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Apr 2012

Volume 131, Issue 4, pp. EL283-3536

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Time reversal acoustic communication for multiband transmission

Aijun Song and Mohsen Badiey

J. Acoust. Soc. Am. Volume 131, Issue 4, pp. EL283-EL288 (2012); (6 pages) | Cited 1 time

Online Publication Date: 14 Mar 2012

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In this letter, multiband acoustic communication is proposed to access a relatively wide frequency band. The entire frequency band is divided into multiple separated sub-bands, each of which is several kilohertz in width. Time reversal decision feedback equalizers are used to compensate for inter-symbol interference at each sub-band. The communication scheme was demonstrated in a shallow water acoustic experiment conducted in Kauai, Hawaii during the summer of 2011. Using quadrature phase-shift keying signaling at four sub-bands over the frequency band of 10–32 kHz, a data rate of 32 kbits/s was achieved over a 3 km communication range.
Show PACS
43.60.Dh Signal processing for communications: telephony and telemetry, sound pickup and reproduction, multimedia
43.60.Mn Adaptive processing
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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Characterization of circumferential guided waves in a cylindrical cortical bone-mimicking phantom

Pierre Nauleau, Etienne Cochard, Jean-Gabriel Minonzio, Quentin Grimal, Pascal Laugier, and Claire Prada

J. Acoust. Soc. Am. Volume 131, Issue 4, pp. EL289-EL294 (2012); (6 pages) | Cited 1 time

Online Publication Date: 14 Mar 2012

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The femoral neck cortical shell was recently demonstrated to act like a waveguide for circumferential waves. Femoral neck assessment with ultrasound could be enhanced by guided waves measurement. In this study, the decomposition of the time reversal operator (DORT) method is used to measure the phase velocities of circumferential guided modes in a circular tube with dimensions characteristic of femoral neck. The tube is made of a bone-mimicking material. Five guided modes are obtained and compared to theoretical predictions. The work substantiates the feasibility of measuring guided waves in a relatively thick tube of attenuating material with the DORT method.
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43.80.Vj Acoustical medical instrumentation and measurement techniques
43.80.Ev Acoustical measurement methods in biological systems and media
43.20.Mv Waveguides, wave propagation in tubes and ducts
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High-frequency modulated signals of killer whales (Orcinus orca) in the North Pacific

Anne E. Simonis, Simone Baumann-Pickering, Erin Oleson, Mariana L. Melcón, Martin Gassmann, Sean M. Wiggins, and John A. Hildebrand

J. Acoust. Soc. Am. Volume 131, Issue 4, pp. EL295-EL301 (2012); (7 pages) | Cited 2 times

Online Publication Date: 14 Mar 2012

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Killer whales in the North Pacific, similar to Atlantic populations, produce high-frequency modulated signals, based on acoustic recordings from ship-based hydrophone arrays and autonomous recorders at multiple locations. The median peak frequency of these signals ranged from 19.6–36.1 kHz and median duration ranged from 50–163 ms. Source levels were 185–193 dB peak-to-peak re: 1 μPa at 1 m. These uniform, repetitive, down-swept signals are similar to bat echolocation signals and possibly could have echolocation functionality. A large geographic range of occurrence suggests that different killer whale ecotypes may utilize these signals.
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43.80.Ka Sound production by animals: mechanisms, characteristics, populations, biosonar
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Modeling interface roughness scattering in a layered seabed for normal-incident chirp sonar signals

Dajun Tang and Brian T. Hefner

J. Acoust. Soc. Am. Volume 131, Issue 4, pp. EL302-EL308 (2012); (7 pages)

Online Publication Date: 14 Mar 2012

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Downward looking sonar, such as the chirp sonar, is widely used as a sediment survey tool in shallow water environments. Inversion of geo-acoustic parameters from such sonar data precedes the availability of forward models. An exact numerical model is developed to initiate the simulation of the acoustic field produced by such a sonar in the presence of multiple rough interfaces. The sediment layers are assumed to be fluid layers with non-intercepting rough interfaces.
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43.30.Hw Rough interface scattering
43.30.Gv Backscattering, echoes, and reverberation in water due to combinations of boundaries
43.30.Ma Acoustics of sediments; ice covers, viscoelastic media; seismic underwater acoustics
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Extracting the Green’s function from measurements of the energy flux

Roel Snieder, Huub Douma, and Ivan Vasconcelos

J. Acoust. Soc. Am. Volume 131, Issue 4, pp. EL309-EL315 (2012); (7 pages)

Online Publication Date: 14 Mar 2012

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Existing methods for Green’s function extraction give the Green’s function from the correlation of field fluctuations recorded at those points. In this work it is shown that the Green’s function for acoustic waves can be retrieved from measurements of the integrated energy flux through a closed surface taken from three experiments where two time-harmonic sources first operate separately, and then simultaneously. This makes it possible to infer the Green’s function in acoustics from measurements of the energy flux through an arbitrary closed surface surrounding both sources. The theory is also applicable to quantum mechanics where the Green’s function can be retrieved from measurement of the flux of scattered particles through a closed surface.
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43.20.Bi Mathematical theory of wave propagation
03.65.-w Quantum mechanics
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Acoustic performance of a duct loaded with identical resonators

X. Wang and C. M. Mak

J. Acoust. Soc. Am. Volume 131, Issue 4, pp. EL316-EL322 (2012); (7 pages)

Online Publication Date: 14 Mar 2012

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This paper presents a theoretical study of a duct loaded with identical side-branch resonators. The Bloch wave theory and the transfer matrix method are used to investigate wave propagation in the duct. It is found that this duct-resonator system has a unique attenuation characteristic brought about by structural periodicity. Three types of stop-bands are discussed and their bandwidths are predicted. All of the results predicted by the theory fit well with a computer simulation using a three-dimensional finite element method. Compared to a single resonator, this structure may have a potential application in broadband noise control.
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43.20.Mv Waveguides, wave propagation in tubes and ducts
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Individual and level-dependent differences in masking for adults with normal and impaired hearing

Amy R. Horwitz, Jayne B. Ahlstrom, and Judy R. Dubno

J. Acoust. Soc. Am. Volume 131, Issue 4, pp. EL323-EL328 (2012); (6 pages) | Cited 1 time

Online Publication Date: 14 Mar 2012

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Simultaneous, on-frequency masking is commonly assumed to be linear with increasing noise intensity. However, some evidence suggests that, expressed in terms of signal-to-noise ratio changes with background level changes, masking slopes can vary from 0 dB/dB. These results and evidence from a large sample of subjects with normal and impaired hearing demonstrate level-dependent changes in masking, large individual differences in masking among subjects with similar thresholds in quiet, and significant correlations of masking slope with other estimates of auditory function measured in the same backgrounds.
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43.66.Dc Masking
43.66.Sr Deafness, audiometry, aging effects
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Axial radiation force exerted by general non-diffracting beams

Likun Zhang and Philip L. Marston

J. Acoust. Soc. Am. Volume 131, Issue 4, pp. EL329-EL335 (2012); (7 pages) | Cited 1 time

Online Publication Date: 21 Mar 2012

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The axial radiation force exerted by a general non-diffracting beam on an object of arbitrary shape in lossless medium is analyzed. The object may be on or off the beam’s axis. The analysis is based on the plane-wave representation of the beam using an azimuthal function and conical angle. The analytical expression relates the force to axial projections of the extracted and scattered momentum. Using an extended optical theorem, the extinction is related to the scattering at the forward direction of the beam’s plane wave components. The axial force is expressed using the scattering amplitude and known angular functions.
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43.25.Qp Radiation pressure
43.30.Hw Rough interface scattering
43.20.Fn Scattering of acoustic waves
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Effects of repeated production on vowel distinctiveness within nonwords

Jayanthi Sasisekaran and Benjamin Munson

J. Acoust. Soc. Am. Volume 131, Issue 4, pp. EL336-EL341 (2012); (6 pages)

Online Publication Date: 21 Mar 2012

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In the present study acoustic distinctiveness of vowels within nonwords with repeated production was investigated. Participants were 9 males and 15 females divided into two groups. Participants repeated 6 nonwords varying in phonemic composition. The mean Euclidean distance (MED) of the vowels from each production of a nonword from the center of the F1/F2 space was calculated. The changes in MED with repeated production were analyzed using linear mixed effects regression. Results revealed an increase in MED, indicating greater vowel dispersion, for the three-syllable nonwords and a significant decrease, i.e., greater reduction, in vowel dispersion for the six-syllable nonwords. Findings support the dynamic influence of sublexical processes on phonetic realization in speech production.
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43.70.Fq Acoustical correlates of phonetic segments and suprasegmental properties: stress, timing, and intonation
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Bidirectional equalization for underwater acoustic communication

H. C. Song

J. Acoust. Soc. Am. Volume 131, Issue 4, pp. EL342-EL347 (2012); (6 pages)

Online Publication Date: 21 Mar 2012

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The bidirectional decision feedback equalizer (BiDFE) that combines the outputs of a conventional decision feedback equalizer (DFE) and backward DFE can improve the performance of the conventional DFE by up to 1–2 dB based on simulations. In this letter, the BiDFE concept is extended to multichannel time reversal communications involving a DFE as a post-processor. Experimental data collected in shallow water (10–20 kHz) show that the performance can be enhanced by 0.4–1.8 dB in terms of output signal-to-noise ratio. In particular, a larger improvement (e.g., 1.8 dB) is achieved for time-varying channels where the channel diversity in opposite directions is more profound.
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43.60.Dh Signal processing for communications: telephony and telemetry, sound pickup and reproduction, multimedia
43.60.Gk Space-time signal processing, other than matched field processing
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Presence detection under optimum fusion in an ultrasonic sensor system

Sriram Srinivasan and Ashish Pandharipande

J. Acoust. Soc. Am. Volume 131, Issue 4, pp. EL348-EL353 (2012); (6 pages)

Online Publication Date: 21 Mar 2012

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Reliable presence detection is a requirement in energy-efficient occupancy-adaptive indoor lighting systems. A system of multiple ultrasonic sensors is considered for presence detection, and the performance gain from optimum fusion is studied. Two cases are considered wherein an individual sensor determines presence based on (i) local detection by processing echoes at its receiver, and (ii) the optimum Chair–Varshney fusion rule using multiple sensor detection results. The performance gains of using optimum fusion over local detection are characterized under different sensor system configurations and it is shown that improved detection sensitivity is obtained over a larger detection coverage region.
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43.60.Bf Acoustic signal detection and classification, applications to control systems
43.60.Cg Statistical properties of signals and noise
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Frequency discrimination under conditions of comodulation masking release (L)

Emily Buss, John H. Grose, and Joseph W. Hall, III

J. Acoust. Soc. Am. Volume 131, Issue 4, pp. 2557-2560 (2012); (4 pages)

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Masked detection thresholds can often be improved by introducing coherent masker amplitude modulation across frequency, a phenomenon referred to as comodulation masking release (CMR). While CMR can be large for detection, it is smaller for supra-threshold tasks, such as intensity discrimination. In this experiment, frequency discrimination for a 1000-Hz tone near threshold was found to be poorer in an amplitude-modulated than a steady bandpass noise. These results parallel previous findings for intensity discrimination. Although this study examined the relatively simple task of frequency discrimination, the results may have implications for more complex tasks, such as speech recognition in fluctuating noise.
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43.66.Dc Masking

Binaural temporal fine structure sensitivity, cognitive function, and spatial speech recognition of hearing-impaired listeners (L)

Tobias Neher, Thomas Lunner, Kathryn Hopkins, and Brian C. J. Moore

J. Acoust. Soc. Am. Volume 131, Issue 4, pp. 2561-2564 (2012); (4 pages) | Cited 2 times

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The relationships between spatial speech recognition (SSR; the ability to understand speech in complex spatial environments), binaural temporal fine structure (TFS) sensitivity, and three cognitive tasks were assessed for 17 hearing-impaired listeners. Correlations were observed between SSR, TFS sensitivity, and two of the three cognitive tasks, which became non-significant when age effects were controlled for, suggesting that reduced TFS sensitivity and certain cognitive deficits may share a common age-related cause. The third cognitive measure was also significantly correlated with SSR, but not with TFS sensitivity or age, suggesting an independent non-age-related cause.
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43.66.Sr Deafness, audiometry, aging effects
43.71.Ky Speech perception by the hearing impaired
43.66.Pn Binaural hearing
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A note on the modal kurtosis and the concentration factor in reverberation rooms

Finn Jacobsen

J. Acoust. Soc. Am. Volume 131, Issue 4, pp. 2565-2569 (2012); (5 pages)

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The effect known as “weak Anderson localization,” “coherent backscattering,” or “enhanced back-scattering” is a physical phenomenon that occurs in random systems, e.g., disordered media and linear wave systems, including reverberation rooms: The mean square response is increased at the drive point. In a reverberation room, this means that one can expect an increase of the reverberant sound field at the position of the source that generates the sound field. This affects the sound power output of the source and is therefore of practical concern. The relative increase of reverberant energy is described by the concentration factor, which is usually assumed to be 2. However, because of the stronger direct sound field at the source position, it is obviously very difficult to measure this quantity directly under steady-state conditions. A related parameter of crucial importance for the ensemble statistics of responses in rooms is the modal kurtosis, which is usually assumed to be 3. The modal kurtosis is also very difficult to measure directly. This paper presents the results of an indirect experimental estimation of the two parameters.
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43.20.Ks Standing waves, resonance, normal modes
43.55.Br Room acoustics: theory and experiment; reverberation, normal modes, diffusion, transient and steady-state response
43.55.Cs Stationary response of rooms to noise; spatial statistics of room response; random testing
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Scattering of time-harmonic elastic waves by an elastic inclusion with quadratic nonlinearity

Guangxin Tang, Laurence J. Jacobs, and Jianmin Qu

J. Acoust. Soc. Am. Volume 131, Issue 4, pp. 2570-2578 (2012); (9 pages) | Cited 1 time

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This paper considers the scattering of a plane, time-harmonic wave by an inclusion with heterogeneous nonlinear elastic properties embedded in an otherwise homogeneous linear elastic solid. When the inclusion and the surrounding matrix are both isotropic, the scattered second harmonic fields are obtained in terms of the Green’s function of the surrounding medium. It is found that the second harmonic fields depend on two independent acoustic nonlinearity parameters related to the third order elastic constants. Solutions are also obtained when these two acoustic nonlinearity parameters are given as spatially random functions. An inverse procedure is developed to obtain the statistics of these two random functions from the measured forward and backscattered second harmonic fields.
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43.25.Ba Parameters of nonlinearity of the medium
43.25.Dc Nonlinear acoustics of solids
43.20.El Reflection, refraction, diffraction of acoustic waves

Adaptive control of contrast agent microbubbles for shell parameter identification

Vera Dadok and Andrew J. Szeri

J. Acoust. Soc. Am. Volume 131, Issue 4, pp. 2579-2586 (2012); (8 pages)

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An adaptive controller design is proposed and simulated for parameter identification and oscillation control in microbubble systems. Lyapunov’s direct method and a Lyapunov-like analysis are used to show stability and convergence of trajectory tracking and parameter adaptation. The method allows for the determination of microbubble contrast agent shell thickness or material parameters in a nondestructive manner.
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43.25.Yw Nonlinear acoustics of bubbly liquids
43.25.Ts Nonlinear acoustical and dynamical systems
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Horizontal refraction of propagating sound due to seafloor scours over a range-dependent layered bottom on the New Jersey shelf

Megan S. Ballard, Ying-Tsong Lin, and James F. Lynch

J. Acoust. Soc. Am. Volume 131, Issue 4, pp. 2587-2598 (2012); (12 pages) | Cited 1 time

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Three-dimensional propagation effects of low frequency sound from 100 to 400 Hz caused by seafloor topography and range-dependent bottom structure over a 20 km range along the New Jersey shelf are investigated using a hybrid modeling approach. Normal modes are used in the vertical dimension, and a parabolic-equation approximate model is applied to solve the horizontal refraction equation. Examination of modal amplitudes demonstrates the effect of environmental range dependence on modes trapped in the water column, modes interacting with the bottom, and modes trapped in the bottom. Using normal mode ray tracing, topographic features responsible for three-dimensional effects of horizontal refraction and focusing are identified. These effects are observed in the measurements from the Shallow Water 2006 experiment. Specifically, signals from a pair of fixed sources recorded on a horizontal line array sitting on the seafloor show an intensification caused by horizontal focusing due to the seabed topography of 4 dB along the array.
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43.30.Bp Normal mode propagation of sound in water
43.20.El Reflection, refraction, diffraction of acoustic waves
43.30.Re Signal coherence or fluctuation due to sound propagation/scattering in the ocean

Blind deconvolution for robust signal estimation and approximate source localization

Shima H. Abadi, Daniel Rouseff, and David R. Dowling

J. Acoust. Soc. Am. Volume 131, Issue 4, pp. 2599-2610 (2012); (12 pages) | Cited 2 times

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Synthetic time reversal (STR) is a technique for blind deconvolution in an unknown multipath environment that relies on generic features (rays or modes) of multipath sound propagation. This paper describes how ray-based STR signal estimates may be improved and how ray-based STR sound-channel impulse-response estimates may be exploited for approximate source localization in underwater environments. Findings are based on simulations and underwater experiments involving source-array ranges from 100 m to 1 km in 60 -m-deep water and chirp signals with a bandwidth of 1.5–4.0 kHz. Signal estimation performance is quantified by the correlation coefficient between the source-broadcast and the STR-estimated signals for a variable number N of array elements, 2 ≤ N ≤ 32, and a range of signal-to-noise ratio (SNR), −5 dB ≤ SNR ≤ 30 dB. At high SNR, STR-estimated signals are found to have cross-correlation coefficients of ∼90% with as few as four array elements, and similar performance may be achieved at a SNR of nearly 0 dB with 32 array elements. When the broadband STR-estimated impulse response is used for source localization via a simple ray-based backpropagation scheme, the results are less ambiguous than those obtained from conventional broadband matched field processing.
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43.30.Cq Ray propagation of sound in water
43.30.Wi Passive sonar systems and algorithms, matched field processing in underwater acoustics
43.60.Jn Source localization and parameter estimation

Low frequency seabed scattering at low grazing angles

Ji-Xun Zhou and Xue-Zhen Zhang

J. Acoust. Soc. Am. Volume 131, Issue 4, pp. 2611-2621 (2012); (11 pages) | Cited 2 times

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Low-frequency (LF) seabed scattering at low grazing angles (LGA) is almost impossible to directly measure in shallow water (SW), except through inversion from reverberation. The energy flux method for SW reverberation is briefly introduced in this paper. The closed-form expressions of reverberation in an isovelocity waveguide, derived from this method, indicate that in the three-halves law range interval multimode/ray sea bottom scattering with different incident and scattering angles in forming the reverberation may equivalently be represented by the bottom backscattering at a single range-dependent angle. This equivalent relationship is used to derive the bottom backscattering strength (BBS) as a function of angle and frequency. The LF&LGA BBS is derived in a frequency band of 200–2500 Hz and in a grazing angle range of 1.1°–14.0° from reverberation measurements at three sites with sandy bottoms. This is based on three previous works: (1) The closed-form expressions of SW reverberation [Zhou, (Chinese) Acta Acustica 5, 86–99 (1980)]; (2) the effective geo-acoustic model of sandy bottoms that follows the Biot model [Zhou et al., J. Acoust. Soc. Am. 125, 2847–2866 (2009)] and (3) A quality database of wideband reverberation level normalized to source level [Zhou and Zhang, IEEE J. Oceanic Eng. 30, 832–842 (2005)].
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43.30.Gv Backscattering, echoes, and reverberation in water due to combinations of boundaries
43.30.Pc Ocean parameter estimation by acoustical methods; remote sensing; imaging, inversion, acoustic tomography
43.30.Dr Hybrid and asymptotic propagation theories, related experiments
43.30.Ma Acoustics of sediments; ice covers, viscoelastic media; seismic underwater acoustics

Anechoic coatings obtained from two- and three-dimensional monopole resonance diffraction gratings

Sven M. Ivansson

J. Acoust. Soc. Am. Volume 131, Issue 4, pp. 2622-2637 (2012); (16 pages)

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Underwater sound reflections can be reduced in magnitude by a rubber coating including three-dimensional (3-D) cavities forming a doubly periodic diffraction grating. A monopole resonance for sphere-like cavities enhances absorption in the surrounding rubber solid. A corresponding resonance for an infinite cylinder is studied in the present paper. Appearing at a considerably lower frequency than for a sphere with the same radius, it suggests the possibility of much thinner anechoic coatings including cylindrical cavities, with axes in a lateral direction, forming a diffraction grating with a single period. This is effectively a 2-D case, because of invariance in the axial direction. Subsequent coating design computations, using the layer-multiple-scattering method and including cavities of different sizes, show improved reflection reduction with coatings only about one third as thick. Still accounting for multiple scattering among the cavities and capturing the essential physics, the monopole approximation is applied to advance the analytic study of the reflection reduction. An energy decomposition relation is derived and used to quantify the absorption of the incident sound energy by cavities of different sizes. Coatings based on filled inclusions and other resonance effects are briefly considered. Again, the 2-D alternative with cylinders of mixed sizes gives thinner coatings.
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43.30.Ky Structures and materials for absorbing sound in water; propagation in fluid-filled permeable material
43.30.Gv Backscattering, echoes, and reverberation in water due to combinations of boundaries
43.20.Ks Standing waves, resonance, normal modes
43.20.Fn Scattering of acoustic waves

A single-scattering correction for the seismo-acoustic parabolic equation

Michael D. Collins

J. Acoust. Soc. Am. Volume 131, Issue 4, pp. 2638-2642 (2012); (5 pages) | Cited 1 time

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An efficient single-scattering correction that does not require iterations is derived and tested for the seismo-acoustic parabolic equation. The approach is applicable to problems involving gradual range dependence in a waveguide with fluid and solid layers, including the key case of a sloping fluid–solid interface. The single-scattering correction is asymptotically equivalent to a special case of a single-scattering correction for problems that only have solid layers [Küsel et al., J. Acoust. Soc. Am. 121, 808–813 (2007)]. The single-scattering correction has a simple interpretation (conservation of interface conditions in an average sense) that facilitated its generalization to problems involving fluid layers. Promising results are obtained for problems in which the ocean bottom interface has a small slope.
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43.30.Ma Acoustics of sediments; ice covers, viscoelastic media; seismic underwater acoustics
43.30.Bp Normal mode propagation of sound in water

Cross-correlation in band-limited ocean ambient noise fields

Michael J. Buckingham

J. Acoust. Soc. Am. Volume 131, Issue 4, pp. 2643-2657 (2012); (15 pages) | Cited 1 time

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Observations of ambient noise in the ocean are generally band limited, because of the natural spectral shape of the noise or the restricted bandwidth of the detection system. Either way, the noise may be regarded as white noise to which a band-limiting filter has been applied. An analysis of the two-point cross-correlation function of such filtered noise is presented for two cases, isotropic and surface-generated noise. The most pronounced effects occur with high-pass and bandpass filters when the low-frequency cut-off falls well above the first few zeros in the coherence function. In this situation, the sensor separation is very many times the longest acoustic wavelength (associated with the lowest frequency) in the passband. The filtering then produces sharp pulses at correlation delays equal to the numerical value of the acoustic travel time between the sensors. Although these pulses are narrow, they have a finite width, within which a fine structure appears in the form of multiple rapid oscillations, due to the differentiating action of the filter. The number of such oscillations increases as the low-frequency roll-off of the filter becomes steeper. This fine structure is evident in several recently published experimental determinations of the cross-correlation function of band-limited ocean ambient noise.
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43.30.Nb Noise in water; generation mechanisms and characteristics of the field

Bayesian geoacoustic inversion using wind-driven ambient noise

Jorge E. Quijano, Stan E. Dosso, Jan Dettmer, Lisa M. Zurk, Martin Siderius, and Chris H. Harrison

J. Acoust. Soc. Am. Volume 131, Issue 4, pp. 2658-2667 (2012); (10 pages) | Cited 4 times

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This paper applies Bayesian inversion to bottom-loss data derived from wind-driven ambient noise measurements from a vertical line array to quantify the information content constraining seabed geoacoustic parameters. The inversion utilizes a previously proposed ray-based representation of the ambient noise field as a forward model for fast computations of bottom loss data for a layered seabed. This model considers the effect of the array’s finite aperture in the estimation of bottom loss and is extended to include the wind speed as the driving mechanism for the ambient noise field. The strength of this field relative to other unwanted noise mechanisms defines a signal-to-noise ratio, which is included in the inversion as a frequency-dependent parameter. The wind speed is found to have a strong impact on the resolution of seabed geoacoustic parameters as quantified by marginal probability distributions from Bayesian inversion of simulated data. The inversion method is also applied to experimental data collected at a moored vertical array during the MAPEX 2000 experiment, and the results are compared to those from previous active-source inversions and to core measurements at a nearby site.
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43.30.Pc Ocean parameter estimation by acoustical methods; remote sensing; imaging, inversion, acoustic tomography
43.30.Ma Acoustics of sediments; ice covers, viscoelastic media; seismic underwater acoustics
43.60.Pt Signal processing techniques for acoustic inverse problems

Sequential Bayesian geoacoustic inversion for mobile and compact source-receiver configuration

Olivier Carrière and Jean-Pierre Hermand

J. Acoust. Soc. Am. Volume 131, Issue 4, pp. 2668-2681 (2012); (14 pages) | Cited 2 times

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Geoacoustic characterization of wide areas through inversion requires easily deployable configurations including free-drifting platforms, underwater gliders and autonomous vehicles, typically performing repeated transmissions during their course. In this paper, the inverse problem is formulated as sequential Bayesian filtering to take advantage of repeated transmission measurements. Nonlinear Kalman filters implement a random-walk model for geometry and environment and an acoustic propagation code in the measurement model. Data from MREA/BP07 sea trials are tested consisting of multitone and frequency-modulated signals (bands: 0.25-0.8 and 0.8-1.6 kHz) received on a shallow vertical array of four hydrophones 5-m spaced drifting over 0.7-1.6 km range. Space- and time-coherent processing are applied to the respective signal types. Kalman filter outputs are compared to a sequence of global optimizations performed independently on each received signal. For both signal types, the sequential approach is more accurate but also more efficient. Due to frequency diversity, the processing of modulated signals produces a more stable tracking. Although an extended Kalman filter provides comparable estimates of the tracked parameters, the ensemble Kalman filter is necessary to properly assess uncertainty. In spite of mild range dependence and simplified bottom model, all tracked geoacoustic parameters are consistent with high-resolution seismic profiling, core logging P-wave velocity, and previous inversion results with fixed geometries.
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43.30.Pc Ocean parameter estimation by acoustical methods; remote sensing; imaging, inversion, acoustic tomography
43.60.Pt Signal processing techniques for acoustic inverse problems
43.30.Ma Acoustics of sediments; ice covers, viscoelastic media; seismic underwater acoustics

A generalized power-law detection algorithm for humpback whale vocalizations

Tyler A. Helble, Glenn R. Ierley, Gerald L. D’Spain, Marie A. Roch, and John A. Hildebrand

J. Acoust. Soc. Am. Volume 131, Issue 4, pp. 2682-2699 (2012); (18 pages) | Cited 1 time

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Conventional detection of humpback vocalizations is often based on frequency summation of band-limited spectrograms under the assumption that energy (square of the Fourier amplitude) is the appropriate metric. Power-law detectors allow for a higher power of the Fourier amplitude, appropriate when the signal occupies a limited but unknown subset of these frequencies. Shipping noise is non-stationary and colored and problematic for many marine mammal detection algorithms. Modifications to the standard power-law form are introduced to minimize the effects of this noise. These same modifications also allow for a fixed detection threshold, applicable to broadly varying ocean acoustic environments. The detection algorithm is general enough to detect all types of humpback vocalizations. Tests presented in this paper show this algorithm matches human detection performance with an acceptably small probability of false alarms (PFA < 6%) for even the noisiest environments. The detector outperforms energy detection techniques, providing a probability of detection PD = 95% for PFA < 5% for three acoustic deployments, compared to PFA > 40% for two energy-based techniques. The generalized power-law detector also can be used for basic parameter estimation and can be adapted for other types of transient sounds.
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43.30.Sf Acoustical detection of marine life; passive and active
43.60.Cg Statistical properties of signals and noise
43.80.Ka Sound production by animals: mechanisms, characteristics, populations, biosonar
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