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Proceedings of Meetings on Acoustics

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POMA - 159th Meeting  Acoustical Society of America/NOISE-CON 2010
Conference Location: Baltimore, Maryland Conference Date: 19 - 23 April 2010
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Concerning the null contours of vector sensors

Dean J. Schmidlin

POMA Volume 9, pp. 070001 (May 2010); (9 pages)

Online Publication Date: May 06, 2010

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A common use of a vector sensor is to maximize the sensing of a plane wave coming from one specified direction while creating a null in regard to a plane wave coming from another direction. It is shown that when this is accomplished, there is a null not only in the desired direction but a whole contour of nulls. One byproduct of the notion of null contours is a method for selecting the coefficients of the vector sensor for the case of two interfering sources. Finally, it is shown that once the null contour is understood for the vector sensor it is a simple matter to extend the concept to directional acoustic sensors of higher order.
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43.60.Fg Acoustic array systems and processing, beam-forming
43.60.Gk Space-time signal processing, other than matched field processing
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An overview of underwater acoustic communication via particle velocity channels: Channel modeling and transceiver design

Ali Abdi, Huaihai Guo, Aijun Song, and Mohsen Badiey

POMA Volume 9, pp. 070002 (May 2010); (5 pages)

Online Publication Date: May 26, 2010

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Over the past few decades, the scalar component of the acoustic field, i.e., the pressure channel, has been extensively used for underwater acoustic communication. In recent years, vector components of the acoustic field, such as the three components of acoustic particle velocity, are suggested for underwater communication. Consequently, one can use vector sensors for underwater communication. The small size of vector sensor arrays is an advantage, compared to pressure sensor arrays commonly used in underwater acoustic communication. This is because velocity channels can be measured at a single point in space. So, each vector sensor serves as a multichannel device. This is particularly useful for compact underwater platforms, such as autonomous underwater vehicles (AUVs). Funded by the National Science Foundation, our research efforts focus on the research problems in two closely-related categories: channel modeling and transceiver design. Channel modeling research aims at characterization of those aspects of acoustic particle velocity channels such as delay and Doppler spread, transmission loss, etc., which determine the communication system performance. Transceiver design addresses optimal use of vector sensors and particle velocity for data modulation and demodulation, equalization, synchronization, coding, etc. (work supported by NSF).
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43.60.Dh Signal processing for communications: telephony and telemetry, sound pickup and reproduction, multimedia
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The statistical interpretation of a simple ambient noise model

Richard B. Evans

POMA Volume 9, pp. 070003 (May 2010); (8 pages)

Online Publication Date: May 26, 2010

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Theoretical analyses of the statistics of ambient noise levels can yield distributions that are either narrow and symmetric, or broad and non-symmetric [I. Dyer, J. Acoust. Soc. Am. 53, 564-570 (1973)]. Their standard deviations vary between nearly zero and 5.6 dB. The assumptions regarding the nature of the noise sources and the processing of the received noise fields are the key in determining what distribution to expect. A simple computational model that exhibits both extremes of the potential statistical distributions can help in understanding what assumptions determine the statistics. The paper presents a simple ambient noise model that allows such a statistical interpretation.
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43.30.Nb Noise in water; generation mechanisms and characteristics of the field
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Amplitude, phase, location and orientation calibration of an acoustic vector sensor array, part II: Experiments

Tom Basten, Jelmer Wind, Buye Xu, Hans-Elias De Bree, and Erik Druyvesteyn

POMA Volume 9, pp. 070004 (June 2010); (8 pages)

Online Publication Date: June 15, 2010

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An acoustic vector sensor array consists of multiple sound pressure microphones and particle velocity sensors. A pressure microphone usually has an omni-directional response, yet a particle velocity sensor is directional and usually has a response pattern as a figure of eight. Currently, acoustic vector sensor arrays are under investigation for far field source localization and visualization. One of the major practical issues in these applications, however, is to determine the accurate position, orientation and complex (phase and amplitude) sensitivity of each sensor within the array. In this study, a new calibration method is verified with experiments. The method determines all the crucial parameters based on a limited number of measurements with a reference sensor and multiple sound sources located at known locations. The experiments are performed in an anechoic room. The results are promising.
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43.58.Dj Sound velocity
43.58.Vb Calibration of acoustical devices and systems
43.60.Fg Acoustic array systems and processing, beam-forming
43.60.Pt Signal processing techniques for acoustic inverse problems
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Oceanic Noise: mechanisms, radiation characteristics, and array results.

William M. Carey

POMA Volume 9, pp. 070005 (June 2010); (20 pages)

Online Publication Date: June 16, 2010

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Noise produced by the oscillation of microbubble distributions and impacts (raindrops and splash) in the air-sea boundary zone results in doublet radiation patterns and noise fields with definitive temporal and spatial characteristics. Turbulence generated noise is quadrupole, and nonlinear wave-wave interactions are infrasonic. Plausible mechanisms provide a framework for a review of directional noise measurements in range dependent oceanic and bathymetric environments. Slope interaction converts higher angles to lower angles and results in a frequency dependent vertical directionality. Low-frequency (0.02 - 1 kHz) measurements reveal a temporally dynamic noise field with persistent directional characteristics. Higher frequency (1 kHz or greater) measurements exhibit a local stationary characteristic influenced by the boundary zone mixed layer. Beam noise cumulative distribution functions are shown to depend on the distribution of ships, basin size, and boundaries. Directional noise computations are presented along with the issues of shipping distributions, the air-sea boundary zone, and assimilated satellite observations of wind speed, white caps, and sea surface temperature. The computation of basin scale directionality basically estimates the persistent characteristic. Improved calculation with the directional radiation from modern ships and the inclusion of the dynamic ship distribution ships are presented to estimate the beam noise statistics.
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43.30.Nb Noise in water; generation mechanisms and characteristics of the field
43.30.Qd Global scale acoustics; ocean basin thermometry, transbasin acoustics
43.30.Zk Experimental modeling
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Amplitude, phase, location and orientation calibration of an acoustic vector sensor array, part I: Theory

Buye Xu, Jelmer Wind, Hans-Elias De Bree, Tom Basten, and Erik Druyvesteyn

POMA Volume 9, pp. 070006 (August 2010); (11 pages)

Online Publication Date: August 06, 2010

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Show Abstract
An acoustic vector sensor array consists of multiple sound pressure microphones and particle velocity sensors. A pressure microphone usually has an omni-directional response, yet a particle velocity sensor is directional. Currently, acoustic vector sensor arrays are under investigation for far field source localization and visualization. One of the major practical issues in these applications, however, is to determine the accurate position, orientation and complex (phase and amplitude) sensitivity of each sensor within the array. In this study, a calibration method is developed to determine each of those crucial parameters based on a limited number of measurements with a reference sensor and multiple sound sources located at known locations. The calibration method is also designed to be robust to mistakenly switched cable connections. Ideally, the calibration process should take place in an anechoic environment, but efforts have been made to compensate for the effects of moderate background noise and reflections.
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43.58.Vb Calibration of acoustical devices and systems
43.60.Fg Acoustic array systems and processing, beam-forming
43.60.Jn Source localization and parameter estimation
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Seismo-acoustic propagation near low-shear speed poroelastic ocean sediments using a hybrid parabolic equation solution

Jon M. Collis

POMA Volume 9, pp. 070007 (December 2010); (11 pages)

Online Publication Date: December 15, 2010

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Accurate and efficient parabolic equation solutions exist for complex propagation environments featuring elastic and porous elastic sediment types. An area of concern has been low-shear wave speed sediments that become singular as their shear modulus tends toward zero. A historic approach for treating sediments of this type has been to assume it is a fluid and that effects due to elasticity are negligible. This approach is limited in accuracy unless shear is accounted for. In this presentation, the ocean bottom sediment interface layer is treated as a porous elastic layer in which poro-elastic momentum equations are solved and combined with an existing elastic parabolic equation implementation. Appropriate boundary conditions are enforced at the fluid-poro-elastic and poro-elastic-elastic interfaces. The new solution is tested on problems with a low-shear ocean bottom interface layer.
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43.30.Dr Hybrid and asymptotic propagation theories, related experiments
43.30.Ma Acoustics of sediments; ice covers, viscoelastic media; seismic underwater acoustics
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