bluuebunny/crossref_metadata_2025 huggingface dataset:
Reflection coefficient measurement using a finite-difference-injection technique
Authors: Börsing Nele , Donahue Carly , van Manen Dirk-Jan , Robertsson Johan O.
Published: June 2017

Experimentally determining the acoustic reflection properties of materials requires accurate knowledge of the incident and reflected wave field at the reflecting interface. Consequently, a number of methods have been proposed for measuring the reflection coefficient, but most are limited to measuring only the normal incidence reflection coefficient or assume plane wave conditions. Here, we derive the reflection coefficient from pressure measurements by using a finite-difference wave field injection technique, which is applicable for a wide range of incidence angles and does not rely on the common plane wave assumption. It requires measurements at three planes parallel to the reflector and addresses two key objectives, namely, (1) the recorded wave field is separated into its incident and reflected components without the need of time-windowing, and (2) the separated components are re-datumed to the reflecting interface. The latter step comprises a forward propagation in time of the incident wave and a time-reversed backward propagation of the reflected wave. We experimentally test the methodology on laboratory data of the reflection from the free surface recorded in water and demonstrate its applicability to accurately measure the reflection coefficient for incidence angles up to 60°.
Roughness parameters imaging with a multibeam echosounder
Authors: Pinson Samuel , Stéphan Yann , Holland Charles W.
Published: June 2017

The aim of the study is to perform quantitative imaging of the seafloor random parameters using a multibeam echosounder. More specifically we present in this communication a focus on the interface roughnesses with controlled parameters using a 3D modeling of a layered media with rough interfaces. The modeling consists of a sum of integrals over each interface of the layered medium that implies a reasonable computation cost and the possibility to perform a high number of numerical experiments. Specular reflection and backscattering are analyzed by estimating their means and variances through imaging algorithms. [Research supported by the ONR Ocean Acoustics Program.]
Interface wave studies on a laboratory test facility
Authors: Potty Gopu R. , Sapiie Rendhy M. , Small Chris J. , Miller James H.
Published: June 2017

Rayleigh wave measurements were made in the Interface Wave Test Facility at the University of Rhode Island to develop techniques to estimate the shear wave properties of near surface sediment. Repeating source events at various ranges spaced equally at 0.15 m from a fixed receiver (accelerometer) created a virtual source array. The source events consisted of dropping a tennis ball thereby exciting Rayleigh waves. A monitoring accelerometer was used to record each source event at a fixed distance from the source location in order to time it. This enabled to calculate the travel time of the Rayleigh waves from the monitoring receiver to the fixed receiver. The phase velocity dispersion is calculated using high resolution frequency-wavenumber processing. The shear wave speed of the sediment layers in the “sand tank” is estimated using an inversion scheme. The shear wave speed estimates is compared to direct measurements using a calibrated bender element system at selected depths. The bender element system was placed in a test tank initially filled with mason sand and the Rayleigh wave inversion system was deployed on the surface of the sand in the tank. [Work supported by Army Research Office and ONR.]
Global scale underwater sound modeling and data analysis
Authors: Oliveira Tiago , Lin Ying-Tsong , Newhall Arthur , Nichols Stephen , Bradley Dave
Published: June 2017

Underwater low-frequency sound can travel great distances in the oceans, and sound triggered in the sea by the mechanical energy transfer from the Earth's crust (e.g., earthquakes or volcanoes) and by the energy transfer occurring at the water surface (e.g., wave storms or ice-quakes) can be detected at thousands of kilometers from the source. However, source characterization based on recorded sound data analysis involves significant scientific challenges and uncertainties. A variety of geological and physical oceanographic features can cause horizontal refraction, reflection, and diffraction on global scale sound propagation. In this regard, three-dimensional underwater sound models are required for accurately predicting global scale sound propagation. In this work, based on a Southern Mid-Atlantic Ridge earthquake event, we show the importance of geological and physical oceanographic features in the long range propagation of oceanic sound. A three-dimensional sound propagation model using the parabolic equation (PE) approximation and the split-step Fourier (SSF) method is used. Numerical results are compared with field data recorded by hydrophones at great distances from the source. Based on the case study, a discussion and recommendation on the global scale underwater sound modeling and data analysis are presented.
Investigation of error of propagated sound due to bathymetric interpolation
Authors: Hafla Erin C. , Johnson Erick , Roberts Jesse
Published: June 2017

Paracoustic is a parallelized acoustic-wave propagation package developed by Sandia National Laboratories to model marine hydrokinetic (MHK) devices in complex environments. It solves a linearized set of the velocity-pressure partial differential equations using the finite-difference method and allows for 3D variations in medium densities, sound speeds, and bathymetry. In-situ measurements of these quantities, or the solution resolution from hydrodynamic models, are sometimes resolved at a coarser spacing than is required to accurately predict the propagated sound levels within Paracousti. This will therefore require interpolation of these quantities onto a refined grid, introducing model errors. The size of the refined grid is determined by the maximum frequency of an MHK source profile and the underwater sound speed. A single point source in a two-layer waveguide with realistic bathymetry is used to compare the model error between three interpolation schemes: nearest-neighbor, linear, and cubic. Preliminary results indicate that there are significant differences in model error due to the particular interpolation scheme used.
Fast multipole accelerated boundary element method for the Helmholtz equation in three dimensions on heterogeneous architectures
Authors: Gumerov Nail A. , Duraiswami Ramani
Published: June 2017

Numerical simulations related to human hearing, architectural and underwater acoustics, and multiple scattering require computational solution of the Helmholtz equation in three dimensions with complex shaped boundaries. Boundary element methods (BEM) are among the most accurate and efficient methods used for this purpose. However, solution of high frequency/large domain problems is challenging due to poor scaling of conventional solvers with the frequency and domain size. The use of the fast multipole methods (FMM) resolves many problems related to the scalability [N.A. Gumerov and R. Duraiswami, J. Acoust. Soc. Am. 125(1), 191205, 2009]. Additional accelerations are needed to be able to solve practical problems over the entire range of human audible frequencies and can be provided using graphics processors (GPUs) with multicore CPUs. In this work, we report development and demonstration of the FMM/GPU accelerated BEM for the Helmholtz equation in 3D designed for hybrid CPU/GPU architectures. Innovations related to choices of preconditioners, parallelization strategies, and choice of optimal parameters will be presented. A single PC version of the algorithm shows accelerations of the order of 10 times compared to the BEM accelerated with the FMM alone. Results for computing head related transfer functions and other standard calculations will be provided.
Geometry-based diffraction auralization for real-time applications in environmental noise
Authors: Stienen Jonas , Vorlaender Michael
Published: June 2017

Geometrical acoustics has become the number one choice in a variety of different virtual acoustics applications, especially if physics-based sound field synthesis at real-time rates is desired. The procedures for interactive auralization on the one hand and calculation of room impulse responses as well as outdoor noise prediction on the other hand are converging if not already merely differ in resolution of parameters, i.e., number of rays or order of image sources. When it comes to diffraction effects at geometrical boundaries, however, the discrepancy between model accuracy and calculation efficiency is still high due to the great computational effort required for geometrical path analysis and propagation simulation. The overall goal of ongoing research in this field aims at closing the gap between the two worlds: making diffraction effects audible in a Virtual Reality application with respect to correct physical sound propagation and true reproduction that is required for serious applications in acoustic consulting business and for research, primarily for outdoor noise situations.
Head-related transfer function personalization for the needs of spatial audio in mixed and virtual reality
Authors: Tashev Ivan J. , Gamper Hannes
Published: June 2017

Virtual Reality (VR) and Mixed reality (MR) devices are typically a head mounted screens, aiming to project objects in an entire environment (VR), or in addition to the existing environment (MR). In both cases, these devices should have the means to create the spatial audio images of the projected objects. Considering the compact form factor of the devices, the most common approach is using binaural audio reproduction through a pair of headphones, isolated (VR) or acoustically transparent (MR). One of the key factors for successful realization of such spatial audio system is personalization of the user Head-Related Transfer Functions (HRTFs). In this paper, we will present and compare several approaches for doing so under the heavy constraints of the VR/MR devices design.
Perceptual evaluation on the influence of individualized near-field head-related transfer functions on auditory distance localization
Authors: Yu Guangzheng , Wu Yuye , Xie Bo-sun
Published: June 2017

It is desired that spatial audio for virtual reality is able to reproduce various auditory localization information so as to recreate virtual source at different directions and distances. Distance-dependent binaural cue (binaural level difference (ILD), loudness, as well as environmental reflections are considered as auditory distance localization cues. In the case of free and near-field within about 1.0 m, the binaural cue which is encoded in near-field head-related transfer function (HRTFs) is an absolute and dominant distance localization cue [D. S. Brungart, JASA, 1999]. However, HRTFs depending on individualized and non-individualized HRTFs are usually used in spatial audio synthesis. In the present work, the perceptual influence of individualized HRTFs distance localization is evaluated by a psychoacoustic experiment. The binaural signals with various bandwidths are synthesized by filtering the input stimuli with individualized and non-individualized near-field HRTFs and then reproduced by headphone. Preliminary results of virtual source localization experiment indicate that individualized HRTFs influences little on distance localization at low frequencies but have some influence at mid and high frequency. [This work was supported by the Natural Science Foundation of China, Grant No. 11574090.]
Algebraic reflections in acoustic ray tracing
Authors: Molin Erik
Published: June 2017

Stochastic ray tracing is currently one of the most popular geometric acoustic algorithms. It is widely used, and it primarily excels for modeling the late room response at high frequencies. A significant bottleneck of the algorithm is the high computational cost of testing rays for intersection with model geometry. Another is the high number of rays required for convergence. Several methods exist to reduce this cost by means of reducing geometric complexity. This paper proposes a method to algebraically compute transmission paths between receivers and sources by use of bidirectional reflectance distribution functions (BRDF), thus decreasing the number of total rays needed. For each ray-geometry intersection, transmission paths are calculated recursively, and several transmission paths can thereby be considered for each intersection test, while allowing for point-like transmitters and receivers.
Update on the change in sound insulation requirements in Canada
Authors: Hoeller Christoph , Mahn Jeffrey
Published: June 2017

In the 2015 edition of the National Building Code of Canada (2015 NBCC, published in January 2016), sound insulation requirements between dwelling units are given in terms of Apparent Sound Transmission Class (ASTC). This is a significant change from the requirements in previous editions of the NBCC which were given in terms of Sound Transmission Class (STC). While the STC rating only accounts for sound transmission through the separating assembly, the ASTC rating also takes into account structural flanking transmission via adjoining building elements. An overview of the change in requirements and of NRC activities to support the code change was given at the ASA meeting in Jacksonville (November 2015). This presentation will provide an update on the implementation of the code change since it came into effect in federal regulations in early 2016. Tools and guidelines provided by the NRC such as Research Report RR-331, “Guide to Calculating Airborne Sound Transmission in Buildings” and the revised version of soundPATHS, NRC’s web application to calculate ASTC ratings, will be presented.
Laminated gypsum wallboard in mid-rise wood construction
Authors: Shi Zhiqiang , Marshall Robert
Published: June 2017

Mid-rise wood construction is a cost-effective and sustainable choice to achieve high performance in commercial and multi-family residential housing. It is gaining popularity in the industry as several building codes, including IBC (2009) and NBCC (2015), now allow five- and six-story constructions, respectively. Acoustic comfort in such buildings is important to attract and retain occupants. Because of its lightweight construction nature, the new code changes the requirements for airborne sound insulation between dwellings from a Sound Transmission Class (STC) rating which only describes the sound insulation of the common partition between rooms to an ASTC rating, which includes contributions from all of the flanking paths. This paper shows laminated SilentFX/QC gypsum wall board is a fast, economical, space-saving, and code-compliant solution in meeting the ASTC requirement of the new building codes with examples. The test methodology is based on ISO 15712 and ISO 10848 standard, and follows the procedure outlined in NRC-331 publication. It consists of testing STC and radiation efficiency of wall partitions and measuring the vibration reduction index of various conjunctions between the partitions and different flanking paths. The ASTC predictions were validated with prior results obtained from the NRC Flanking Facility.
Long-term voice monitoring with smartphone applications and contact microphone
Authors: Astolfi Arianna , Carullo Alessio , Corbellini Simone , Spadola Massimo , Accornero Anna , Puglisi Giuseppina E. , Castellana Antonella , Shtrepi Louena , D'Antonio Gian Luca , Peretti Alessandro , Marcuzzo Giorgio , Pierobon Alberta , Bartolucci Giovanni B.
Published: June 2017

In recent years, the growing interest in the recognition of voice disorders as occupational diseases has required screening methods adaptable to the clinical requirements, capable to extend the collection of baseline data. In this framework, the use of smartphones has gained increasing interest, thanks to advancements in digital technology, which made them suitable for recording and analyzing acoustic signals. Two smartphone applications, based on the Voice Care® technology, have been developed for long-term monitoring of voice activity when combined with a cheap contact microphone embedded in a collar. The applications have been tested in laboratory and used for the monitoring of teachers at kindergarten, primary school, and university. Vocal Holter App allows the selection of short and long term monitoring mode, and three different clusters of vocal parameters related to intensity, intonation, and load, respectively. Most of the results are based on the distributions of occurrences of vocal parameters. A headlight informs the person under monitoring of pathologic voice. Vocal Holter Rec allows data recording and to perform a personalized analysis based on updated parameters. The equipment allows downloading and saving data on a dedicated web site for further processing, comparisons over time, or sharing with physicians or rehabilitators.
Individual factors and its association with experienced noise annoyance in Swedish preschools
Authors: Sjödin Fredrik
Published: June 2017

Studies have shown that preschool teachers often report having a troublesome working environment in terms of high noise levels. Noise annoyance is often reported from employees working under poor acoustical conditions. The aim of the study was to investigate whether there is an association between rated noise annoyance and actual noise exposure for Swedish preschool teachers. Furthermore, the study also aimed to investigate whether preschool teacher with different individual characteristics differs in their rated noise annoyance at work. The study included 90 preschool teachers in Sweden. Data were collected by use of personal carried noise dosimeters and by questionnaires during one representative work week. The average equivalent noise exposure was 71 dBA and the average rated noise annoyance was 65 on a 0-100 mm scale. Rated noise annoyance was not correlated to the sound exposure during a work week (r = 0.66, P = 0.42). Analysis of differences in noise annoyance ratings between preschool teachers with different individual characteristics (hearing impairment, tinnitus, age, and gender) revealed no significant statistical group differences. Other factors needs to be investigated to better explain what affects differences in rated noise annoyance at work among preschool teachers in Sweden.
One-year longitudinal study on teachers’ voice parameters in secondary-school classrooms: Relationships with voice quality assessed by perceptual analysis and voice objective measures
Authors: Castellana Antonella , Puglisi Giuseppina E. , Calosso Giulia , Accornero Anna , Cantor Cutiva Lady Catherine , Fanari Fiammetta , Pellerey Franco , Carullo Alessio , Astolfi Arianna
Published: June 2017

This longitudinal work explores the relationships between three analyses used for assessing teachers’ voice use: the voice monitoring during lessons that describes the teachers’ Vocal Behavior (VB), the perceptual assessment of voice by speech-language pathologists and the estimation of objective parameters from vocalizations to define teachers’ Vocal Performance (VP). About 30 Italian teachers from secondary schools were involved at the beginning and at the end of a school year. In each period, teachers’ vocal activity was monitored using the Voice Care device, which acquires the voice signal through a contact microphone fixed at the neck to estimate sound pressure level, fundamental frequency, and voicing time percentage. Once in each period, two speech-language pathologists performed a perceptual assessment of teachers’ voice using the GIRBAS-scale. On that occasion, teachers vocalized a sustained vowel standing in front of a sound level meter in a quiet room. Jitter, Shimmer and other parameters were extracted using Praat, while a new metric of Cepstral-Peak-Prominance-Smoothed was estimated with a MATLAB script. Several relationships between the outcomes of each analysis were investigated, e.g., statistical differences between the dimension “G” from GIRBAS-scale and objective measures for VB and VP, and correlations between objective measures and perceptual ratings were assessed.
Speech sound pressure level distributions and their descriptive statistics in successive readings for reliable voice monitoring
Authors: Castellana Antonella , Carullo Alessio , Fugiglando Umberto , Puglisi Giuseppina E. , Astolfi Arianna
Published: June 2017

Due to the high prevalence of voice disorders among teachers, there is a growing interest in monitoring voice during lessons. However, the reliability of the results is still to be deepened, especially in the case of repeated monitoring. The present study thus investigates the speech Sound Pressure Levels (SPL) variability under repeatability conditions aiming to provide preliminary normative data for the results assessment. In a semi-anechoic chamber, 17 subjects read twice and subsequently two phonetically balanced passages, which were simultaneously recorded with a sound level meter, a headworn microphone, and a portable vocal analyzer. Each speech sample was characterized through the distribution of SPL occurrences and several descriptive statistics of SPL distribution were calculated. For each subject, statistical differences between the two SPL distributions related to each passage were investigated using the Mann-Whitney U-test. For each group of subjects using the same device, the Wilcoxon signed-rank test was applied to the paired lists of descriptive statistics related to each passage. For mean, mode, and equivalent SPL, the within-speaker and the within-group variability were assessed for each device. For all the devices and SPL parameters, the within-speaker variability was not higher than 2 dB while the within-group variability reached 5.3 dB.
Norwegian experiences of acoustics in classrooms
Authors: Homb Anders
Published: June 2017

During the last decades, the investments on new school buildings and retrofitting of existing buildings have been considerable in Norway and it will continue for the next years. A characteristic of this period have also been a development of the teaching methods and as a consequence of that, a change of the area planning and room layout, in the beginning without considering the acoustic challenges sufficiently. The acoustical norms, guidelines, and recommendations for schools were revised afterwards. Important issues in these documents were on reverberation time, speech intelligibility, and on background noise necessary for sufficient conditions during the educational process. The paper will present the development of the acoustical requirements and recommendations in this period together with some layout examples. The revised requirements and recommendations have been based on international experiences and some Norwegian research studies. The paper will present some results from these studies, both from measurements of relevant parameters and evaluation of student perception. The analysis will focus on the reverberation time, signal no noise ratio, and how to prevent noise in the classroom area from adjacent spaces. Finally, the paper will give some suggestions on how to improve the acoustical conditions in the spaces for the future.
Acoustical measurement of modern Japanese libraries
Authors: Shamoto Kazuma , Ikawa Mai , Itsumura Hiroshi , Ishida Koji , Terasawa Hiroko
Published: June 2017

The function of modern libraries is transforming from a quiet reading space to an active, social, and interactive learning place for old and young people including children. We investigate the room acoustics of modern libraries in order to examine if they can accommodate both needs of silence and bustling communication. We measured impulse responses and sound-decay distribution patterns at three libraries (two university libraries and a public library) with different architectural styles. In addition, we measured the noise level during the library opening hours with active visitors. Every library showed different patterns of sound propagation and visitor activities. Library spaces with densely installed shelves highly absorb noises, while spaces with few shelves and a multiple-height structure were highly echoic. Some carefully designed spaces showed a clear acoustical zoning, that the sound from bustling noise area hardly reach to the quiet reading area even with a high ceiling and sparse shelves.
First harmonic shape analysis of Brazilian free-tailed bat calls during emergence
Authors: Fu Yanqing , Kloepper Laura
Published: June 2017

Echolocating bats can adapt calls when facing challenging echolocation tasks. Previous studies have shown that bats can change their pulse duration, pulse repetition rate, or vary their start/end/peak frequencies depending on behavior. Even though this kind of signal investigation reveals important findings, these approaches to analysis use bulk parameters that may hide subtleties in the call structure that could be important to the bat. In some cases, calls may have the same start and end frequencies but have different FM shapes and meet different sensory needs. In the present study, we demonstrate an algorithm for extracting the first harmonics of the Brazilian free-tailed bat (Tadarida brasiliensis) to investigate how the shape of the call changes. High pass filtering, power banded time-frequency analysis, and search algorithms were used to isolate the first harmonics. By tracking the first harmonics, the detailed frequency modulation shapes of different bat group sizes were obtained, and the difference among those traces was measured. The detailed shape analysis will provide a new insight into the adaptive call design of bats.
Vocalization in clouded leopards and tigers: Further evidence for a proximate common ancestor
Authors: Walsh Edward J. , Robertson Heather , Skeba Sandy , McGee JoAnn
Published: June 2017

Previously, we reported that clouded leopards (Neofelis nebulosa) share an unusual auditory response timing characteristic with tigers (Panthera tigris) and possibly other representatives of the genus Panthera. Peripheral auditory response timing, or latency, and stimulus frequency relationships obey a rule in these species that is more parabolic in nature than the commonly observed inverse rule. That is, neural response latencies to low frequencies are as short, or shorter, than those measured at higher frequencies in the measurable response spectrum. In this report, we consider the possibility that clouded leopards may share other bioacoustic qualities that differentiate large roaring cats from smaller members of the cat family, Felidae. In that context, vocalizations were recorded from young adult clouded leopards at the Nashville Zoo at Grassmere and distinctive similarities within a subset of P. tigris calls were observed. The acoustic properties of the low level, friendly greeting known as prusten, more commonly known as chuffing, were of particular interest. Although similar in nature, quantitative and structural differences clearly differentiate the intraspecies call and differences may provide insight to production mechanisms. This observation is of particular interest in an evolutionary context because N. nebulosa and P. tigris shared a proximate common ancestor.
A first description of rhythmic song in Omura’s whale (Balaenoptera omurai)
Authors: Cerchio Salvatore , Dorning Sandra , Andrianantenaina Boris , Cholewiak Danielle
Published: June 2017

Omura’s whale is a recently described tropical Balaenopterid whale with virtually nothing known about their acoustic behavior. Recordings have revealed a stereotyped 15-50 Hz amplitude-modulated vocalization, rhythmically repeated in a typical Balaenoptera song manner. In order to describe the characteristics of the song, continuous recordings were made using archival recorders during 21 days at 4 sites off the northwest coast of Madagascar in documented Omura’s whale habitat. A total of 926 hours of recordings were manually browsed to identify all occurrences of the song vocalizations, logging 9117 individual song units. Occurrence varied among sites spread across 40 km of shelf habitat, indicating heterogeneous distribution of whales and use of habitat over space and days. Diel variation indicated higher incidence of song during daylight hours, counter to trends found in other Balaenopterid whales. A total of 215 different individual series were identified ranging from 3 to 252 consecutive song units. For 121 individuals with more than 20 consecutive song units, the interval ranged from 147.4 s to 289.0 s with a mean of 200.3 s (s.d. 25.9), and recorded song duration ranged up to 13.33 hr. This represents the first description of singing behavior for this species, suggesting a time-intensive behavioral display likely related to breeding.
Two new whale calls in the southern Indian Ocean, and their geographic and seasonal distribution over five sites and seven years
Authors: Leroy Emmanuelle C. , Samaran Flore , Bonnel Julien , Royer Jean-Yves
Published: June 2017

Since passive acoustic is widely used to monitor cetaceans, unidentified signals from biological sources are commonly reported. The signal's characteristics and emission patterns could give keys to identify the possible sources. Here, we report two previously unidentified signals found in acoustic records from five widely spread sites in the southern Indian Ocean and spanning seven years (2007, 2010 to 2015). The first reported signal (M-call) consists of a single tonal unit near 22 Hz and lasting about 10 s. The second signal (P-call) is also a tonal unit lasting about 10 s, but at a frequency near 27 Hz. The latter has often been interpreted as an incomplete Antarctic blue whale Z-call (Balaenoptera musculus intermedia). From a systematic analysis of our acoustic database, we show that both signals have similar characteristics as blue whale vocalizations, but with spatial and seasonal patterns that do not resemble any of the known populations dwelling in the southern Indian Ocean. M-calls are recorded only in 2007, while P-calls are present every recording year, with an increasing abundance with time. P-calls may co-occur with but are clearly distinct from Z-calls. The sources of the two new calls have yet to be visually identified.
What's in the water? Remote sensing of currents and “stuff” in the ocean
Authors: Crawford Gregory B.
Published: June 2017

High frequency acoustic remote sensing of the ocean was still in its infancy in the early 1980s. This paper reviews some early collaborative work with, and subsequent studies informed and inspired by Dr. David Farmer. We summarize early efforts to assess ocean currents, turbulence, and air-sea gas exchange. We will also review a few somewhat serendipitous research studies involving the acoustic assessment of fish wakes and sand dollar populations. More recent results associated with the measurement of tsunami currents will be presented, which provide a gentle reminder to those who would use acoustic velocity estimates to ask: what’s in the water?
Imaging and mapping water mass intrusions and internal waves
Authors: Duda Timothy F. , Lavery Andone C. , Gawarkiewicz Glen
Published: June 2017

Oceanic intrusions and internal waves can each be imaged with echo sounders for dynamics and flux studies. We have recently investigated signatures of intrusions, while internal-wave imaging is long established, with Farmer as a leader. Intrusive flow at fronts with counteracting temperature and salinity gradients along isopycnals is one of many mixing phenomena in the ocean. Advection within the intrusions is accompanied by diapycnal mixing above and below that may provide buoyant forcing. Probable double-diffusive mixing processes can create sharp interfaces and microstructure that can provide intrusion-following echo patterns. This backscattering is weaker than that from shear-generated turbulence microstructure, but it can be spatially coherent along intrusions and thus robustly detectable. Mapping of intrusion features with a shipboard system using this method may enable targeted physical measurements within intrusions to advance our knowledge, and can provide 2D structure maps if augmenting dropped probes are used. Note that plankton backscattering may mask these signals in some environments and seasons. Internal-wave imaging by recording the geometry of passive tracers moved vertically by the wave motions can be accomplished with even modest narrowband systems in plankton-rich environments, as shown with Quantifying, Predicting, and Exploiting Uncertainty program data from the East China Sea.
Observations of Langmuir circulation in the open ocean using acoustic instrumentation mounted on a subsurface drifting package
Authors: Zedel Len
Published: June 2017

The air-sea interface of the ocean is an energetic and dynamic environment that poses challenges for the positioning of instrumentation. One way to avoid the complexities of placing instrumentation at the ocean surface is to position a platform at some distance below the surface and sample surface processes remotely using acoustic systems. David Farmer recognized the value of such a sampling approach and led the Ocean Acoustics group at the Institute of Ocean Sciences to develop the required capabilities in the late 1980s. We report on observations made during a cruise to Ocean Station Papa in October 1987. Acoustic instruments revealed persistent bands of subsurface bubble clouds spaced by 5 to 10 m and extending in length up to 100 m. The clouds were aligned with the prevailing wind direction consistent with the organization expected from Langmuir circulation. Average downward velocities of 6 cm/s were observed in the bubble plumes that extended to a depth of 15 m. These early observations of near-surface processes motivated a series of instrumentation developments that have helped to explore the richness and complexity of movements within the ocean mixed layer.
Passing on the excitement of experimental oceanography
Authors: McNeil Craig L. , D'Asaro Eric , Shcherbina Andrey
Published: June 2017

Having graduated from the University of Victoria in 1995 with David Farmer as my advisor, I learned how exciting it is to work at the cutting-edge of experimental oceanography. During my Ph.D., I studied bubble mediated air-sea gas exchange which involved chasing winter storms in the NE Pacific by ship. That work inspired our study of the role of tropical cyclones in the global carbon cycle using air deployed gas sensing floats equipped with ambient noise recorders to evaluate wave breaking effects. I was also inspired when David enthusiastically showed me on the echosounder internal waves passing under the boat in Knight Inlet. I will present our recent AUV measurements made in prominent estuarine features (e.g., salt wedge and internal hydraulic jump) and discuss the impact of these features on suspended sediment distributions and underwater acoustic communications.
Thirty years of scintillating acoustic data in diverse ocean environments, thanks to David Farmer
Authors: Di Iorio Daniela
Published: June 2017

The acoustic scintillation method was first applied in a coastal tidal channel in the early 1980s by David Farmer and this laid the foundation for studies of estuarine channel flows, bottom boundary layer dynamics, deep-sea hydrothermal plumes, and now more recently hydrocarbon seeps. Over short distances, using high frequencies and high transmission rates, amplitude and phase fluctuations measured over transmitter and receiver arrays have been used to infer horizontal (or vertical) flows and turbulent motions, all averaged along the acoustic path over the range separating transmitters and receivers. Autonomous and cabled instrumentation have provided measurements of temporally and spatially averaged quantities, continuously in time. This ability to make long-term continuous measurements has shown major advances in our understanding of acoustic forward scatter from velocity and temperature fluctuations in moving random media and for identifying strong turbulence levels in a variety of ocean settings. Much of the measurements described here would not have been possible without the generous contributions of David Farmer.
Fullwave simulations of ultrasound propagation in the human body: Applications to imaging and motion estimation
Authors: Pinton Gianmarco
Published: June 2017

The Fullwave simulation tool, which solves a modified Westervelt equation, can model 3D ultrasound propagation in the human body. It includes the effects of nonlinearity, frequency dependent attenuation, and scattering. This high order finite difference simulation has a high dynamic range and ability to include sub-resolution scattering physics enabling it to tackle the computationally challenging problem of generating ultrasound images directly from the first principles of propagation and reflection. Three dimensional acoustical maps of the human body are derived from the Visible Human project, which provides the high degree of anatomical fidelity required to model sources of image degradation such as reverberation clutter and aberration. A three dimensional intercostal imaging scenario shows how the ribs degrade the image quality via reverberation and yet can improve the beam shape via apodization. It is shown that the in situ Mechanical Index (MI) in the human body differs significantly from derated estimates in a homogeneous medium. Due to tissue heterogeneities, the peak MI is close to the transducer and far from the focal region. Finally, we present a numerical model of subresolution displacements by using an impedance flow model applied to a scatterer composed of two elements. This shows that the numerical model can support displacements that are over three orders of magnitude smaller than the grid spacing. Applications to acoustic radiation force, elastography, and shear shock wave tracking are discussed.
Imaging cortical bone using the level-set method to regularize travel-time and full waveform tomography techniques
Authors: Fincke Jonathan R.
Published: June 2017

Regularizing travel-time and full waveform tomographic techniques with level set methods enables the recovery of cortical bone geometry. Bone imaging and quantification is of general clinical utility. Applications include prosthetic fitting, fracture detection, and the diagnosis of osteoporosis as well as monitoring the disease’s progression. Recently, there is significant interest in imaging through the skull, imaging long bones as well as estimating their material properties. In this case, a cylindrical acquisition geometry is used, allowing the bone to be insonified from all angles. Frequencies between 200 kHz and 800 kHz are used to enable penetration into the bone region.
Real-time ablation monitoring and lesion quantification using harmonic motion imaging guided focused ultrasound (HMIgFUS)
Authors: Konofagou Elisa
Published: June 2017

High-Intensity Focused Ultrasound (HIFU) monitoring is currently hindered by time- and cost-inefficient or inconclusive warranting, thus an imaging technique for efficient and reliable guidance. Harmonic Motion Imaging (HMI) uses a focused ultrasound (FUS) beam to generate an oscillatory acoustic radiation force for an internal, non-contact palpation to internally estimate relative tissue hardness. HMI also uses ultrasound imaging with parallel beamforming and estimates and maps the tissue dynamic motion in response to the oscillatory force at the same frequency based on consecutive RF frames. HMI has already been shown feasible in simulations, phantoms, ex vivo human and bovine tissues as well as animal tumor models in vivo. Using an FUS beam, HMI can also be seamlessly integrated with thermal ablation using HIFU, which leads to changes in the tumor stiffness. In this paper, an overview of HMI will be provided, including the capability of HMI to characterize and image the tumor prior to ablation, localize the beam for treatment planning, as well as monitor subsequent lesioning in real time. The findings demonstrate that HMI is capable of both detecting and characterizing the tumor prior to HIFU ablation as well as correctly depict and quantify the lesion during treatment. More importantly, HMI is shown capable of distinguishing the tumor margins from those of the thermal lesion in vivo in order to accurately determine treatment success. HMI thus constitutes an integrated, real-time method for efficient HIFU monitoring.
Real-time feedback control of high-intensity focused ultrasound thermal ablation using echo decorrelation imaging
Authors: Abbass Mohamed A. , Killin Jakob K. , Mahalingam Neeraja , Mast T. Douglas
Published: June 2017

The feasibility of controlling high-intensity focused ultrasound (HIFU) thermal ablation in real time using echo decorrelation imaging feedback was investigated in ex vivo bovine liver. Sonication cycles (5.0 MHz, 0.7 s per HIFU pulse, 20-24% duty, 879-1426 W/cm2 spatial-peak, and temporal peak intensity) performed by a linear image-ablate array were repeated until the minimum cumulative echo decorrelation within the focal region of interest exceeded a predefined threshold. Based on preliminary experiments (N = 13), a threshold of −2.7 for the log10-scaled echo decorrelation per millisecond was defined, corresponding to 90% specificity of local ablation prediction. Controlled HIFU thermal ablation experiments (N = 10) were compared with uncontrolled experiments employing 2, 5, or 9 sonication cycles. Controlled trials showed significantly smaller average lesion area (4.78 mm2), lesion width (1.29 mm), and treatment time (5.8 s) than 5-cycle (7.02 mm2, 1.89 mm, 14.5 s) or 9-cycle (9.31 mm2, 2.4 mm, 26.1 s) uncontrolled trials. Prediction of local ablation using echo decorrelation was assessed using receiver operator characteristic (ROC) curve analysis, in which controlled trials showed significantly greater prediction capability (area under the ROC curve AUC = 0.956) compared to 2-cycle uncontrolled trials (AUC = 0.722). These results suggest that ablation control using echo decorrelation may improve the precision, reliability, and duration of ultrasound-guided HIFU treatments.
Real-time acoustic-based feedback for histotripsy therapy
Authors: Macoskey Jonathan J. , Sukovich Jonathan R. , Hall Timothy L. , Cain Charles A. , Xu Zhen
Published: June 2017

Histotripsy uses high-pressure microsecond ultrasound pulses to generate cavitation to fractionate cells in target tissues. Two acoustic-based feedback mechanisms are being investigated to monitor histotripsy therapy in real-time. First, bubble-induced color Doppler (BICD) is received by an ultrasound probe co-aligned with the histotripsy transducer to monitor the cavitation-induced motion of residual cavitation nuclei in tissue throughout treatment. Second, acoustic backscatter of the histotripsy pulse from the cavitation bubbles is received by directly probing elements of histotripsy transducer to monitor acoustic emissions from the cavitation bubbles during treatment. In these experiments, histotripsy was applied to agarose phantoms and ex vivo tissue by a 112-element, 500 kHz semi-hemispherical ultrasound array with a 15 cm focal distance. The BICD signals were collected on a Verasonics system by an L7-4 probe. The BICD and backscatter signals were compared to high-speed optical images of cavitation in phantoms and histology of tissue. A consistent trend was observed in both the BICD and backscatter waveforms throughout treatment in both tissue and agarose phantoms that correlated with high-speed imaging and histological analysis. These results suggest that BICD and acoustic backscatter can provide non-invasive, real-time, quantitative feedback of tissue treatment progression during histotripsy, thus improving treatment efficiency and accuracy.
Acoustic radiation force on a sphere in tissue due to the irrotational component of the shear field body force
Authors: Treweek Benjamin C. , Ilinskii Yurii A. , Zabolotskaya Evgenia A. , Hamilton Mark F.
Published: June 2017

Acoustic radiation force on a sphere in soft tissue can be written as the sum of four distinct contributions. Two arise from incident and scattered compressional waves only, one from direct integration of the time-averaged Piola-Kirchhoff stress tensor over the surface of the sphere, and one from the irrotational component of the body force producing deformation of the surrounding medium. The other two contributions also incorporate scattered shear waves, and they are found by the same procedures. Three of these terms are known analytically [Ilinskii et al., Proc. Meet. Acoust. 19, 045004 (2013)], but the contribution relating to the shear field body force must be found numerically. Preliminary results for this term were obtained through simplifying approximations and presented at the fall 2016 ASA meeting; the present submission extends this work to cases where these approximations do not hold. Helmholtz decomposition of the shear field body force is performed using 3D Fourier transforms, then the irrotational potential is integrated over the surface of the sphere. Various sphere materials are considered, and comparisons are made with known results for a sphere in an ideal fluid. [Work supported by the ARL:UT McKinney Fellowship in Acoustics.]
Investigation of the source of histotripsy acoustic backscatter signals
Authors: Sukovich Jonathan R. , Hall Timothy L. , Macoskey Jonathan J. , Cain Charles A. , Xu Zhen
Published: June 2017

Recent work has demonstrated that acoustic backscatter signals from histotripsy-generated bubble clouds may be used to localize generated bubble clouds and perform non-invasive aberration correction transcranially. However, the primary source of the measured signals, whether from emissions generated during bubble expansion, or scattering of the incoming pulses off of the incipient bubble clouds, remains to be determined and may have important implications for how the acquired signals may be used. Here, we present results from experiments comparing the acoustic emissions and growth-collapse curves of single bubbles generated optically to those generated via histotripsy. Histotripsy bubbles were generated using a 32-element, 1.5 MHz spherical transducer with pulse durations <2-cycles; optical bubbles were nucleated using a pulsed Nd:YAG laser focused at the center of the histotripsy transducer. Optical imaging was used to capture the time evolution of the generated bubbles from inception to collapse. Acoustic emissions from the generated bubbles were captured using the receive-capable histotripsy transducer elements as well as with a commercial hydrophone mounted within. Imaging results indicated that optically nucleated bubbles experienced more rapid growth than histotripsy generated bubbles. Acoustic emissions from both sets of bubbles were comparable, however, suggesting the primary component of the measured histotripsy “backscatter” signal is an emission generated during bubble expansion.
Sensitivity study of exhaust system using the Moebius transformation
Authors: Zhang Yitian
Published: June 2017

The performance of exhaust system is not only dependent on the system itself, but also on the boundary conditions, which are the impedances at the inlet and outlet. For many cases, the exact value of these impedances are not known or easily measured. It is of interest to see the range of performance variation, given the range of possible values of impedance. An exhaustive method to determine the response variation can be used, but is computationally expensive. However, it can be proved that the relationship between boundary impedance and response is in the form of the Moebius transformation, which is a conformal transformation. Taking advantage of this property, the computation can be much reduced. It is also shown that the sensitivity of this dependence can be studied visually using the Moebius transformation.