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Oct 2009

Volume 126, Issue 4, pp. 1657-2316

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The Experimental Media and Performing Arts Center (EMPAC) at Rensselaer Polytechnic: Defining, building, and using highest‐quality spaces for hearing, seeing, and moving in space with integrated multi‐modal media technology. (A)

Johannes Goebel

J. Acoust. Soc. Am. Volume 126, Issue 4, pp. 2155-2155 (2009); (1 page) | Cited 1 time

Online Publication Date: 06 Oct 2009

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This paper discusses studios and performance spaces built for multi‐modal production, presentation, and research without compromises. Hearing, seeing, and moving in space were treated as equal in the definition of the physical properties of all spaces. Special diffusive acoustics were developed for a concert hall, a theater, and studios to be able to support any instrumental, vocal, or electronic sound from anywhere. The noise floor of the theater is as low as in the concert hall as in a studio used for video (NR 15). Only sine‐wave dimmers are allowed. The integrated digital technology allows creating, recording, and projecting sound, images, and movement through thousands of audio channels, hundreds of high definition video channels, and with computer controlled rigging and flying. The world of the human senses is bridged with the digital world of technology. All noisy equipment is banned from any venue. All venues are acoustically extremely separated with one studio resting on springs, the other studio having a separate foundation, and acoustical joints everywhere. The team comprises artistic curators as well as engineers and researchers; artists and scholars are in residence; the task is to span arts, science, and technology. The center opened 2008.
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43.55.Fw Auditorium and enclosure design
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Small room production before large room performance. (A)

Alex U. Case

J. Acoust. Soc. Am. Volume 126, Issue 4, pp. 2155-2155 (2009); (1 page)

Online Publication Date: 06 Oct 2009

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Large scale works almost always begin their acoustic life in a small room. Sound designers and composers need studio spaces that enable creativity while keeping technical matters in check. The stereo recording studio requires a paradigm shift when scaling up to four, eight, or more channels. While fundamental issues of isolation, noise control, user comfort, and ergonomics remain ever‐important, new challenges arise. Despite the growth in electroacoustic complexity that accompanies multichannel systems, the sound∕music creator needs core issues of level, timbre, localization, distance, envelopment, space, and so on to be presented as faithfully as possible, predictive of the future large space performance, without corruption by the small room.
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43.38.Md Sound recording and reproducing systems, general concepts
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Utilizing reciprocal maximum length sequences within a multichannel context to generate a natural, spatial sounding reverberation. (A)

Uday S. Trivedi and Ning Xiang

J. Acoust. Soc. Am. Volume 126, Issue 4, pp. 2155-2155 (2009); (1 page)

Online Publication Date: 06 Oct 2009

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The development of artificial reverberation has made considerable progress in recent years. Simultaneous advances in knowledge and computational power have allowed for a rapid development and application in the design of virtual room environments. Within such situations, simulating room acoustics is critical for producing a convincing immersive experience. This research explores the application of a multi‐channel loudspeaker setup that can be employed in simulating such an environment. An algorithm to shape and vary the spaciousness within the context of an artificially generated reverberation is implemented. The pseudo‐random properties of reciprocal maximum‐length sequences (R‐MLSs) allow for a deterministic decorrelation between all channels. The use of R‐MLS also provides several advantages over using traditional random noise. This paper will discuss the potential applications in creating virtual spaces and variable acoustic environments using multiple channel systems.
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43.55.Ka Computer simulation of acoustics in enclosures, modeling
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Binaural reproduction of spherical microphone array signals. (A)

Joshua D. Atkins

J. Acoust. Soc. Am. Volume 126, Issue 4, pp. 2156-2156 (2009); (1 page)

Online Publication Date: 06 Oct 2009

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An efficient method for the production of binaural audio signals from spherical microphone array signals using head related impulse responses (HRIRs) is presented. The processing is done directly in the spherical Fourier transform domain which offers significant speed advantages over the conventional method of beamforming toward each HRIR measurement point. The encoding of HRIRs into the spherical Fourier domain is complicated by the fact that the available HRIR databases (CIPIC, MIT, KEMAR) use irregular sampling positions around the sphere and do not contain data for sound coming from angles below the subject. However, for spatially bandlimited processing it is possible to use an LMS technique with regularization to perform the spherical Fourier transform of these HRIRs. A real‐time system with head‐tracking using the eigenmike (TM) and the CIPIC HRIR database is presented which processes spherical harmonics up to third order. Since the head‐rotation operation is performed digitally, this technique is especially useful for remote surveillance and virtual reality systems with complex acoustic scenes.
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43.60.Fg Acoustic array systems and processing, beam-forming
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Mixing studios complications. (A)

K. Anthony Hoover

J. Acoust. Soc. Am. Volume 126, Issue 4, pp. 2156-2156 (2009); (1 page)

Online Publication Date: 06 Oct 2009

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A new suite of mixing and teaching studios had been discussed for many years at Berklee College of Music in Boston. The authorization to proceed with design and construction of the studios finally came with a new Dean of the Music Technologies Department, who, without benefit of much of the background and previous discussions, contacted an old colleague for the final studio design and contracted with a reputable full‐service contractor for construction services. Problems developed during construction, which apparently sensitized the client to subsequent situations, in turn requiring acoustical consulting services. This paper will review some of the project history, outline the problems, and discuss solutions and recommendations, and will address some of the concerns with the specialized construction and unusual complications.
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43.55.Ti Sound-isolating structures, values of transmission coefficients
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I did not see that one coming. (A)

Richard Talaske, Gregory Miller, Byron Harrison, and Evelyn Way

J. Acoust. Soc. Am. Volume 126, Issue 4, pp. 2156-2156 (2009); (1 page)

Online Publication Date: 06 Oct 2009

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Occasionally we encounter something we have not before, to our detriment. Only by looking back do we gain the proper perspective to know how to avoid similar concerns in the future. We will share several examples from the Talaske body of work where things turned out differently that we had anticipated. Examples will include a theatre wall system which provided more diffusion and absorption than laboratory tests had indicated, a contractor construction error that had negative acoustic implications which were not caught until it was too late to correct, and an acoustic isolation concern between a dance studio and a theatre that passed the boundaries of our analytical assumptions. In each case, the analytical, practical, and political hurdles required to resolve each issue will be presented.
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43.55.Fw Auditorium and enclosure design
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Key planning steps for performance based designs. (A)

Joshua Cushner

J. Acoust. Soc. Am. Volume 126, Issue 4, pp. 2156-2156 (2009); (1 page)

Online Publication Date: 06 Oct 2009

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In architecture and engineering, leading firms will often value the opportunity to collaborate with unconventional clients to create bespoke building designs. However, such projects also require greater early planning and create new risks for the project team to manage. When generating “customized” designs with a specific tenant in mind rather than simply relying on industry standards for similar facilities, the rigors of a performance‐based design must be understood. This case study reviews a project where key planning steps for this type of design approach were overlooked, which created conflicting project goals that were never fully resolved. While efforts were made by team members over time to improve collaboration, the process‐related problems which manifested early in the project persisted, and the design team was never able to establish cohesion amongst themselves or with the owner. This case study details the main elements which predicated the project failures and suggests alternate approaches which could have better served the goals of the project. As a more successful framework, a broadened use of the performance‐based design model is reviewed.
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43.55.Br Room acoustics: theory and experiment; reverberation, normal modes, diffusion, transient and steady-state response
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Biggest mistakes encountered on projects without acoustical consultants. (A)

Benjamin Markham, Alicia Wagner, Jeffrey Fullerton, and Jennifer Hinckley

J. Acoust. Soc. Am. Volume 126, Issue 4, pp. 2157-2157 (2009); (1 page)

Online Publication Date: 06 Oct 2009

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As consultants, the authors have been called into dozens of projects built without the benefit of guidance from an acoustician, and the results are often disastrous (and in many cases, litigious). This presentation, replete with photographic evidence, outlines some of the biggest mistakes encountered recently by design teams that lack a critical team player: the qualified acoustical consultant. Consider a natatorium with all hard surfaces and a 6‐s reverberation time to match, a fieldhouse gymnasium with a 70‐dB background noise level, and a distressingly common problem in New England: residential condominiums converted from an old mill building with nothing between stacked residences except exposed, unimproved hardwood decking. Other examples relate to inadequate (or altogether absent) vibration isolation of elevator machinery and other mechanical equipment, cacophonous restaurant acoustics, blatant disregard for a nearby railway, and poor music practice facilities.
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43.55.Ti Sound-isolating structures, values of transmission coefficients
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Sound transmission through a fluctuating ocean (1979) and ocean acoustic tomography (1995): An intertwined history. (A)

Peter F. Worcester and Walter H. Munk

J. Acoust. Soc. Am. Volume 126, Issue 4, pp. 2157-2157 (2009); (1 page)

Online Publication Date: 06 Oct 2009

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Early attempts at understanding scintillations in sound transmission through the ocean assumed that ocean fine structure is homogeneous and isotropic. It is, in fact, dominated by internal waves, which are neither homogeneous nor isotropic. Sound Transmission Through a Fluctuating Ocean (Flatté et al., Cambridge University Press, Cambridge, England 1979) combined recently developed internal‐wave models with path‐integral methods to predict the fluctuations of resolved acoustic multipaths. At that time, Ocean Acoustic Tomography (Munk et al., Cambridge University Press, Cambridge, England 1995), which uses ray travel times to determine large‐scale ocean structure, had just been proposed. The wideband acoustic sources and receivers required to make travel‐time measurements for tomography also provided the technology needed to quantify acoustic fluctuations. Conversely, internal‐wave‐induced scattering limits travel‐time measurement precision. Tomography experiments at 25‐km range provided some of the earliest tests of path‐integral predictions. Subsequent tomography experiments provided data at ever‐increasing ranges and decreasing frequencies. The Acoustic Thermometry of Ocean Climate project made measurements at megameter ranges with 1400‐m vertical line array receivers. The next step is a modular distributed VLA capable of spanning the full water column that is under development to enable separation of acoustic modes using spatial filtering and to fully characterize deep‐water acoustic time fronts.
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43.30.Re Signal coherence or fluctuation due to sound propagation/scattering in the ocean
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Center for the studies of nonlinear dynamics, 1982–1985. (A)

Frank S. Henyey

J. Acoust. Soc. Am. Volume 126, Issue 4, pp. 2157-2157 (2009); (1 page)

Online Publication Date: 06 Oct 2009

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Stan Flatte was the third director of the Center for the Studies of Nonlinear Dynamics (CSND), from 1982 to 1985 (and for another year after he returned to Santa Cruz). Upon joining CSND, he assembled a group to work on the path integral method for predicting internal wave effects on acoustic propagation in the ocean. This talk discusses the work done by that group. Topics of this work include travel time bias, relation to moment equation methods, fourth moment calculations, and pulse spread.
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43.30.Re Signal coherence or fluctuation due to sound propagation/scattering in the ocean
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Scaling turbulent dissipation and finestructure: The wave‐propagation method. (A)

Timothy F. Duda

J. Acoust. Soc. Am. Volume 126, Issue 4, pp. 2158-2158 (2009); (1 page)

Online Publication Date: 06 Oct 2009

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In the 1980s the team of Flatté et al. developed a theory relating the turbulent kinetic energy dissipation rate in the open ocean to finestructure feature observations (1–100 m scale), building on work of Henyey and Pomphrey. Formulas derived from this work are now prevalently used for indirectly estimating cross‐isopycnal ocean mixing, a process of critical interest, using platforms and sensors unable to directly measure viscous‐scale dissipation and associated turbulent transport processes. The method originally involved the internal‐wave energy level. Revisions of the method introduced by follow‐on investigators involve internal‐wave shear and strain. The physics behind the method is that short‐wavelength shear‐rich internal waves propagate in a background of larger‐scale internal waves, with action conserved, and can have their energy concentrated spatially. The concentrated waves are inferred to break, and in doing so provide the energy to support diapycnal mixing. The approach is one of “wave propagation in random media,” a specialty of Flatté.
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43.20.Bi Mathematical theory of wave propagation
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Ray methods in long‐range deep ocean sound propagation. (A)

Michael G. Brown, Ilya A. Udovydchenkov, and Irina I. Rypina

J. Acoust. Soc. Am. Volume 126, Issue 4, pp. 2158-2158 (2009); (1 page)

Online Publication Date: 06 Oct 2009

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Although ray methods have limitations, they remain extremely important because they provide insight into the underlying wave propagation physics that is difficult, if not impossible, to obtain by any other means. In this talk the utility of ray methods in long‐range deep ocean sound propagation will be discussed and illustrated. Topics to be discussed include ray‐mode duality and action quantization; adiabatic invariance for rays and modes; beamforming and Radon transforms; caustics and catastrophes; travel time sensitivity kernels, Fresnel zones and other measures of ray widths; nonlinear resonances, KAM theory, and mode coupling; the waveguide invariant and its ray equivalent; and beam dynamics—from weakly divergent to explosive. [Work supported by ONR.]
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43.20.Dk Ray acoustics
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Flatte fluctuation theory and its use by the US Navy. (A)

Arthur B. Baggeroer

J. Acoust. Soc. Am. Volume 126, Issue 4, pp. 2158-2158 (2009); (1 page)

Online Publication Date: 06 Oct 2009

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Fluctuations of narrowband signals and spreading of broadband ones are important concepts in the design of the sonar receiver. The first determines how long one can integrate or equivalently how narrow a bandwidth can be used to increase the gain and the second leads to the convolution of the ambiguity function and the scattering function to determine where energy from the transmission will appear in the range‐Doppler plane, hence the region over which one wants to collect energy for a detection. The seminal book “Sound Transmission through a Fluctuating Ocean” by Flatte et al. essentially defined the concepts of saturated, partially saturated, and unsaturation transmissions which parsed the problem in the “lambda‐phi” for designing sonar transmitters and receiver appropriate for the dynamics of an oceanographic region.
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43.30.Re Signal coherence or fluctuation due to sound propagation/scattering in the ocean
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Acoustic signal horizontal coherence variability: Relationship to internal tide and storm events. (A)

Marshall H. Orr, Peter C. Mignerey, and David Walsh

J. Acoust. Soc. Am. Volume 126, Issue 4, pp. 2158-2158 (2009); (1 page)

Online Publication Date: 06 Oct 2009

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Acoustic signal horizontal coherence has been extracted from a 31‐day data set taken during the late fall∕early winter time period. The coherence variability for both 300‐ and 500‐Hz acoustic signals appears coupled to shelf∕slope frontal motion, internal tides, and associate internal waves as well as changes in the surface gravity field. Acoustic signal and environmental data illustrating the coupling will be presented. The data were taken on the New Jersey Shelf with a 460‐m‐long bottomed array placed in ∼89 m of water. The cross shelf propagation range was ∼20 km. The acoustic sources were in ∼60 m of water.
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43.30.Re Signal coherence or fluctuation due to sound propagation/scattering in the ocean
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Cross‐mode coherences and decoupling of equations for mode intensities in two‐dimensional and three‐dimensional fluctuating ocean. (A)

Alexander G. Voronovich, Vladimir E. Ostashev, John A. Colosi, and Andrey K. Morozov

J. Acoust. Soc. Am. Volume 126, Issue 4, pp. 2158-2158 (2009); (1 page) | Cited 1 time

Online Publication Date: 06 Oct 2009

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Sound waves propagating in the ocean are scattered by internal waves (IWs) and spice. A modal approach for studies of low‐frequency, long‐range sound propagation in a fluctuating ocean seems to be the most adequate. This approach has been employed in a number of works, including recently published papers [A. G. Voronovich and V. E. Ostashev, J. Acoust. Soc. Am. 125, 99–110 (2009)] and [J. A. Colosi and A. K. Morozov, J. Acoust. Soc. Am. 124, 2598 (2008)]. Based on these two papers, in this presentation important aspects of sound scattering in a fluctuating ocean are considered for both two‐dimensional (2‐D) and three‐dimensional (3‐D) geometries. First, we compare equations for the coherence function of a sound field in 2‐D and 3‐D fluctuating ocean. Then, decoupling of equations for the mode intensities from equations for the cross‐mode coherences is studied for the two geometries. Numerical examples of evolution of the mode intensities and cross‐mode coherences with range are presented and discussed. Finally, insonification of an acoustic shadow zone by sound waves scattered by IWs is studied. [Work supported by ONR.]
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43.30.Re Signal coherence or fluctuation due to sound propagation/scattering in the ocean
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Antipodal acoustic propagation and a half‐century of ocean warming. (A)

Brian D. Dushaw

J. Acoust. Soc. Am. Volume 126, Issue 4, pp. 2158-2158 (2009); (1 page)

Online Publication Date: 06 Oct 2009

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In 1960, sound signals traveling from Perth, Australia were recorded at Bermuda. Previous work focused on the path traveled by the sound [Munk et al., JPO, 1876–1898 (1988)]. Calculation of the horizontal refraction of sound, across the Southern Ocean in particular, gave the perplexing result that Bermuda was in the shadow of Africa. Heaney et al. [J. Acoust. Soc. Am., 2586–2594 (1991)] used low‐resolution atlases for global sound speed and bathymetry to obtain two viable acoustic paths between Perth and Bermuda, both influenced by bathymetry. From a modern perspective, however, the explanation of Heaney et al. is unconvincing [Dushaw, GRL (2008)]. High‐resolution ocean models put the Perth‐to‐Bermuda acoustic problem into a new light. These models suggest that intense, small‐scale features, e.g., Agulhas rings near the Cape of Good Hope, would greatly influence the acoustic paths. The antipodal travel time, 13 382 s, is a measure of the ocean temperature in 1960. If the acoustic propagation issues can be fully understood, data‐assimilating ocean general circulation models might be used to calculate a present‐day travel time. The travel‐time change over the past half‐century, expected to be about 10 s based on nominal estimates of ocean warming, is a measure of ocean climate change.
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43.30.Qd Global scale acoustics; ocean basin thermometry, transbasin acoustics
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Characterization of deep acoustic shadow zone arrivals. (A)

Lora J. Van Uffelen and Peter F. Worcester

J. Acoust. Soc. Am. Volume 126, Issue 4, pp. 2159-2159 (2009); (1 page) | Cited 1 time

Online Publication Date: 06 Oct 2009

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Acoustic shadow‐zone arrivals first observed in the late 1990s on horizontal receiving arrays in the North Pacific Ocean revealed significant acoustic energy penetrating the geometric shadow by an estimated 500–1000 m. An extensive vertical line array deployed in conjunction with 250‐Hz acoustic sources at ranges of 500‐ and 1000‐km during SPICEX, a long‐range propagation experiment conducted from June to November 2004 in the North Pacific, confirmed the presence of these anomalously deep arrivals and enabled an examination of their vertical structure. Parabolic equation simulations incorporating scattering consistent with the Garrett–Munk internal‐wave spectrum at full strength are able to describe both the energy contained in and vertical extent of deep shadow‐zone arrivals. Several hundred acoustic receptions were recorded during the experimental deployment, enabling a statistical characterization of the energy and vertical extent of these arrivals as well as an investigation of the evolution of the arrivals throughout the nearly 6 months of acoustic receptions.
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43.30.Re Signal coherence or fluctuation due to sound propagation/scattering in the ocean
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Seismo‐acoustic modal scattering by volume heterogeneities in shallow water sediments. (A)

Darin J. Soukup and Robert I. Odom

J. Acoust. Soc. Am. Volume 126, Issue 4, pp. 2159-2159 (2009); (1 page)

Online Publication Date: 06 Oct 2009

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Elastic anisotropy is a nearly ubiquitous feature of marine sediments. The simplest type of sediment anisotropy is transverse isotropy, characterized by five elastic constants, and results from layered deposition. A modal scattering theory for volume perturbations of the sediment elastic moduli is presented. The scattering theory is based on the coupled mode formulation for propagation in range dependent fluid‐elastic media. The Born approximation is employed to derive a modal scattering matrix. Although the perturbations of the elastic moduli are random, they may not be arbitrary in the sense that certain symmetry and energy constraints among the moduli must be respected. Mode‐mode coupling matrices are computed for quasi‐P‐SV‐SH seismo‐acoustic modes, which show mode mixing and the importance of non‐nearest neighbor interactions. The effects of volume scattering can be combined with rough surface scattering and also incorporated into mode coupling caused by deterministic range dependence of the material properties. This work has implications for acoustic loss estimates for low‐frequency shallow water acoustic propagation. [Work supported by ONR.]
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43.30.Ma Acoustics of sediments; ice covers, viscoelastic media; seismic underwater acoustics
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Deep seafloor arrivals: Scattering or multi‐path from ocean thermal structure? (A)

Ralph A. Stephen, Matthew A. Dzieciuch, Peter F. Worcester, Rex K. Andrew, James A. Mercer, John A. Colosi, and Bruce M. Howe

J. Acoust. Soc. Am. Volume 126, Issue 4, pp. 2159-2159 (2009); (1 page)

Online Publication Date: 06 Oct 2009

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An unexplained set of arrivals has been observed on ocean bottom seismometers (OBSs) during the NPAL04 long‐range ocean acoustic propagation experiment in the North Pacific. The observed intensity pattern of the OBS arrivals is significantly more complex than the waterborne arrivals seen on the deep vertical line array (DVLA). These “deep seafloor” arrivals occur later than the first PE predicted arrival; their arrival time is not predicted by acoustic PE propagation models, they do not correspond to decay from shallower turning points (as is the case for deep shadow zone arrivals), and they are not readily observed on the DVLA hydrophone just 750 m above the seafloor. The arrival structure in the observed data, in time and amplitude, varies substantially between three OBSs that are separated by less than 4 km. Could these unexplained arrivals be scattering or horizontal multi‐path from persistent ocean thermal structure?
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43.30.Gv Backscattering, echoes, and reverberation in water due to combinations of boundaries
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Internal wave strength inversion based on the shape of the axial finale. (A)

Kevin D. Heaney

J. Acoust. Soc. Am. Volume 126, Issue 4, pp. 2159-2159 (2009); (1 page)

Online Publication Date: 06 Oct 2009

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Flatte had a significant impact on my dissertation and early education in the field of ocean acoustic propagation. In particular, Flatte’s work on the impact of internal wave scattering on deep ocean propagation was central to my early work in adiabatic mode scattering in the presence of deep water internal waves. In this paper, we will revisit some of Flatte’s wave propagation in a random media theory and show its phenomenological impact on deep water propagation, primarily within his explanation of the Slice89 experiment. In this experiment the axial finale (latest arriving energy) is broadened in depth. Flatte correctly asserted that this was due to internal wave scattering to higher modes (with larger depth extents) and used this as a method for heuristically determining the internal wave strength. Results from Heaney [Ph.D. thesis, SIO‐UCSD (1997)] will be presented using the ATOC experiment. More recent results using NPAL data as well as more recent modeling will be presented. The impact of these results on deep water anti‐submarine warfare and the extension of these results to basin scale propagation (>10000‐km ranges) will be made.
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43.30.Re Signal coherence or fluctuation due to sound propagation/scattering in the ocean
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Comparison of three coordinate mapping methods for sound propagation over irregular terrain. (A)

Santosh Parakkal, Kenneth E. Gilbert, and Xiao Di

J. Acoust. Soc. Am. Volume 126, Issue 4, pp. 2160-2160 (2009); (1 page)

Online Publication Date: 06 Oct 2009

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In propagation calculations, a coordinate mapping to “flatten” irregular terrain is an attractive approach. However, coordinate mapping methods can be as computationally intensive as the propagation calculation itself. Hence a judicious choice of the mapping method is critical for practical calculations. We compare three coordinate mapping methods: (1) conformal mapping; (2) transformation to polar coordinates; and (3) a simple mapping introduced 30 years ago by Beilis and Tappert . The first two methods are essentially exact, while the third is, in principle, applicable only to small slopes and low propagation angles. The three approaches are outlined and a comparison is made of the accuracy and computational demands of the methods. Also, the theoretical predictions from the three methods are compared to field measurements of sound propagation over a hill. [Research supported by the U.S. Army TACOM‐ARDEC at Picatinny Arsenal, NJ.]
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43.28.Js Numerical models for outdoor propagation
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Sound propagation in a refractive, turbulent atmosphere above a statistically rough, impedance ground surface. (A)

Vladimir E. Ostashev, D. Keith Wilson, and Sergey N. Vecherin

J. Acoust. Soc. Am. Volume 126, Issue 4, pp. 2160-2160 (2009); (1 page)

Online Publication Date: 06 Oct 2009

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In recent years, considerable effort has been devoted to studies of sound propagation in a turbulent atmosphere. It was shown that temperature and wind velocity fluctuations can significantly diminish the coherence of a sound wave and, hence, degrade performance of modern acoustic sensor arrays for source detection. Outdoor sound waves are also affected by a rough, impedance surface of the ground. This paper is devoted to studies of the effects of a statistically rough, impedance ground surface on the coherence of a sound wave propagating in a refractive, turbulent atmosphere. Using the Beilis–Tappert transformation, the considered problem is reduced to sound propagation over a flat impedance surface in an atmosphere with an effective turbulence spectrum. Then, a closed equation for the coherence function of a sound field is derived using the Markov approximation similarly to that in the work of Wilson and Ostashev [J. Acoust. Soc. Am. 109, 1909–1922 (2001)]. The previously developed moment‐screen method is used to numerically solve the closed equation for the coherence function. Possible approaches are discussed for comparing the relative roles of atmospheric turbulence and surface roughness in diminishing the coherence of a sound wave.
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43.28.Lv Statistical characteristics of sound fields and propagation parameters
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Molecular simulation of sound propagation in a gas. (A)

Takeru Yano

J. Acoust. Soc. Am. Volume 126, Issue 4, pp. 2160-2160 (2009); (1 page)

Online Publication Date: 06 Oct 2009

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Molecular dynamics simulation is carried out to clarify the propagation process of high frequency and large amplitude sound in a gas. Numerically, the inter‐molecular potential is assumed to be the Lennard‐Jones 12‐6 potential and the motions of molecules are determined by solving Newton’S equation of motion for each molecule with the leap‐frog method. The gas, where the sound propagates, is sufficiently rarefied or low density so that its behavior may be governed by the Boltzmann equation. Comparison of the numerical results based on the molecular dynamics, the Boltzmann equation, and the Navier–Stokes equations, the nonequilibrium effects due to the high frequency and nonlinearity are demonstrated.
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43.25.Cb Macrosonic propagation, finite amplitude sound; shock waves
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Sound propagation classes for long‐range assessment algorithms. (A)

Michelle E. Swearingen and Michael J. White

J. Acoust. Soc. Am. Volume 126, Issue 4, pp. 2160-2160 (2009); (1 page)

Online Publication Date: 06 Oct 2009

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Preparing noise assessments for military training activities is a significant challenge due to the short duration of the individual signals and the lack of highly detailed atmospheric conditions, due to either an absence of necessary meteorological sensors or a need to perform the assessment without prior atmospheric knowledge. To overcome these difficulties, a set of sound propagation classes has been developed. These classes narrowly define the atmospheric and ground properties and have associated mean and variance as a function of distance. This talk will provide a description of these classes and examples of how they are used.
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43.28.Fp Outdoor sound propagation through a stationary atmosphere, meteorological factors
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Exact image solution approach for multiple reflections. (A)

Ambika Bhatta, Miroslava Raspopvic, Max Denis, and Charles Thompson

J. Acoust. Soc. Am. Volume 126, Issue 4, pp. 2160-2160 (2009); (1 page)

Online Publication Date: 06 Oct 2009

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In this paper a modified method using the solution of the Laplace transform based formulation for the Sommerfeld integral to determine the strength of image sources and boundary reflections is presented. It is shown that multiple reflections can be expressed in terms of elemental branch integrals. This formulation allows for a rigorous derivation of the pressure field using numerical methods.
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43.20.Mv Waveguides, wave propagation in tubes and ducts
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