bluuebunny/crossref_metadata_2025 huggingface dataset:
Developing a bilingual communication aid for a Japanese ALS patient using voice conversion technique
Authors: Iida Akemi , Kajima Shimpei , Yasu Keiichi , Kominek John M. , Aikawa Yasuhiro , Arai Takayuki
Published: May 2008

A bilingual communication aid for a Japanese amyotrophic lateral sclerosis (ALS) patient has been developed. From our previous research, a corpus-based speech synthesis method was ideal for synthesizing speech with voice quality identifiable as the patient's own. However, a recording of a large amount of speech, which is a burden for the patient, is required for such system. In this study, a voice conversion technique was applied so that a smaller amount of recording is needed for synthesis. An English speech synthesis system with the patient's voice was developed using Festival, a corpus-based speech synthesizer with voice conversion technique. Two methods for Japanese speech synthesis were attempted using HTS toolkit. The first used an acoustic model built from all 503 recordings of the patient. The second used an acoustic model built from 503 wavefiles of which voice was converted to the patient's from a native speaker's. The latter method requires fewer recordings of the patient's. The result of the perceptual experiment showed that the voice synthesized with the latter was perceived to have a closer voice quality to the patient's natural speech. Last, GUI on windows was developed for the patient to synthesize speech by typing in the text.
The acoustic manifestation of consonant gradation in Northern Sami
Authors: Karlsson Fredrik , Sullivan Kirk P. , Svonni Mikael , Van Doorn Jan , Wennstedt Ola
Published: May 2008

Consonant gradation is a feature of Sami and is realised in Northern Sami in changes from nominative singular to genitive plural form, e.g., “heavdni” (spider) and “heavnni-t” (spiders). The data examined in this paper was collected in 2007 and represents the first acoustic analysis of consonant gradation in Northern Sami. The data was collected in Övre Soppero in Northern Sweden using an elicitation technique that was designed to collect phonetically controlled material for analysis. The nouns were elicited in singular or plural form using picture prompts and the participants were asked to give the word in the carrier sentences “Lea okta __ govas” (“There is a ___ in the picture”) and “Leat guokte __ govas” (“There are two ___ in the picture”). The recordings were labeled in Wavesurfer at a phonetic level and the segments relating to consonant gradation extracted for acoustic analysis. In the paper we present our initial findings.
The use of fundamental frequency information by cochlear implant patients with residual low-frequency hearing
Authors: Herf Stephanie , Liss Julie , Spahr Anthony , Dorman Michael
Published: May 2008

Recent studies have demonstrated significant benefits of complementing the electric hearing provided by a cochlear implant (CI) with residual low-frequency acoustic hearing. It has been suggested that the benefit of low-frequency hearing (<250 Hz) is due to improved representation of fundamental frequency (F0). It was hypothesized that removing F0 information would negatively impact speech perception in bimodal CI patients (EAS) more so when they are using both modes of perception. It was further hypothesized that these patients' more effective use of F0 information would result in higher intelligibility scores and less unpredicted lexical boundary errors (LBEs) in a speech transcription task. Six EAS patients transcribed normal and F0-flattened phrases. Results indicate EAS patients demonstrated a significant benefit from the residual low-frequency acoustic hearing and perform better in this mode. Five of the six EAS patients were able to transcribe the normal phrases with greater accuracy than the flat F0 phrases in both conditions. These patients correctly parsed lexical boundaries and transcribed phonemic targets with greater accuracy in the bimodal condition. These results demonstrate the importance of pitch and low frequency spectral information in the perception of speech.
Digital acquisition of ultrasound imaging of the tongue
Authors: Noiray Aude , Iskarous Khalil , Whalen D.h. H.
Published: May 2008

One of the goals of speech production research is to understand the functioning of the tongue in the production of overlapping lingual segments. This is especially important since all vocalic and most consonantal contrasts involve a tongue gesture. An obstacle to progress in this area has been the difficulty of observing tongue motion in enough spatial and temporal detail to develop theory on its linguistic functioning. Ultrasound has become increasingly popular in tongue imaging, since it allows the researcher to observe most of the tongue dynamically, while being clinically safe. However, a limitation of this technique is the slow 30 Hz rate of analog acquisition. We have developed a new method for digital acquisition of ultrasound data at over 100 Hz, with simultaneous synchronized acquisition of audio and Optotrak data. Acquisition of the ultrasound digital video data is externally triggered using a novel pulse sequence that is simultaneously captured by the audio and Optotrak acquisition device. We will illustrate the detail of the dynamics of the tongue in an experiment on the coproduction of rhotic and vocalic segments (seven American English subjects), where digital ultrasound was captured at 127 Hz (Funded by NIH DC-02717).
Speech transcription for Embodied Conversational Agent animation
Authors: Zouari Leila , Chollet Gerard
Published: May 2008

This article investigates speech transcription within a framework of Embodied Conversational Agent (ECA) animation by voice. The idea is to detect some pronounced expressions/keywords in order to animate automatically the face and the body of an avatar. Extensibility, speed and precision are the main constraints of this interactive application. So after defining the set of the relevant words (to the application), a fast large vocabulary speech recognition system was developped and the keyword detection was evaluated. In order to fasten the recognition system without decreasing its efficiency, the acoustic models have been shortened by an original process. It consists in decreasing the number of shared central states of context dependant models which are considered stationary. The shared states situated in the border of the models remain inchanged. Then all the models are retrained. The system is evaluated on an hour of the ESTER database (a French broadcast news database). The experiments show that reducing the number central states of triphones is advantageous. Indeed, the length of models is reduced by 20% with no loss of accuracy.
A cross-dialect acoustic description of vowels: Peruvian versus European Spanish
Authors: Chladkova Katerina , Escudero Paola , Boersma Paul
Published: May 2008

This paper aims to provide acoustic description and comparison of vowel properties of two major dialects of Spanish: Peruvian and European. The method of data collection and acoustic analyses reported in Escudero et al. (submitted) for Portuguese is replicated in order to allow for future comparisons across languages. Each of the five Spanish monophthongs /i, e, a, o, u/ was produced in stressed position in the first syllable of a CVCV (consonant-vowel-consonant-vowel) frame. The CVCV words were read both in isolation and in a carrier sentence. Vowel tokens were examined between voiceless stops /p, t, k/ and fricatives /f, s/, which supplied five variable consonantal contexts. We analyzed the vowels' first and second formants (F1 and F2) as well as their fundamental frequency and duration. Unsurprisingly, a main effect of vowel identity and gender on formant values was found. Most importantly, unlike Morrison and Escudero (2007), we found for Spanish an interaction between dialect and vowel identity, implying that the F1 and F2 values of some vowels are significantly different between dialects.
Talker-specific and accent-general perceptual adaptation to Korean-accented English
Authors: Sidaras Sabrina K. , Alexander Jessica E. , Nygaard Lynne C.
Published: May 2008

The present study investigated the relative contribution of talker-specific and accent-general learning to the perceptual adaptation of accented speech. Adult native English-speaking listeners were asked to transcribe Korean-accented English words in a brief, high variability perceptual learning paradigm. During training, listeners transcribed individual words produced by six Korean-accented speakers and were given feedback on their transcription performance. Controls were either trained with native English speakers or were given no training. At test, listeners were presented with Korean-accented speech produced by both familiar and unfamiliar talkers. The results suggest that listeners learned accent-general properties of nonnative speech. Listeners showed better transcription performance for both familiar and unfamiliar accented talkers relative to English and no training controls. However, talker-specific properties such as individual talker familiarity and baseline intelligibility also influenced transcription performance at test. These findings suggest that although listeners are sensitive to multiple sources of variation in speech, they appear to engage in accent-general perceptual adaptation to non-native speech.
Effect of musical experience on Mandarin tone and vowel discrimination and imitation
Authors: Gottfried Terry L. , Xu Yangqing
Published: May 2008

Recent studies have demonstrated a relation between musical experience and accuracy in speaking and perceiving unfamiliar speech contrasts. For example, Gottfried [in Bohn and Munro, Eds., John Benjamins, 221-237 (2007)) found that native speakers of American English with musical training perform better than non-musicians when discriminating and imitating the four lexical tones of Mandarin Chinese. In this study, four native speakers of Mandarin (Chengdu region) produced target words in a fixed carrier sentence. Their productions of high unrounded /i/ and high rounded /u/ were significantly affected by the initial consonant, especially /u/ (which is often transcribed as two different vowels in pinyin, u and ü, according to the initial consonant). Vowels that followed consonants with more anterior articulation (pinyin j, q, x) had lower F1 and higher F2 than vowels that followed more posterior consonants (pinyin zh, ch, sh). The F0 of the word immediately preceding the target words (kan4) was significantly affected by the tone of the target word. Current research tests whether musicians and nonmusicians differ in their ability to discriminate and imitate these phonemic contrasts according to native speakers' phonemic categories, which allow contextual variation in acoustic information.
Providing simultaneous visual feedback may ameliorate speech disruptions caused by exposure to delayed auditory feedback
Authors: Jones Jeffery , Striemer Danielle
Published: May 2008

Speakers exposed to delayed auditory feedback (DAF) are often dysfluent. We investigated the possibility that providing visual feedback in addition to DAF would reduce speech disruption. Participants repeated sentences while they heard their auditory feedback delayed with and without simultaneous visual feedback. Replicating previous work, DAF led to increased sentence durations and an increased number of speech disruptions. Results showed that visual feedback did not reduce DAF effects on duration, however, a nonsignificant trend was observed that indicated fewer speech disruptions occurred when visual feedback was provided. This trend was significant in speakers who were overall less affected by DAF. These results suggest the possibility that speakers can strategically use alternative sources of feedback.
Attentional modulation of the perception of illusory vowels and sound onsets: A functional magnetic resonance imaging (fMRI) study
Authors: Heinrich Antje , Davis Matthew H. , Carlyon Robert P. , Johnsrude Ingrid S.
Published: May 2008

In a previous study, we exploited the Gestalt principle of closure to create illusory vowel sounds and examined the neural correlates of their perception using fMRI. When two formants of a synthetic vowel are presented in an alternating pattern, filling the gaps in each formant with bursts of noise causes the formants to be heard as continuous and more vowel-like. When this "Illusion" condition was modified by increasing the formant-to-noise ratio (FNR), the formants were heard as interrupted (“Illusion Break” condition) and less vowel-like. BOLD signal in the Middle Temporal Gyrus (MTG) was greater for Illusion than for Illusion-Break stimuli, reflecting the difference in speechlikeness. Primary auditory areas (PAC) exhibited the opposite pattern, probably because Illusion-Break stimuli contain more perceived sound onsets than the Illusion stimuli. In the current study we examine whether the neural activation to illusory vowels and sound onsets is modulated by attention. Participants were scanned while listening to Illusion, Illusion Break, and two types of intact vowels and simultaneously directing their attention either to the vowel stimuli or to auditory or visual distractors. Preliminary analyses suggest that activation to intact and illusory vowels in MTG, and to sound onset in PAC, is modulated by attention.
Effect of head covers on directivity pattern of human head
Authors: Todoroviæ Dejan
Published: May 2008

In this paper are presented the experimental results of changes in directivity patterns of artificial head with three different types of head covers. The mathematical model of human head approximated by radially vibrating spherical cap set in a sphere is discussed. For the purpose of this research, the physical model of a human speaker head is constructed, and the far-field detailed directivity patterns of the model with and without head covers is measured. Hair as porous absorber, cap and straw hat, as sound barriers, are discussed, and their influence on sound wave propagation is considered. Measured detailed directivity pattern changes affected by head covers in far field are calculated in step of ten degrees for spherical coordinates (polar angle and azimuth) and presented in form of two- and three-dimensional polar plots.
English and Polish glides compared
Authors: Balas Anna
Published: May 2008

This paper compares acoustic features of (1) Polish and English glides before vowels, and (2) Polish glides in vowel-plus-glide sequences with English diphthong offglides. Contrary to traditional articulatory descriptions, the results presented, based on acoustic measurements and vector length calculations, do not reveal that Polish glides in vowel-plus-glide sequences are characterized by more extreme formant values than English diphthong offglides. The difference between English diphthongs and Polish vowel-plus-glide sequences is attributed to timing properties, which are shown to be relatively easily acquired by Polish learners of English, probably because of a universal tendency for the first element to be longer than the second one. Preliminary results, however, point to acoustic differences between Polish glides before and after vowels, the former being more consonantal than the latter.
Multiinput multioutput OFDM for shallow-water UWA communications
Authors: Emre Yunus , Kandasamy Vinod , Duman Tolga M. , Hursky Paul , Roy Subhadeep
Published: May 2008

We investigate performance of turbo coded multiple-input multiple-output (MIMO)-OFDM systems with layered space time (LST) architectures for underwater acoustic (UWA) channels by using simulations and results from the AUVfest experiment performed in June 2007. MIMO systems have been shown to be promising in the sense that they increase the reliable transmission rates significantly without consuming additional bandwidth and power. Robustness of OFDM systems with cyclic prefix or zero padding to ISI channels are also well known; so the combination of MIMO techniques and OFDM can be regarded as a promising technology for shallow water UWA communications which is characterized by severe bandwidth limitations and long intersymbol interference (ISI) spans. The paper reviews necessary components of a MIMO-OFDM communication system, including, time and frequency synchronization, channel estimation, and tracking of the varying channel parameters. Modifications necessary to make the system suitable for UWA channels are summarized. Results of the AUVFest 2007 experiment are very promising; for instance, 2×2 MIMO-OFDM can reach up to 60 Kbps transmission for a bandwidth of 16 KHz with simple receiver structures for a range of 2000 m. In addition to the coherent system, differential and unitary space-time coded MIMO-OFDM scenarios are also considered.
The effects of a shallow-water acoustic channel on Right whale vocalisations
Authors: Mohammad Bashar , McHugh Ron , Bell Judith
Published: May 2008

For mitigation and monitoring of Right whales, identifying their presence from their vocalisations is a key research issue. Their vocalisations are characterized as frequency modulated up-sweeps with duration of ̃1s and a frequency range from 50Hz to 200Hz. Acoustic methods to classify these received calls are assessed by the variation in the received data set. As well as the natural variation in vocalisation within the species, the received acoustic signals are also influenced by the effect of the acoustic channel. The shallow water of Cape Cod Bay is one of the favoured habitats for the Northern Right whale. Such waters act as an acoustic waveguide where multiple reflections off boundaries cause calls to become dispersive in nature. In this paper we discuss the effects of channel environmental parameters such as water depth and sediment type on first the FM deviation and second on the time difference of arrival between the first and second modes, which in turn influences acoustic range estimation. Such channel effects were studied using the normal mode acoustic propagation model (PROSIM). An analysis of real acoustic data recorded in Cape Cod Bay (2001 obtained from IFAW) will be also presented in terms of dispersion results.
Measurements of the scattering characteristics of sediment suspensions having broad particle size distributions
Authors: Moate Benjamin D. , Thorne Peter D.
Published: May 2008

Profiles of suspended sediment concentration and mean size can be measured in underwater environments using Acoustic Backscatter Systems (ABS). Inversion of ABS measurements into sediment size and concentration requires knowledge of the backscattering form function, f, and the total normalised scattering cross section, χ. Previous studies have measured these parameters for sediments sieved over narrow size ranges only. Narrow size ranges are unrealistic compared to the broad Particle Size Distributions (PSD) that typically occur in nature however, and it is known that f and χ are significantly altered by changes from narrow to broad PSDs. Theoretically, these changes can be accounted for in ABS inversions by taking values of f and χ obtained from narrow size ranges, and integrating them over the suspended PSD, though this theory has not been validated for real suspended sediments. Here, we compare the results of this integration with measured values of f and χ for suspensions of (irregularly shaped) sandy sediments having broad PSDs. The results show that as the standard deviation of the size distribution increases, acoustic scattering is increased in the Rayleigh regime whilst being reduced in the geometric regime. These changes significantly affect acoustic estimates of suspended sediment concentration and size.
A very shallow water ray propagation model
Authors: Pautet Lucie , Tesei Alessandra
Published: May 2008

For applications such as minehunting, communications, high frequency time-reversal, there has been a need for reliable and fast propagation models able to correctly treat scattering at the rough waveguide boundaries. Data and scattering models have shown that as signal frequency or surface roughness increases, the scattering pattern from the ocean bottom and ocean surface evolves from specular to quasi omni-directional. Ray propagation models are fast but, a priori, they would treat surface bounces as perfectly specular which would not account for the angular spread observed on multipath structures. The idea followed by the authors over the past few years has been to introduce in the Bellhop ray tracing model a reflection kernel including deterministic properties of the sea surface and bottom. Simulations using this kernel display a significant effect of the multipath structure similar to the angular spread observed in in-situ data. Simulation results are compared with a recent experimental study at 10-20 KHz (BARRIER'04 at NURC) on the influence of wind strength on surface bounce spreading and subsequent TR-focus spread.
Multifrequency interferometry on synthetic aperture sonar images
Authors: Sæbo/ Torstein Olsmo , Hansen Roy E. , Callow Hayden J.
Published: May 2008

Interferometric processing on synthetic aperture sonar (SAS) images can provide accurate bathymetric maps with very high spatial resolution. Often, bathymetric precision is limited by two-pi phase ambiguities in the interferogram. Several phase-unwrapping algorithms exist, but they all depend on some type of continuity throughout the interferogram. The locations of the phase ambiguities are dependent on the carrier frequency of the transmitted signal. Dividing the frequency band into multiple subbands provides multiple interferograms, each with a unique carrier frequency and thus differing ambiguity positions. In this paper, we investigate how to take advantage of subband interferograms to reduce phase ambiguities at the expense of accuracy. This is performed by using the phase differences between the individual subband interferograms. We also present a method were we use the differences in subband interferograms to eliminate the phase ambiguities in both the original interferogram, and in the subband interferograms themselves. Both methods are tested on simulated data and field data collected by the HUGIN autonomous underwater vehicle carrying the Kongsberg HISAS 1030.
Circular synthetic aperture sonar results from autonomous underwater vehicle trials
Authors: Hansen Roy E. , Sæbo/ Torstein Olsmo , Callow Hayden J.
Published: May 2008

The principle of synthetic aperture sonar (SAS) is to combine successive pings coherently from different observation angles in order to increase the azimuth resolution. By collecting data along a circular track, a circular SAS (CSAS) image, or tomographic image, can be made. The image reconstruction can be done either incoherently, fully coherently, or partially coherently where each subaperture of coherent processing consists of a section of the circle. In target classification, CSAS has several benefits: the object is observed from all aspect angles giving a better perception; the resolution in the image increases. In this paper, we calculate required accuracy in navigation, bathymetry and sound velocity for successful circular SAS. Finally, we show circular SAS images of small targets from real data collected by the HUGIN autonomous underwater vehicle carrying the Kongsberg HISAS 1030. We test different beamforming strategies, and show the effect of coherent and incoherent tomographic imaging.
Autofocus of synthetic aperture sonar data using the phase adjustment by contrast enhancement algorithm
Authors: Callow Hayden J. , Sæbo/ Torstein Olsmo , Hansen Roy E.
Published: May 2008

Imagery from synthetic aperture systems often suffers from imperfect image formation due uncertainties in the collection geometry or environmental parameters. Autofocus techniques aim to estimate and subsequently eliminate the effect of these uncertainties---automatically adjusting focus parameters to obtain a “better” image. Typically, autofocus algorithms will optimise for reduced Doppler phase gradients or improved image contrast. The phase adjustment by contrast enhancement (PACE) algorithm belongs to the second class and was first proposed for use in synthetic aperture radar (SAR) autofocus. The algorithm is somewhat unusual for a contrast optimisation in that it avoids lengthy computation through directly solving the equations for optimum contrast. This advance allows for rapid autofocus without the need for complicated iterative optimisers. We compare results from using the PACE algorithm on local region of strip-map synthetic aperture sonar (SAS) data collected with the HUGIN AUV and compare against a benchmark phase gradient autofocus (PGA) algorithm. We also demonstrate the effect of using the algorithm in circular SAS imagery, something not currently possible with standard PGA-based autofocus.
Planar synthetic aperture processing (P-SAS) to real acoustic data of underwater imaging
Authors: Jammali Adel , Belkacem Afif , Besbes Kamel , Zakharia Manell E.
Published: May 2008

Planar synthetic aperture technique has been validated on both simulated and tank data. It showed a significant improvement of 3D representation of bottom and subbottom. In this paper we present its application to real data acquired during sea experiments on a dump site. Data were acquired during the SITAR (Seafloor Imaging and Toxicity: Assessment of Risks caused by buried waste) project. The transmitter was a parametric array (TOPAS). Two central frequency were explored, 10 kHz and 20 kHz. The transmitter was fixed on a ROV which position was monitored. As P-SAS algorithm was designed for data obtained on a regular planar grid important modification were required to handle real sea data and “realistic” navigation conditions (irregular grid): a “re-arrangement” algorithm was designed for preprocessing actual data and correct for trajectory disturbances (in 2D). This algorithm is the re-projection of data to a new (virtual) regularly grid. The algorithm was validated on tank experimental data prior to application to sea data. Both conventional and SAS data will be presented. A strata representation technique was used for analyzing the seafloor, the subbottom and the localization of buried objects on a dump site in the Baltic sea.
An optimization approach to the automatic identification of signals originating from underwater explosions
Authors: Prior Mark K.
Published: May 2008

Data recorded by the International Monitoring System (IMS) of the Comprehensive Test-Ban Treaty Organization are used to illustrate the different types of signal that are routinely received on IMS hydrophone stations. It is shown that automated methods for characterizing the source of these signals sometimes fail to identify signals arising from underwater explosions. A new approach to the automatic identification of such signals is presented. The approach uses Receiver Operating Characteristic (ROC) curves to investigate the trade-off between false-alarm rate and probability of detection. It applies a threshold to a parameter developed as a measure of the likelihood of a signal being associated with an explosion. A numerical Measure of Performance (MoP) is derived from the ROC curves and the definition of the likelihood parameter is tuned so as to maximize this MoP. Optimization of the parameter definition is achieved using an approach based on genetic algorithms.
High data rate coherent underwater acoustic communications during KauaiEx and MakaiEx
Authors: Song Aijun , Badiey Mohsen , Song Heechun , Hodgkiss William
Published: May 2008

During two acoustic communications experiments conducted around Kauai Island, Hawaii (KauaiEx, 2003 and MakaiEx, 2005), various coherent communications data with concurrent environmental measurements were collected under different experimental settings. The collected communications data are processed by a newly proposed receiver, which consists of time-reversal multichannel combining followed by a single channel DFE. Continuous channel updates along with Doppler tracking are used prior to time reversal combining to combat fast channel variations. The receiver can successfully demodulate different types of coherent communications signals, including phase shift keying (PSK) and quadrature amplitude modulation (QAM) signals, at different symbols rates for different source/receiver settings, such as fixed source/receiver, drifting source/receiver, and towed source. Selected high data rate communication results will be presented to show the effectiveness of the receiver. The receiver performance in relation to the environmental variability also will be shown.
Experimental analysis of statistical characteristics of a very shallow underwater acoustic channel
Authors: Kim Sea-Moon , Byun Sung-Hoon , Lim Yong-Kon
Published: May 2008

Underwater acoustic channel is characterized as a time-varying and multipath environment. Not only each propagation path changes randomly but also the scattered waves from the surface and bottom deteriorate signal transmission resulting in fading channels and poor communication performance. In order to design communication algorithms and determine modem parameters the characteristics of random ocean channel must be analyzed in advance. In this paper we investigate the statistical channel properties with experimental data gathered in a very shallow water near the southern coast of South Korea using band-limited signals with center frequencies of 20-40 kHz. The impulse responses at several distances up to 4km are estimated and their statistical characteristics in the complex domain are analyzed. We found that the statistical properties are highly dependent on the channel impulse response and the carrier frequency.
Capacity estimations for underwater acoustic communication systems with source power constraints
Authors: Wang Haibin , Meng Di , Yang Hua
Published: May 2008

Channel capacity is an important parameter of underwater acoustic communication (UWAC) systems. For a certain channel and source power, water-filling algorithm of information-theory can be used to estimate the capacity. However, in practice, there are many constraints of the source transmission power. One of the most important constraints is that many communication nodes may exist in a local area, which means that the source power of each node should be confined in order to keep all nodes working normally. Considering this constraint and applying acoustic propagation modeling, this paper estimates the capacities of an UWAC system in some typical propagation conditions. The results are very useful for analyzing the maximum data rate of a practical acoustic channel and providing the optimal parameters of an UWAC system.
Synchronisation of underwater communication receivers by means of broadband sweep-spread pulses
Authors: Kebkal Konstantin G. , Bannasch Rudolf , Kebkal Alexey G.
Published: May 2008

Using sweep spread pulses a variety of multipath components of a receive signal can be often resolved in time-frequency domain. In result of synchronisation of the receiver with the most powerful component, other multipaths can be effectively suppressed by means of a matched filter. Owing to exact synchronisation, the difference frequency will be equal to zero and outputs of matched filters will be good for estimation of (information) parameters. However, the synchronous component (as well as others) can occasionally turn out to be composite and to contain energy of several non-resolved multipaths. In this case, the synchronisation time of the receiver will be not exact and the difference frequency of demodulated signal will differ from zero. This effect will cause a systematic error in estimation of the information parameter. This paper represents the results of mathematic modeling of the systematic error (for receivers, utilising the sweep-spread carrier technology), as well as, experiments on synchronisation of the receiver by means of wideband sweep spread pulses.
Measurement of angular power profile at an array receiver in a shallow underwater acoustic channel
Authors: Byun Sung-Hoon , Kim Sea-Moon , Lim Yong-Kon , Seong Woojae
Published: May 2008

In the design of broadband underwater acoustic communication system, proper analysis of underwater acoustic channel characteristics is required to determine communication system parameters. Especially for high channel capacity transmissions such as multiinput multioutput (MIMO) systems, the spatial correlation characteristics among multiple sensors determine communication performance and they are affected by the angular power distribution of the incoming acoustic waves. In this study, we suggest a model-based array signal processing technique for measuring the angular power profile and apply it to experimental data gathered from very shallow water of 20 to 30 m water depth near the southern coast of South Korea. At first we show the variation of the angular power profile over different transmitter/receiver ranges and then its impact on the spatial correlation characteristics between two different array elements. Finally we discuss the expected spatial diversity effects from the viewpoint of underwater acoustic channel modeling.
Modeling high-frequency reverberation and propagation loss in support of a submarine target strength trial
Authors: Vasiliev Boris , Collier Art
Published: May 2008

The presentation reviews the environmental modeling conducted in support of a submarine acoustic target strength trial. The measurements at 20-40 kHz were collected at a shallow site in North West Atlantic. The site bottom was gravel; surface winds were 2-6 m/s. For ranges less than 1.8 km, the CW reverberation at 24, 28, and 39 kHz agreed with CASS-GRAB predictions; beyond 1.8 km, the model output underestimated the measurements. The predictions were computed for APL-UW surface and bottom models appropriate for trial conditions: negligible surface reflection loss and scattering strength, low bottom reflection loss and high bottom scattering strength. The LFM reverberation at 21, 28, and 36 kHz for 2 kHz bandwidth signals matched the CW reverberation after compensation for the pulse range resolution and frequency differences in the beam responses and volume attenuation. Agreement among CASS-GRAB prediction and data verified the assumed sonar and environmental parameters used in propagation loss modeling and increased confidence in the target strength estimates. The latter were consistent with previously reported values.
Performances of a multistatic model of sound scattering by rough surfaces
Authors: Jaud Virginie , Gervaise Cédric , Khenchaf Ali
Published: May 2008

The ocean floor is far from being a smooth and perfectly rigid surface. That is why its sound scattering properties are a useful input to the analysis of this medium as for acoustic data inversion. Thus, multi-static scattering coefficients have been investigated in a frequency range of order of 10 kHz to 300 kHz. The Kirchhoff Approximation and the Small Perturbation Method could be cited respectively in the case of dimensions of a rough surface larger and smaller than the wavelength. Nevertheless, for those frequencies, hence for those wavelengths, a rough surface should be considered at different scales compared to the wavelength. As a part of the incident wave is transmitted to the seabed medium, it is also important to know the effect of the scattering coming from the volume. Jackson's scattering model takes these considerations into account. The aim of the study is first to show an improvement of the surface scattering method using the Small Slope Approximation and keeping the initial method of Jackson's model to describe the scattering from the volume. Comparisons with well-known models are presented to show the performances of this new approach and comparisons between different multistatic geometries are analyzed to show the most useful configuration of the model.
Complex interfaces of granular media: multiscale characterization and effective medium modeling
Authors: Le Gonidec Yves
Published: May 2008

Seafloor is a complex geological interface : the acoustic reflectivity strongly depends on the sonar frequency which can be from few to hundreds kHz. In order to understand the physical processes involved, we have developed a multiscale acoustic method based on the wavelet transform properties: we introduce this theoretical approach first applied on homogeneous discontinuities. Then, we have developed acoustic experiments where the discontinuties are complex interfaces: we present the experimental setup and describe the results measured on granular media made of monodisperse glass beads. For this seafloor modeling, where all parameters are known, we put in evidence five frequency ranges corresponding to particular acoustic regimes: we give physical interpretations based on the analysis of effective medium modeling. From low to high frequencies, a strong transition is observed between propagation and scattering phenomena. Going further in this study, we illustrate the results on a bimodal glass bead distribution where high frequency scattering can be isolated using an original experimental approach.
Acoustics for underwater neutrino telescopes
Authors: Ardid Miguel , Bou-Cabo Manuel , Martínez-Mora Juan Antonio , Camarena Francisco , Espinosa Víctor
Published: May 2008

In this communication we present the research activities in underwater acoustic sensors and arrays used in underwater neutrino telescopes. These activities are developed in two areas. First, in optical based underwater neutrino telescopes, an acoustic positioning system is used in order to monitor the position and orientation of the optical modules in deep sea. In the second field, there is the idea to build underwater telescopes composed of arrays of acoustic sensors in order to detect the weak thermoacoustic pulse which will be produced when a very high energy neutrino interacts in the water. For both, a challenging and very specific acoustic system is needed. After the description of these systems and a brief review of the status of the field, our work in the area in the frames of ANTARES and KM3NeT neutrino collaborations is shown.
Interferometric synthetic aperture processing: a comparison of sonar and radar
Authors: Hayes Michael , Gough Peter T.
Published: May 2008

Interferometric aperture synthesis is an inverse problem that attempts to form an elevation map of the earth (in the case of radar) or a bathymetric map of the seafloor (in the case of sonar). In both cases, a pair of (nominally) vertically displaced transducers is configured as an interferometer. After aperture synthesis is performed to produce a pair of images, the height of each resolvable scatterer can be estimated using time delay estimation between the image pairs and knowledge of the system geometry. While interferometric synthetic aperture sonar (InSAS) seems like an obvious extension of the methods of interferometric synthetic aperture radar (InSAR), the height estimation algorithms are surprisingly different. In this paper we start with the principle of generalised correlation for optimal time delay estimation. This filters the signals to maximise their coherence since the accuracy of the time delay estimates, and thus the height estimates, strongly depends upon the signal coherence. We then consider the fundamental differences between InSAR and InSAS; namely the relative signal bandwidth, aperture sampling rate, and geometry and show how application of generalised correlation time delay estimation leads to the differences in how InSAS and InSAR signals are processed.
A qualitative and quantitative analysis of impulse responses from balloon bursts
Authors: Cheenne Dominique J. , Ardila Mauricio , Lee Connie G. , Bridgewater Ben
Published: May 2008

Anechoic recordings of balloon bursts were systematically acquired for various conditions of balloon diameters, puncture location, and inflation pressure. The recordings were analyzed to derive the average frequency spectrum over the effective duration of the acoustic impulse. Although the data show the well-known limitations for the impulse responses (in terms of repeatability and directional behavior) when viewed at high resolution, the results are quite consistent when averaged over one-third octave bands and reveal that the diameter factor (the ratio between the diameter of the inflated balloon to that of its stated maximum), rather than the overall diameter of the balloon, is a good indicator of the sound pressure level, especially above 200 Hz. The study proposes some simple empirical formulas to predict the quantitative sound pressure level and the qualitative spectral response (using the spectral centroid and skewness) from balloon bursts, based on the inflation factor as a variable. The study also offers suggestions to maximize the value of the balloon-burst methodology in building acoustics measurements by describing an effective way to measure reverberation time while simultaneously acquiring useful directional information associated with the reflected sound.
Modeling and analysis of acoustically coupled spaces using a diffusion equation model
Authors: Jing Yun , Xiang Ning
Published: May 2008

Acoustically coupled spaces have been studied and applied to concert halls due to a number of interesting phenomena inside the spaces, including nonexponential energy decays, which are believed to benefit both desired clarity and reverberance. A diffusion equation model has been recently applied to acoustically coupled spaces to predict both steady-state and time-dependent sound field [A. Billon, et. al., J. Acoust. Soc. Am., 120, 2006, pp. 2043-2054], good agreements between simulations and experimental measurements have been found. In this paper, the diffusion equation along with a recently proposed modified boundary condition [Y. Jing and N. Xiang, J. Acoust. Soc. Am., 123, 145-153 (2008)] is used, to reveal intriguing characteristics of coupled spaces, including the sound pressure level distribution along the aperture, energy flow in both rooms, and location dependence of the acoustic source on energy decay characteristics. Experimental results are employed to verify the model, and show the capability of the diffusion equation model for guiding the design of coupled spaces.
Low frequency evaluation of steady-state pressure distribution and reverberation time in two-room coupled system
Authors: Meissner Miroslaw
Published: May 2008

A modal expansion method supported by a numerical implementation has been used for studying acoustic properties of coupled room system composed of two connected rectangular enclosures. In a theoretical model a low frequency limit was considered, where modes are lightly damped, thus they were approximated by eigenmodes of a hard-walled room. Eigenfunctions and eigenfrequencies were computed numerically via an application of the forced oscillator method. Calculation results have shown a great influence of absorbing material location and sound source position on the distribution of acoustic pressure and sound decay inside enclosures. As was shown it is the result of a modal localization caused by a generation of modes with eigenfrequencies very close to frequencies of modes in rectangular prisms having the same dimensions as enclosures. When one of enclosures was much more absorbent than the other one, calculation data have demonstrated an interaction of modes during a sound decay that produces reverberant curves with a rapid initial decay and a shallow late decay slope. As was found a “sagging” appearance of decay curves occurs when a late sound decay is dominated by a decay of eigenmodes localized in an enclosure with a weak sound damping.
Sound-speed estimation from RAFOS transmissions
Authors: Skarsoulis Emmanuel , Piperakis George
Published: May 2008

Acoustic navigation of Lagrangian (moving) floats is carried out by measuring travel times from a number of fixed stations/moorings. A minimum of two fixed stations are needed for location estimation in the horizontal, whereas an additional fixed station is commonly used to remove left-right ambiguity. The signals (RAFOS) and sampling schemes used in ocean acoustic navigation are characterized by limited time resolution (order of 200 msec), much smaller than the resolution used in travel-time tomography (order of 1-10 msec). The possibility of combining navigation signals (travel times) from three fixed stations to multiple moving floats for simultaneous sound-speed estimation and float localization is examined here. The redundant travel-time information in this case offers a significant advantage and makes the accurate estimation of the speed of sound feasible. It is shown that the estimation error for the sound speed decreases with the number of floats, and thus the estimation accuracy improves as the set of floats grows larger. This procedure also leads to improved location estimates for the individual floats. A number of numerical experiments are used to demonstrate the performance of the method. [Work supported by EU/FP6 Damocles project.]
Dual confocal ultrasound system for shear wave elastography
Authors: Gray Michael D. , Martin James S. , Rogers Peter H.
Published: May 2008

A dual confocal transducer system for ultrasound-based elastography is presented. The system is intended to noninvasively measure the complex shear speed in cetacean head tissues, including brain, jaw fat, and melon. The system instrumentation features a pair of dual-element confocal ultrasound transducers, one of which is used to remotely generate low frequency (100-1000 Hz) shear waves in soft tissues via radiation force, and the other is used to measure the resulting shear wave displacements using Doppler techniques. One transducer is configured as an open ring into which the other transducer can be placed and translated. The relative positions of the transducers are mechanically manipulated in order to measure short-path propagation and estimate shear wave speed and loss. Work supported by ONR.
Nonlinear ultrasonic imagery of high contrast objects
Authors: Guillermin Régine , Lasaygues Philippe
Published: May 2008

This study is concerned whith the ultrasonic imagery of elastic materials like cylinders or tubes by diffraction tomography technic. The aim of this work is then to solve a nonlinear inverse scattering problem. Various methods can be employed, generally involving a minimization of the differences between modeling data and measurements. The Distorted Born Iterative (DBI) method belongs to the class of algebraic reconstruction algorithms and have therefore been investigated in literature. Very promising results have been obtained both on synthetic and experimental data especially for electromagnetic inverse diffraction problems, but as far as the authors know few ultrasonic experimental results are available. This method was developed to increase the domain of application of the Born approximation to high contrast targets. Iterations are performed numerically solving a forward and an inverse problems at every iteration. This yields quantitative information about the scatterer, such as the speed of sound. Inversions of both numerical and experimental data are presented.
Inverse scattering in modern ultrasound imaging
Authors: Simonetti Francesco
Published: May 2008

Progress in solid state electronics and sensor manufacturing has led to the rapid development of ultrasound arrays over the last decade resulting in prototypes with thousands of transreceivers. Ultrasound scanners that use this technology are widely used in medical imaging and are based on beamforming techniques. In a similar fashion to an optical lens, the array forms an aperture which can focus and steer an ultrasound beam in space as it is done by microscopes and telescopes. The beamforming process can be seen as an inverse scattering problem whereby the scattering measurements are used to reconstruct the structure of the object being probed. To achieve this, a model that describes the interaction of the probing wave with the object is required. Beamforming assumes that scattering events occurring at different locations within the object are independent of each other, thus neglecting multiple scattering. Here, it is argue that accounting for more accurate wave-matter interaction models in the inverse scattering problem leads to greater image quality than that obtained with conventional beamforming. Experimental images with unprecedented resolution beyond the classical diffraction limit are presented along with tomographic reconstructions of a complex 3D breast phantom that show striking similarities with x-ray CT.