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  • 1
    Online Resource
    Online Resource
    Acoustic Backscattering From a Sand and a Sand/Mud Environment: Experiments and Data/Model Comparisons
    Institute of Electrical and Electronics Engineers (IEEE) ; 2009
    In:  IEEE Journal of Oceanic Engineering Vol. 34, No. 4 ( 2009-10), p. 388-398
    Details
    In: IEEE Journal of Oceanic Engineering, Institute of Electrical and Electronics Engineers (IEEE), Vol. 34, No. 4 ( 2009-10), p. 388-398
    Type of Medium: Online Resource
    ISSN: 0364-9059 , 1558-1691
    URL: Article
    DOI: 10.1109/JOE.2009.2018335
    Language: Unknown
    Publisher: Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2009
    detail.hit.zdb_id: 2025369-2
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  • 2
    Online Resource
    Online Resource
    Seafloor Roughness Measured by a Laser Line Scanner and a Conductivity Probe
    Institute of Electrical and Electronics Engineers (IEEE) ; 2009
    In:  IEEE Journal of Oceanic Engineering Vol. 34, No. 4 ( 2009-10), p. 459-465
    Details
    In: IEEE Journal of Oceanic Engineering, Institute of Electrical and Electronics Engineers (IEEE), Vol. 34, No. 4 ( 2009-10), p. 459-465
    Type of Medium: Online Resource
    ISSN: 0364-9059 , 1558-1691
    URL: Article
    DOI: 10.1109/JOE.2009.2026986
    Language: Unknown
    Publisher: Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2009
    detail.hit.zdb_id: 2025369-2
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  • 3
    Online Resource
    Online Resource
    Scattering by surfaces with sub-Bragg structure
    Acoustical Society of America (ASA) ; 2006
    In:  The Journal of the Acoustical Society of America Vol. 119, No. 5_Supplement ( 2006-05-01), p. 3310-3310
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 119, No. 5_Supplement ( 2006-05-01), p. 3310-3310
    Abstract: The scattering from a rough pressure release surface, where the spectrum of the surface only contains wavelengths considerably shorter than half the acoustic wavelength, is considered. The amplitude of the surface may be larger than that for which perturbation theory would be appropriate. We show that the surface can be replaced by an effective surface containing waves longer than half the acoustic wavelength. This effective surface is close to the envelope of the actual surface; this effective problem is likely to be much easier to solve than the original problem. We investigate the relationship between the problems and adjust parameters of the effective surface, by solving both problems with the integral equation.
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.4808853
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2006
    detail.hit.zdb_id: 1461063-2
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  • 4
    Online Resource
    Online Resource
    The evolution of vertical spatial coherence with range from source.
    Acoustical Society of America (ASA) ; 2009
    In:  The Journal of the Acoustical Society of America Vol. 125, No. 4_Supplement ( 2009-04-01), p. 2511-2511
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 125, No. 4_Supplement ( 2009-04-01), p. 2511-2511
    Abstract: Vertical spatial coherence for shallow water propagation at frequencies 1–10 kHz is studied as function of range (50 to 5000 m), as part of the Shallow-Water 2006 program that took place off the coast of New Jersey in August 2006 in waters 80 m deep. An acoustic source was deployed from the R/V Knorr at depths 30 and 40 m and signals were recorded on a moored receiving system consisting of two 1.4 m long vertical line arrays (VLA) centered at depths 25 and 50 m. At all ranges, spatial coherence, Γ (normalized spatial correlation), is locally stationary and depends on element vertical separation d up to the maximum kd (59) afforded by the VLA, where k is acoustic wave number. For range normalized by depth, r*, less than about 10, Γ is oscillatory, with non-zero imaginary part, reflecting the inclusion of multipaths for which no single path dominates. For r* greater than 10, Γ tends to exhibit a monotonic decay with kd and the imaginary part vanishes reflecting symmetry about 0 deg vertical arrival angle. The coherence also increases with r* reflecting the change in modal structure. [Research supported by ONR Ocean Acoustics.]
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.4783430
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2009
    detail.hit.zdb_id: 1461063-2
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  • 5
    Online Resource
    Online Resource
    Measurement and modeling of broadband Bragg scattering from a sinusoidal surface.
    Acoustical Society of America (ASA) ; 2009
    In:  The Journal of the Acoustical Society of America Vol. 125, No. 4_Supplement ( 2009-04-01), p. 2661-2661
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 125, No. 4_Supplement ( 2009-04-01), p. 2661-2661
    Abstract: While the mechanism of Bragg scattering is well known, most experimental work has been concentrated in the area of narrow band sound sources and in the far-field. Motivated by underwater detection problems in the presence of sediment ripple fields, we report laboratory measurements of broadband sound scattering from a sinusoidal surface machined on a polyurethane board. The surface has a wavelength of 8 mm and peak-to-peak height of 2 mm. Coherently scattered sound data were taken in near-field geometries and in the frequency band of 150–400 kHz. The measurement geometry is such that a broad range of Bragg angles corresponding to the frequency band are covered. We observe that the scattered sound demonstrates a down chirp time dependence when the incident sound is a short pulse. Models based on first order perturbation theory were developed which explain the observed scattered sound in both magnitude and phase. In addition, we also measured second order Bragg scattering. This motivates modeling efforts on higher order Bragg scatter. [Work supported by ONR.]
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.4784203
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2009
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  • 6
    Online Resource
    Online Resource
    Ambient noise directivity in the East China Sea: Model/data comparison
    Acoustical Society of America (ASA) ; 2006
    In:  The Journal of the Acoustical Society of America Vol. 119, No. 5_Supplement ( 2006-05-01), p. 3218-3218
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 119, No. 5_Supplement ( 2006-05-01), p. 3218-3218
    Abstract: In general, the vertical directivity pattern of high-frequency ambient noise is anisotropic. For measurements made beneath a shallow-water mixed layer, the observed noise directivity often displays a trough in the horizontal called the ambient noise notch. This notch develops because noise sources near the sea surface generate sound that propagates at relatively steep grazing angles. The directivity pattern is also generally asymmetric about the horizontal notch. This asymmetry develops because the seabed is an imperfect reflector of sound relative to the sea surface. In the present work, ambient noise data taken in the 1- to 5-kHz band during the 2001 East China Sea Experiment are analyzed and compared to models. The noise notch model integrates three components: an internal wave model, a noise model, and an acoustic propagation model that uses transport theory. It is shown how the depth and width of the observed noise notch are consistent with model predictions when internal waves of moderate strength are included in the calculation. The observed asymmetry in the directivity pattern is consistent with predictions when the correct bottom reflectivity is used. Future ambient noise measurements and tests for the models are described. [Work supported by ONR.]
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.4785909
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2006
    detail.hit.zdb_id: 1461063-2
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  • 7
    Online Resource
    Online Resource
    Backscattering from sediments: Comparison of scattering strengths from a simple sand and from a sand/mud environment
    Acoustical Society of America (ASA) ; 2006
    In:  The Journal of the Acoustical Society of America Vol. 120, No. 5_Supplement ( 2006-11-01), p. 3144-3144
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 120, No. 5_Supplement ( 2006-11-01), p. 3144-3144
    Abstract: Two sediment acoustics experiments were carried out within 1 km of each other off the coast of Florida, the first in 1999 and the second in 2004. Though close in space the sediment was very different due to the effects of Hurricane Ivan in 2004. Hurricane Ivan resulted in the deposition of mud patches on top of the medium sand. Subsequent weather events deposited sand on top of these patches. The backscattering at each site will be presented for frequencies from 20 to 1000 kHz and grazing angles from 20 to 45 deg. At angles below the critical angle (30 deg) and frequencies below 150 kHz the backscattering measured in the two experiments is consistent given the difference in the sediment roughness spectra. Above the critical angle, however, the backscattering measured in the 2004 experiment is several dB higher than in the 1999 experiment and increases immediately above the critical angle instead of decreasing. This difference is attributed to an increase in sediment volume scattering in 2004. From 150 to 1000 kHz the data from both years indicate a change in scattering mechanism below the critical angle to a mechanism differing from sediment interface roughness scattering. [Work supported by ONR.]
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.4787785
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2006
    detail.hit.zdb_id: 1461063-2
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  • 8
    Online Resource
    Online Resource
    Inversion of bottom sound speed and dispersion using boat noise
    Acoustical Society of America (ASA) ; 2005
    In:  The Journal of the Acoustical Society of America Vol. 118, No. 3_Supplement ( 2005-09-01), p. 1856-1856
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 118, No. 3_Supplement ( 2005-09-01), p. 1856-1856
    Abstract: An experiment was conducted near shore in water depth between 2 and 10 m. The sediment consists of uniform sand. A lone hydrophone was moored 2 m above the bottom at 6 m depth. A small boat traveling at constant speed was used as the sound source, and ran both parallel and perpendicular to shore. Thus, both the range-independent as well as range-dependent cases can be investigated. Environmental parameters in both the water column and the sediment are independently measured. We first will study the propagation of broadband noise from bubbles emitted from a small boat in this special environment, especially the interferences of modes in the wedge-shape waveguide. Both analytical and numerical approaches are used to simulate the field experiment and to obtain general conclusions concerning mode interference in range-dependent environments. Then we will use the data to invert for sediment sound speed as a function of frequency. This is achieved by investigating mode cut-off for different frequencies at different water depths. In the present work, sediment sound speed is estimated over the frequency range of 500 C–4500 Hz. [Work supported by the U.S. ONR.]
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.4778826
    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
    Online Resource
    Online Resource
    Effect of nonlinear internal waves on midfrequency acoustic propagation on the continental shelf
    Acoustical Society of America (ASA) ; 2006
    In:  The Journal of the Acoustical Society of America Vol. 119, No. 5_Supplement ( 2006-05-01), p. 3345-3345
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 119, No. 5_Supplement ( 2006-05-01), p. 3345-3345
    Abstract: Packets of nonlinear internal waves and strong sound-speed variability due to neutrally buoyant intrusions were measured in detail using a towed conductivity, salinity, pressure (CTD) chain. The measurements were taken in October 2005, on the continental shelf south of Rhode Island. Acoustic propagation through the measured sound-speed field is modeled. The waves in October are qualitatively different from the more familiar summertime nonlinear waves. Further measurements using the CTD chain will be made in the summer of 2006, in association with acoustic propagation measurements.
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.4808854
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2006
    detail.hit.zdb_id: 1461063-2
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  • 10
    Online Resource
    Online Resource
    Measurements of acoustic propagation with accompanying high-resolution sound speed structure containing internal waves.
    Acoustical Society of America (ASA) ; 2009
    In:  The Journal of the Acoustical Society of America Vol. 125, No. 4_Supplement ( 2009-04-01), p. 2512-2512
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 125, No. 4_Supplement ( 2009-04-01), p. 2512-2512
    Abstract: During the Shallow Water 2006 experiment, simultaneous measurements were made of the sound speed structure associated with nonlinear internal waves and acoustic propagation at frequencies of 2–10 kHz over a 1 km path. The internal waves were measured by a towed CTD chain in order to get high resolution. These measurements were coordinated so that the nonlinear waves can be interpolated onto the acoustic path, allowing predictions of their effects on the acoustics. An internal wave train was measured that passed the acoustic path on August 13. When the wave train was in between the sound source and receiver, distinctive arrival time oscillations on three acoustic paths were measured, which are all rays having an upper turning point. Using the CTD chain data, a deterministic explanation is given to the arrival time oscillations.
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.4783434
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2009
    detail.hit.zdb_id: 1461063-2
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