bluuebunny/crossref_metadata_2025 huggingface dataset:
Vocal tract normalization in articulatory space using thin-plate spline method
Authors: Wei Jianguo , Dang Jianwu
Published: May 2008

Inter-subject normalization is a key issue of group analysis of articulatory data to obtain a general description of kinematic properties of human speech production. Multisubject articulatory study however is scarce due to the difficulty of normalization in articulatory domain. In order to reduce intersubject variations among articulatory space, a simple normalization procedure was proposed using a Thin-plate spline method. The purpose of this normalization processing is to reduce the morphological differences of vocal tracts such as shape and size among different subjects. Nonlinear factors of the reduction are considered in this normalization procedure. The electromagnetic Articulographic (EMMA) data were used in our experiments, which were obtained from the NTT EMMA database for three subjects data included. A physiological articulatory model has been used to serve as the template. The landmarks were defined consistently in vocal tract space over the template and all subjects. The evaluations showed that the variances over subjects have been reduced 2.1 mm for consonants and 2.3 mm for vowels averaged over all tongue pellets.
A comparison of coarticulation in conversational and clear speech
Authors: Andruski Jean E.
Published: May 2008

Coarticulation may either hinder speech perception by increasing variability and altering the distinctive features of speech sounds, or enhance speech perception by providing additional cues to nearby sounds and spreading these cues out over time. This study examines the clear and conversational speech of 16 English speakers (8 females and 8 males) to compare the amount of coarticulation in clear and conversational speech when distinctive features are changed, as opposed to when nondistinctive features are changed. Devoicing of voiced fricatives and voicing of /t/ are investigated as examples of distinctive feature changes. Vowel nasalization and lip rounding in /s/ and /z/ are examined as examples of nondistinctive feature changes. Percentage of voicing during frication noise is used as a measure of fricative devoicing; voice onset time and percentage of voicing during the closure are used as measures of voicing in /t/; amplitude of the nasal formant and nasal formant onset time are used as measures of vowel nasalization; and center of gravity of the final 50% of the frication noise is used as a measure of lip rounding in /s/ and /z/. Results are compared across clear and conversational speech and across speaker gender. Individual speaker differences are also examined.
Transforming modal voice into irregular voice by amplitude scaling of individual glottal cycles
Authors: Bőhm Tamás , Audibert Nicolas , Shattuck-Hufnagel Stefanie , Németh Géza , Aubergé Véronique
Published: May 2008

Irregular phonation can serve as a cue to segmental contrasts and prosodic structure as well as to the affective state and identity of the speaker. Thus algorithms for transforming between voice qualities, such as regular and irregular phonation, may contribute to building more natural sounding, expressive and personalized speech synthesizers. We describe a semiautomatic transformation method that introduces irregular pitch periods into a modal speech signal by amplitude scaling of the individual cycles. First the periods are separated by windowing, then multiplied by scaling factors, and finally overlapped and added. Thus, amplitude irregularities are introduced via boosting or attenuating selected cycles. The abrupt, substantial changes in cycle lengths that are characteristic of naturally-occurring irregular phonation can be achieved by removing (scaling to zero) one or more consecutive periods. A freely available graphical tool has been developed for copying stylized pulse patterns (glottal pulse spacings and amplitudes) from an irregular recording to a regular one, allowing the scaling factors to be refined and the waveform regenerated interactively. We present the effects of the transformation on harmonic structure, and perceptual test results showing that transformed signals are similar to natural irregular recordings in both roughness and naturalness.
Landmark-based analysis of sleep-deprived speech
Authors: Boyce Suzanne , Macauslan Joel , Bradlow Ann , Smiljanic Rajka
Published: May 2008

The speech of sleep-deprived persons has been variously described as more “slurred” or “tired-sounding” than speech by the same speakers in a rested condition. Although sleep deprivation is a major focus of research for public safety and health reasons, there has been notably little research on the connection between sleep deprivation and speech. Using an automatic system for detecting “landmarks”, i.e., important perceptual and articulatory events in the acoustic signal, we compared sleep-deprived and rested speech recorded during two well-controlled studies of sleep deprivation. Our results show that sleep-deprived speech is significantly different from rested speech for both the number and pattern of landmarks detected. These results are similar in detail to differences previously found between clear and conversational styles of speech. The relevance of these findings for speech as a marker of sleep-deprivation will be discussed, along with potential applications in public safety and health. [Research supported by NIH.]
Correlations among three audiovisual (AV) speech tasks
Authors: Irwin Julia , Brancazio Lawrence
Published: May 2008

Visual speech information influences what listeners hear. When the place of articulation of visual and auditory speech tokens are incongruent, perceivers often report hearing a visually influenced response (the “McGurk effect”, McGurk and MacDonald, 1976). However, individual differences in this visual influence are poorly understood. Extending work by Grant & Seitz (1998) and Conrey and Pisoni (2006), we examined correlations between susceptibility to the “McGurk effect” and performance on three related audiovisual tasks. (1) AV speech in noise: we assessed visual gain by comparing word identification in audio-only and AV conditions. (2) AV asynchrony detection: Participants made asynchrony judgments of speech and nonspeech stimuli with asynchronies ranging from +250 ms visual to +250 ms auditory lead. The speech stimuli were CV syllables and the nonspeech stimuli consisted of lissajous circles paired with sine waves. In one set of nonspeech stimuli, the lissajous was modeled on the lip aperture of the CV and the sine wave, amplitude and frequency were derived from the CV. For the other set, the lissajous and sine wave were derived from clapping hands. (3) Speechreading: Participants identified isolated words presented visually. Factors associated with a strong McGurk effect will be discussed. [Work supported by NIH.]
Sustained and transient brain activations in bilingual control
Authors: Wang Yapeng , Kuhl Patricia K. , Li He , Dong Qi
Published: May 2008

Behavioral and neuroimaging evidence shows that bilinguals experience interference and competition during bilingual processing. The neural basis of bilingual language control is not well understood. Using mixed blocked and event-related design, the present study explored the sustained and transient activations during bilingual control. 15 Chinese-English bilingual speakers were scanned when they performed language switching tasks. The results showed that, compared to single language condition, the mixed language condition (sustained control) induced the activation in the bilateral prefrontal (BA6/BA8/BA10), middle frontal (BA45/46) and parietal lobes (BA7/ BA40/BA49); In contrast, relative to the no switch condition, language switching (transient control) activated the left superior, inferior parietal lobe (BA2/ BA40) and middle frontal (BA11/46). These results suggested that sustained and transient language control induced differential lateral activation patterns.
Automatic acoustic analysis of substitute speech characteristica by speech recognition technique
Authors: Schuster Maria , Maier Andreas , Haderlein Tino , Eysholdt Ulrich , Noeth Elmar
Published: May 2008

Tracheo-esophageal (TE) substitute speech is often used after total laryngectomy as it resembles normal speech more than other substitute speech methods. However, TE speech still shows restrictions and is perceived as hoarse, rough, with strain, and usually monotone, e.g., due to augmented irregularity of the voice signal. Commonly used diagnostic tools to describe the acoustic properties of TE speech are mostly not applicable. Before, automatic speech recognition has been shown to serve as a appropriate acoustic tool for the quantification of TE speech intelligility. We now applied an automatic speech recognition system with prosody module on speech data of 41 laryngectomees. The prosody module extracted 150 parameters. Factor analysis revealed five principal components. They show high correlation to perceptively described TE speech characteristica. Automatic prosody analysis by speech recognition technique allows to detect and quantify characteristics of highly disordered speech.
High rate acoustic communications based on orthogonal frequency division multiplexing
Authors: Stojanovic Milica
Published: May 2008

Orthogonal frequency division multiplexing (OFDM) offers simplicity of FFT-based implementation with frequency-domain channel equalization, and has emerged as a standard in many terrestrial systems. Its application to underwater systems, however, is challenged by the motion-induced Doppler distortion, which creates nonuniform frequency offset in a wideband acoustic signal. To counteract this problem, recent research has focused on synchronization methods, demonstrating the feasibility of wideband OFDM in initial sea trials. We consider the design of a complete OFDM receiver based on three key techniques: adaptive carrier tracking, spatial diversity combining, and sparse channel estimation. In particular, we focus on time-domain channel estimation, which provides a natural platform for channel sparsing. Sparsing of the impulse response, or discarding of its insignificant coefficients, is shown to offer performance gains on acoustic channels, since they are often naturally sparse. Decision-directed operation, which is made possible by adaptive carrier tracking, yields a low overhead, and further improves the performance of channel estimation beyond that of nonadaptive pilot-based schemes. The technique proposed is applied to experimental data recorded in a shallow water channel over 1 km. Results show excellent performance of coded OFDM signals, transmitted in the 19-31 kHz band with a varying number of subcarriers.
Experimental assessment of time-reversed OFDM underwater communications
Authors: Gomes Joao , Silva Antonio , Jesus Sergio
Published: May 2008

OFDM communication has recently been demonstrated in underwater channels at rates exceeding 7 kbps. This is a popular modulation in wireless communications due to its flexibility for spectrum management and the simplicity of transmitters/receivers. Despite widespread interest, experimental data on the performance of underwater OFDM are scarce. This work aims to contribute to a better understanding of this technique by examining results from the UAB'07 experiment, conducted in Norway in September 2007. Data were transmitted in a fjord using several formats with bandwidths of 3 and 7.5 kHz, and recorded at a range of 800 m in a 16-hydrophone array. Significant multipath was observed over at least 40 ms, which would call for a rather large OFDM prefix/guard interval and hence drastically reduce the data rate. Passive time reversal is used here as a computationally inexpensive scheme to shorten the channel length to less than 10 ms, so that moderate guard intervals can be used with a conventional OFDM receiver. The same preamble/postamble signals used for synchronization and Doppler precompensation are reused as probes for passive time reversal, so the latter entails no loss in efficiency. The performance of time-reversed OFDM is compared with plain QPSK modulation using either time reversal or multichannel equalization at the receiver.
Linear and circular adaptive beamforming arrays for high bandwidth acoustic communications
Authors: Neasham Jeffrey , Howarth David , Sharif Bayan , Hinton Oliver
Published: May 2008

This paper will discuss the development of a new generation of high bandwidth (up to 32 kbits/s) underwater communication products for ranges up to 4 km. Multipath propagation is the dominant factor in system performance in both shallow water, horizontal channels and deep water, vertical channels. The properties of such channels will be analysed and the design of both linear and circular receiver arrays will be discussed to maximise reliability. We will then describe how these arrays are combined with the latest “software” receiver principles to create a powerful and flexible system, incorporating adaptive signal processing with minimal hardware complexity. Finally the performance of this system will be illustrated with results from experimental trials.
Investigation of modal processing for low frequency acoustic communications in shallow water
Authors: Morozov Andrey , Preisig James , Papp Joseph
Published: May 2008

Acoustic receptions at a vertical line array collected during the SW06 experiment were processed to show the feasibility of broadband mode decomposition as a preprocessing method to shorten time-spread and concentrate received signal energy in a small number of independent channels. The vertical array spanned the water column from 12 m depth to the bottom. PSK m-sequence modulated signals with different carrier frequencies were transmitted from a distance of 19.2 km. Signals were processed for both the case of ordinary internal waves activity and the case with abnormally strong internal wave solitons. The measured sound velocity and known bottom properties were accounted for. Mode filtering was based on a broadband pseudo-inverse processing of the received VLA signals. The broadband mode filtering decomposed the received signal into a number of independent signals with a reduced time-spread. The constellation of signals from the output of mode filters showed that a simple demodulator can achieve a high quality reception. Even during strong internal waves activity the acoustic energy was concentrated in a small number of the first acoustical modes. The receiver estimated the mode-time intensity distribution and used the strongest modes for demodulation. High quality reception is demonstrated with the data.
Very broadband high frequency underwater acoustic communications
Authors: Freitag Lee , Singh Sandipa , Ball Keenan
Published: May 2008

Many new applications for underwater observatories and sensor systems do not require long ranges, but do require very power-efficient, high-throughput communications. Recent work in phase-coherent underwater acoustic communications has shown that signal bandwidths of 10-40 khz at carrier frequencies from 80 to 120 khz may be used to achieve throughputs of up to 80 kbps at ranges of 100-500 m in shallow water. The work has included channel impulse response measurements over time and with respect to range, and application of the adaptive decision feedback equalizer using signals at multiple bandwidths. The broadband, high-frequency propagation environment is characterized, and its impact on the reliability of very wide band signals (relative to the signal carrier) is presented.
Experiments of wideband color image transmission
Authors: Ochi Hiroshi , Watanabe Yoshitaka , Shimura Takuya , Hattori Takehito
Published: May 2008

In JAMSTEC, we have been studying about a high-speed underwater acoustic communication for color image transmission from underwater vehicle of deep water. The objective of our research is to transmit a JPEG compressed color image within once a second. Experiments were carried out at the depth of 1000 m area. The distance of transmission was 250 - 600 m. Four omni-directional hydrophones were used for receiving. QPSK and 8PSK were used as its modulation method. The four-channel decision feedback equalizer with phase compensator was applied for the demodulation algorithm. Because of this experiment was carried out at deep sea environment, the communication channel characteristics was relatively simple. In these experiment, when the SNR was higher than 12 dB, error free communication was carried out in case of QPSK. And also when the SNR was higher than 20 dB, error free communication was carried out in case of 8PSK
Spatial and temporal variations in acoustic propagation in Dabob Bay during PLUSNet'07 Exercise
Authors: Xu Jinshan , Lermusiaux Pierre , Haley Patrick , Leslie Wayne , Logutov Oleg
Published: May 2008

We present spatial and temporal variability of the acoustic field in Dabob Bay during the PLUSNet'07 (Persistent Littoral Undersea Surveillance Network) Exercise. The study uses a 4D (3D in space plus 1D in time) data-assimilative numerical ocean model to provide inputs to an acoustic propagation model. The Havard-Ocean-Prediction-System with in-situ CTD measurement assimilation provided output forecasts with a 300-m and 1-to-5-m resolution in the horizontal and vertical direction, for a 3-h interval within a 15-day period. This environmental data as the input to acoustic modeling allowed prediction and study of the (semi-)diurnal temporal variations of the acoustic field, as well as the varying spatial structures of the field. Using the one-way coupled-normal-mode code, along- and across-sections in the Dabob Bay acoustic field structures at 100, 400, and 900 Hz were forecasts and studied for various source depths. Interesting propagation effects such as the acoustic transmission-loss fluctuations with respect to the source depth and frequency as a result of the regional ocean variability, wind forcing, and tidal effects are discussed. The novelty of this work lies in the accuracy of the acoustic transmission-loss prediction in the littoral region by physically coupling the real-time ocean prediction system to acoustic modeling. This work also offers a potential extension to a 4D acoustic modeling.
On shallow water ocean acoustic tomography system based on parametric arrays physical properties evaluation
Authors: Semenov Andrew
Published: May 2008

Unsophisticated acoustic tomography system properties using envelope of radiated acoustic signal for ocean long-range inhomogeneities control, presumably, in most unfavorable, in the author view, shallow water regions, are evaluated. Unique solution to be used there is a narrow directional parametric radiation array. When pump wave signal decay range to array Frauengopher zone dimension ratio exceeds pump wave frequency to radiated signal frequency ratio, parametric radiation array operation model turns to “horn” model instead of “traveling wave” model conventionally used for consumed power prediction. For utmost distance achievement both ends of tomography system should be designed as narrow directional parametric arrays working on optimal frequency basic propagation (first) mode. For instance, signal optimum frequency 40 Hz. is shown to be necessary for model inhomogeneity (100 m long cylinder) control on 500-km radiation array distance in water layer of depth 200 m with unfavorable attenuation properties. Major lobe solid angle should be chosen not wider than 0,03 radians. Array frequency ratio is advised to be of an order of 10, while array length - 100 half wavelength for pump sound field frequency. Then estimate of power consumption looks like 180-200 kWt of pump signal acoustic power.
The analysis of underwater environmental factors in relation to the harbor protection in Tzoin-Kaohsiung areas
Authors: Liu Jin-Yuan , Huang Chen-Fen
Published: May 2008

Harbor is an important shipping traffic area. The intrusion or threatening by outsiders in the harbor area will certainly cause great panic of the society, and therefore, the protection of harbor and its nearby water is utterly important. The Tzoin harbor is primarily serviced for navy, and is under planning for further expansion. Therefore, a complete control of the Tzoin-Kaohsiung marine environment, both geographical and acoustical, is necessary for military applications. The purpose of this study is to conduct a complete survey of the environment in the designated area, covering the first seaway of the Kaohsiung harbor and off coast water of the Si-Tze bay area. The survey of the marine environment includes seafloor topography, morphology, subbottom profile, waves, currents, and wind fields. In acoustic aspect, the survey emphasizes the harbor ambient noise measurement. The data obtained shall be thoroughly examined and analyzed. The results provide a foundation for future underwater experimental studies, including target localization, geoacoustic inversion, and active sonar reverberation.
Classification of angular backscattered responses obtained at sea with a forward looking sonar system
Authors: Cervenka Pierre , Marchal Jacques
Published: May 2008

The prototype of a multibeam front-scan sonar has been developed within the frame of a MAST contract (n° MAS3-CT97-0090 DG12-ESCY, acronym COSMOS). A large amount of data has been collected at sea. With the forward looking geometry of acquisition, the foot-prints of successive pings overlap largely, so that most parts of the surveyed areas are seen under a large range of incidence angles. It gives the capability to derive the local angular response of the bottom, which is indeed an important information for characterizing the nature of the seafloor. This presentation addresses the successive steps that were undergone to classify the backscattered responses: Data are conditioned to perform principal component analyzis; an original clustering identification process is also described; resulting maps are finally presented.
Acoustic scattering by deformed elongated objects: bent or rough finite cylinders, bent edges, and other stuff
Authors: Stanton Timothy K. , Chu Dezhang , Norton Guy
Published: May 2008

Predicting acoustic scattering by deformed elongated objects remains a challenge as there are no exact analytical solutions. Numerical solutions are also challenged through various computational issues. In this research, we have developed and applied an approximate analytical approach for predicting scattering by various deformed elongated objects, including bent or rough finite cylinders and deformed edges. The formulation is based on a line integral in which the scattering or diffraction per unit length of the exact solution to an infinitely long, straight undeformed object is integrated along the length of the finite-length deformed object, accounting for variations along the length of phase and certain local properties of the object. Predictions concerning various types of deformed finite cylinders are first discussed (including Stanton, J. Acoust. Soc. Am. 86, 691-705 (1989) and subsequent papers), followed by recent predictions concerning deformed finite edges (Stanton et al., J. Acoust. Soc. Am. 122, 3167-3176 (2007)). These latter predictions using the approximate line integral compare favorably with predictions based on the T-matrix numerical method, which is formally exact. Also discussed are: dependences upon length, orientation, bend, and roughness; comparisons with experimental data concerning machined objects and marine life; and range of validity of the approach.
A review of the scattering properties of suspended sandy sediments for the application of acoustics to sediment transport studies
Authors: Thorne Peter D. , Meral Ramazan
Published: May 2008

Multi-frequency acoustics backscattering has been used for over a decade, to quantitatively measure, in the marine environment, near-bed profiles of suspended sediment particle size and concentration. Central to obtaining the sediment parameters from the backscattered signal, is a description of the scattering properties of irregularly shaped particles randomly distributed in space. Formulations are therefore required for both the attenuation and backscattering properties of suspensions of sedimentary particles with size and acoustic frequency. There is no rigorous analytical solution or single formulation for these scattering properties and different researchers have used somewhat different expressions. However, all these expressions are based on a variation of sphere scattering, modified to fit available scattering data. Here we bring together four decades of published data on the acoustic scattering properties of suspensions of sandy sediments. These data are reformulated in terms of the usual acoustic scattering nomenclature, that is the form function and the normalised total scattering cross-section and simple heuristic generic expressions, based on a sphere scattering model, are formulated to describe the sediment scattering properties. The expressions are not limited to sand particles, but should have broad applicability to irregularly shaped particle scattering.
On the angular dependence of sound scattering from natural sand in turbulent suspensions
Authors: Hay Alex E. , Moore Stephanie A. , Paul Wesley
Published: May 2008

We report on measurements of the variation with scattering angle of the differential scattering cross section of particles embedded in turbulence. The experimental apparatus consists of a turbulent round water jet carrying the particles, and a pair of broadband MHz-frequency transducers operating as transmitter and receiver and arranged in a bistatic geometry centred on the jet axis. The purpose of the jet is to confine the scatterers within a restricted range interval and thereby eliminate the need to correct the signal for attenuation due to scattering along the transmit and receive paths. Measurements were made at scattering angles between 90 and 170 degrees, for both natural sand grains and spherical glass beads in narrow size distributions with median diameters ranging from 200 to 500 μm. Particle size distributions were determined using different methodologies to obtain both volumetric and projected area estimates of equivalent spherical size. The results are compared to the theory for scattering by a solid sphere. Implications regarding the choice of equivalent sphere size for sound scattering by natural sand grains in suspension are discussed.
Acoustic scattering from double-diffusive microstructure
Authors: Lavery Andone , Ross Tetjana
Published: May 2008

Laboratory measurements of high-frequency broadband acoustic backscattering (200-600 kHz) from the diffusive regime of double-diffusive microstructure have been performed. This type of microstructure, which was characterized using direct microstructure and optical shadowgraph techniques, is identified by sharp density and sound speed interfaces separating well-mixed layers. Acoustic backscattering measurements were performed for a range of physical parameters controlling the double-diffusive microstructure. The echoes have been analyzed in both the frequency domain, providing information on the spectral response of the scattering, and in the time domain, using pulse compression techniques. High levels of variability were observed, associated with interface oscillations and turbulent plumes, with many echoes showing significant spectral structure. Acoustic estimates of interface thickness, obtained for the echoes with exactly two peaks in the compressed pulse output, were in good agreement with estimates based on direct microstructure and optical shadowgraph measurements. Predictions based on a one-dimensional weak-scattering model that includes the actual density and sound speed profiles agree reasonably with the measured scattering. A remote-sensing tool for mapping oceanic microstructure, such as high-frequency broadband acoustic scattering, could lead to a better understanding of the extent and evolution of double-diffusive layering, and to the importance of double diffusion to oceanic mixing.
Towards an understanding of how a synthetic aperture sonar images buried targets
Authors: Gough Peter T. , Hayes Michael
Published: May 2008

One of the useful features of synthetic aperture sonar (SAS) is that in the reconstructed image, the cross-track resolution is inversely proportional to the bandwidth and the along-track resolution is proportional to the transducer's along-track extent and that these are more or less independent of the center frequency. An unexpected aspect of SAS imaging so far is that objects buried in sand/sediment are sometimes visible even at geometries where the incident angle far exceeds the critical angle for the bulk materials. It is surmised that the roughness of the sea/sea-floor interface is the significant contributing factor. So as an adjunct to the main Kiwi SAS programme, a seafloor “document” camera colocated with a three-transducer active sonic probe has been designed and deployed in controlled circumstances. The intention is to estimate the critical parameters that best describes the roughness of the sea floor and perhaps how these parameters relate to the way the SAS images shallow buried targets. In regions of reasonable visibility, the camera is used to provide ground-truth. The paper details the construction of the camera and sonic probe as well describes some preliminary results using smooth and raked sand.
Imaging buried objects using synthetic aperture processing
Authors: Schock Steven
Published: May 2008

FM sonar generates images of buried objects using synthetic aperture processing. A spherical projector illuminates objects buried in the seabed out to the range associated with the critical angle. Scattering off buried targets is measured with one meter long line hydrophone arrays embedded in sonar vehicle wings. The histories of the projector and hydrophones positions, used for compensating acoustic data during synthetic aperture processing, are calculated based on navigation data provided by an inertial measurement unit and Doppler velocity log. Three orthogonal image projections of the seabed containing 5, 7.5, 10, and 15 cm diameter cylinders, buried up to 30 cm in seabeds consisting of sand and sandy mud in three meters of water, show the burial depth and orientation of the cylinders. The temporal resolution of the imagery is approximately 6 cm. The azimuthal resolution varies between 5 and 20 cm and is a function of target range and relative bearing with respect to the sonar vehicle. This imaging technique can be applied to marine archeological investigations in water depths of two meters and greater.
Seafloor Geodetic Networks for monitoring tectonic plate motion and deformation
Authors: Peroutsea Stavroula , Doukakis Efstratios
Published: May 2008

This paper argues that seafloor geodetic networks, monitoring tectonic plate motion and deformation, supplementing terrestrial geodetic networks, can provide important information for the understanding of crustal processes, globally. The proposed monitoring system consists of three main components: real-time kinematic-differential GPS ship positioning, precise acoustic ranging between ship and seafloor transponders - which establish the network nodes- and near-bottom direct acoustic measurements of the network baselines. The coordinates of the transponders in a goedetic reference system can be determined from these observations and a sound-speed structure model. The motion and deformation of the tectonic plate can be traced as a change of coordinates and/or the internal geometry of the network. Stochastic and mathematic models, algorithms and data analysis are crucial for achieving the necessary accuracy in such a demanding process regarding seafloor position estimation.
Confined deep water acoustic noise study within the Bahamian TOTO
Authors: Deveau David
Published: May 2008

The three-sided deep coral reef that borders Andros Island, Bahamas is populated with deep water acoustic sensors that presents a unique opportunity to study the impact of wind and wave in a physical environment with limited man-made noise sources over a wide acoustic band (50-40 kHz). This area is known as the “Tongue of the Ocean” (TOTO) for its unique satellite viewed shape. The region's deep acoustic channel (∼1550 m) is surrounded by steep walls and only one outlet suggesting a highly reverberant cavity where weather produced ambient noise signatures may persist over greater periods producing levels greater than typically observed in the open ocean. In this study, daily acoustic spectra are gathered on two sensors spaced 20 km apart with accompanied wind and weather information. The spectra will be correlated to advancing and receding weather fronts in an effort to relate the surface changes to the deep water ambient noise levels. This study also serves as a precursor to a shallow water acoustic noise intensity study where similar weather comparisons will be made and compared to the deep water counterpart.
Basic at-sea experiment for long horizontal time-reversal communication in deep ocean
Authors: Shimura Takuya , Watanabe Yoshitaka , Ochi Hiroshi , Hattori Takehito
Published: May 2008

In our research program, a long cruising autonomous underwater vehicle (AUV) has been developed and a project on a second AUV is planned, for wide-areal observation in the deep ocean. In such AUV operation, it is preferred to ensure acoustic communication with AUV even at low data-transmission rate. Time-reversal techniques have a possibility to achieve such long horizontal communication. We have proposed a method of combining time reversal and an adaptive equalizer to realize communication even with a sparse time-reversal array (TRA) and communication with a moving target. To verify the performance of such time-reversal communication, at-sea experiments were executed at the various distances. In the experiment of 10 km at a water depth of 1000 m, bidirectional time-reversal communication between the focus point and TRA was achieved successfully and the effects of the TRA depth and its channel number are investigated. In the experiments of 20, 30, 40 km at the slight sloping area, the performance on the distances are discussed. In the experiment of 100 km at a water depth of 4000 m, the convergence by passive time reversal was verified.
Optimal placement of array elements for time-reversal mirror
Authors: Joo Jae Hoon , Kim Jea Soo
Published: May 2008

In the application of time-reversal mirror (TRM) to the underwater acoustic communication, the optimal placement of the transmit/receive array can enhance the signal-to-noise ratio at the foci when a number of array elements is limited. In this presentation, the optimal location of individual elements is determined by maximizing contrast between the focal location and the area of interest using genetic algorithm. As a result of optimization, the contrast as well as the intensity at foci is increased when compared to the conventional TRM. The optimal number of array elements is also investigated based on the objective function of genetic algorithm in connection with finding optimal placement of array. Numerical examples for TRM and contrast-maximization are presented and discussed.
Characterization of long-range time-varying underwater acoustic communication channels
Authors: Smedsrud Morten , Jenserud Trond
Published: May 2008

We present communication channel characterizations performed on in-situ measurements from the Baltic and North Sea. The communication channels were probed using pseudorandom binary sequences (PRBS), obtaining time-variant channel impulse responses through wideband matched filtering. Characteristics central to communications were obtained. Included are: scattering functions, coherence-times and coherence bandwidths. The validity of the quasi wide sense stationary uncorrelated scattering (quasi-WSSUS) assumption was also investigated for the measured channels. Measurements were acquired in the joint European project “UUV Covert Acoustic Communications.” The project aims to design an acoustic communication system between an unmanned underwater vehicle (UUV) and a support mother ship. The first sea trials of the project focused on the acquisition of noise and long-range, low-frequency communication channel data for the explicit purpose of building an acoustic channel simulator.
A novel architecture for multihops routing ad hoc underwater acoustic sensor networking
Authors: Diamant Roee , Sinai Azriel
Published: May 2008

Underwater acoustic communication networks are an innovative issue, which faces difficult medium problems, such as long propagation time and dynamic network topology. In addition, due to high error probabilities typical for this channel it is preferred to use anti collision network mechanism. Because of the long propagation time, methods such as CTS/RTS, requiring transmissions of pre-messages, achieve relatively low network efficiency. Moreover, TDMA methods do not utilize the network resources allowing reuse in the code domain (using CDMA) and in the spatial domain in case of nonhomogenic network topology which includes obstructions in the acoustic line of sight. In this paper we introduce a network concept based on the CDMA method confronting the acoustic underwater network challenges, such as the “near-far” problem, fast time varying topology, multihops routing and message distribution protection. Using this concept, a sea trial including broadcast, multicast and unicast transmissions of SMS and navigation control messages was carried out in various scenarios including multihops near the shores of Israel. We present results from this sea trial demonstrating the efficacy of the proposed networking scheme.
Performance modeling and tradeoffs studies for hybrid sensing networks
Authors: Jespers Stéphane
Published: May 2008

The transformation of naval forces in support of expeditionary operations requires substantial endurance enhancement of their existing undersea reconnaissance and surveillance functions. Concepts of operations for distributed sensor fields - to be deployed in littoral waters - are now being proposed, encouraged by the favourable outlook for network technologies. The renewed attention for multistatic sonar is one example of this trend. Predicting the performance of distributed sensor fields for ASW applications, with sensors involving the use of acoustics and non-acoustics is complex. Though it is a great chance for optimizing the use of assets, the impact of sensor platforms' mobility (AUVs or gliders) adds yet another level of space-time complexity. Prior to any large scale test or development, system and operational studies must be able to determine optimal architectures and node placement as function of mission requirements. A major constraint is that of the limitations imposed on autonomous and covert data exchange in the maritime and underwater domains. This speeks for the design of hybrid sensor network architectures, as they appear to be well suited in dealing with substantial sensor data and command control data (e.g., backseat-driver paradigm) communication requirements.
Sound strength and reverberation time in small concert halls
Authors: Aretz Marc , Orlowski Raf
Published: May 2008

Many small concert halls are being built in music departments in schools and universities and these have to cater for a wide variety of musicalensembles ranging from orchestras to solo performers. Such diverse musical forces require different acoustic conditions in terms of reverberation and loudness and so variable acoustics are frequently provided. However, introducing absorption decreases reverberation and loudness and so a careful balance needs to be struck between controlling loudness and maintaining reverberation. In the course of this study a series of measurements was carried out in six small concert halls in Cambridge, UK, which accommodate a range of sizes of musical ensembles from quartets to orchestras, in order to determine the range of reverberation times and sound strengths, including changes due to variable absorption. The measured strength levels were compared to values derived from traditional and revised theory on strength calculations in order to assess the accuracy of the theories for small chamber music halls. The measured values of strength levels were observed to be mostly lower than the predicted ones. In order to account for this difference (particularly in spaces with added absorption) a combination of Barron's revised theory and the Vorländer correction factor is proposed.
Early reflection surfaces in Concert Halls - a new quantitative criterion
Authors: Jurkiewicz Yann , Kahle Eckhard
Published: May 2008

A new acoustic parameter has been defined for the acoustic brief of the Philharmonie de Paris Concert Hall. With a seating capacity of 2400 and the audience enveloping the performers on all sides, the new hall will be at the upper limit of the ideal range for symphonic music, and an efficient acoustic design was called for. In order to relate architectural design to acoustic efficiency, and based on quantitative study of existing halls, an early efficiency parameter was developed. For the Paris Philharmonie the brief requested a total area of 1400 m2 of surfaces being able to create early reflections, with 500 m2 being less than 15 m from the stage. The studies leading to the definition and the justificantion of the parameter will be presented. Another, more accurate definition expresses the early efficiency parameter in terms of the solid angle for a source on stage, allowing generalization of the new criterion for all hall sizes.
Experiments with the orchestral impulse response
Authors: Siebein Gary W. , Lilkendey Robert M. , Paek Hyun , Jones Chris , Fisher Joshua , Kwon Youngmin
Published: May 2008

Experiments were conducted in a large multipurpose performance hall to examine the differences in listening quality and physical acoustical measurements that resulted from using a single dodecahedral loudspeaker as the sound source and an array of multiple directional loudspeakers spread across the stage to simulate the various sections of an orchestra. Significant differences in listening qualities were recorded by listeners at three locations in the hall. The impulse responses recorded using the two systems varied dramatically in structure and in some of the typical acoustic metrics measured. However, there were also similarities among many measurements using the two systems. The research indicates the need for new measurement parameters to express the significant architectural features of the room and the physical acoustical difference that caused the perceived qualities of the sound field to vary. Preliminary analysis of the existing and proposed parameters will be presented.
Soundfields in coupled rooms: A theoretical and phenomenological synopsis
Authors: Summers Jason E.
Published: May 2008

In systems of acoustically coupled rooms, energy in the reverberant field is exchanged between constituent rooms via transondentboundaries. Energy in the direct field can be distributed between rooms by the same mechanism. These exchanges of energy have been able to explain the phenomenon of multiple-slope decay curves. Likewise, they result in spatial and spectral variations in steady-state SPL and decay-curve shape. The basic form of the decay curve is governed by the gross locations of the source(s) and receiver: which room(s) they occupy, in addition to properties of the rooms themselves: volume, surface area, and absorption. Historically, these basic dependencies have been well explained by statistical-acoustics (SA) models. More subtle variations in decay-curve shape result from the fine-scale locations of source(s) and receivers relative to one another and boundary regions through which energy is exchanged (e.g., apertures). By accounting for radiation from boundaries, and propagation delays within and between rooms, more sophisticated SA models can reproduce these effects. Even so, these models fail when SA assumptions are violated or energy transfer becomes so great (e.g., large aperture areas) that room boundaries are ambiguous. In these cases, newer computational models yield accurate predictions and physical insight. [Work supported by ONR.]
Multivariable analysis of energy decay in coupled volume rooms: How can we objectively describe what we perceive in coupled volume performance spaces
Authors: Brooks Todd L. , Pyper Ted , Aston Kelly A. , Doria Damian J.
Published: May 2008

The behavior of coupled volumes in room acoustics is commonly characterized by multiple slopes observed in sound energy decay curves, as measured (or modeled) using an omnidirectional receiver. This characterization is often limiting and can not adequately explain the change in character of sound energy decay with time that we perceive as listeners in music performance spaces that employ coupled volumes. By investigating energy decay as a function of several independent variables, including time, frequency, and direction of energy arrival, we seek to forge new objective measures that relate to what a listener actually hears in a coupled volume concert hall. We will discuss relevant geometry and materials of several coupled volume performance spaces designed by Artec Consultants Inc, describe subjective phenomena we have observed in these halls, and present results of our ongoing investigation of new objective metrics geared to better characterize coupled volume music performance spaces.
Ocean acoustic tomography using a double-beamforming algorithm
Authors: Iturbe Ion , Roux Philippe , Nicolas Barbara , Mars Jérôme I.
Published: May 2008

Since Munk and Wunsch proposed the basis for ocean acoustic tomography, many experiments have been performed to estimate sound speed fluctuations in the ocean, using ray identification and measurement of their travel times. However, technical limitations appeared such as the precision of the arrival time measurements or the number of ray arrivals that can be extracted from the signal. Recently, technical improvements allowed more complete experiments using two vertical arrays of sensors (source array and hydrophone array). In this configuration, the signals between each source and receiver are recorded which greatly improve the available information to identify the acoustic rays. One way to increase the number of rays in the tomography algorithm is to perform double-beamforming on the source and receive arrays. With double-beamforming, ray arrivals are separated by emission angle, reception angle and arrival time. Thus, we solve more ray arrivals than with a single beamforming or with a point-to-point approach. In order to avoid previous limitations and to explore acoustical limitations, we study two simple cases through the double-beamforming algorithm: with simulated data and with ultrasonic small-scale experimental data.
A simulation study of shallow water tomography for coastal monitoring
Authors: Carrière Olivier , Hermand Jean-Pierre , Stephan Yann
Published: May 2008

Developing operational oceanographic models for coastal environment is an exciting challenge for the next decades. The typical sparsity of assimilated in-situ observations often creates biases in the model predictions reducing the overall accuracy of the forecasting. In such a highly dynamic environment, acoustic tomography can be a good candidate to provide synoptic measurements over wide areas while a range-dependent inversion scheme allows to achieve a reasonable spatial resolution. In this work, we present simulation results of a Kalman-based assimilation of ocean-acoustic data for a basic model of the Ushant front west off Britanny. In a first part, a single vertical slice tomography experiment is simulated for a static front model to study in which way the modal propagation of a multifrequency acoustic signal is affected by the characteristics of the front (position, intensity). In a second part, the problem of assimilating full-field acoustic data into a dynamic model and tracking of the range-dependent sound-speed field is addressed.