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  • Hodgkiss, William S.  (8)
  • Comparative Studies. Non-European Languages/Literatures  (8)
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  • Comparative Studies. Non-European Languages/Literatures  (8)
RVK
  • 1
    Online Resource
    Online Resource
    Twinkling of low-frequency tones from a moored source transmitting through and away from the surf zone
    Acoustical Society of America (ASA) ; 1997
    In:  The Journal of the Acoustical Society of America Vol. 101, No. 5_Supplement ( 1997-05-01), p. 3031-3031
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 101, No. 5_Supplement ( 1997-05-01), p. 3031-3031
    Abstract: During a recent seismoacoustics experiment, a moored, near-bottom, source just outside the surf zone (approximately 500-m seaward) in 9-m deep water, transmitted 8 tones from 70 to 700 Hz. Recordings were made by several fixed sensor systems, including: 1) a bottom hydrophone/3-component geophone package 15-m distant; 2) two horizontal bottom hydrophone arrays in a nearly perpendicular configuration in 12-m water 1.23 km away and 1.06 km farther offshore; and 3) five 3-component geophones buried at approximate 14-m spacing across the beach at 480–530 m range. These data were used to create 5-min time series of the spectral levels and directionality of the tones every 1/2 h over an 8-h period. Results indicate that within a 5-min period, fluctuations of 10–15 dB occur in the bottom hydrophone array signal levels which, typically, are not correlated from frequency to frequency. Fluctuations in the land geophone data are somewhat smaller, and only the 2 or 3 highest-frequency tones are detectable. Variations in water depth, measured by a package also located just outside the surf zone, are used with an adiabatic normal mode model to predict the fluctuation effects of ocean surface wave activity alone. [Work supported by ONR, Code 32].
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.418579
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 1997
    detail.hit.zdb_id: 1461063-2
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  • 2
    Online Resource
    Online Resource
    Features of the seismoacoustic ambient noise field in a near-shore environment
    Acoustical Society of America (ASA) ; 1995
    In:  The Journal of the Acoustical Society of America Vol. 98, No. 5_Supplement ( 1995-11-01), p. 2952-2952
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 98, No. 5_Supplement ( 1995-11-01), p. 2952-2952
    Abstract: This paper presents the features of the 1- to 750-Hz ambient noise field recorded during MPL’s adaptive beach monitoring experiment, a near-shore seismoacoustic experiment off the Camp Pendleton Marine Base north of San Diego, CA. Signal propagation characteristics in this environment are presented in a companion paper. The data were recorded by two nearly orthogonal, horizontal hydrophone arrays located 3.4 km offshore in 20-m water. The most predominant aspect is the sounds created by biologics, particularly night-time ‘‘cycling’’ choruses of fish. Ideas on the use of these sounds for determining the geoacoustic properties of the ocean bottom are discussed. Also present at night are strong lines at 85 Hz and its two higher harmonics, associated with water pumps on the marine base used to fill wells in the surrounding hills. A still-puzzling feature is the broadband pulses (50–200 Hz) that occur at a 7.5-s repetitition period; they possibly also are of a biological nature. Fluctuations in the infrasonic band are associated with ocean surface wave propagation, thereby providing a means of determining the ocean surface wave directional spectrum. Finally, by judicious selection of data, noise generated by breaking surf can be measured. [Work supported by ONR, Code 32.]
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.414057
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 1995
    detail.hit.zdb_id: 1461063-2
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  • 3
    Online Resource
    Online Resource
    Geoacoustic inversion using fish sounds
    Acoustical Society of America (ASA) ; 1996
    In:  The Journal of the Acoustical Society of America Vol. 100, No. 4_Supplement ( 1996-10-01), p. 2665-2665
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 100, No. 4_Supplement ( 1996-10-01), p. 2665-2665
    Abstract: During a recent near-surf-zone experiment, the underwater acoustic noise field was dominated by biological sounds over the 50-Hz to 10-kHz band. At night, members of the croaker (Sciaenidae) family migrated from the surf zone out to the 20-m water, where two bottom hydrophone arrays were located. Often during the night, individual vocalizing fish came within several meters of an array element so that the fish’s sequence of 7–13 knocks, each with peak-to-peak source levels of about 160 dB re: 1 μPa @ 1 m, was clearly discernible above the background din. The arrivals from some of these knocks display low-frequency (around 60 Hz) oscillatory tails due to excitation of interface waves at the ocean bottom. These Scholte waves have phase velocities around 110 m/s and a group velocity near 30 m/s. Using adjacent array elements to locate the fish at each knock, its movement over the sequence creates a synthetic aperture that is used in inversion for the shear wave velocity in the uppermost part of the ocean bottom. [Work supported by ONR, Code 32.]
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.417484
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 1996
    detail.hit.zdb_id: 1461063-2
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  • 4
    Online Resource
    Online Resource
    Incoherent beamforming with interference patterns
    Acoustical Society of America (ASA) ; 2000
    In:  The Journal of the Acoustical Society of America Vol. 108, No. 5_Supplement ( 2000-11-01), p. 2645-2646
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 108, No. 5_Supplement ( 2000-11-01), p. 2645-2646
    Abstract: A conventional coherent plane wave beamformer exploits the phase evolution of the wave field across the array aperture, using the phase at one element as reference, to obtain information on source location. Alternatively, in a multipath environment, the phase of one mode or multipath can be used as reference for the phase evolution of the other multipaths in the wave field. This ‘‘intermode interferometry’’ is the basis of an incoherent beamformer presented here. It involves summing together individual element autospectra, after performing a frequency-domain dilatation/contraction operation based upon a hypothesized source location. Because it uses autospectra rather than element time series, this processing provides no gain of signal over background noise. Therefore, its usefulness in its basic form is restricted to localization of strong signals. However, it is not limited to line arrays with equal element spacing, and the array element positions need only be known to a fraction of an interference wavelength rather than an acoustic wavelength. Examples of the incoherent beamforming results from simulation and actual ocean acoustic data collected during the shallow-water (200 m) SWellEx-3 experiment will be presented. Emphasis is placed on 2D passive synthetic aperture applications. [Work supported by ONR, Code 321US.]
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.4743857
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2000
    detail.hit.zdb_id: 1461063-2
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  • 5
    Online Resource
    Online Resource
    Offshore geoacoustic inversions using sounds from land vehicle activity
    Acoustical Society of America (ASA) ; 1998
    In:  The Journal of the Acoustical Society of America Vol. 103, No. 5_Supplement ( 1998-05-01), p. 2936-2936
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 103, No. 5_Supplement ( 1998-05-01), p. 2936-2936
    Abstract: Land-based vehicle activity can be clearly detected and tracked by underwater acoustic sensors located outside the surf zone. This capability has been demonstrated with nearshore seismoacoustic data collected during the Marine Physical Lab’s Adaptive Beach Monitoring (ABM) program. The purpose of this paper is to demonstrate how the sounds from these land vehicles can be used to perform inversions for the offshore geoacoustic properties, somewhat akin to the use of Vibroseis in geophysical exploration. The event of interest here is where four tracked vehicles traveled down the beach at a speed of 10 m/s, creating signal beam levels that exceeded background levels by 35 dB in the 30- to 70-Hz band. The signal-to-background noise ratio in single element spectra also is sufficiently high that these vehicles can be used as sources of opportunity. The datum for the inversions is the strong frequency dependence of the phase velocity of the arrivals in this frequency band. Forward modeling is performed with a parabolic equation (PE) code written by Mike Collins. Results are compared to those obtained from the offshore arrivals of broadband detonations conducted on the beach. [Work supported by ONR, Code 32.]
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.422183
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 1998
    detail.hit.zdb_id: 1461063-2
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  • 6
    Online Resource
    Online Resource
    Surf noise and biological sounds in the near-surf-zone environment.
    Acoustical Society of America (ASA) ; 1996
    In:  The Journal of the Acoustical Society of America Vol. 99, No. 4_Supplement ( 1996-04-01), p. 2453-2457
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 99, No. 4_Supplement ( 1996-04-01), p. 2453-2457
    Abstract: The Marine Physical Lab’s Adaptive Beach Monitoring Experiment was conducted from 24 April to 14 June 1995, in and near the surf zone off the S. California coast. Other participants included NRaD/NCCOSC, NRL, ARL/PSU, and ARL/UT. The focus here is on the underwater acoustic noise field properties. Contributions of breaking surf are studied in the 1- to 400-Hz band using a 35-element subsection of a bottom hydrophone array oriented perpendicular to the coast and located 3.4-km offshore in 20-m water. A 3-week time series of endfire-beamforming results are compared to the ocean surface wave height data collected over the same period. Source tow data quantify the propagation effects of surf noise to the array site and permit inversions for bottom geoacoustic properties. The array data are supplemented by the distance dependence from shore of data from bottom-mounted sonobuoys in the 100-Hz–20-kHz band, and air acoustic data recorded just landward of the shoreline. Biologics are a substantial component of the noise field and must be accounted for in evaluating the contribution from surf. Fish sounds themselves can be used as novel sources in inversion for bottom geoacoustic properties. [Work supported by ONR, Code 32.]
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.415459
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 1996
    detail.hit.zdb_id: 1461063-2
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  • 7
    Online Resource
    Online Resource
    Detection and tracking of land vehicle activity by offshore underwater acoustic arrays
    Acoustical Society of America (ASA) ; 1997
    In:  The Journal of the Acoustical Society of America Vol. 102, No. 5_Supplement ( 1997-11-01), p. 3193-3193
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 102, No. 5_Supplement ( 1997-11-01), p. 3193-3193
    Abstract: Land-based vehicle activity can be tracked by underwater acoustic sensors located at least as far as 3.4 km offshore. This capability is demonstrated with data from two near-surf-zone experiments as part of the Marine Physical Laboratory’s Adaptive Beach Monitoring program. In one case, four tracked vehicles spaced every 150 m traveled down the beach. Spectra estimated from a single hydrophone of a bottom line array 1.5 km offshore in 12-m water show a high-pass character compared to land geophone recordings because of the coupling characteristics between the land seismic and underwater acoustic fields. Adaptive plane-wave beamforming over the 30- to 70-Hz band shows, at times, beam-peak-to-background levels exceeding 35 dB. The acoustic tracks agree with those from visual logs and suggest that the four vehicles can be enumerated acoustically, particularly when combined with results from the 120- to 130-Hz band. In a second case, plane-wave beamforming results for two tracked vehicles traveling on the beach and recorded by a bottom array 3.4 km offshore in 20-m water show a beam-peak-to-background level approaching 20 dB. A videotape shows the evolution of 2-D wave-number spatial spectra during the vehicle transit. [Work supported by ONR, Code 32.]
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.420892
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 1997
    detail.hit.zdb_id: 1461063-2
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  • 8
    Online Resource
    Online Resource
    Coupling of land-based signals into the nearshore underwater acoustic field
    Acoustical Society of America (ASA) ; 1997
    In:  The Journal of the Acoustical Society of America Vol. 102, No. 5_Supplement ( 1997-11-01), p. 3193-3193
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 102, No. 5_Supplement ( 1997-11-01), p. 3193-3193
    Abstract: Small, controlled land detonations on and near the beach recorded by land geophones and by offshore seismoacoustic sensors are used to characterize the coupling between land seismic and underwater acoustic fields. These data were collected in the Marine Physical Laboratory’s Adaptive Beach Monitoring program. The predominant arrival on land is an elastic surface wave. Although an ocean bottom interface wave can be seen clearly in seismoacoustic recordings just outside the surf zone, it attenuates to nearly background noise levels by the time it reaches a bottom hydrophone array 1.5 km offshore in 12-m water. Travel-time and frequency/wave-number analyses indicate that the hydrophone array’s received energy is composed mostly of dispersive body waves propagating as the lowest water-borne mode, with frequency-dependent phase and group velocities around 2.0 and 1.8 km/s, respectively. The frequency at which this lowest mode cuts off is the corner frequency of the high-pass filter representing the propagation from land to the underwater acoustic field. These results and numerical modeling, guided by insights obtained from classic work on acoustic propagation in a fluid wedge, are used to explain offshore underwater recordings of land vehicle activity. [Work supported by ONR, Code 32.]
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.420893
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 1997
    detail.hit.zdb_id: 1461063-2
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