bluuebunny/crossref_metadata_2025 huggingface dataset:
Baleen whale responses to low-frequency human-made underwater sounds
Authors: Clark Christopher W. , Fristrup Kurt M.
Published: October 2013

Baleen whales are vulnerable to impact from human-made underwater sounds. Most species produce communication calls and some sing, with most sound energy between 20 and 2000 Hz. Cochlear mechanics indicate inner ears well adapted for hearing below 1000 Hz. Many species breed and calve in coastal habitat, or feed along shelf edges or areas of ocean upwelling, and are frequently exposed to noise from commercial and recreational activities. Humans have become increasingly more adept at and dependent on exploring the ocean with acoustic probes. Sound sources are typically high intensity and in the primary acoustic production and perception frequencies of the baleen group. Evaluation of impact is difficult, confounded by a general lack of basic knowledge on baleen whale behavioral ecology, distribution, and abundance, and signal function. Results from three integrated research projects investigating whale responses to controlled exposures to Navy low-frequency sonar (LFA) indicate relatively low levels of short-term responses, even at received exposures as high as 150 dB re: 1 Pa. Results are interpreted relative to possible population level impact from an operational source. Results support a conceptual shift in impact from a single source, while emphasizing the need for a coherent, cautionary policy regarding cumulative and long-term impacts on the ocean environment. [Research supported by ONR.]
Ocean ambient noise from anthropogenic and natural sources in the context of marine mammal acoustics
Authors: Cato Douglas H. , McCauley Robert D.
Published: October 2013

The effect of anthropogenic ambient noise on great whales is difficult to assess because of the limited knowledge of the way in which these whales used sound. Some idea of the impact can be obtained by comparing anthropogenic noise with the natural ambient noise, i.e., the background noise that whales have always experienced. Most measurements of ambient noise, however, have been made in the northern hemisphere where there is significant contamination from anthropogenic noise. Around Australia, there are many areas where anthropogenic noise is low or negligible because of the relative isolation of the continent, and this has allowed us to make reliable measurements of the natural ambient noise throughout the frequency range of relevance to marine mammals, and in areas frequented by vocalizing whales. The results show that there is more than 30-dB temporal variation in natural ambient noise, with 20 dB being common. Much of the variation is due to the contribution of biological sources, especially fish and whale choruses, and sea surface noise (wind-dependent noise). Natural ambient noise levels are often comparable to those of traffic noise (noise from distant shipping), and at times reach the high-traffic noise levels of the northern hemisphere.
Dynamic structural-acoustic-piezoelectric finite element analysis of a layered 1-3 composite, half-wavelength resonator underwater transducer array
Authors: Koch Robert M. , Benjamin Kim C.
Published: October 2013

The coupled structural, acoustic, and piezoelectric noise propagation physics within a layered 1-3 composite, half-wavelength resonator transducer array for high-frequency, broadband underwater applications is modeled herein using dynamic finite element analysis (FEA). This analysis is being performed primarily to evaluate the complex steady-state dynamic response of the multiple-layered composite array in order to ensure bond structural integrity during high-frequency operation. Specifically, various geometric configurations of the individual array layers will be examined to determine their effect on both array performance and structural integrity (e.g., relative PZT element spacing between layers, bond materials, joining layer thickness). The results of the present analysis will also be compared to experimental data being collected on prototype layered 1-3 composite arrays.
The design, fabrication, and acoustic calibration of a conical, octahedral array using 1-3 piezoelectric composite
Authors: Benjamin Kim C. , Forsythe Steve E.
Published: October 2013

Continuing to exploit the unique characteristics of 1-3 piezoelectric composite for wide-band acoustic array applications, a 120-element conical array was successfully fabricated and calibrated in less than 3 months. The eight-sided approximation of the conical aperture had dimensions 18.3 cm high, with a 13.3-cm base, and a 20 conical half-angle. Each of the 8 staves had 15 elements. The upper portion of the conical surface (cone tip) was not populated. The substrate thickness used in this demonstration was 1.8 cm providing a half-wave resonance frequency of approximately 86 kHz. The 1-3 piezocomposite configuration consisted of injection molded Navy type VI ceramic with a rigid epoxy back-fill that has proven to be both rugged and easily machined. The array was air backed. The array and tooling of the mechanical components were modeled using a computer-aided design package, and subsequently fashioned using stereo-lithography apparatus thus making this array a paperless design. Radiation modeling was accomplished using the Combined Helmholtz Intergral Equation Formulation (CHEIF). Measured results will include in-air laser vibrometer scans, and in-water transmit and receive beam patterns. [Work supported by Naval Sea Systems Command Div. Newport (Code 82).]
Analysis and comparison of pressure gradient sensors of the fixed dipole and diffraction type with pressure gradient sensors of the motion accelerometer type
Authors: Brown David A. , Aronov Boris , Oishi Tetsuro
Published: October 2013

Acoustic pressure sensors (hydrophones) and pressure gradient sensors are often used in combinations to characterize the acoustic sound field and to obtain compact devices with figure-of-eight and cardiod directivity patterns. Pressure gradient sensors of the fixed type can be realized by using pairs (doublets) of hydrophones spaced by a distance smaller than the acoustic wavelength or by using single elements whose size and geometry introduce a pressure difference from the diffraction of an acoustic wave. Pressure gradient sensors of the motion type are realized by using motion sensors such as accelerometers, velocimeters, or displacement sensors (seismometers) in a near neutrally buoyant package. Eulers’ linear force equation confirms that the pressure gradient is proportional to the acoustic acceleration. We present our analysis of pressure gradient sensors of different types and show that a device of the fixed diffraction type can have the same sensitivity as a motion type accelerometer with comparable dimensions and using the same electroacoustic flexural disk transducer. Analysis of the response of sensors to unwanted actions is also presented. [Work supported in part by BTECH and ONR 321SS.]
Time–domain synthesis of conical bore instruments
Authors: Scavone Gary P.
Published: October 2013

A series of approaches are presented for discrete time–domain synthesis of conical bore instrument sounds. This study uses a simple clarinet-like system, involving a memoryless nonlinear ‘‘reed’’ function and a distributed cylindrical air column model, as a point of departure for subsequent development. The generation of steady, self-sustained oscillations in such a system is complicated by properties inherent to truncated conical waveguides. Alternative methods include a structure equivalent to Benade’s ‘‘cylindrical saxophone,’’ with two separate parametrization schemes. Finally, a more general ‘‘virtual’’ model is presented that is capable of synthesizing both half-wave and quarter-wave resonators. This structure provides a rich variety of possible sounds and offers an interesting perspective on conical waveguides.
Fractal dimensions of initial transients of musical instruments
Authors: Bader Rolf
Published: October 2013

Fractal dimensions of initial transients are calculated for musical instruments. There are significant differences between a classical guitar, a violin, a clarinet, and a balinese Gender dasa. As the guitar and the clarinet have a maximum correlation-dimension of around D=4, the violin reaches up to D=5.5. The gender with its intensive inharmonic overtone structure can be up to D=6.8, and about D=2.0 within the steady state. Instruments with harmonic overtones always have D=1 during their steady state. These values seem to correspond to the number of rules governing the transient, which can be shown using zooming-in wavelet transform. In a sample of some hundred examined sounds, the guitar had just a light tendency for louder, higher, and Apoyando plucked tones to be more chaotic than for softer, lower-pitched, and Tirandu-played ones. The violin sounds differed extremely within these categories. The clarinet was also examined during pitch changes in melody. Here an information structure is proposed, which is the second derivation of time of a multifractal information-dimension and shows the stucture of information gain for these transients.
Aircraft noise propagation in coastal areas
Authors: Zusman Alan F.
Published: October 2013

Department of Defense (DoD) environmental noise management efforts employ computer models to project noise exposure around military installations, ranges, and operating areas. Both the DoD airfield noise model (noisemap) and the heavy weapons noise model (bnoise) assume propagation over land. In order to ensure the accuracy of these models for Navy and Marine Corps installations in coastal areas, the U.S. Navy has been funding studies of propagation over water. These studies have included: (1) joint work with the Swedish Air Force, (2) helicopter noise measurements along the southern California shore, (3) aircraft noise propagation studies in Florida and California, and (4) studies of gun fire propagation at the land–water boundary. Lessons learned from these efforts have been incorporated into the design of a new study of aircraft noise to be conducted this year.
Low frequency sound propagation across a land–water boundary
Authors: White Michael , Pater Larry
Published: October 2013

Army noise assessment capability has recently been improved to account for the effects of land–water transitions on a received sound level. Sound waves propagating beyond a shoreline experience changes in surface impedance, surface roughness, and refraction profile. Measurements of the temperature and wind with tethersonde balloons indicate significantly weaker sound speed gradients over water than over land. When a temperature inversion was observed over land, the inversion was always smaller over the water. When the solar heating produced strong upward refraction near the land surface, the temperature profile over water was neutral (lapse). Simulations were run with a parabolic equation model incorporating range-dependent boundary refraction profiles and range-dependent boundary conditions. The signal levels exhibit changes with distance due to strong refraction over land, but the changes nearly cease in places where the propagation extends over water. Measured spectrum levels from explosion sound propagating across land–water boundaries agree well with the simulations. [Work supported by the USACERL, USACHPPM, and NAVFAC.]
Annoyance of infrasounds
Authors: Panuszka Ryszard , Damijan Zbigniew
Published: October 2013

At the present developed procedures of evaluation of annoyance of low frequency noise (LFN) on human and occupational health are based on international standards, ISO 7196 and ISO 9612. These standards are based on levels of thresholds of the human auditory system and subjective observations of vibrations of human body impacted by infrasound waves. In 1998 the first limits of exposure to infrasound and low frequency sounds were introduced to the guidelines of the American Conference of Governmental Industrial Hygienists (1999). Recent discoveries resulted significant sensitivity of the central nervous system on infrasonic waves especially below 10 Hz and the observed follow-up effects in the brain. New obtained results showed the impact of LFN on the electrical potentials in the brain accordingly to pressure of waves on the human body. Signals recorded in industrial workplaces were used for further studies with typical LFN spectra with 5 Hz in chamber at laboratory. External noise, electromagnetic fields, temperature, dust and other elements were controlled. Results show that follow-up effect is observed for 70% of the population. Multi-channel system of acquisition of signals was used for sound pressure levels, EEG-potentials, blood pressure monitoring, temperature, and pulse. Laboratory test included 45 volunteers of healthy people.
Comparison of linear and nonlinear experiments for landmine detection
Authors: Nock George , Ali Manaf , Sabatier James M. , Korman Murray S.
Published: October 2013

When airborne sound couples into the ground, so-called ‘‘slow’’ compressional waves can interact with a target buried in the soil and effect the vibration velocity of the surface. Donskoy [SPIE Proc. 3392, 211 (1998); 3710, 239 (1999)] has suggested a nonlinear technique that can detect an acoustically compliant buried mine that is insensitive to relatively noncompliant targets. A VS 1.6 inert antitank mine (23 cm diam) was buried in the natural loess soil at the test site. In the linear experiment, a pair of subwoofers were sinusoidally swept from 70 to 600 Hz. The geophone’s response was measured along a 1 m scan segment across the mine. A 107 Hz resonance was chosen and the nonlinear experiment was performed by driving the woofers at f1=300 Hz and f2=407 Hz and detecting at the difference frequency. Nonlinear scan profiles over the mine have more relative sensitivity than the linear profiles. When a 30 cm diam, 4 cm thick concrete disk was buried, it could be detected ‘‘linearly’’ but not ‘‘nonlinearly’’ in agreement with Donskoy. Nonlinear theories will be discussed. [Work supported by the United States Army Communications-Electronics Command Night Vision and Electronic Sensors Directorate.]
Experimental tests of a generalized acoustic triangulation method
Authors: Williams Jay E. , Williams Chad M. , Frazier William G. , Gilbert Kenneth E.
Published: October 2013

A generalized acoustic triangulation method has been developed that takes into account the finite propagation speed of sound. The method has been tested using two 3-microphone arrays separated by 1 km, together with a low-flying commercial jet tracked via the Global Positioning System (GPS). The tests show that generalized triangulation is accurate as long as the bearing errors are small relative to the effective aperture of the two arrays. When the bearing errors are not small relative to the effective array aperture (e.g., at longer ranges), it is shown that significantly improved tracking accuracy can be obtained by assuming a constant speed target and using a bearings-only solution instead of triangulation. Wind noise is shown to be the major source of bearing errors. The degradation of bearing and tracking accuracy due to wind noise is demonstrated using field data, and possible approaches for wind-noise reduction are discussed. [Work supported by the U.S. Army Space and Missile Defense Command.]
Scattering from a coated cylindrical shell comparison of ray and exact computations
Authors: Norris Andrew
Published: October 2013

We discuss sequentially the following: a homogenized shell theory and how it differs from uniform shell theory; high-frequency analysis of the quasi-P and S membrane wave solutions; the application of ray and coupling theory to the coated shell to predict the scattered response for oblique plane wave incidence; and numerical benchmarking against the exact code for thick coated shells. The shell theory is based on composite plate theory, with shell stresses modeled by the Kirchhoff assumption. The ray theory generalizes the theory developed for uniform thin shells, and accounts for the simultaneous P and S supersonic waves, and resulting resonances. The numerical comparisons demonstrate that the ray theory is accurate for undamped coatings, for which the excited resonances are strong. With damping present in the coating two unexpected discrepancies arise in the ray theory predictions. First, the damping of the excited structural waves is underestimated, even for relatively low damping in the coating, on the order of 0.1. At higher damping, e.g. 0.5, the same problem persists and is exacerbated by the degeneration of the background or specular approximation that is used in the asymptotic ray theory model. Refinements of the model to successfully address these is discussed.
A numerical technique for computation of flow-induced vibration and noise
Authors: Hwang Y. F. , Hambric Stephen
Published: October 2013

This paper discusses the use of commercially available structural acoustics solvers for computation the flow-induced vibration and noise at low speed. The major issue of this problem is the modeling turbulent boundary layer (TBL) forcing function for finite-element models of structures. Predictions of structural vibrations using the TBL cross-spectral density function directly is not computationally tractable for large complex structures, because extremely fine finite-element meshes had to be used to resolve the TBL pressure fluctuating scales. This paper discusses a more practical approximated discrete forcing function model, which represents only the low-wave number region of the TBL excitation in terms of the cross-spectral function of grid forces. The high-wave number (convective ridge) content of the excitation, which is insignificant for large structures with fixed boundaries, is thus ignored. This method is more feasible in practice because the finite-element meshes now need only resolve the structural wave scale instead of the convective turbulence scale. Numerical examples on the flow-induced vibration of a clamped plate, and the flow-induced noise radiated from a ribbed cylindrical shell will be discussed. [Work supported by ONR, Code 333.]
Prediction of elastic material properties via an adjoint formulation
Authors: Oberai Assad , Feijoo Gonzalo , Pinsky Peter
Published: October 2013

The prediction of elastic material properties via an adjoint formulation in this talk an efficient computational formulation to determine the acoustic properties of an elastic material, given its response to a time-harmonic excitation, is presented. Such problems arise in biomedical imaging using techniques such as Magnetic Resonance Elastography. The problem is posed as an inverse problem and its solution is computed using a mathematical programming algorithm (from mathematical programming). The functional to be minimized is the norm of the difference of the ‘‘measured’’ and a ‘‘trial’’ velocity field. At every iteration the trial velocity field is determined by solving the Helmholtz equation. The derivatives of the functional with respect to material properties, which form the input to the optimization algorithm, are computed by solving an adjoint problem. Using this formulation, the cost of computing derivatives is independent of the number of parameters used to represent the material properties, and thus the overall problem is rendered computationally tractable. A description of this methodology and an illustrative example to indicate its effectiveness will be presented.
A new implementation of the finite elements method applied to vibro-acoustic analysis using object oriented programming
Authors: Lamary Pierre , Chevalier Yvon
Published: October 2013

The aim of this paper is to present the most interesting points encountered in the creation of a new vibro-acoustic software. This program, named cavok (Computational Acoustics and Vibro-acoustics OK) applies specifically to the field of transportation (car, train, airplane). The originality of this work comes from the implementation of the finite elements method (FEM) proposed. Using an object oriented language (OOL) it has been shown possible to solve partial differential equations formally. First, it will be seen that the high level of abstraction proper to OOL facilitates software design. Secondly, we shall demonstrate the acuity of this approach for the treatment of acoustic insulating panels of aircraft. In such solutions, several physical domains interact, and must take into account the elastic behavior of the frame, the poro-elastic behavior of the absorbent material (glass wool), and the acoustic properties of air layers. The first results obtained are encouraging, and we shall conclude with the future research perspectives envisaged. In Particular, the cavok software will permit the comparison of different variational formulas of poro-elastic finite elements.
A description of midsagittal tongue movement in terms of secant line kinematics
Authors: McGowan Richard S.
Published: October 2013

Tongue shape is a major determiner of the shape of the air channel in the vocal tract, and, hence, the acoustic signal during speech production. Flesh-point movement is a way that midsagittal tongue motion in speech production is examined, such as with the EMMA system and the x-ray microbeam system. We propose to transform the Cartesian coordinates of the flesh-points into one that specifies the position of the centers of the secant lines between each neighboring pair of flesh points, as well as the length and orientation of each secant line in this coordinate system, motion is considered in terms of translational, rotational, and stretching motions of the secant lines, with the former specifying gross motion and the latter two specifying local motion. Utterances from the X-Ray Microbeam Speech Production Database involving consonants with alveolar place of articulation are examined for kinematic differences resulting from differences in manner, vowel context, and syllable position. A further refinement of the secant line coordinates will be offered in terms of midsagittal secant line position and orientation relative to the palate and pharynx. This coordinate system should be helpful for interpreting flesh-point kinematics with regard to acoustic output.
FEM analyses of three-dimensional vocal tract models after tongue and mouth floor resection
Authors: Nishimoto Hironori , Akagi Masato , Kitamura Tatsuya , Suzuki Noriko , Saito Hiroto
Published: October 2013

The accuracy of vocal tract transfer functions estimated by Finite Element Method (FEM) analyses was evaluated to find relationships between structural characteristics of vocal tracts and their acoustical characteristics. Three-dimensional vocal tract models were constructed from MR Images of four speakers (two normal persons and two patients after tongue and mouth floor resection), uttering the Japanese vowel /i/. Vocal tract transfer functions of the models were estimated by FEM and one-dimensional models, and peak positions of these functions were compared with formant frequencies of these speaker’s speech waves. The patient speech waves had a peculiar formant at around 1500 Hz. The peak positions of the patients estimated by FEM were similar to the formant frequencies of the patients, especially the formant at 1500 Hz. However, the transfer functions by the one-dimensional models had no peak at around 1500 Hz and the number of peaks was fewer than that by FEM. Since the patient vocal tract shapes were not symmetrical and bent right and left, sound pressure distributions estimated by FEM showed that the waves in the patient vocal tracts cannot be assumed as plane waves. Then, the one-dimensional models cannot describe acoustical characteristics of the patient vocal tracts.
Rear pharyngeal wall placement during vowel production
Authors: Magen Harriet S. , Kang A. Min
Published: October 2013

While the rear pharyngeal wall has been assumed to be stationary during speech, this needs to be confirmed. The present study used midsagittal magnetic resonance images to determine whether the posterior pharyngeal wall shows vowel-specific movement during the sustained production of 11 English vowels. Distances were measured between the most posterior portion of the vertebral body and the pharyngeal wall at four points. The first traversed the junction between the dens and body of the second vertebra (C2). The next three traversed the inferior border of the bodies of C2, C3, and C4. These ranged from a level just below the velopharyngeal port to one near the larynx. In preliminary measurements for one speaker, only the uppermost location showed significant variation due to vowel quality; at the other locations, differences were less than 1 mm. Further subjects are being studied. These findings confirm, at least for vowels, the assumption that the rear pharyngeal wall is stationary during speech. Therefore, midsagittal distances in the pharyngeal region can be inferred from measurements of the anterior pharyngeal wall in relation to the fixed features of the vocal tract. [Work supported by NIH Grant DC-02717.]
Fusion of aspiration noise in voice synthesis
Authors: Payri Blas , Kreiman Jody
Published: October 2013

Synthesizing natural-sounding aspiration noise and breathiness remains challenging, because added noise may be masked or may fail to fuse with the harmonic component of the voice source, resulting in the perception of two separate sound channels. This study investigated the conditions leading to fusion and masking of aspiration noise in voice synthesis. Sustained vowels were synthesized using combinations of three noise-to-signal ratios, three F0 levels, two different versions of the harmonic component of the source, three sets of formants, and three differently shaped noise spectra. For each sample, expert and naive listeners judged whether they heard breathiness, and whether this breathiness noise was part of the voice or separate from it. Effects of the different experimental variables on masking and fusion will be discussed in an auditory scene analysis framework, combined with the perception of speaker naturalness.
Phonation types in Suai
Authors: Abramson Arthur S. , Luangthongkum Theraphan
Published: October 2013

Many Mon-Khmer languages have such phonologically distinctive phonation types as modal, breathy, and creaky voice. The Suai language studied here is spoken in northeastern Thailand. Literature exists on these phonation types (‘‘voice registers’’), including some attention to acoustics; however, no perceptual studies appear to have been published. Suai was chosen here because it has just two contrasting categories conventionally labeled modal voice versus breathy voice. The Klatt synthesizer was used to control five of its parameters: F0, amplitude of turbulence, open quotient of the voicing waveform, overall gain, and spectral tilt. All combinations of these parameter settings yielded 51 variants of a basic syllable. These stimuli were identified by native speakers as one word or the other of a minimal pair. The results showed breathiness and pitch to be major cues. The original recordings of our informants, however, appeared only to have a pitch difference, an impression tested by acoustic analysis. A reliable difference was found only in F0 contours, with a lower one on the ‘‘breathy’’ type. There appears to be evidence for an ongoing shift from a system of phonation types to one of tones. [Work supported by NIH Grant DC-02727 and the Thailand Research Fund.]
CW-based proximity distance measurement by ultrasonic sensors
Authors: Li Xi , Li Jian , Sheplak Mark
Published: October 2013

With conventional pulse-echo ranging approaches, it is difficult to obtain an accurate range measurement needed by a proximity ultrasonic sensor system due to the limited bandwidth of the transducer. However, based on the continuous wave (CW) method (i.e., the transducer is excited by a set of continuous harmonic signals), the high accuracy can be obtained even with a narrow-band transducer. By using a set of orthogonal sinusoid signals and simultaneously measuring the phase shifts corresponding to all of the frequencies, we obtain a fast measurement scheme with respect to the traditional CW method that measures the phase shifts for each frequency separately. This method can be efficiently implemented by FFT by currently available dedicated DSP chips. To estimate the unknown distance based on the phase shifts, two-stage fast optimization algorithm has been presented. Numerical results show that this algorithm can approach the Cramer–Rao bound (CRB) for high signal-to-noise ratio.
Unperturbed normal mode method for surface wave effects on acoustic propagation in a shallow water waveguide
Authors: Henyey Frank S. , Thorsos Eric I. , Reynolds Stephen A.
Published: October 2013

A computational method is presented for propagation in an ocean waveguide with a wavy surface. This method is based on the expansion of the wave function into the vertical normal modes of the flat-surface problem. Unlike the traditional boundary perturbation technique for elliptic problems, this method is incorporated into an initial-value normal mode framework. The truncated modal expansion is supplemented by an additional function to remove the Gibbs phenomenon at the unperturbed surface. This additional function is approximately a sine integral. The mode coupling equations and the expression for the amplitude of the sine integral are derived. In comparison to local normal modes, the coupling is local at the surface, and the modes are range independent if the unperturbed waveguide is. The coupling matrix is rank 1, enhancing the computational efficiency. [Work supported by ONR.]
Rapid assessment of gently varying bathymetry using TRM reverberation
Authors: McDonald B. Edward , Holland Charles
Published: October 2013

A concept for rapidly probing shallow water bathymetry [B. E. McDonald and Charles Holland, J. Acoust. Soc. Am. 109, 2495 (2001)] using reverberation from a time reversed mirror (TRM) is further developed. Adiabatic modal analysis and WKB methods applied to a mildly range-dependent shallow water waveguide lead to a simple relation between TRM focal shifts and range integrated bathymetric variations. This relation is compared with RAM simulations carried out in conjunction with the July 1999 Saclantcen–Scripps bottom reverberation experiment near Elba. Our integral expression is found to agree satisfactorily with focal spot shifts predicted by RAM. Simulation studies using the Saclantcen prosim reverberation model are also presented to help explain details of the July 1999 data. Experimental implications for rapid assessment of unknown or shifting shallow bathymetry are discussed. [Work supported by NRL.]
Relating changes in reverberation envelope statistics to changes in sonar system parameters
Authors: Abraham Douglas A.
Published: October 2013

The reverberation component of the matched filter envelope in active sonar systems operating in shallow water environments has often been observed to have probability density function tails heavier than the traditionally assumed Rayleigh distribution. Recent research has shown that exponential point scattering leads to a K-distributed envelope (D. A. Abraham and A. P. Lyons, in Proceedings of the MTS/IEEE Oceans Conference, Honolulu, Hawaii, Nov. 2001). Under this model, the reverberation statistics change as the number of scatterers within a range-bearing resolution cell changes. For example, doubling the bandwidth of a transmission will halve the number of scatterers, resulting in a heavier reverberation distribution tail. This relationship is examined using low frequency active sonar data collected during SACLANT Undersea Research Center’s SCARAB 1997 sea-trial (Charles Holland, Chief Scientist) by evaluating the effective number of scatterers parameter (α) of the K-distribution as estimated from the data for varying transmit waveform bandwidths and receiving array beamwidths. It was observed that, within the accuracy of the parameter estimation, α varied as the scattering model predicted; that is, it changed proportionally to resolution cell size. [Work sponsored by ONR under Contract No. N00014-00-G-0058, D.O. 0009.]
A hidden Markov approach for the probabilistic treatment of competing acoustic scattering mechanisms
Authors: Soukup Raymond J. , Howell William C.
Published: October 2013

A variety of acoustic scattering phenomena are encountered in the ocean, such as the rough air–sea interface, bubble clouds, biologics, and the ocean bottom. As a result of their relative dependence on sonar parameters such as transmit frequency and launch angle, there are scenarios where a dominant phenomenon (or state) can be observed in reverberation data. Furthermore, important environmental parameters needed by physics-based models to predict such scattering behavior are either temporally/spatially varying or difficult to measure, and must be treated probabilistically. In this paper we present a model based on a hidden Markov approach that describes the probabilities that certain states will be encountered, and that transitions from one state to another will arise due to changes in the environment and the system. This Hidden Markov Model (HMM) integrates physical knowledge of the competing mechanisms in such a way as to illustrate the overall scattering behavior of the ocean environment and to suggest methodologies for reducing the local reverberation. The virtues and features of the HMM are demonstrated using measured data collected in the Gulf of Alaska, where near-surface scattering due to the air-sea interface, bubble clouds, and salmon are all possibly dominant under certain conditions. [Work supported by ONR.]
Dive patterns and source levels of sperm whales off New Zealand
Authors: Frankel Adam S.
Published: October 2013

Diving sperm whales off Kaikoura, NZ were recorded using a 4-element vertical linear hydrophone array deployed from a small boat. The boat was frequently within close proximity to the whale dove. Whales began to click almost immediately after leaving the surface. Dive patterns of whales were determined by estimating the location of each click using an advanced time-of-arrival algorithm developed at Cornell University. Analysis of dive patterns showed near vertical descents with speeds ranging from 1–2 m/s. Received click levels were determined and source levels were estimated using a spherical-spreading loss term, as the ranges to the whales were less than the water depth. Preliminary estimates of peak-to-peak source levels range from 191 to 201 dB re: 1 Pa at 1 m (peak-to-peak). On one occasion, a sperm whale clicked rapidly at close range (∼8 m) from a hydrophone element. Click rates as high as 22/s suggest that the whale was interrogating the metal weight at the end of the array. The source level of these clicks ranged from 170 to 205 dB. [Research supported by the Smithsonian Institute and the Cornell University Bioacoustics Research Program.]
Impedance tuning of an electromechanical acoustic liner
Authors: Horowitz Stephen B. , Nishida Toshikazu , Cattafesta Louis N. , Sheplak Mark
Published: October 2013

The results of a theoretical and experimental study of the impedance tuning capabilities of an electromechanical acoustic liner are presented. An electromechanical acoustic liner utilizes an array of Helmholtz resonators, each containing an electroactive, compliant-walled cavity, to couple the electrical, mechanical and acoustical energy domains. Due to this coupling, the acoustic impedance of this liner is a function of elements from all of these energy domains. Therefore, the acoustic impedance of the liner can be modified via an electrical network. In this study, a prototype of a single cell of an electromechanical acoustic liner is developed and tested. The prototype consists of a cylindrical Helmholtz resonator with a circular, piezoelectric composite backplate, consisting of a thin brass disk bonded to a disk of PZT. An electrical network of resistors, inductors, and capacitors was connected across the terminals of the PZT to implement tuning. Normal-incidence acoustic impedance measurements were taken in an impedance tube from 1 to 6.4 kHz for various values and combinations of electrical components. The measured impedance spectra are then compared to theoretical impedance spectra based on lumped element modeling.
Dynamic stability of a beam excited by moving masses
Authors: Mackertich Seroj
Published: October 2013

The dynamic stability of an elastically supported Timoshenko beam excited by constant velocity equally spaced traveling masses has been investigated. The regions of dynamic stability are determined for different values of the elastic foundation stiffness. Floquet theory is utilized to study the parametric regions of stability and instability, which are displayed in graphical form. Since the occurrence of this dynamic instability reduces the axial buckling load of the beam, the result is important for the study of buckling of a continuous beam.
Variable structure control of vibration of the simply-supported plates
Authors: Pan Jiaqiang , Pan Shuwen
Published: October 2013

Robust active vibration control technology is still on its way to develop, though there has been a great number of studies on active vibration control (AVC) topic published since 1980s. The key is to find a good control strategy fitting AVC use and with strong control robustness, in addition to other qualities. As a newer member of robust control strategies, variable structure control (VSC) has attracted control researchers to study its application potentiality at different engineering areas for recent years. Few of them, however, have already paid attention to use in AVC area. In this paper, VSC design methodology used for AVC of a simply-support rectangular plate is investigated. The control design process at the modal state-space is deduced and the matching conditions introduced. Numerically simulated results by using VSC under scheme of the independent modal space control are obtained and compared to those obtained by using least quadratic control and the poles allocation method. It shows that VSC has advantages over the traditional control strategies at control robustness and can control more vibratory modes. [Work supported by the Zhejiang Science and Technology plan fund, PRC.]
Discrete type dynamic synapses neural network: Speech recognition application
Authors: Namarvar Hassan Heidari , Liaw Jim-Shih , Berger Theodore W.
Published: October 2013

A discrete type of the Dynamic Synapses Neural Network (DSNN) has been developed and applied to speech recognition. In order to speed up the training time of the network, a new discrete time implementation of the original DSNN [J.-S. Liaw and T. W. Berger, 1996] has been introduced based on the impulse invariant transformation. The new architecture of the network was trained with the Genetic Algorithms [H. H. Namarvar et al., 2001] and tested against the continues-type DSNN. The overall speed of the new algorithm with discrete-time difference equation set is about 13 times faster than the same algorithm with the continuous differential equation set. This significant reduction of processing time not only decreases the training time but also makes the system better suited for real-time speech recognition tasks. [Work supported by DARPA.]
Tactical communications bring new challenges to automatic speech recognition
Authors: Crystal Thomas H. , Schmidt-Nielsen Astrid , Marsh Elaine
Published: October 2013

Automatic speaker-independent recognition of conversational speech has been making significant progress in recent years. Military communications challenge the robustness of current recognition systems. Compared to telephone conversations or news broadcasts, tactical communication has a reduced vocabulary. It consists of short utterances, limited to the task at hand, with occasional chat words. What makes recognition difficult is high levels of background noise in tactical environments (helicopters, tanks) and the degradation of the signal by military microphones, including noise canceling microphones. Of perhaps more importance, people alter their speech to overcome these degradations and the loss of intelligibility from communicating over vocoders. The DARPA-sponsored spine program is exploring these issues using speech from pairs of participants performing a collaborative task while communicating between separate sound booths. Each person sits in an accurately reproduced military background noise environment and uses the type of microphone and ear protection that would normally be found in that environment. The communication is conducted through vocoders. This presentation will review results from the spine evaluations of state-of-the-art speech recognition systems and from analyses of the transcripts in an attempt to understand how environmental factors and speaking changes affect recognizer performance. [Work supported by DARPA.]
A novel method to estimate voice source and formant parameters based on an ARX speech production model
Authors: Ohtsuka Takahiro , Kasuya Hideki
Published: October 2013

A novel method is presented to automatically estimate voice source and formant parameters from a speech utterance based on an autoregressive with exogenous input (ARX) speech production model. The method has been tested with both synthetic and natural speech materials and compared with the well-established linear prediction (LP) method in terms of the accuracy of estimated formant frequencies. The new method always revealed better performance than the LP method. In particular, the error of the proposed method was as small as 6% for the materials of an average pitch frequency of 447 Hz, while the LP method gave an error of 21%. The result clearly indicates superiority of the proposed method over the LP method for very high-pitched voices generated by females and children. Other key features of the proposed method include: (1) very low first formant frequencies of the high vowels /i/ and /u/ can be accurately estimated; (2) voicing source amplitude and open quotient of the glottal flow pulse are both reliably estimated; and (3) the implementation of an adaptive prefilter in the analysis remarkably improves the accuracy of estimated parameter values.
A nonstationary speech production model based on a
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m
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x analysis
Authors: Huang Jun , Levinson Stephen
Published: October 2013

Speech production is a very complicated process which includes both the linear propagative mode and the nonlinear flow mode. The plane wave propagation mode has been modeled by an autoregressive (AR) process and resulted in the widely used linear predictive (LP) model in speech production. In this work, we introduce an autoregressive moving average exogenous (armax) model for speech production. We model the additional turbulence-induced acoustic sources and sinks by a nonstationary exogenenous noise process. First, we classify the English phonemes into five broad phonetic categories, namely, vowels, semi-vowels, stops, fricatives, and stops. Then we identify the model orders of each phonetic category from the acoustic observation. The model parameters are estimated by the Gauss–Newton algorithm. Finally, the prediction of the speech signal is performed through a recursive way after the model parameters of each phoneme are estimated. We tested this speech production model by synthesizing English phonemes and continuous sentences. Experimental results show that we can synthesize almost humanlike, natural quality speech signal based on this nonstationary speech production model.
Bistatic synthetic aperture imaging of buried objects from an AUV
Authors: LePage Kevin D. , Schmidt Henrik
Published: October 2013

During SACLANTCEN’s GOATS98 experiment an assortment of proud and buried objects were ensonified above and below critical angle by a parametric array and their scattered fields were observed bistatically on the nose array of a MIT Odyssey class AUV. Here the challenges of synthetic aperture sonar (SAS) processing for bistatic data sets are addressed and the detection of buried objects at subcritical ensonification angles is demonstrated. In addition, the differences between the measured resonant characteristics of spherical target scattering at below and above critical grazing angles is discussed.
Buried target classification with bistatic synthetic aperture sonar
Authors: Edwards Joseph R. , Schmidt Henrik
Published: October 2013

Buried target classification is of paramount importance in mine countermeasures (MCM) applications. Traditional methods use optimal detection techniques, e.g., monostatic synthetic aperture sonar (SAS) imaging, to classify objects by target shape. The shape of a target, however, does not necessarily indicate whether it is manmade (mine) or natural (rock), thus creating the possibility of an unacceptably high false alarm rate. Furthermore, the limited resolution available at the low frequencies required for seabed penetration may prevent the shape-based classification altogether, as the imaging wavelength is typically on the order of the target size. For these reasons, additional information about the character of the target is required. The current work investigates the use of frequency and aspect dependence of the target scattering for classification of canonical minelike targets, using a bistatic AUV-borne sonar receiver to interrogate spheres and cylinders in various burial conditions. Experimental evidence from goats98, an at-sea experiment performed off the coast of Elba Island, and supporting evidence from oases−3d models are used to demonstrate clear distinctions between these canonical targets, and to illustrate the potential of a multi-static system for rapid and robust MCM. [Work supported by ONR and SACLANT.]
Impulse scattering processes of an elastic sphere
Authors: Feuillade Christopher
Published: October 2013

The ‘‘movable rigid sphere’’ scattering model of Hickling and Wang [J. Acoust. Soc. Am. 39, 276–279 (1966)] incorporates the translational ‘‘rebound’’ response of the scatterer to the incident field. However, as a physically unrealizable object, the rigid sphere has limited applicability. Recently, it was shown [J. Acoust. Soc. Am. 106, 553–564 (1999)] that both the movable rigid sphere and Anderson’s fluid sphere model [J. Acoust. Soc. Am. 22, 426–431 (1950)] are limiting cases of Faran’s elastic sphere scattering theory [J. Acoust. Soc. Am. 23, 405–418 (1951)]. In this paper, the time domain impulse response is used to demonstrate the three dimensional scattering of an elastic sphere and its special cases. The critical factor is the shear rigidity modulus. For normal elastic values of the modulus, shear waves dominate the scattering response. When the rigidity is high, the shear waves travel more rapidly through the sphere, and its motion becomes increasingly characterized as a rebound translation without change of shape. Wave conversion at the boundary is also inhibited. For low or vanishing rigidity, only compressional waves are supported, and these determine the scattering response. The presentation will be illustrated by movie animations. [Work supported by ONR.]
Passive sonar calibration spheres
Authors: Deveau David M.
Published: October 2013

The need for calibrated sonar targets is addressed with the development and testing of a set of thin-walled spheres filled with a high-density fluid. Using historical research information as a guide, a set of thin-walled metal spheres was developed and filled with a high-density fluid. The combination of the spherical shape and the acoustic focusing effects of the fluid enhanced the acoustic scattering strength of the shape so that it was not only stable with temperature but also significantly greater in amplitude. The simple passive nature of the spheres makes them ideal acoustic targets for long-term unattended deployments. Using a reference level measurement, each sphere was calibrated over a wide frequency range in order to provide the user with a curve of measured scattering strength vs frequency. The resulting curves showed a high degree of correlation between the individual spheres and the modeling that was used to extrapolate the theoretical values.