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  • Acoustical Society of America (ASA)  (12)
  • 1
    Online Resource
    Online Resource
    An investigation of the capabilities of a short hydrophone array towed by an ocean glider
    Acoustical Society of America (ASA) ; 2007
    In:  The Journal of the Acoustical Society of America Vol. 122, No. 5_Supplement ( 2007-11-01), p. 3009-3009
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 122, No. 5_Supplement ( 2007-11-01), p. 3009-3009
    Abstract: During the Shallow Water Experiment (SW06) a Webb Slocum glider, deployed by Rutgers University, demonstrated that gliders are promising vehicles for towing short acoustic arrays. The gliders saw-tooth trajectory allows for sampling the water column at varying depths and ranges. Further, the glider provides a low-speed platform, allowing for a flow-noise free towed array, which is ideal for the processing of low level signals. One attractive application for glider-towed arrays is target tracking. By using the passive synthetic aperture effect, coupled with a near-field model for the signal, the coordinates of an acoustic source can be estimated using a Kalman filter, but without the necessity of the maneuver normally required by bearings-only tracking. This is possible since the large aperture traced out by the glider permits wavefront curvature to be exploited for range estimation. Using synthetic narrowband data, it is shown that the range and bearing of a low-level acoustic source can be estimated without changing the gliders course. The algorithm is based on an Unscented Kalman Filter. Also, an approach for the broadband problem is outlined. [Work sponsored by the Office of Naval Research.]
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.2942749
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2007
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  • 2
    Online Resource
    Online Resource
    Acoustic measurements in shallow water using an ocean glider
    Acoustical Society of America (ASA) ; 2007
    In:  The Journal of the Acoustical Society of America Vol. 121, No. 5_Supplement ( 2007-05-01), p. 3108-3108
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 121, No. 5_Supplement ( 2007-05-01), p. 3108-3108
    Abstract: Acoustic data was collected on a single hydrophone attached to a Webb Slocum glider deployed by Rutgers University during the Shallow Water Experiment (SW06) on the continental shelf off New Jersey. The geometry of the experiment provided for adequate recording of the 224 and 400 Hz WHOI tomography sources. The glider periodically surfaced for GPS fixes and data transfer via satellite phone. A synthetic aperture is created through coherent processing of the acoustic data as the glider traveled through the water. A number of issues including varying depth and nonsteady motion must be accounted for due to the trajectory of the glider. However, the glider provides a low-noise and low-speed platform, potentially enabling detection of low level signals. Initial results show that the phase of the tomography signals is linear as the glider traverses the sound field. An acoustic normal mode representation of the field provides the basis for processing of the data similar to Hankel transform approach of Frisk and Lynch [J. Acoust. Soc Am. 76, 205–216 (1984)] and Holmes, Carey, and Lynch [J. Acoust. Soc. Am. 119, 3346 (2006)]. Effects of spatial variations in sound speed are examined. [Work sponsored by the Office of Naval Research.]
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.4782037
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2007
    detail.hit.zdb_id: 1461063-2
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  • 3
    Online Resource
    Online Resource
    An acoustic array to be towed behind an autonomous underwater vehicle
    Acoustical Society of America (ASA) ; 2004
    In:  The Journal of the Acoustical Society of America Vol. 115, No. 5_Supplement ( 2004-05-01), p. 2621-2621
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 115, No. 5_Supplement ( 2004-05-01), p. 2621-2621
    Abstract: The use of a towed array from a small autonomous underwater vehicle, AUV, such as the WHOI-Remus vehicle is discussed as a valuable ocean acoustics measurement tool for of 3-D characterization of shallow water regions. The feasibility of towing a 10-m-long, small-diameter fluid-filled hydrophone array behind Remus was investigated with a laboratory-prototype array and preliminary tests from the WHOI pier. Preliminary results on array self-noise are presented for low tow speeds. The flow noise, vehicle noise, and other unwanted signal degrading noise sources are examined, discussed, and shown by theoretical arguments to be reduced to low levels by proper array design. This paper examines current technology for such an array with digital sampling and recording equipment incorporated in the Remus vehicle. Consideration is also given to the deployment problem of array on an autonomous vehicle. [Work supported by the College of Engineering, Boston University.]
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.4784817
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2004
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  • 4
    Online Resource
    Online Resource
    The applicability of a small autonomous vehicle towed array system to ocean acoustic measurements and signal processing
    Acoustical Society of America (ASA) ; 2008
    In:  The Journal of the Acoustical Society of America Vol. 123, No. 5_Supplement ( 2008-05-01), p. 3905-3905
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 123, No. 5_Supplement ( 2008-05-01), p. 3905-3905
    Abstract: An array was developed to demonstrate, and quantify the performance characteristics of an autonomous-vehicle towed-array system. This technology provides for a cost effective tool for the measurement of coherent signal propagation, depth dependent and directional noise fields and to establish quantitative limits on array performance. The tangential drag on a 40-m length array composed of a reinforced tube with an outer diameter of 2.8 cm is extrapolated to be between 20-28 N for diameter Reynold's number of approximately 4 104. The hydrophone- preamplifier groups have a sensitivity of –174±1.5 dB re 1μPa/V between 100 Hz to 10 kHz. with an adjustable spacing between 0.5 and 1.5 m. The system tow stability enabled the use of the synthetic Hankel transform to estimate the modal horizontal wave number spectrum and the identification of interface wave speeds at frequencies up to 1000 Hz. The formation of synthetic apertures combined with model based extended Kalman filter techniques was found to demonstrate both narrow band and broadband tracking. Finally the system is shown to provide a unique measurement capability for directional noise measurement in shallow water environments.
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.2935894
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2008
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  • 5
    Online Resource
    Online Resource
    Results from an autonomous underwater vehicle towed hydrophone array experiment in Nantucket Sound
    Acoustical Society of America (ASA) ; 2006
    In:  The Journal of the Acoustical Society of America Vol. 120, No. 2 ( 2006-08-01), p. EL15-EL21
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 120, No. 2 ( 2006-08-01), p. EL15-EL21
    Abstract: Shallow water experiments have been conducted in Nantucket Sound with an autonomous underwater vehicle towed hydrophone array system in an area proximate to that of a previous experiment [Frisk and Lynch, J. Acoust. Soc. Am. 86, 1928–1939 (1989)]. Transmission loss was measured, for frequencies between 220 and 1228Hz in an ocean waveguide, under conditions of an isovelocity water column with an approximate depth of 13m over a sandy-silty bottom. Results obtained at 415Hz show classic isovelocity waveguide phenomena that include interference effects, mode stripping due to modal attenuation, and transmission loss proportional 15 to 10log10(R).
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.2219106
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2006
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  • 6
    Online Resource
    Online Resource
    Low-frequency sound reflection and conversion to Darcy-type type diffusion waves at bottom interfaces with marine sediments
    Acoustical Society of America (ASA) ; 2006
    In:  The Journal of the Acoustical Society of America Vol. 119, No. 5_Supplement ( 2006-05-01), p. 3253-3253
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 119, No. 5_Supplement ( 2006-05-01), p. 3253-3253
    Abstract: The upper medium is sea water, and the bottom medium is a marine sediment whose physical description is consistent with the theory advanced by Frenkel in 1944 and with the model proposed by Biot in 1961 for a porous medium at low frequencies. Within the sediment, three generic types (modes) of wavelike disturbances are possible. These three modes are here termed the acoustic, shear, and Darcy modes. The first two are governed by propagating wave equations and the third by a diffusion equation. The first and third are dilatational. All three are nominally uncoupled, although coupling occurs at interfaces. When an obliquely incident acoustic wave impinges from the water on the interface, all three types of disturbances are in principle excited in the sediment, and the details of the excitation are governed by interface conditions, whose derivation is reported in the present paper. Each mode has its own characteristic parameters, and the sediment reflection coefficient, considered as a function of angle of incidence and of frequency, implicitly depends on all of these parameters. The question is addressed as to how, given such reflection coefficient data, one might extract the parameters for the Darcy mode for representative realistic experimental circumstances.
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.4786073
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2006
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  • 7
    Online Resource
    Online Resource
    Passive synthetic aperture as an experimental tool
    Acoustical Society of America (ASA) ; 2008
    In:  The Journal of the Acoustical Society of America Vol. 123, No. 5_Supplement ( 2008-05-01), p. 3906-3906
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 123, No. 5_Supplement ( 2008-05-01), p. 3906-3906
    Abstract: The use of autonomous undersea vehicle towed arrays offer an inexpensive way to carry out oceanographic measurements. Due to the small size and limited power of such vehicles, the physical aperture of the array is necessarily limited and the tow speed is low. However, there is an advantage in that short arrays at low speeds can have no flow noise. In addition the use of passive synthetic aperture (PSA) to provide spatial resolution and gain can play a major role. Here, we describe the use of two forms of passive synthetic array processing used in a shallow-water experiment. A six-element towed array, with 0.75 m spacing, was used to estimate the horizontal wave numbers of a propagation channel. A narrow-band form of PSA will be described which was used to generate coherent spatial gain by generating an aperture hundreds of wavelengths and provided accurate estimates of the horizontal modal wave numbers at frequencies les than 600 Hz. A broadband form of PSA was used to provide bearing estimation of a ferry passing through the area. The ferry's broadband propulsion noise, which was in the 900 Hz region, was used as the source. An overall increase in gain is demonstrated.
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.2935896
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2008
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  • 8
    Online Resource
    Online Resource
    An autonomous underwater vehicle technique for in situ waveguide characterization
    Acoustical Society of America (ASA) ; 2005
    In:  The Journal of the Acoustical Society of America Vol. 118, No. 3_Supplement ( 2005-09-01), p. 2042-2042
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 118, No. 3_Supplement ( 2005-09-01), p. 2042-2042
    Abstract: Results from an autonomous underwater vehicle (AUV) towed hydrophone array experiment are presented as a demonstration of a new in situ measurement technique. In this technique, a source is deployed from a small vessel and the AUV navigates along a pre-programmed path towing the hydrophone array. The added degrees of freedom associated with an array towed by an AUV provides for rapid characterization of the shallow-water waveguide. Using a synthetic aperture, the horizontal wave number spectrum is measured and the modal eigenvalues are experimentally measured by picking off the peak locations in the wave number spectrum. The modal amplitudes are found by using the finite aperture array approximation to the Hankel transform in which the amplitude of the spectral peaks are finite and proportional to the mode excitation amplitude as shown by Frisk et al. [J. Acoust. Soc. Am. 86, 1928–1939 (1989)]. By measuring the modal attenuation, one can determine the effects of bottom interaction. Another measurement technique using the same towed hydrophone system is described in which signal path bottom reflection results are obtained using a parametric source.
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.4785852
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2005
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  • 9
    Online Resource
    Online Resource
    Shallow-water waveguide characterization using an autonomous underwater vehicle-towed hydrophone array
    Acoustical Society of America (ASA) ; 2006
    In:  The Journal of the Acoustical Society of America Vol. 119, No. 5_Supplement ( 2006-05-01), p. 3346-3346
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 119, No. 5_Supplement ( 2006-05-01), p. 3346-3346
    Abstract: Sound transmission results are reported for frequencies of 220, 415, 635, 823, 1031, and 1228 Hz in an iso-velocity waveguide 13 m deep with known bottom properties. The experiments were conducted in Nantucket Sound in proximity to the Lynch-Frisk (1982) experiment in an area surveyed prior to the experiments. A fixed source and an autonomous underwater vehicle six-element towed hydrophone array were used. The experimental track consisted of two 2–4-km straight legs with measurement of the bathymetry and currents performed by the vehicle. Transmission results show stable modal-multipath interference effects with predictable phase rate variations. Coherent processing using vehicle estimates of ground speed and position yields results close to theoretical expectations and indicates a constant depth stable tow was realized. Horizontal wave-number spectra using coherent synthetic aperture Hankel transforms are presented and shown to be calculable and comparable to the previous work. The demonstration of this measurement capability provides for cost effective measurements of the sound field at sea.
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.4786457
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2006
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  • 10
    Online Resource
    Online Resource
    An overview of unmanned underwater vehicle noise in the low to mid frequency bands.
    Acoustical Society of America (ASA) ; 2010
    In:  The Journal of the Acoustical Society of America Vol. 127, No. 3_Supplement ( 2010-03-01), p. 1812-1812
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 127, No. 3_Supplement ( 2010-03-01), p. 1812-1812
    Abstract: Unmanned (autonomous) underwater vehicles offer a unique, cost-effective platform for performing ocean acoustic measurements and surveys because multiple systems can be deployed from a single research vessel. Various data surveys can be performed including on-the-bottom geo-acoustic surveys over large areas, sub-sea-surface turbulence and microbubble structure surveys, and bi-static fish population surveys. To take advantage of the autonomous survey capabilities of underwater vehicles, sufficient signal-to-noise ratio and acoustic aperture (resolution) are required for acoustic measurements. The most commonly used vehicle sonar systems provide images utilizing high frequency hull mounted arrays and sources. In the lower-frequency band (100 Hz–10 kHz), however, vehicle noise levels and aperture remain the two most significant challenges, especially for passive systems. Previous experimental and analytical work has shown that a towed array with synthetic aperture processing can be used to obtain the necessary aperture. The major challenge of vehicle radiated noise is the focus of this paper, and both measured and archival results on vehicle noise are presented including an overview of levels, spectral character, and noise mechanisms for several vehicles. In particular, fundamental vehicle propulsion system noise is discussed along with implications on measurement performance and possible mitigation strategies.
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.3384121
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2010
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