bluuebunny/crossref_metadata_2025 huggingface dataset:
Littoral and deep-seafloor sediment characterization from recent chirp sonar surveys
Authors: Turgut Altan , Soukup Raymond J. , Kunz Edward L. , Wood Warren T.
Published: October 2011

Sediment sound-speed and attenuation were estimated from the chirp sonar reflection data that were collected during recent surveys in the New Jersey Shelf and northern Gulf of Mexico. Physical properties of the sediment were also estimated using the Biot–Stoll model outlined in [Schock, IEEE J. Ocean. Eng. 29(4) (2004)]. In addition, independent measurements of sound-speed and attenuation were also conducted using acoustic probes and light-bulb implosions. Results from independent measurements were in agreement with those of chirp sonar data. Measured sound speed and attenuation values are typical of silty-sand sediments in the New Jersey Shelf and silty-clayey sediments in the northern Gulf of Mexico. Finally, frequency-dependence of sound-speed and attenuation was estimated within a wide frequency band using the data from co-located light-bulb implosion (0.5–4 kHz), chirp-sonar, (2–12 kHz), and sediment acoustic-probe (5–120 kHz) measurements. Observed small frequency-dependence of sound-speed and linear frequency-dependence of attenuation are in agreement with those predicted by an extended Biot–Stoll model. [Work supported by ONR.]
Modeling backscatter from a series of sediment rough interfaces and mud inclusions by a normal incident chirp sonar
Authors: Tang Dajun , Hefner Brian
Published: October 2011

A chirp sonar measures reflection and backscatter of normal incident sound from sediment interfaces and volume heterogeneity. Motivated by using such chirp sonar data to invert for goeacoustic parameters, a forward model has been developed and reported that uses an exact method on which practical models can be based. Further development of the model is presented to (1) investigate spatial resolution of rough interface scatter for given bandwidth and (2) to include the scattering from volume heterogeneity such as mud inclusions.
Lab vibration complaints due to secondary or questionable indicators
Authors: Evans Jack B. , Himmel Chad N.
Published: October 2011

Researchers complained about lab vibration in a new multi-floor academic laboratory building after observing surface ripples in water glasses on lab shelves. Structural vibration and low frequency noise can effect sensitive laboratory equipment, degrade experimental specimens and reduce staff efficiency and productivity. Investigatory observations and measurements were undertaken to determine vibration and noise conditions and develop a plan of mitigation. Permissible 1/3 octave Vibration Criteria (VC) and full-octave background noise Room Criteria (RC), including maximum limits for low frequency noise, had been used for building design. Central plant equipment, including pumps and compressors are on ground level. The facility is served by remote campus chillers. The building air handlers, exhaust fans, and boilers are in a penthouse mechanical equipment room and on roof. Structure borne vibration and airborne noise may be transmitted to laboratory spaces via building columns and beams, in pipes and ducts and through vertical duct and pipe shafts. Floor vibration and airborne sound spectra were measured during normal business hours (while the facility was occupied) at various locations for comparison with vibration and noise criteria. Results will be graphically shown on charts. Mitigation measures implemented by the facility management will be enumerated with subjectively determine results.
Vibrational and acoustical response of a railroad bridge with vehicle loading
Authors: Costley R. Daniel , Diaz-Alvarez Henry , McKenna Mihan H.
Published: October 2011

A finite element model has been developed for a Pratt truss railroad bridge located at Ft. Leonard Wood, MO. This model was used to investigate the vibration responses of the bridge under vehicle loading. Modeling results have been obtained for a single axle with two wheels traversing the bridge at different speeds. Superposition of multiple axles have been used to represent various combinations of locomotives and flatcars transiting the bridge. The analysis includes examining the vibrational response of the bridge. The output of the vibration response is used as an input to an acoustic FE model to determine the vibrational modes that radiate infrasound. The vibration and acoustic models of the railroad bridge will be reviewed and results from the analysis will be presented. Experimental results will also be presented.
Doorway states in elastic one dimensional systems
Authors: Méndez-Sánchez Rafael A. , Díaz-de-Anda Alfredo , Flores Jorge , Gutiérrez Luis , Monsivais Guillermo , Morales Alejandro
Published: October 2011

Whenever a state of a “distinct” and simple nature is immersed in a sea of states of a different, more complicated, structure a strength function phenomenon appears: the amplitude of the distinct state is spread over the complicated eigenstates with a Lorentzian-like shape. The distinct state acts as a doorway state whenever this state is coupled to the continuum and to the sea of complicated states, but the latter are coupled to the continuum only through the distinct state. We present numerical and experimental results for an elastic system which presents a doorway state and the temporal evolution of the phenomenon is measured directly for the first time. The delayed and stationary responses of the system are discussed.
Real time simulation of element level time series for active sonars in deep ocean environment
Authors: Danesh Sheida
Published: October 2011

The simulation of experiments in deep ocean environments is becoming increasingly important to researches due to expensive and complex modern equipment. Accurate simulations allow for more efficient use of ship time. LAMSS (Laboratory for Autonomous Marine Sensing Systems) at MIT has developed an indispensable tool for simulating real time active sonar experiments using a combination of ray tracing software (Bellhop), MATLAB, and MOOS-IvP (Mission Oriented Operating Suite - Interval Programming). A new key component to this toolbox is a module that models surface reverberation. Experiments in deep ocean environments are subject to environmental effects, such as the scattering of acoustic ray bundles on the ocean boundary due to upward refraction. Therefore, modeling surface reverberation is essential in deep ocean simulations when identifying target signatures in real time through active sonar. The implementation of this model is intended to simulate deep ocean active sonar experiments more accurately, thus optimizing on site data collection and evaluation.
Three-dimensional surface scattering using a parabolic equation model
Authors: Smith Kevin B. , Badiey Mohsen , Senne Joseph
Published: October 2011

Calculations of acoustic rough surface scattering have previously been performed by numerous researchers using parabolic equation models in two dimensions. Approaches have varied from exact solutions that re-map the rough interface to the pressure release boundary condition through a generalized method of images, approximate methods based on a perturbation approach valid for small slopes, and extended domain approaches that define the rough surface as a boundary between water and air with an additional absorbing boundary above the rough surface. In this work, we examine extensions of these approaches to the three-dimensional propagation. It is shown that the exact solution based on a generalized method of images does not yield realizable expressions for implementation. The other approaches are relatively easily adapted to three-dimensions, and some simple test cases involving Bragg scatter are analyzed for accuracy. Implications for other rough surface scattering model studies are also discussed.
Energy conservation in the Kirchhoff approximation
Authors: Joshi Sumedh M. , Isakson Marcia J.
Published: October 2011

The scattering of sound from rough interfaces is frequently modeled using the Kirchhoff approximation. As has been shown by Lynch and Wagner [J. Acoust. Soc. Am. 47(3)] and others, for the case of a pressure-release surface, the Kirchhoff approximation fails to conserve energy. In particular, Lynch and Wagner derive an analytical expression for the proportion of incident energy conserved for a surface with a Gaussian roughness spectrum. They demonstrate that energy is not conserved near normal incidence due to the failure of the Kirchhoff approximation to multiply scatter rays back into the upper half-space. In this work, a Monte Carlo technique is used to quantify the degree to which energy is not conserved in the three-dimensional Kirchhoff approximation; these results are compared with theoretical prediction of Lynch and Wagner for the Gaussian spectrum. A similar Monte Carlo analysis is undertaken for other roughness types. Finally, it is shown that the integral solution, a model that accounts for multiple scattering and shadowing, conserves energy in the pressure-release case. [Work supported by ONR, Ocean Acoustics.]
Crosscorrelation of broadband signals scattered by a random pressure-release surface
Authors: Welton P. J.
Published: October 2011

An expression for the crosscorrelation of omnidirectional, broadband acoustic signals scattered by the sea surface is derived for both vertically separated and horizontally separated hydrophones using an integral equation approach in conjunction with the Fresnel phase approximation, and the specular point approximation, i.e., the approximation that most of the scattered energy comes from regions close to the specular point. The resulting expressions are simple and have an obvious physical interpretation. In the limit as the surface becomes perfectly smooth, the expressions reduce to the image solution, thus ensuring conservation of energy.
A study on subcritical penetration into rough seafloor
Authors: Peng Linhui , Yu Gaokun , Lu Jianhui
Published: October 2011

Bragg scattering from rough interface of seafloor is one of the main causes of subcritical penetration of sound into seafloor. In this paper, the mechanism of subcritical penetration into rough seafloor is analyzed by Bragg scattering from sinusoidal fluctuation surface, and the condition that subcritical penetration can be induced is discussed. Because the refraction angle of minus order Bragg scattering waves is always smaller than refraction angle of Snell's penetration wave, the subcritical penetration attributes to the minus order Bragg scattering waves which propagate as normal plane wave below the critical grazing angle. So, in order to obtain the subcritical penetration, the minus order Bragg scattering wave should be considered detailed. The first order perturbation approximation is used for rough surface scattering usually. In this paper the validity of first order perturbation approximation for rough surface scattering is also checked by comparing the first order Bragg scattering wave with high order Bragg scattering waves.
Don't get caught with your mics open
Authors: Britton Deborah J.
Published: October 2011

Designing sound systems for legislative facilities often presents numerous challenges. From creating intelligible sound reinforcement and broadcast feeds in highly ornate, reverberant spaces to using digital signal processing to ensure that “off-the-record” side conversations are not made public, many different elements contribute to the final design. This presentation discusses a few of these specific challenges and how they were overcome.
Energy-based measurements in reverberation chambers
Authors: Leishman Timothy W. , Xu Buye , Sommerfeldt Scott D. , Eyring Nicholas J.
Published: October 2011

Standardized reverberation chamber measurements, including those of absorption coefficients, scattering coefficients, and sound power, rely on the acquisition and processing of squared acoustic pressure (or potential energy density) from many sound field locations. Kinetic energy density, total energy density, and the newly defined generalized energy density exhibit greater spatial uniformity in enclosed fields (especially at lower frequencies), which makes them more favorable quantities for these measurements. They produce greater accuracy or require fewer source-receiver positions to produce acceptable levels of accuracy. This paper explores their use and provides several analytical and experimental results to demonstrate their benefits.
Diffusion and scattering: An improved method of measuring both at the same time
Authors: Sauro Ronald
Published: October 2011

ISO-17497-1 and ISO-17497-2 describe methods of measuring the properties of diffusers and scattering devices. The result of these measurements is a description of the quality of the diffuser and the quantity of energy scattered. This paper will describe an improved method of measurement that enables both properties being simultaneously measured using the same procedure. The hope is that this method will produce a simplified database mimicking the directivity measurements of sound sources for use in simulation programs and in comparing various diffuser designs.
Predicting scattering at the mid-frequency range
Authors: Hart Carl R. , Lau Siu-Kit
Published: October 2011

Predicting scattering characteristics of isolated surfaces is problematic in the mid-frequency range, due to high computational costs. In the mid-frequency range, techniques such as the finite element method or the boundary element method require extremely fine mesh structures, leading to the solution of very large matrices. A gap exists for predicting acoustic scattering in the mid-frequency range with low computational costs. A geometric acoustic time domain method, incorporating diffraction, is proposed to bridge the gap in current prediction methods. The geometric acoustic method utilized is adaptive beam tracing. Adaptive beam tracing is advantageous, compared to other geometric methods, since it does not generate aliasing errors and faulty image sources, which are shortcomings of ray tracing and the image source method, respectively. The scattering characteristics of a periodic rigid geometry are investigated. Relationships between geometry dimensions and frequency of excitation are studied. Furthermore, the importance of accounting for single diffraction or multiple diffractions will be discussed. The spatial, temporal, and frequency characteristics of the scattering geometry are quantified.
Correlation detection of bat echolocation calls
Authors: Skowronski Mark D.
Published: October 2011

In an experiment comparing detection of echolocation calls between humans and automated methods, an optimal linear detector (matched filter) out-performed humans by 5 dB and model-based automated methods by 9 dB [Skowronski and Fenton, J. Acoust. Soc. Am. 125, 513–521 (2009)]. While optimal linear performance cannot be achieved in practice, near-optimal performance may be reached if the detection filter nearly matches the target calls. Bat calls from a species are fairly stereotypic, so designing a test call (or bank of test calls) for a correlation detector is feasible. Model-based detectors collect information over short analysis windows and piece that information together to form a detection decision, a bottom-up strategy that is good at collecting local information but poor at arranging local information to form a global detection decision. By contrast, a correlation detector operates at one time scale, the global call duration, and may be considered a top-down strategy of detection. The strengths and weakness of a correlation detector are discussed, including designing filters for a given species, the tradeoff between filter bank size (computational cost) and detector sensitivity, species classification, and the effect of filter bank size on false positive rate.
Matched-field processing and modal filtered range estimates of bowhead whale calls detected in the Alaskan Beaufort Sea
Authors: Thode Aaron M
Published: October 2011

In 2010, a 15-element autonomous vertical array was deployed roughly 35 km north of Kaktovik alongside a distributed array of directional autonomous seafloor acoustic recorders (DASARs). Matched-field processing and geoacoustic inversion techniques were used to extract the range, depth, bottom sound speed profile, density, and attenuation from one close-range whale call. The inversion localized the call at 1.2 km range and 44 m depth in 55 m deep water. The inverted propagation model was used to derive the group and phase velocities of the normal modes in the region surrounding the array. The vertical array spanned sufficient aperture in the water column to permit isolation of the first and second mode arrivals from any given call. A range- and frequency-dependent phase shift was applied to each modal arrival to remove geometric dispersion effects. The modeled range that time-aligned the modal arrivals was selected as the range estimate. The modal filtering technique is demonstrated on additional whale calls produced at 17.3 km and 35 km range from the vertical array, with the range estimates independently confirmed by triangulating bearings of call detections on surrounding DASARs. [Work supported by the North Pacific Research Board, Shell Exploration and Production Company, and Greeneridge Sciences Incorporated.]
Periodic metal structures for acoustic wave control
Authors: Norris Andrew
Published: October 2011

Passive control of acoustic waves, such as steering energy around an object (acoustic cloaking), requires non-standard materials. Either the density or the bulk modulus or both must be anisotropic. This explains why the phenomenon is not observed in nature. The focus of the talk is the design of metamaterials that have the desired anisotropic stiffness, with isotropic density. This is achieved by periodic metal lattices with sub wavelength cell size. The simplest example is “Metal Water” which is a foam-like periodic structure with the wave speed and density of water, and low shear modulus. The small shear is important in order to get the material to behave acoustically like water but is large enough to provide structural stability. When “deformed” the structure becomes anisotropic with the desired wave steering properties. The simple idea behind this class of acoustical metamaterial has simple consequence in design of cloaking devices, including the concept of conservation of cloaking space. These ideas will be explained and illustrated through scattering simulations.
Three-dimensional acoustic scattering by layered media: A novel surface formulation with operator expansions implementation
Authors: Nicholls David
Published: October 2011

The scattering of acoustic waves by irregular structures plays an important role in a wide range of problems of scientific and technological interest. This talk focuses upon the rapid and highly accurate numerical approximation of solutions of Helmholtz equations coupled across irregular periodic interfaces meant to model acoustic waves incident upon a multi-layered medium. A novel surface formulation for the problem is described in terms of boundary integral operators (Dirichlet–Neumann operators), and a boundary perturbation methodology (the method of operator expansions) is proposed for its numerical simulation. The method requires only the discretization of the layer interfaces (so that the number of unknowns is an order of magnitude smaller than volumetric approaches), while it avoids not only the need for specialized quadrature rules but also the dense linear systems characteristic of boundary integral/element methods. The approach is a generalization to multiple layers of Malcolm & Nicholls' Operator Expansions algorithm for dielectric structures with two layers. As with this precursor, this approach is efficient and spectrally accurate.
Optical imaging of bubbles
Authors: Matula Tom
Published: October 2011

Slow-motion imaging provides a useful way to image various phenomena, from ballistics to biomechanics to fluid dynamics. Such images lead to discoveries and better understanding of concepts. Our lab uses optical imaging to visualize bubbles under various conditions. The results of some of these images have resulted in paradigm shifts. For example, the famous “Crum bubble” showed clearly the formation and propagation of a liquid jet through a bubble. That image has led to numerous publications attempting to model jetting, and the liquid jet concept is now used extensively to explain various phenomena, including pitting of hardened materials and the destruction of kidney stones. In this paper, I will discuss typical imaging setups and provide examples of imaging bubbles under different conditions. Topics will include high-speed imaging, strobe imaging, and shock wave imaging. Phenomena will include sonoluminescence, snapping shrimp, and ultrasound contrast agents. [Work is supported by NIH NIBIB.]
Measurements of electrical transfer characteristics with soundcards as classroom activity
Authors: Paul Stephan , Dietrich Pascal
Published: October 2011

Measurements of transfer functions and impulse responses of different types of systems are an important part in acoustics and should be an integral part in acoustics education. Nevertheless, usually expensive equipment is required to carry out such measurements making it difficult to realize hands-on measurement classes. Contrarily the transfer characteristics of electrical systems can be measured much easier. Electrical systems and acoustics meet in electro-acoustic equipment such as soundcards, which can be found as onboard and external devices and in a wide variety. Input and output of soundcards can be connected by different types of transmission systems that might use different types of electrical circuits adding a variety of transfer characteristics. The inherent transfer characteristics of the given soundcard can be analyzed and compensated before assessing the transfer characteristics of different electrical circuits (black boxes). Thus, the experimental measurement of soundcards together with different black-boxes connected to them can be a good means to perform comprehensive measurements of IR and FRF. Using a MATLAB based measurement software, a measurement set-up has been developed to be used by students in a classroom experience. This contribution discusses the set-up, the results of the different scenarios measured and the feedback of the students.
Synthesis of new bowed-string sounds using physical models
Authors: Manoury Philippe
Published: October 2011

With a virtual bowed-string model, natural aspects of the sound and sound production, such as bow pressure, position, and velocity, control the realization of new synthetic sounds. It is the best way to resolve many problems in synthetic music involving phrasing, transitions, irregularity, and regularity. But what happens when you ask the model to simulate bow movements which are quite impossible for a human being? For example, to produce vertically an exaggerated pressure at the same time as an exaggerated slow motion of the bow across a string? That is even more interesting than to reproduce a simply natural acoustical sound.
Sound synthesis and musical composition with the physical modeling formalism Cordis-Anima
Authors: Cadoz Claude , Castagne Nicolas , Tache Olivier
Published: October 2011

The two historical starting points of Computer Music, in 1957, were digital sound synthesis, founded by Max Mathews (Bell Labs), and automatic composition, founded by Lejaren Hiller and Leonard Isaacson (University of Illinois). Digital sound synthesis and computer aided musical composition then developed and are today essential components of computer music. As said by Jean-Claude Risset, sound synthesis allowed to compose the sound itself. At the end of the 1970s, a new paradigm appeared, no more based on the synthesis of the sound signal, but on the simulation of the physical objects that produce the sound. The Cordis-anima language, created by Claude Cadoz and his colleagues Annie Luciani and Jean-Loup Florens at the ACROE lab, in Grenoble (France), is one of the most important representatives of this approach. We will present this language, which allows simulating the various components of a musical instrument, but also complex orchestras and dynamic objects with macro temporal behaviors. We will then demonstrate how this language enables linking sound creation and musical composition within a single and global paradigm using the GENESIS environment, created at ACROE for musical applications of Cordis-anima, and we will play extracts of musical pieces composed with GENESIS.
Individual expectations and noise policy in quiet residential settings
Authors: Timmerman Nancy S.
Published: October 2011

Consultants in the noise field tend to encounter the more sensitive individuals. These people may feel entitled to not hear anyone else. This paper will characterize the quiet acoustical setting, and consider the expectations of the more normal individuals. It quiet settings, it is as easy to be heard as to hear. The author, whose family owned a cottage in the Manistee National Forest in Michigan, will recount some personal acoustical observations from being there in the summer. This paper will also examine noise policies for these settings and look at “dB above ambient” as a criterion, since it is in use in Massachusetts, where this consultant practices. Illustrations will also be taken from clients of the author in western Massachusetts and in Maryland.
Simulations of self-organization of bubbles in acoustic fields in three dimensions
Authors: Gumerov Nail A. , Akhatov Iskander S. , Volkova Yekaterina V. , Agisheva Uliana O.
Published: October 2011

Self-organization of bubbles (structure formation) and related self-action of the acoustic field is a strongly non-linear phenomenon, which is observed, e.g., in acoustic cavitation and sonochemical reactors. The phenomenon is a manifestation of a two-way field-particle interaction, when the bubbles change their position and sizes due to the Bjerknes and other forces and rectified diffusion, and affect the acoustic properties of the medium, which leads to restructuring of the acoustic field. The models of this phenomenon available in literature are revised, and a model based on the spatio-temporal averaging, which includes the above mentioned effects, is derived. Based on this model, a 3-D pseudospectral code for simulation of bubble self-organization is developed and tested. Simulations show interesting spatio-temporal behavior of the bubbles and the acoustic field, which is initialized as a standing wave but may drastically change its structure due to bubble dynamics (especially near the resonance). Bubble pattern formation is sensitive to many parameters including parameters of the acoustic field, bubble initial size, number density, spatial distribution, and ambient conditions. The effects found in the result of simulations are discussed. [This research is supported by the Grant of the Ministry of Education and Science of the Russian Federation (G34.31.0040).]
Sonic boom structural response simulation of an historic structure
Authors: James Michael M. , Downing J. Micah , Garrelick Joel M.
Published: October 2011

The potential for structural damage from sonic booms can be assessed by using stationary sound sources. Such sources simulate sonic booms as incident, linear, and plane acoustic waves. In theory, the source simulates the pressure field on a structure arising from this incident wave, including influences from the surrounding acoustic environment. In practice, compromises must be made in the placement of the acoustical source and its orientation to the structure and the resulting change in the expected incident angle of a sonic boom. In this effort, we evaluated multiple structural elements of Fort Jefferson in the Dry Tortugas, Fl which ranged from structurally sound to fragile. The structural concern was damage to the more fragile elements from sonic booms generated in the surrounding airspace. The methodologies and results will be discussed. [Work sponsored by Naval Facilities Command, Southeast.]
Speak, memory—Wherefore art thou, invariance?
Authors: Greenberg Steven
Published: October 2011

Spoken language is highly variable, reflecting factors of environmental (e.g., acoustic-background noise, reverberation), linguistic (e.g., speaking-style), and idiosyncratic (e.g., voice-quality) origin. Despite such variability, listeners rarely experience difficulty understanding speech. What brain mechanisms underlie this perceptual resilience, and where does the invariance reside (if anywhere) that enables the signal to be reliably decoded and understood? A theoretical framework—DejaNets—is described for how the brain may go from “sound to meaning.” Key is speech representations in memory, crucial for the parsing, analysis, and interpretation of sensory signals. The acoustic waveform is viewed as inherently ambiguous, its interpretation dependent on combining data streams, some sensory (e.g., visual-speech cues), others internal, derived from memory and knowledge schema. This interpretative process is mediated by a hierarchical network of neural oscillators spanning a broad range of time constants (ca. 15–2 000 ms), consistent with the time course and temporal structure of spoken language. They reflect data-fetching, parsing, and pattern-matching involved in decoding and interpreting the speech signal. DejaNets accounts for many (otherwise) paradoxical and mysterious properties of spoken language including categorical perception, the McGurk effect, phonemic restoration, semantic context, and robustness/sensitivity to variation in pronunciation, speaking rate and the ambient acoustic environment. [Work supported by AFOSR.]
On the non-acoustic nature of acoustic invariants
Authors: Whalen D. H.
Published: October 2011

Various proposals have attempted to put speech targets into invariant “acoustic” form, sometimes with an additional transformation into “auditory” space. These targets, however, are not strictly acoustic. Targets for vowels, for example, are transformed so that vocal tract length differences (between talkers, especially across men, women, and children) are taken into account. Such a transformation makes the resultant targets combinations of articulatory and acoustic information. The auditory transformation improves automatic speech recognition, but the theoretical underpinnings for this result have been unclear. Ghosh, Goldstein, and Narayanan [J. Acoust. Soc. Am. 129, 4014–4022] shows that the articulatory information is maximized by the auditory transform, indicating that this transform is not solely in the acoustic domain. Moreover, a lowered F3 has been proposed as the production target for American English /r/ [e.g., Nieto-Castanon et al., J. Acoust. Soc. Am. 117, 3196–3212], but synthesis that retains an exemplary /r/ F3 while altering F1 and F2 results in other percepts, such as /w/ or a pharyngeal glide. F3 as an acoustic target is insufficient by itself and must incorporate articulatory dynamics implied by the other formants. Thus, “acoustic” invariants, to the extent they work at all, do so by incorporating articulation.
Modeling and tracking temporal fluctuations for underwater acoustic communications
Authors: Preisig James
Published: October 2011

High-rate, phase-coherent communications through the underwater acoustic channel requires implicitly or explicitly tracking the fluctuations of the channel impulse response. Current techniques estimate the time-varying channel impulse response using observations of signals that have propagated through the channel over some averaging interval and often rely on some method of representing the time variability in the channel. For example, the work by Stojanovic that enabled phase-coherent communications through the underwater channel represented the time-variation as a common phase rotation (Doppler shift) of all taps of the channel impulse response. The tracking of channel fluctuations involves a fundamental trade-off between the number of independent parameters used to represent both the channel impulse response coefficients (i.e., the dimensionality of the estimation problem) and their temporal variations, the rate of channel fluctuations that can be tracked, and the signal to noise ratio (SNR). This talk will present new and review established techniques for modeling time variability and reducing dimensionality in underwater acoustic channel. The performance of these approaches as a function of SNR and rate of channel fluctuation will be compared and their computational complexity will be discussed.
A wave-making towing tank for underwater communication in a multi-path environment using time reversal method
Authors: Too Gee-Pinn James
Published: October 2011

A 4 m × 8 m × 176 m wave-making towing tank, which is original, used for resistance measurement for boats is a perfect test platform for underwater communication in a multi-path environment. The objective in the present study is to establish a process of underwater communication in a multi-path environment using the time reversal method. The source projector sends out a BPSK signal, while the signal is received and processed in order to restore the original signal at the source by time reversal method. The communication process is conducted via both numerical simulation and experiment for cases of underwater communication in a 4 m × 8 m × 176 m towing tank. It is found that TRM process reduces the error rate of the transmission significantly and improves the communication quality in multi-path environment. [Works are supported by National Science Council of Taiwan.]
Dominant mode rejection beamformer notch depth: Theory versus experiment
Authors: Wage Kathleen E. , Buck John R. , Dzieciuch Matthew A. , Worcester Peter F.
Published: October 2011

The dominant mode rejection (DMR) adaptive beamformer attenuates loud interferers by directing beampattern nulls toward signals contained in the dominant subspace [Abraham/Owsley, Proc. Oceans, 1990]. The dominant subspace is defined by the eigenvectors associated with the largest eigenvalues of the sample covariance matrix. DMR performance is primarily determined by how closely the eigenvectors of the sample covariance matrix match the true interferer directions. Random matrix theory (RMT) describes how the accuracy of the sample eigenvectors varies with the interferer-to-noise ratio (INR), array size, and the number of snapshots used to estimate the sample covariance. A simplified analytical model based on RMT predicts the mean DMR notch depth as a function of INR, array size, interferer location and the number of snapshots. This talk compares the RMT predictions with experimental results obtained by cancelling array strum in data from a vertical array deployed in the Philippine Sea. The array strum interference predominantly falls within the subspace spanned by the first two eigenvectors of the covariance matrix. Notch depth statistics obtained using a large set of receptions show good agreement between theory and experiment. [Work supported by ONR.]
Integrated approaches to tracking in cluttered environments
Authors: Allen John S. , Pusey Grant , Gebbie John , Siderius Martin
Published: October 2011

A variety of acoustic applications encompass the detection and tracking of signals in highly cluttered environments. Despite the interdisciplinary nature of this problem, often novel approaches and advances are not well known and hence not typically applied outside their respective sub-fields. In this study, we highlight array processing, time frequency analysis and non-stationary signal processing techniques with respect to applications in both physical and underwater acoustics. In particular, we examine the acoustic tracking of small vessels, divers and AUVs in shallow water, harbor areas. An examination of the underlying physical acoustics of the ambient noise sources is a significant factor in the development of improved and novel tracking methods. Time scale filters are investigated for ambient noise reduction from snapping shrimp. The signal processing advantages of a combined two array systems in an L shaped configuration are discussed. Theoretical predictions and simulations are compared with experiments results from a synchronized system of two 24 element arrays deployed at the Kilo Nalu Nearshore Observatory (Honolulu, HI) near the Honolulu Harbor. Novel acoustic tracking techniques based on depth are explored with the two array systems. [Work sponsored by DHS.]
Tracking a defect in the multiple scattering regime
Authors: Thomas Planes , Eric Larose , Vincent Rossetto , Ludovic Margerin
Published: October 2011

We describe a time-resolved monitoring technique for heterogeneous media, especially multiply scattering media. Our approach is based on the spatial variations of the cross-coherence of diffuse waves acquired at fixed positions but at different dates. The technique applies to all kind of waves, but a particular attention will be paid to ultrasound propagating in concrete. To locate and characterize a defect occurring between successive acquisitions, we use a maximum likelihood approach combined with a diffusive propagation model. We quantify the performance of this technique called LOCADIFF with numerical simulations. In several illustrative examples, we show that the change can be located with a precision of a few wavelengths and that its effective scattering cross-section can be retrieved. We investigate how the accuracy and precision of the method depends on the number of source–receiver pairs, on the time window used to compute the cross-correlation and on the errors in the propagation model. Applications can be found in nondestructive testing (civil engineering), seismology, radar, and sonar location.
Variability in normal-incidence acoustic response in shallow-water marine sediments
Authors: Meredith Roger W. , Faas Richard W. , Lambert Douglas N.
Published: October 2011

Due to several processes, lateral deviations in geotechnical properties of sediments occur at many spatial scales and in all types of sediments. These deviations influence sediment bulk elasticity and density and determine the degree and type of acoustic response. Small changes in one or more properties can produce a wide variation in the acoustic response and empirical curve fitting most often serves as models for these relationships. Sedimentary data and acoustic variability at 30 and 50 kHz from three sites in the Mississippi Sound [Lambert et al., Mar. Geol. 182 (2002)] have been further analyzed and compared with the available Shepard's sediment classes. Initial observations revealed trends in sediment variability that affect the accuracy of sediment classifications based on acoustic response. This analysis deviates from traditional sediment classification schemes and utilized hierarchical clustering with user-selected combinations of geotechnical parameters to group individual sediment samples. The sediment properties are correlated with the acoustic coefficient of variation of the ensemble-averaged acoustic response and with the group-averaged acoustic response. The variability of sediment properties and acoustic response show varying degrees of correlation between parameters of major and minor importance.
Results of the development of a long-range acoustic homing system for autonomous underwater vehicles
Authors: Heard G. J. , Pelavas N. , Lucas C. E. , Fleming R.
Published: October 2011

Modified international submarine engineering (ISE) explorer AUVs with an endurance of over 400 km are being used to aid in the mapping of the under-ice Arctic seafloor. The explorers are equipped with a DRDC-developed acoustic homing system built into the AUV nose cone. The acoustic receiver consists of seven digital hydrophones arranged in a tri-axis cross-dipole array. A controller/data processor located within the AUV pressure hull handles the real-time acoustic arrival azimuth and elevation estimation, as well as the control and calculations for an on-demand short-range three dimensional (3-D) localization system, and the control of vehicle telemetry data flow. The processor and array consume less than 2 W. A small, easily transportable, DRDC-designed acoustic transducer provides a powerful acoustic homing signal. Using the homing system, the vehicles were able to locate an acoustic beacon at a randomly drifting Ice Camp from a range in excess of 50 km (100-km ranges possible). The design, development, and use of the homing system are described in this paper. In addition, on-going software improvements providing enhanced capabilities and system miniaturization are described.
Supervised machine learning for real time classification of underwater targets from sampled scattered acoustic fields
Authors: Fischell Erin M. , Schmidt Henrik
Published: October 2011

Autonomous underwater vehicles (AUVs) are often used for bottom surveys in the ocean, but the collected data is usually processed on shore. The ability to identify and classify targets while in flight would allow more effective use of mission time and reduce the need for additional surveys. It is demonstrated that geometry can be classified from hydrophone sampling of the scattering field off of a target in the presence of an acoustic source in real time simulation. Scattering field data for multiple target shapes is simulated using the OASES and SCATT software packages. This data is then used to produce training data sets for a support vector machine (SVM), a type of supervised machine learning that generates a classifying hyperplane. The trained SVM classifies new data, such as that collected by an AUV in a real or simulated scattered field, with minimal computation by comparing it to the hyperplane. The SVM also identifies divergence between target classes, allowing identification of regions where targets will look the most different to sampling, enabling optimized path planning for classification. This would allow a vehicle looking for a particular geometry to shift its search pattern to best identify relevant features.
Time-varying spatial spectrum estimation using a maneuverable sonar array
Authors: Odom Jonathan L. , Krolik Jeffrey L.
Published: October 2011

This paper addresses the problem of spatial spectrum estimation in dynamic environments with a maneuverable sensor array. Estimation of the time-varying acoustic field directionality is of fundamental importance in passive sonar. In this paper, mobility of the array is treated as a feature allowing for left-right disambiguation as well as improved resolution toward endfire. Two new methods for on-line spatial spectrum estimation are presented: (1) recursive maximum likelihood estimation using the EM algorithm and (2) time-varying spatial spectrum estimation via derivative-based updating. A multi-source simulation is used to compare the proposed algorithms in terms of their ability to suppress ambiguous array backlobes. A broadband method is presented utilizing knowledge of the source temporal spectrum. Detection performance of weak high-bearing rate sources in interference-dominated environments is evaluated for a flat spectrum. [This work was supported by ONR under grant N000140810947.]
Active acoustic treatment
Authors: Schwenke Roger W.
Published: October 2011

We call building materials “acoustic treatment” when they change the response of a room to sounds that occur in it. Absorption reduces the reverberation time of a room as well as strength. Reverberant chambers increase the cubic volume of the room and increase the reverberation time without significantly changing the strength. Diffusion changes the distribution of reflections in time and level. Electro-acoustic systems using microphones, signal processors, and speakers can also be used to change the response of a room to the sounds that occur in it. This paper will illustrate many ways that Electro-acoustics can be thought of as an active acoustic treatment—one of the many acoustic treatments acousticians have in their palette to achieve their design goals.
Acoustic characteristics of floor treatments for elementary school classrooms
Authors: Lesser Ari M. , Wells Adam P. , Vigeant Michelle C. , Celmer Robert D.
Published: October 2011

Phase 1 of this study [J. Acoust. Soc. Am. 129(4), 2523 (2011)], determined the effects of hard versus soft flooring on overall speech and activity noise levels in elementary classrooms. A significant decrease in overall levels was found in carpeted rooms. This phase sought to investigate a range of floor materials and their pertinent properties. Nine different floor materials were mounted to 3 in. concrete slabs and evaluated using a battery of acoustic, impact, and chair scrape tests. Tested materials included vinyl composition tile, resilient rubber athletic flooring (virgin, blended/synthetic, and recycled), polyurethane, vinyl cushion tufted textile carpet, and rubber-backed commercial nylon carpet. Impedance tube measurements of sound absorption were made using International Organization for Standardization (ISO) 10534-2, while sound power measurements according to ISO 3741 were made while either (a) tapping on each mounted sample with a standard tapping machine or (b) while reciprocating an elementary classroom chair back and forth to produce repeatable scraping sounds. In general, the two carpet samples resulted in the lowest sound levels and the highest absorption. The relative performance of each material will be presented along with a discussion of additional usability factors, such as maintenance, cost, and durability. [Work supported by Paul S. Veneklasen Research Foundation.]
Perspective of tomography inversion using direction-of-arrival and direction-of-departure
Authors: Aulanier Florian , Nicolas Barbara , Roux Philippe , Mars Jèrôme
Published: October 2011

In the ocean, local sound speed variations induce acoustic path changes. Travel-time (TT) variations of acoustic paths are classically used to perform ocean tomography inversion. Initially introduced to cope with multi-arrival interferences and to separate eigenray paths, source–receiver arrays combined with array processing techniques now give access to new observables that could be used for tomography such as direction-of-arrivals (DOAs) and direction of departure (DOD). The cumulative use of TT, DOA, and DOD in the inversion process first requires to study the forward problem which links sound speed variations to these observables measured through array processing from two source–receiver arrays. The so-called sensitivity kernels are established using (1) the first order Born approximation that relates the sound speed variation to the amplitude and phase change of the perturbed received signal and (2) a first order Taylor development which links the received signal perturbations to the relevant observables. In the present work, theoretical TT, DOA, and DOD sensitivity kernels are compared with parabolic equation simulations and tank experiment estimations.
Passive matched-field inversion using a horizontal planar array
Authors: DelBalzo Donald R. , Leclere James H.
Published: October 2011

Shallow-water acoustic predictions are severely limited by uncertainty in sediment property characteristics. Inverse methods with controlled active sources and vertical arrays have been used to estimate seabed properties; however, some applications require a covert approach and horizontal bottomed arrays. This study addresses the accuracy of low-frequency (100–200 Hz) matched-field correlations using broadband signals from surface ships with unknown source levels at unknown ranges. Matched-field techniques are applied in a realistic shallow-water environment with a horizontal planar array and high signal-to-noise ratios. The simulations indicate significant potential for accurate estimates of thick-sediment characterizations of grain size out to ranges of tens of water depths in shallow water, despite moderate mismatch conditions in the environmental model. The results show that: (1) the horizontal aperture should contain at least three hydrophones per wavelength to ensure high quality inversions; (2) the horizontal aperture should be several times longer than a vertical aperture; (3) coherent (phase-only) matched-field processing outperforms standard intensity processing by about 2 dB in good input SNR conditions; (4) incorrect assumptions about the assumed sound-speed profile (e.g., incorrect mixed-layer-depth) do not significantly affect the inversion results. [Work sponsored by QinetiQ North America.]