bluuebunny/crossref_metadata_2025 huggingface dataset:
Diffraction formulation for the sound radiation of a loudspeaker on a rigid convex edged shape enclosure
Authors: Roggerone Vincent , Corteel Etienne , Boutillon Xavier
Published: June 2017

We present a method for calculating the sound radiation of a loudspeaker on a box-shape enclosure. This method is based on the iterative Asheim-Svensson formulation [Asheim et al. J. Acoust. Soc. Am., 2013]. In this geometrical acoustical model, the radiated sound is given by the addition of the direct sound of a baffled piston and the sound scattered by the edges of the loudspeaker enclosure. The latter are expressed in the form of multiple-order edge diffraction components. This method becomes particularly attractive at high frequencies since the maximum order required to get a correct estimation decreases with frequency. Altogether, the method becomes less costly than the Boundary Element Method (BEM) beyond a given frequency. The convergence of the method can be estimated by considering the distance traveled by the creeping wave on the enclosure instead of considering the successive orders of diffraction by each edge. An iterative formulation follows which is well-suited to slender objects such as a sound bar. Comparisons with measurements and results of a BEM calculation will be presented. [Work supported by the ANR-13-CORD-0008 EDISON 3D grant from the French National Agency of Research.]
Reduced order modeling in topology optimization of vibroacoustic problems
Authors: Creixell Mediante Ester , Jensen Jakob Søndergaard , Brunskog Jonas , Larsen Martin
Published: June 2017

There is an interest in introducing topology optimization techniques in the design process of structural-acoustic systems. In topology optimization, the design space must be finely meshed in order to obtain an accurate design, which results in large numbers of degrees of freedom when designing complex 3D parts. The optimization process can therefore become highly time consuming due to the need to solve a large system of equations at each iteration. Projection-based parametric Model Order Reduction (pMOR) methods have successfully been applied for reducing the computational cost of material or size optimization in large vibroacoustic models; however, new challenges are encountered when dealing with topology optimization. Since a design parameter per element is considered, the total number of design variables becomes very large; this poses a challenge to most existing pMOR techniques, which suffer from the curse of dimensionality. Moreover, the fact that the nature of the elements changes throughout the optimization (material to void or material to air) makes it more difficult to create a global basis that is accurate throughout the whole design space. In this work, these challenges are investigated and different approaches to achieving an efficient reduction technique for such problems are discussed.
Definition of appropriate indicator and threshold values for intelligibility: Application for rolling stock’s public address systems
Authors: Aubin Fabrice , DuBois Françoise , Mellet Cyril , Gerault Christophe , Lambourg Christophe , Peyret Paul
Published: June 2017

The rolling stock’s public address systems are used to broadcast safety information from the driver cab or the train supervisor. EU legislation request an audible information using the STI-PA intelligibility indicator be at least 0.45 in the whole train. The purpose of the study is to assess the current intelligibility indicator according to the operating conditions of the rolling stock in comparison with other indicators in the literature, then to study the correlation between indicators and the passenger perception and to define threshold values and objective scales of comfort. The first step was to define a methodology to characterize the rolling stock’s public address systems. Secondly, two kinds of measurements were performed in a high speed train at several positions: the end-to-end public addresses system regarding its linear and non-linear characteristics in order to simulate distortion occurrence in the transmission channel at various operating condition. As a result of this study, standard intelligibility indicators showed poor correlations with intelligibility scores from the listening test, especially when the degradation is due to distortion. Fields of improvement are investigated using intelligibility indicators based on clean and degraded speech signal comparison.
Introduction of real-time visual feedback impairs intelligibility when other senses are degraded
Authors: Casserly Elizabeth D. , Marino Francesca
Published: June 2017

Sensory feedback allows talkers to accurately control speech production. Under ordinary circumstances, real-time speech feedback is available in the auditory and somatosensory modalities. When sensation in these modes is degraded, the accuracy of speech motor control is impaired and intelligibility decreases. In the present study, we documented this drop in intelligibility for speech produced with degraded sensory feedback in the auditory (8-channel cochlear implant simulation) and somatosensory (1 mL benzocaine topical application) domains. Speakers (N = 15) were also asked, however, to produce speech in front of a mirror while their senses were degraded, giving them access to an alternate fully-specified but atypical source of sensory feedback. Given the large body of work showing the benefits of visual speech information in perception, we predicted that speakers would use the visual feedback to improve real-time control. Contrary to that prediction, naïve participants (N = 38) found speech produced with visual feedback (and degraded acoustic/somatosensory feedback) to be less intelligible overall than speech produced without it (and other senses still degraded). This deleterious effect of visual feedback was found for both aural intelligibility and visual (lipread) intelligibility.
Isolating sources of acoustic variability that diminish spectral contrast effects in vowel categorization
Authors: Assgari Ashley , Theodore Rachel M. , Stilp Christian
Published: June 2017

Spectral contrast effects (SCEs) occur when spectral differences between earlier sounds (a precursor sentence) and a target sound are perceptually magnified. For example, listeners label a vowel as /ɪ/ (low F1) more often when following a high-F1 precursor sentence, and report /ɛ/ (high F1) more often following a low-F1 precursor sentence. Recently, these context effects were shown to be modulated by the acoustic variability across precursor sentences. When sentence mean f0 was highly variable from trial to trial, SCEs in categorization of /ɪ/ and /ɛ/ were significantly smaller than when mean f0 was more consistent across sentences (Assgari, Theodore, & Stilp, 2016 ASA). But, is acoustic variability in f0 the best predictor of context effects that influence categorization of vowels differing in F1? Here we tested whether F1 variability in precursor sentences has a comparable effect on vowel categorization to f0 variability. Listeners heard precursor sentences filtered to add a low-F1 or high-F1 spectral peak to produce SCEs in categorization of subsequent tokens from an /ɪ—ɛ/ continuum. Sentences were blocked based on low or high variability in f0 and/or F1 regions. Comparisons of how f0 variability versus F1 variability influence context effects in vowel categorization will be discussed.
Psychophysiological indices of listening effort due to noise masking and nonnative-accent
Authors: Francis Alexander L. , Schumaker Jennifer , Bent Tessa , Zhang Rongrong
Published: June 2017

Physiological responses linked to listening effort may differ depending on whether the increased effort is due to masking vs. distortion of the speech signal (Francis, et al. 2016; Zekveld, et al. 2014), suggesting that listeners may engage different cognitive strategies to compensate for different sources of reduced intelligibility. Here, we assessed physiological and behavioral indices of effort in participants listening to short stories in two conditions: (1) nonnative-accented speech in quiet and (2) native-accented speech masked by speech-shaped noise. Compared to previous studies, stories were used instead of sentences to investigate effort over longer durations, while accented speech was used to reduce intelligibility more naturally than noise vocoding or text-to-speech synthesis. Masker noise levels were adjusted for each participant to ensure comparable word recognition performance across conditions. Individual characteristics including age, hearing thresholds, vocabulary, selective attention, working memory capacity, personality traits, and noise sensitivity were also measured. Smoothing spline ANOVAs and growth curve analysis will be used to determine overall effects of condition, as well as which traits best predict patterns of effort-related responses over time. Different sources of listening effort are predicted to induce different patterns of physiological response reflecting engagement of different cognitive processes, possibly in a trait-dependent manner.
The intelligibility of glimpsed speech: Effect of competing amplitude modulation
Authors: Miller Rachel E. , Gibbs Bobby E. , Fogerty Daniel
Published: June 2017

The present study investigated how amplitude modulation of an interrupted noise influences the intelligibility of glimpsed speech. Prior studies have demonstrated that amplitude modulation can aid speech intelligibility when speech is periodically interrupted. This study used a competing talker to define high-intensity and low-intensity speech glimpses that were used to interrupt the target speech. These interrupted intervals were filled by one of five different types of amplitude modulated noise; each noise was presented at two different presentation levels. Silent interruption was also examined. This resulted in 22 different experimental conditions. The results indicated effects of glimpsed speech level, noise modulation, and noise level. In agreement with previous studies using periodic interruption, significant benefit was obtained when the noise was amplitude modulated by the missing speech segment, but only when the modulation came from high-intensity speech segments. In contrast, amplitude modulation of the noise by previous high-intensity, preserved portions of the target sentence produced lower intelligibility scores. Additionally, speech recognition with noise amplitude modulated by a competing talker interacted with the glimpsed speech level. These results indicate that amplitude modulation of an interrupted noise can have different effects on sentence recognition, dependent on the informational content of the modulation.
Articulatory peripherality modulates relative attention to the mouth during visual vowel discrimination
Authors: Masapollo Matthew , Franklin Lauren , Morgan James , Polka Linda
Published: June 2017

Masapollo, Polka, and Ménard (2016) have recently reported that adults from different language backgrounds show robust directional asymmetries in unimodal visual-only vowel discrimination: a change in mouth-shape from one associated with a relatively less peripheral vowel to one associated with a relatively more peripheral vowel (in F1-F2 articulatory/acoustic vowel space) results in significantly better performance than a change in the reverse direction. In the present study, we used eye-tracking methodology to examine the gaze behavior of English-speaking subjects while they performed Masapollo et al.'s visual vowel discrimination task. We successfully replicated this directional effect using Masapollo et al.'s visual stimulus materials, and found that subjects deployed selective attention to the oral region compared to the ocular region of the model speaker's face. In addition, gaze fixations to the mouth were found to increase while subjects viewed the more peripheral vocalic articulations compared to the less peripheral articulations, perhaps due to their larger, more extreme oral-facial kinematic patterns. This bias in subjects’ pattern of gaze behavior may contribute to asymmetries in visual vowel perception.
The effects of phonotactic probability on auditory recognition of pseudo-words
Authors: Kelley Matthew C. , Tucker Benjamin V.
Published: June 2017

A number of speech perception studies have been carried out to investigate how we process audio signals containing real words. However, comparatively fewer studies have been conducted looking at how we process audio signals containing phonotactically valid pseudo-words. Many traditional metrics, such as lexical frequency, used as predictors in this kind of analysis are difficult or impossible to calculate for pseudo-words, but other metrics like phonotactic probability can be calculated for such pseudo-words. Phonotactic probability is the likelihood that a particular sequence of phones occurs in a particular language, and it can be easily calculated using existing pronunciation and lexical frequency data. The present study uses the CMU Pronouncing Dictionary and the Google Ngram datasets to calculate phonotactic probability measures for each stimulus in an existing set of English auditory lexical decision responses and then statistically models the influence of phonotactic probability on the participants’ reaction times to the stimuli. This modeling shows a general trend of response times decreasing as phonotactic probability increases. The results are then framed in the greater picture of speech perception and word recognition overall.
The effect of allophonic variation and phonotactic restriction on categorization
Authors: Lu Yu-an , Hwang Jiwon
Published: June 2017

This study presents a case from Korean which demonstrates that allophonic and phonotactic knowledge has an effect on listeners’ categorization choices. In Korean, voicing is generally treated as redundant on consonants since the only voiced consonants are nasals and liquids. However, voiced oral stops can occur intervocalically as allophones of the voiceless lenis counterpart. A further restriction comes from the velar nasal [ŋ], which is restricted to coda position. Two identification experiments, in which Korean listeners were presented with a 10-step continuum from voiced oral to nasal stop in three places of articulation and were asked to decide whether they heard a nasal or not, showed an earlier boundary shift in the nasal responses in the initial position than in the medial position. This finding suggests that Korean listeners do perceive the redundant/allophonic [voice] feature and are likely to interpret a stop containing this feature as nasal in initial position but as an allophonic oral variant in medial position. An effect of place was also observed: Korean listeners were significantly more likely to perceive a nasal segment on the labial/dental continuum than on the velar continuum, suggesting a bias against hearing the phonotactically illegal *ŋ in onset.
On the nature of vocalic representation during lexical access
Authors: Franklin Lauren , Morgan James
Published: June 2017

The current study explores vowel perception and its effects on lexical access by asking the following questions: (1) how does severity of mispronunciation in vowels affect listeners’ ability to recognize familiar words? (2) What is the appropriate metric for measuring severity of vowel mispronunciation? (3) How do vowel mispronunciations and consonant mispronunciations compare in effects on spoken word recognition? Forty-eight monolingual American English speaking adults were tested in an eye tracking task requiring listeners to look to either a referent of a familiar label or a novel referent with no known label when the vowel of the familiar label was altered along one, two, or three phonological dimensions. Results showed that participants were sensitive to changes in vowels; time course analyses showed earlier divergence for vowel mispronunciations than for consonant mispronunciations in previous studies. However, vowel mispronunciations had less effect on activation of target lexical items than had consonant mispronunciations. A continuous measure of psychophysical acoustic difference better predicted participants’ looking patterns than a discrete measure of phonological features (height, backness, and roundedness). Together, these results suggest that in American English, vowels condition lexical access less strongly than consonants, perhaps due in part to their more continuous perception.
Reduplication and the perception of consonants under repetition
Authors: Zukoff Sam , Storme Benjamin
Published: June 2017

This paper tests a hypothesis about the perception of consonants under repetition. In the Indo-European languages, stop-sonorant-initial roots reduplicate by copying C1: pa-plana (schematic); however, other cluster types, including stop-stop-initial roots, display different behaviors: e.g. pta-ptana (cluster-copying), ta-ptana (C2-copying), a-ptana (non-copying), never *pa-ptana. Zukoff (2015) proposed that this divergent behavior is induced by perceptual factors: Hypothesis1: Given the same segmental context (here, VC), a consonant is more confusable with similar consonants (e.g. p ~ k) if it is immediately preceded by an identical consonant than a non-identical consonant—i.e. better identification of p as p in […tapt…] than in […papt…]. Hypothesis2: This effect is smaller when the repeated consonant has robust acoustic cues to contrast—i.e. better identification of repeated p as p in […papl…] than in […papt…]. Two native French speakers were recorded reading nonce words of the shape [{p,t,k}a{p,k}{t,l}ana]. 37 English speakers listened to the stimuli mixed with a speech-shaped noise (SNR = 3 db), and were asked to identify the second consonant ([p] or [k]). On average, the percent of correct identification was smallest when the first and second consonants were identical and the second consonant was followed by [t], in accordance with the hypotheses.
Effects of frequency region and number of formants in an interferer on the informational masking of speech
Authors: Roberts Brian , Summers Robert J.
Published: June 2017

This study explored whether the extent of informational masking depends on the frequency region and number of formants in an interferer. Target formants—monotonized three-formant analogues of natural sentences—were presented monaurally, with the target ear assigned randomly on each trial. Interferers were presented contralaterally. In experiment 1, single-formant interferers were created using the time-reversed F2 frequency contour and constant amplitude, RMS-matched to F2. Interferer center frequency was matched to that of F1, F2, or F3, while maintaining the extent of formant-frequency variation (depth) on a log scale. In experiment 2, the interferer comprised either one formant (F1) or all three, created using the time-reversed frequency contours of the corresponding targets and RMS-matched constant amplitudes. Including the higher formants had little effect on interferer intensity. Interferer formant-frequency variation was scaled to 0%, 50%, or 100% of the original depth. Adding an interferer lowered target intelligibility; frequency region had relatively little effect, but increasing depth of formant-frequency variation and number of formants had independent and additive effects. This suggests that the impact on intelligibility depends primarily on the number of formants and the overall extent of frequency variation in the interferer, not on any particular frequency region. [Work supported by ESRC.]
Impact of noise and noise reduction on processing effort: A pupillometry study
Authors: Wendt Dorothea , Hietkamp Renskje K , Lunner Thomas
Published: June 2017

Speech understanding in adverse listening conditions induces cognitive demands. Processing effort typically increases for acoustically degraded speech. Moreover, processing effort depends on listener-specific factors, such as cognitive abilities and hearing loss. While noise reduction schemes are able to attenuate interfering noise, the impact on processing effort has not yet been clarified. The present study examined the benefit of noise reduction on processing effort allocated for speech recognition. The influence of noise reduction on processing effort was evaluated by measuring the Peak Pupil Dilation (PPD) of 24 hearing-impaired listeners while performing a speech recognition task. Speech recognition performances and PPDs were measured at two different signal-to-noise ratios (SNRs) corresponding to either the individual 50% correct (L50) or the 95% correct (L95) performance level with and without noise reduction. Processing effort increased at the L50 compared to the L95. Moreover, the benefit of the noise reduction was demonstrated for both the L50 and the L95, i.e., where speech recognition was at ceiling performance. The results emphasized the relevance of the PPD measure as an indicator of processing effort in situations where the traditional speech reception measures fail due to ceiling effects.
Processing speaker variability in Mandarin word recognition
Authors: Zhang Yu , Lee Chao-Yang
Published: June 2017

The effect of speaker variability on Mandarin word recognition was investigated in two short-term priming experiments. Prime-target pairs that are identical (e.g., 画面image—画面image) or semantically related (e.g., 声音sound—画面image) were presented to native listeners auditorily in a lexical decision task. Since identical or related pairs usually elicit faster response relative to unrelated pairs, the question is whether prime and target pairs spoken by different speakers would affect the magnitude of priming. Forty-eight listeners made lexical decisions on the targets, and the speed and accuracy of the responses were measured. It was hypothesized that speaker variability between prime and target would result in reduced priming. However, contrary to previous studies using English materials, results from neither experiments support the hypothesis. The effect of speaker variability on priming appears to depend on listeners’ language background, suggesting tone-language users may be less susceptible to speaker variability in spoken word recognition.
Automated change detection for synthetic aperture sonar
Authors: G-Michael Tesfaye
Published: June 2017

Change detection in seabed mapping is the process by which regions of interest are highlighted through the comparison of current scene data with historical data, and involves techniques that have application to a wide variety of disciplines and sensing modalities. Automated comparison of multi-temporal sidescan sonar images at the pixel (or parcel) level is challenging as the background pixels change due to a variety of factors. These include image resolution that degrades as a function of range, and temporal changes in the propagation medium and seafloor structure. With the advent of synthetic aperture sonars (SAS), which provide constant resolution over the swath and are deployed on actively navigated platforms capable of precise track repetition, the automated comparison of multi-temporal seabed images has in recent years been shown to be feasible. Change detection through the automated comparison of multi-temporal SAS imagery can be generally categorized as incoherent or coherent, where incoherent implies identifying changes in the amplitude, and coherent implies detecting changes in both amplitude and phase of the images. Utilizing the phase component may lead to detection of a physical disturbance in the scene. This presentation will provide an overview of the state-of-the-art of automated sonar seabed change detection.
Depth estimation of water column objects using interferometric synthetic aperture sonar
Authors: Sæbø Torstein O. , Hansen Roy E. , Synnes Stig A. , Lorentzen Ole E.
Published: June 2017

Synthetic Aperture Sonar (SAS) is a technique which delivers sonar images of the seabed with both high resolution and large area coverage rate. SAS is therefore a well suited sensor for search of small objects on the seafloor, and is an important tool in many emerging mine countermeasures (MCM) systems. An interferometric SAS system can also resolve the angle of arrival in the vertical plane, and thus estimate the depth of an object. In this talk, we present techniques using SAS imaging for depth estimation of small objects, not on the seafloor, but located in the water column. We consider the effect of geometry, sensor settings and processing parameters. For objects of interest, we present a belief propagation inspired method for estimating the depth of the objects. This method is CPU intensive, but avoids the phase ambiguity problem encountered in standard SAS interferometry. We compare this method to a coarse depth estimate acquired from the multipath response in the SAS images as well as to ground truth. We show example images and depth estimates from the Kongsberg HISAS interferometric SAS collected by a HUGIN autonomous underwater vehicle.
Synthetic aperture sonar calibration using active transponders
Authors: O'Donnell Brian , Cook Daniel
Published: June 2017

There is an emerging desire within the synthetic aperture sonar community to establish the theory and practical means for calibrating imagery, such that each pixel value represents an actual backscatter coefficient. Image calibration has long been standard practice for remote sensing synthetic aperture radar. However, there are a number of challenges that make calibration of sonar imagery more difficult. Among these is the fact that good inexpensive passive targets (like corner reflectors used in radar) do not have an exact counterpart in underwater acoustics. Passive calibration targets for imaging sonar, such as solid spheres or specially-designed focusing spheres, are used in practice, but active transponders offer far more capability and flexibility. The advantages and applications of active transponders are discussed, along with the current development status of a project at GTRI to design and build an affordable and recoverable calibration device.
Signal processing trade-offs for the representation and quality assessment of acoustic color signatures
Authors: Park J. D. , Cook Daniel , Hunter Alan J.
Published: June 2017

Acoustic color is a representation of an object, typically 2-D, which is constructed to show the evolution of the spectral response over the aspect of the object. The two natural axes for this representation are frequency and the aspect to the object. It is intuitive to assume finer resolution in both dimensions would lead to more information extractable for improved quality. However, with conventional linear track data collection methods, there is an inherent trade-off between signal processing decisions and the amount of information that can be utilized without loss of quality. In this work, this trade-off is investigated for an object with a simple geometry, and various quality metrics are discussed. For objects with spectral response that changes slowly over aspect, quality can be improved with methods such as synthetic aperture sonar processing. However, the effect of these processing decisions can depend on the type of object being represented. Other representation approaches as extensions of acoustic color will also be explored, such as time-evolving acoustic color that shows how the spectral response changes within a ping cycle.
Performance of coherence based adaptive sonar beamformers
Authors: Austeng Andreas , Rindal Ole Marius H. , Rodriguez-Molares Alfonso , Hansen Roy E.
Published: June 2017

Recent progress in hardware and computing power has lead to an increased interest in adaptive beamforming for sonar imaging. Several algorithms that for each pixel scale the original sonar image with a coherence estimate of the received data have been proposed. All of these algorithms claim to improve both contrast and resolution. Close examination of the claimed improvement reveals that parts of the reported effects stem from stretching of the dynamic range in the images. This effect is generally unwanted as it can be obtained without extra computation. Of importance is the actual improvement stemming from coherence scaling. In this work we examine the performance of several different coherence based adaptive beamformers (Coherence factor (CF), Generalized CF, Scaled CF, Phase CF, Spatio-Temporally Smoothed CF, and Scaled Wiener postfilter) after removing the unwanted effect from dynamic range stretching. The contrast and resolution performance are compared on simulated and experimental side scan sonar images. Even though dynamic range stretching explains most of the earlier reported improvements, there are differences among the approaches that are worth to take into consideration when choosing which algorithm to apply.
Evolving the audio equalizer
Authors: Yonovitz David
Published: June 2017

Current audio equalization techniques include Shelf, Parametric, and Graphic Equalizers. They are prevalent in all professional and commercial audio implementations. These techniques modify spectral components within specified bands by applying gain or attenuation. However, current techniques each have inherent issues with their use. The issues of concern are dynamic spectrum input and the degradation of Signal-to-Noise Ratio (SNR). In the former, the input spectrum is not static, yet all the current implementations of equalization are. The equalization must be dynamic and “track” the input signal spectrum to be effective. In the case of SNR, output noise is increased when no signal is present in the spectral band when adding gain. In addition, current techniques do not posses the precision required to only encompass the signal spectral components. in an evolution of equalization with input tracking capability, signal spectral components are identified; all other spectrum may be considered as noise and can be attenuated. The evolution of audio equalizers has progressed that negates the stated issues. Its implementation is realized in the Harmonic Tracking Equalizer (HTEq). Emulations of current techniques with improvement, noise reduction, and spectral modification will be presented.
Global acoustic propagation and the link between hydroacoustics and infrasound
Authors: Heaney Kevin D.
Published: June 2017

The ocean is nearly transparent for acoustic propagation at low frequencies, leading to the detection of signals (seismic events, volcanoes and man-made signals) at distances as large as the ocean basin. When the ocean depth approaches the acoustic wavelength (~ 1500m for 1 Hz energy) the potential for conversion of energy from ocean acoustic propagation to atmospheric infrasonic propagation exists. This was observed in an earthquake off the coast of Australia (Evers et al. GRL 2014) energy was observed as seismic waves, hydro-acoustic waves and then infrasound waves, the latter two on the International Monitoring System (IMS) of the Comprehensive Test Ban Treaty Organization. In this paper, global scale hydro-acoustic propagation modeling from earthquakes and volcanoes will be presented with an emphasis on the locations where conversion to atmospheric propagation will is possible. Recent observations at the Aloha Cables Observatory (Butler JASA 2016) indicate the possibility of a loss of energy from 1-5 Hz as hydro-acoustic signals propagate over the Oahu-Kauai ridge (the Kauai “Keyhole”). Hydro-acoustic and infrasound modeling of this event will be presented.
Infrasound propagation in the atmosphere with mesoscale fluctuations induced by internal gravity waves
Authors: Chunchuzov Igor , Kulichkov Sergey , Popov Oleg , Perepelkin Vitaly
Published: June 2017

The influence of the mesoscale wind velocity and temperature fluctuations induced by internal gravity waves (IGWs) on infrasound propagation in the atmosphere is studied. The statistical characteristics of the fluctuations in the parameters of infrasonic signals (such as variances and temporal spectra of the fluctuations in travel time and angle of arrival, amplitude and time duration) caused by gravity wave-associated fluctuations are studied based on the nonlinear model of shaping of the 3-D spatial spectrum of the fluctuations. The nonlinear shaping mechanism for the 3-D spectrum is associated with both the non-resonance interactions between IGWs and wave breaking processes caused by the wave-induced shear or convective instabilities. The 1-D wave number spectra (vertical and horizontal) of the mesoscale fluctuations obtained from the 3-D model are compared with the observed spectra derived from the radar, lidar and airplane temperature and wind measurements in the middle atmosphere. The results of theory and numerical modeling of infrasound scattering from gravity wave-associated fluctuations are presented. The vertical profiles of the wind velocity fluctuations in the stratosphere and lower thermosphere up to the altitudes of 130 km are retrieved from the infrasound scattered from the mesoscale wind velocity and temperature fluctuations. The results of acoustic probing of the stably stratified atmospheric boundary layer using detonation source of acoustic pulses are discussed.
Caustics of waves in the thermally conducting, viscous atmosphere
Authors: Godin Oleg A.
Published: June 2017

This paper considers waves in the atmospheric as linear acoustic-gravity waves, in which fluid’s buoyancy and compressibility simultaneously serve as restoring forces. Atmosphere is modeled as an inhomogeneous, moving fluid with nearly horizontal winds and gradual variation of its composition, sound speed and wind velocity having representative spatial scales that are large compared to the wavelength. Uniform short-wave asymptotic expansions of the wave field in the presence of a simple caustic are derived and utilized to quantify and compare the effects of wave diffraction and dissipation. Unlike acoustic waves, the geometric, or Berry, phase plays an important role in the caustic asymptotics of acoustic-gravity waves. The uniform asymptotic expansion of acoustic-gravity wave field in the presence of a caustic agrees with known results in the acoustic limit. Away from the caustic on its insonified side, the uniform asymptotic solution reduces to ray-theoretical results. When the source and receiver are located sufficiently far from the caustic, ray-theoretical calculations of the wave absorption are found to be applicable for rays that approach and leave the caustic.
Rayleigh scattering of a cylindrical sound wave by an infinite cylinder
Authors: Baynes Alexander B. , Godin Oleg A.
Published: June 2017

Rayleigh scattering is often considered assuming plane incident waves. However, the full Green’s function is required in a number of problems, e.g., when a scatterer is located close to the ocean surface or the seafloor. This paper considers the Green’s function of the two-dimensional problem that corresponds to scattering of a cylindrical wave by an infinite cylinder embedded in a homogeneous fluid. Soft, rigid, and impedance cylinders are considered. Exact solutions of the problem involve infinite series of products of Bessel functions. Here, closed-form asymptotic solutions are derived, which are valid for arbitrary source and receiver locations outside the cylinder as long as its diameter is small relative to the wavelength. The scattered wave is given by fields of two linear image sources. The image sources are located within the cylinder at its center and at the Kelvin inversion point. The latter originated in the classical electrostatic problem involving a grounded sphere and a point charge. The new asymptotic Green’s functions are employed to characterize infrasound reception by sensors mounted on cylindrical bodies. Further applications of the new asymptotic Green’s functions include image-source analytical solutions to scattering problems in complex interface geometries that typically require numerical methods to be solved.
Remote detection of cryoacoustic signals using noise interferometry of seafloor pressure data
Authors: Ball Justin S. , Sheehan Anne F. , Scambos Ted
Published: June 2017

We have observed a large number of 5-15 Hz hydroacoustic arrivals in seafloor pressure data collected in 2009-2010 by the Marine Observations of Anisotropy Near Aoteroa (MOANA) experiment offshore the South Island of New Zealand. Preliminary manual picking revealed that a small number (<10%) of these signals appeared to originate from Antarctica (potentially related to ice disintegration events). Automatic detection of Antarctic signals in MOANA data using frequency-wavenumber (f-k) analysis is precluded in the 5-15 Hz band by spatial aliasing. Instead we have developed a two-stage directional detection scheme based on ambient noise Green’s functions between MOANA stations, which reveal noise directivity in the amplitude asymmetry between forward and reverse lags. For each 20-minute time window of the continuous dataset, we cross-correlate all pressure data, and tabulate windows containing significant energy at the predicted acoustic arrival times between stations and originating from backazimuths consistent with Antarctica. We then beamform each candidate window to estimate signal approach angles. We find that our noise-based approach succeeds in detecting our initial manually-picked events. Back-projecting our detections indicates that many correlate with known iceberg locations from satellite remote sensing studies. We also observe that detection frequency is comparatively lowest in Austral winter, as expected.
Seismic and hydroacoustic analysis of four large underwater explosions off the east coast of Florida
Authors: Pulli Jay J. , Heaney Kevin D.
Published: June 2017

During the summer of 2016, the US Navy detonated four large underwater explosions off the east coast of Florida as part of shock wave testing for the Littoral Combat Ships USS Jackson and USS Milwaukee. The water depth at the explosion site is 900 m. Videos of the events provide further insight into the sources. Originally listed as magnitude 3.7 earthquakes in USGS bulletins, the source types were changed to “Experimental Explosion” as the Navy began releasing information to local news stations. These explosions were recorded on US seismic stations to distances of ~2000 km and on the hydroacoustic array at Ascension Island at a distance of ~8100 km. Seismic signals are complex but cepstral analysis reveals a clear bubble pulse period of 1.15 sec, corresponding to source depths of 50 meters. At Ascension the signals arrive at an RMS level of 136 dB at an SNR of 30 dB. We modeled the propagation loss from the source to Ascension using broadband PE and find the propagation loss to be 126 dB. Backing out this loss, we estimate source levels for the two explosions at 262 dB corresponding to explosion yields of 11,000 lbs.
Underwater acoustic monitoring of regulatory fish criteria within a high flow environment
Authors: Varnik Kristjan , Kalapinski Erik J.
Published: June 2017

Underwater acoustic monitoring addressed at assessing compliance with regulatory fish criteria, was performed in the Kennebec river. The acoustic criteria was based on sound pressure levels, although particle velocity is also an area of increasing concern. The velocity and direction shifts of the strong currents created unique challenges in the study design, deployment and data processing of hydroacoustic monitoring equipment. Both floating and static systems were needed to capture sound pressure levels at multiple river locations.
Underwater measurement of source level in waveguides using equivalent source method
Authors: He Tengjiao , Mo Shiqi , Fang Erzheng
Published: June 2017

This paper develops a method to evaluate the source level of the underwater structure in shallow water waveguides. This method requires the measurement of the pressure on a closed surface surrounding the underwater structure and the knowledge of waveguide parameters, or the measurement of the pressure and the velocity on a closed surface surrounding the underwater structure. The calculation makes use of equivalent source method(ESM), and is performed in two steps. First, the reflected and scattered fields are removed to obtain the free-field pressure that would be radiated by the measured structure in an anechoic environment. Then the recovered free-field pressure field is used to calculate the source level of the measured structure. Numerical calculation was investigated to demonstrate the feasibility of the method. The results from numerical calculations indicate that the source level of underwater structures can be obtained by using the method accurately. Furthermore, the method shows a promising way to engineering applications.
Potential impact of global warming on sound propagation in monsoon induced surface mixed layers
Authors: Browning David , Herstein Peter
Published: June 2017

Acoustic surface ducts in mixed layers can be an important mode of sonar propagation. The precipitation from monsoons seasonally create mixed surface layers near the equator in every major ocean. Although not as robust as mixed layers that occur at higher latitudes, they may provide the best examples of the possible global warming impact on sound propagation. This would include acoustic duct propagation properties such as attenuation, surface loss, cutoff frequency, and ambient noise. This is just a first attempt, based on preliminary estimates, to evaluate possible change. To be considered are direct effects such as ocean acidification and warming water; the seasonal impact on monsoons, like greater precipitation and duration; and finally individual transient events such as storm intensity and number (including typhoons). Given the usual monsoon variability, it may be challenging to sort out changes, but monsoon duct acoustics may be a promising new area for investigators.
Effects of depth-dependent sound speed on Lloyd mirror patterns
Authors: Martinelli Sheri , Holland Charles W.
Published: June 2017

The classical Lloyd mirror describes the interference pattern in pressure magnitude between direct and reflected propagation paths arising from a point source at depth d in the water column at a receiver located at range R, R >> d. In a homogeneous medium, the magnitude of acoustic pressure has a simple expression in terms of (approximate) propagation angle: |p|=(2/R0)|sin kd cos Θ0. For fast calculation of reverberation strength, we can apply this pattern to capture the effects of reflections from an idealized flat sea surface. However since we are interested in long range calculations, it is expected that the existence of sound speed gradients will affect the shape of this pattern, but how significant are these effects? To study this question, we derive a generalized Lloyd mirror for a linear-in-depth sound speed profile. We present results and discuss the implications. [Work supported by ONR through a STTR partnership with OASIS.]
Estimating the influence of ice thickness and elasticity on long-range narrow-band reverberation in a representative Arctic environment
Authors: Frank Scott D. , Ivakin Anatoliy N.
Published: June 2017

A full-field perturbation approach [A. Ivakin (2016), J. Acoust. Soc. Am., 140(1), 657-665] is modified for an ice-covered ocean and applied to estimating narrow-band long-range reverberation caused by roughness of the ice-water interface. First-order approximation of the approach is used which requires the roughness amplitudes be small compared to the acoustic wavelength. An upward refracting sound speed water column profile typical for Arctic conditions is assumed. To obtain the zeroth-order Green’s function and transmission loss field used in the reverberation model, elastic parabolic equation solutions [J. Collis, S. Frank, et al. (2016), J. Acoust. Soc. Am., 139(5), 2672-2682] are generated in range-independent environments. Ice is represented by two layers. The first approximates acoustic properties of a relatively thin, water-saturated transitional ice layer and is described as a stratified fluid with sound speed increasing with the distance from the ice-water interface. Second layer is introduced as a homogeneous isotropic elastic medium with fixed complex shear and longitudinal wave speeds. Effects of ice properties are discussed and demonstrated by comparing reverberation calculated for different ice layer thicknesses and shear speeds varying from zero (for a fluid model) to typical ice values. [Work supported by ONR.]
An
In Vitro
Enzyme System for the Production of
myo
-Inositol from Starch
Authors: Fujisawa Tomoko , Fujinaga Shohei , Atomi Haruyuki
Published: June 2017

We developed an
in vitro
enzyme system to produce
myo
-inositol from starch. Four enzymes were used, maltodextrin phosphorylase (MalP), phosphoglucomutase (PGM),
myo
-inositol-3-phosphate synthase (MIPS), and inositol monophosphatase (IMPase). The enzymes were thermostable: MalP and PGM from the hyperthermophilic archaeon
Thermococcus kodakarensis
, MIPS from the hyperthermophilic archaeon
Archaeoglobus fulgidus
, and IMPase from the hyperthermophilic bacterium
Thermotoga maritima
. The enzymes were individually produced in
Escherichia coli
and partially purified by subjecting cell extracts to heat treatment and removing denatured proteins. The four enzyme samples were incubated at 90°C with amylose, phosphate, and NAD
+
, resulting in the production of
myo
-inositol with a yield of over 90% at 2 h. The effects of varying the concentrations of reaction components were examined. When the system volume was increased and NAD
+
was added every 2 h, we observed the production of 2.9 g
myo
-inositol from 2.9 g amylose after 7 h, achieving gram-scale production with a molar conversion of approximately 96%. We further integrated the pullulanase from
T. maritima
into the system and observed
myo
-inositol production from soluble starch and raw potato with yields of 73% and 57 to 61%, respectively.

IMPORTANCE
myo
-Inositol is an important nutrient for human health and provides a wide variety of benefits as a dietary supplement. This study demonstrates an alternative method to produce
myo
-inositol from starch with an
in vitro
enzyme system using thermostable maltodextrin phosphorylase (MalP), phosphoglucomutase (PGM),
myo
-inositol-3-phosphate synthase, and
myo
-inositol monophosphatase. By utilizing MalP and PGM to generate glucose 6-phosphate, we can avoid the addition of phosphate donors such as ATP, the use of which would not be practical for scaled-up production of
myo
-inositol.
myo
-Inositol was produced from amylose on the gram scale with yields exceeding 90%. Conversion rates were also high, producing over 2 g of
myo
-inositol within 4 h in a 200-ml reaction mixture. By adding a thermostable pullulanase, we produced
myo
-inositol from raw potato with yields of 57 to 61% (wt/wt). The system developed here should provide an attractive alternative to conventional methods that rely on extraction or microbial production of
myo
-inositol.