seamounts, (iii) any backscattering from the seamounts, and (iv) the modal content of the signals by travel time methods. In addition, directional spectra of ambient noise were measured.
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.4809449
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2005
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  • 2
    Online Resource
    Online Resource
    Stochastic matched field processing
    Acoustical Society of America (ASA) ; 1999
    In:  The Journal of the Acoustical Society of America Vol. 106, No. 4_Supplement ( 1999-10-01), p. 2126-2126
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 106, No. 4_Supplement ( 1999-10-01), p. 2126-2126
    Abstract: Stochastic matched field processing was introduced [Baggeroer and Kuperman, J. Acoust. Soc. Am. 91] as a means to address stochastic variability and signal gain degradation in a replica signal. The approach parallels what is usually termed the ‘‘random signal in noise’’ problem in time series analysis wherein one uses a stochastic model to respond to the signal gain degradation issue when high-fidelity replicas cannot be generated. For stochastic MFP the important issues are: (i) the signal power scatters into a ‘‘red’’ spectra of eigenvalues where only a small number are significant, (ii) the eigenvectors are predictable based upon a priori environmental data such as internal wave or signal motion models in addition to nominal sound speed models. For many environments these conditions are met and, and importantly, more robust, MFP can be obtained. This presentation will review (i) stochastic matched field, (ii) apply it to deep and shallow water random ocean models, and (iii) assess its performance using Chernoff detection theory bounds for low signal-to-noise ratio scenarios.
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.427999
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 1999
    detail.hit.zdb_id: 1461063-2
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  • 3
    Online Resource
    Online Resource
    Modal leakage in range-dependent oceans
    Acoustical Society of America (ASA) ; 1998
    In:  The Journal of the Acoustical Society of America Vol. 103, No. 5_Supplement ( 1998-05-01), p. 2751-2751
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 103, No. 5_Supplement ( 1998-05-01), p. 2751-2751
    Abstract: The validity of the adiabatic approximation for modal propagation at low frequencies and over long megameter ranges is evaluated. A dynamical ocean model for the sound speed profile perturbations is superimposed upon a canonical Munk profile to represent a range-dependent ocean. The channel is excited with a single mode and propagated with the Collin’s FEPE code which was tuned to conserve the energy in each mode in a range-independent ocean. Modal amplitudes were determined by projecting the field on the local range-dependent modes. If one uses displacements which correspond to nominal experimental levels in the Atlantic, mode coherence is maintained only for ranges less than 1 megameter at 75 Hz; the energy appears to approach equipartitioning. Results starting with mode 1 and mode 10 were qualitatively the same. If the displacements are reduced by a factor of three, possibly more representative of Pacific levels, modal coherence is maintained for more than four megameters.
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.422811
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 1998
    detail.hit.zdb_id: 1461063-2
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  • 4
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    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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  • 5
    Online Resource
    Online Resource
    Time-dependent wave-vector analysis of the near-field pressure of a fluid-loaded cylinder
    Acoustical Society of America (ASA) ; 1991
    In:  The Journal of the Acoustical Society of America Vol. 89, No. 4B_Supplement ( 1991-04-01), p. 1956-1956
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 89, No. 4B_Supplement ( 1991-04-01), p. 1956-1956
    Abstract: The response of a ribbed cylinder to impulsive excitation was measured on a cylindrical scan surface in the evanescent near field of a cylinder and previously reported [J. A. Clark, and D. Feit, L Acoust. Soc. Am. Suppl. 1 84, S87 (1986)]. The present paper describes the application of a modified maximum-likelihood array processing algorithm to the spatial array data in conjunction with short time FFT processing of selected temporal portions of the transient response, to provide high resolution wave-number-frequency-time information about the field. Slowness (reciprocal phase velocity) versus time plots of the response for each frequency band reveal the time of arrival and the phase velocity of the various waves traveling past the array, which are compared to theoretically predicted dispersion curves for a water loaded infinite cylindrical shell. [Work supported by DARPA/ONR.]
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.2029665
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 1991
    detail.hit.zdb_id: 1461063-2
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  • 6
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    Edge wave observation using remote seismoacoustic sensing of ice events in the Arctic
    American Geophysical Union (AGU) ; 1998
    In:  Journal of Geophysical Research: Oceans Vol. 103, No. C10 ( 1998-09-15), p. 21775-21781
    Details
    In: Journal of Geophysical Research: Oceans, American Geophysical Union (AGU), Vol. 103, No. C10 ( 1998-09-15), p. 21775-21781
    Abstract: As part of the Office of Naval Research Sea Ice Mechanics Initiative, a real‐time monitoring and processing program for acoustic emission from ice fracture and ridge‐building events was established. A wide‐aperture, horizontal hydrophone array was used in combination with a vertical line array to record the acoustic signals, which were then passed through a focused beam former for real‐time generation of ice seismicity maps. A number of rapidly deployable geophone arrays were used in active zones to measure the acoustic emissions in the near field for detailed seismic event analysis. During one such deployment, a highly regular transient arrival structure was recorded on all sensors located near a major lead, with a transient appearing every 5 s. These data have been processed using frequency‐wavenumber analysis to show that the transients correspond to “edge waves” propagating forth and back along the edges of the lead, with the probable source being a “stick‐slip” mechanical phenomenon toward the ends of the lead.
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/98JC01268
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1998
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    detail.hit.zdb_id: 3094104-0
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    detail.hit.zdb_id: 2403298-0
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    detail.hit.zdb_id: 2969341-X
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    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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  • 7
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    The Geoclutter Experiment 2001: Remote acoustic imaging of sub-bottom and seafloor geomorphology in continental shelf waters
    Acoustical Society of America (ASA) ; 2002
    In:  The Journal of the Acoustical Society of America Vol. 112, No. 5_Supplement ( 2002-11-01), p. 2280-2280
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 112, No. 5_Supplement ( 2002-11-01), p. 2280-2280
    Abstract: In the Geoclutter experiment of April–May 2001, an active sonar system was used to remotely and rapidly image geomorphology over wide areas in continental shelf waters by long-range echo sounding. The bistatic system, deployed in the strataform area south of Long Island, imaged extensive networks of buried river channels and inclined subseafloor strata over tens of kilometers in near real time. Bathymetric relief in the strataform area is extremely benign. The vast majority of features imaged apparently correspond to sub-bottom geomorphology that sound waves reach after tunneling as well as propagating through the overlying sediment. Returns from buried river channels were often found to be as discrete and strong as those from calibrated targets placed in the water column. Since buried river channels are expected to be ubiquitous in continental shelf environments, sub-seafloor geomorphology will play a major role in producing ‘‘false alarms’’ or clutter in long-range sonar systems that search for submerged objects such as underwater vehicles or marine mammals. Wave guide scattering and propagation are inherent to this new remote sensing technology because source signals are transmitted over hundreds of water-column depths in range to image sub-seafloor and seafloor geomorphology.
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.4779145
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2002
    detail.hit.zdb_id: 1461063-2
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  • 8
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    Online Resource
    Basin Acoustic Seamount Scattering Experiment (BASSEX ’04) III. Array performance
    Acoustical Society of America (ASA) ; 2005
    In:  The Journal of the Acoustical Society of America Vol. 117, No. 4_Supplement ( 2005-04-01), p. 2472-2472
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 117, No. 4_Supplement ( 2005-04-01), p. 2472-2472
    Abstract: The ONR Five-Octave Research Array (FORA) was employed as the acoustic receiving system during the Basin Acoustic Seamount Scattering Experiment (BASSEX04). The array was primarily used in a towed configuration with receptions recorded for source/receiver separation distances ranging from 500–3200 km. Measurements made in proximity to the 75 Hz source moored near Kauai used a vertical array configuration. This paper presents array capabilities and performance during this first deep-water application of the FORA. Both acoustic and non-acoustic array performance during the BASSEX will be examined. In particular, array attitude and stability will be reviewed for different tow conditions, and for the array vertically deployed. Flow noise over the array will be examined for different tow speeds. Own-ship noise contamination will be presented for the array deployed vertically. Acoustic data will be presented as both individual channel measurements and beamformed output for a variety of source/receiver geometries and propagation conditions. Data quality will be assessed as it pertains to the stated objectives of a particular measurement. Based on both acoustic and non-acoustic performance characteristics the advantages and/or deficiencies of the FORA will be discussed for its use in future low-frequency long-range acoustic propagation research. [Work supported by ONR Ocean Acoustics Program.]
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.4787494
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2005
    detail.hit.zdb_id: 1461063-2
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  • 9
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    Reliable acoustic path and convergence zone bottom interaction in the Philippine Sea 09 Experiment.
    Acoustical Society of America (ASA) ; 2010
    In:  The Journal of the Acoustical Society of America Vol. 128, No. 4_Supplement ( 2010-10-01), p. 2385-2385
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 128, No. 4_Supplement ( 2010-10-01), p. 2385-2385
    Abstract: One of the objectives of the Philippine Sea 09 (PhilSea09) was to examine the multipath structure of RAP propagation at the seafloor. For a source near the surface, a receiver at the seafloor, and ranges approaching one-half a CZ, one expects a direct path, seafloor reflected and refracted paths plus water column multiples. These were measured using the bottom elements of the SIO deep vertical line array. Similarly, for both a source and a receiver at the surface and at CZ ranges, these same paths propagate back to the surface. These were also measured with the PSU FORA (five octave research array). The experiment was part of an NPAL Group effort. [Work supported by ONR Ocean Acoustics.]
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.3508530
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2010
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  • 10
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    Noise field statistics and coherence on the NPAL array
    Acoustical Society of America (ASA) ; 2001
    In:  The Journal of the Acoustical Society of America Vol. 109, No. 5_Supplement ( 2001-05-01), p. 2386-2386
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 109, No. 5_Supplement ( 2001-05-01), p. 2386-2386
    Abstract: While the NPAL array was primarily deployed to examine the spatial coherence of the Hawaii source, it is also a rich data set for ambient noise studies. Shipping noise, earthquakes and biologics all have been identified in the NPAL data. Moreover, ambient noise coherence is the primary issue in maximizing the SNR output of a sonar system. The first and second order statistics of data from the NPAL ‘‘noise only’’ segments have been analyzed with the following results: (i) There is a wide spread in the peak levels, most likely due to the proximity to shipping lanes. The maximum peak level in the recording band is 117 dB. (ii) Full broadband coherences tend to be low because of the presence of many ships. (iii) If one examines frequency bands of 1–2 Hz, then lines of individual ships can be identified and associated and they are very coherent across NPAL aperture. (iv) Vertical beamforming indicates relatively highly directional spectra at low grazing angles and ‘‘noise notch’’ for the spectra at higher frequencies. Horizontal beamforming has been difficult to implement due to element positioning errors and the large array transit time.
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.4744417
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2001
    detail.hit.zdb_id: 1461063-2
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