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James C Preisig - One of the best experts on this subject based on the ideXlab platform.
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underwater Acoustic communication channels Propagation models and statistical characterization
IEEE Communications Magazine, 2009Co-Authors: Milica Stojanovic, James C PreisigAbstract:Acoustic Propagation is characterized by three major factors: attenuation that increases with signal frequency, time-varying multipath Propagation, and low speed of sound (1500 m/s). The background noise, although often characterized as Gaussian, is not white, but has a decaying power spectral density. The channel capacity depends on the distance, and may be extremely limited. Because Acoustic Propagation is best supported at low frequencies, although the total available bandwidth may be low, an Acoustic communication system is inherently wideband in the sense that the bandwidth is not negligible with respect to its center frequency. The channel can have a sparse impulse response, where each physical path acts as a time-varying low-pass filter, and motion introduces additional Doppler spreading and shifting. Surface waves, internal turbulence, fluctuations in the sound speed, and other small-scale phenomena contribute to random signal variations. At this time, there are no standardized models for the Acoustic channel fading, and experimental measurements are often made to assess the statistical properties of the channel in particular deployment sites.
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Acoustic Propagation considerations for underwater Acoustic communications network development
Proceedings of the 1st ACM international workshop on Underwater networks, 2006Co-Authors: James C PreisigAbstract:Underwater Acoustic communications systems are significantly challenged by the Acoustic Propagation characteristics of the underwater environment. There are a wide range of physical processes that impact underwater Acoustic communications and the relative importance of these processes are different in different environments. In this paper some relevant Propagation phenomena are described in the context of how they impact the development and/or performance of underwater Acoustic communications networks. The speed of sound and channel latency, absorption and spreading losses, waveguide effects and multipath, surface scattering, bubbles, and ambient noise are all briefly discussed.
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high frequency Acoustic Propagation in littoral and surf zone environment the analysis of temporal fluctuations and development of adaptive signal processing algorithms
2005Co-Authors: James C PreisigAbstract:Abstract : There are three long term goals of this work. The first is to the characterize features of high frequency Acoustic Propagation in shallow water that are relevant to the performance and design of Acoustic communications systems. The second is to develop closed form expressions for the performance of channel identification and Acoustic communications algorithms as a function of environmental conditions. The final goal is to develop improved channel estimation and demodulation algorithms for phase coherent Acoustic communications in this environment.
Dajun Tang - One of the best experts on this subject based on the ideXlab platform.
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simultaneous nearby measurements of Acoustic Propagation and high resolution sound speed structure containing internal waves
IEEE Journal of Oceanic Engineering, 2010Co-Authors: Frank S Henyey, Kevin L. Williams, Jie Yang, Dajun TangAbstract:During the 2006 Shallow Water (SW06) experiment, simultaneous measurements were made of the sound-speed field as a function of range and depth associated with nonlinear internal waves and Acoustic Propagation at frequencies of 2-10 kHz over a 1-km path. The internal waves were measured by a towed conductivity-temperature-depth (CTD) chain to get high resolution. These measurements were coordinated so that the nonlinear waves could be interpolated onto the Acoustic path, allowing predictions of their effects on the Acoustics. Using the measured sound-speed field, the Acoustic arrivals under the influence of the internal waves are modeled and compared to data. The largest impact of measured moderate amplitude internal waves on Acoustics is that they alter the arrival time of the rays which turn at the thermocline.
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shallow water 06 a joint Acoustic Propagation nonlinear internal wave physics experiment
Oceanography, 2007Co-Authors: Dajun Tang, Timothy F Duda, James F Lynch, Philip Abbot, Glen Gawarkiewicz, Scott Glenn, James N Moum, Ross Chapman, Peter H Dahl, John A GoffAbstract:Author Posting. © Oceanography Society, 2007. This article is posted here by permission of Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 20, 4 (2007): 156-167.
John A Colosi - One of the best experts on this subject based on the ideXlab platform.
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observations of upper ocean sound speed structures in the north pacific and their effects on long range Acoustic Propagation at low and mid frequencies
Journal of the Acoustical Society of America, 2020Co-Authors: John A Colosi, Daniel L RudnickAbstract:Three 1000-km long, high resolution conductivity, temperature, depth sections in the North Pacific Ocean obtained by the ship towed vehicle SeaSoar are analyzed to quantify 2005 March/April upper-ocean sound-speed structure and determine the effects on low to mid-frequency transmission loss (TL) through numerical simulation. The observations reveal a variable mixed layer Acoustic duct (MLAD) with a mean sonic layer depth of 91-m, and an even higher variability, 80-m-average-thickness transition layer connecting the mixed layer (ML) with the main thermocline. The sound-speed structure is hypothesized to be associated with thermohaline processes such as air-sea fluxes, eddies, submesoscale, fronts, internal waves, turbulence, and spice, but the analysis does not isolate these factors. Upper-ocean variability is quantified using observables of layer depth, ML gradient, and sound speed to compute low order moments, probability density functions, horizontal wavenumber spectra, and empirical orthogonal function decomposition. Coupled mode Acoustic Propagation simulations at 400 and 1000 Hz were carried out using the sound-speed observations from the upper 400-m appended to climatology, which reveal Propagation physics associated with diffraction, random media effects, and deterministic feature scattering. Statistics of TL reveal important energy transfers between the MLAD and the deep sound channel.
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observations of low frequency long range Acoustic Propagation in the philippine sea and comparisons with mode transport theory
Journal of the Acoustical Society of America, 2019Co-Authors: Tarun K Chandrayadula, Peter F. Worcester, Matthew A Dzieciuch, James A Mercer, John A Colosi, Sivaselvi Periyasamy, Rex K AndrewAbstract:The year-long Philippine Sea (2010–2011) experiment (PhilSea) was an extensive deep water Acoustic Propagation experiment in which there were six different sources transmitting to a water column spanning a vertical line array. The six sources were placed in an array with a radius of 330 km and transmitted at frequencies in the 200–300 Hz and 140–205 Hz bands. The PhilSea frequencies are higher than previous deep water experiments in the North Pacific for which modal analyses were performed. Further, the Acoustic paths sample a two-dimensional area that is rich in internal tides, waves, and eddies. The PhilSea observations are, thus, a new opportunity to observe Acoustic modal variability at higher frequencies than before and in an oceanographically dynamic region. This paper focuses on mode observations around the mid-water depths. The mode observations are used to compute narrowband statistics such as transmission loss and broadband statistics such as peak pulse intensity, travel time wander, time spreads, and scintillation indices. The observations are then compared with a new hybrid broadband transport theory. The model-data comparisons show excellent agreement for modes 1–10 and minor deviations for the rest. The discrepancies in the comparisons are related to the limitations of the hybrid model and oceanographic fluctuations other than internal waves.The year-long Philippine Sea (2010–2011) experiment (PhilSea) was an extensive deep water Acoustic Propagation experiment in which there were six different sources transmitting to a water column spanning a vertical line array. The six sources were placed in an array with a radius of 330 km and transmitted at frequencies in the 200–300 Hz and 140–205 Hz bands. The PhilSea frequencies are higher than previous deep water experiments in the North Pacific for which modal analyses were performed. Further, the Acoustic paths sample a two-dimensional area that is rich in internal tides, waves, and eddies. The PhilSea observations are, thus, a new opportunity to observe Acoustic modal variability at higher frequencies than before and in an oceanographically dynamic region. This paper focuses on mode observations around the mid-water depths. The mode observations are used to compute narrowband statistics such as transmission loss and broadband statistics such as peak pulse intensity, travel time wander, time spread...
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temporal and spatial dependence of a yearlong record of sound Propagation from the canada basin to the chukchi shelf
Journal of the Acoustical Society of America, 2019Co-Authors: Megan S Ballard, John A Colosi, Yingtsong Lin, Mohsen Badiey, Sean Pecknold, Altan Turgut, Jason D Sagers, Andrey Proshutinsky, Richard A Krishfield, Peter F. WorcesterAbstract:The Pacific Arctic Region has experienced decadal changes in atmospheric conditions, seasonal sea-ice coverage, and thermohaline structure that have consequences for underwater sound Propagation. To better understand Arctic Acoustics, a set of experiments known as the deep-water Canada Basin Acoustic Propagation experiment and the shallow-water Canada Basin Acoustic Propagation experiment was conducted in the Canada Basin and on the Chukchi Shelf from summer 2016 to summer 2017. During the experiments, low-frequency signals from five tomographic sources located in the deep basin were recorded by an array of hydrophones located on the shelf. Over the course of the yearlong experiment, the surface conditions transitioned from completely open water to fully ice-covered. The Propagation conditions in the deep basin were dominated by a subsurface duct; however, over the slope and shelf, the duct was seen to significantly weaken during the winter and spring. The combination of these surface and subsurface conditions led to changes in the received level of the sources that exceeded 60 dB and showed a distinct spacio-temporal dependence, which was correlated with the locations of the sources in the basin. This paper seeks to quantify the observed variability in the received signals through Propagation modeling using spatially sparse environmental measurements.
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the north pacific Acoustic laboratory deep water Acoustic Propagation experiments in the philippine sea
Journal of the Acoustical Society of America, 2012Co-Authors: Peter F. Worcester, Matthew A Dzieciuch, James A Mercer, John A Colosi, Rex K Andrew, Brian D Dushaw, Arthur B Baggeroer, Kevin D Heaney, Gerald L Dspain, Ralph A StephenAbstract:The North Pacific Acoustic Laboratory (NPAL) Group has performed a series of experiments to study deep-water Acoustic Propagation and ambient noise in the northern Philippine Sea: (i) 2009 NPAL Pilot Study/Engineering Test (PhilSea09), (ii) 2010–2011 NPAL Philippine Sea Experiment (PhilSea10), and (iii) Ocean Bottom Seismometer Augmentation of the 2010–2011 NPAL Philippine Sea Experiment (OBSAPS). The goals are to (i) understand the impacts of fronts, eddies, and internal tides on Acoustic Propagation in this oceanographically complex and dynamic region, (ii) determine whether Acoustic methods, together with other measurements and ocean modeling, can yield estimates of the time-evolving ocean state useful for making improved Acoustic predictions and for understanding the local ocean dynamics, (iii) improve our understanding of the physics of scattering by small-scale oceanographic variability, and (iv) characterize the depth dependence and temporal variability of the ambient noise field. In these experiments, moored and ship-suspended low-frequency Acoustic sources transmitted to a newly developed Distributed Vertical Line Array (DVLA) receiver capable of spanning the water column in deep water. The Acoustic transmissions and ambient noise were also recorded by the towed Five Octave Research Array (FORA), by Acoustic Seagliders, and by ocean bottom seismometers during OBSAPS. [Work supported by ONR.]
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the range evolution of the mean wavefront intensity for the long range ocean Acoustic Propagation experiment loapex off axis source transmissions
Journal of the Acoustical Society of America, 2006Co-Authors: John A Colosi, Peter F. Worcester, Bruce M Howe, James A Mercer, Rex K Andrew, Matthew A DzieciuchAbstract:One of the main objectives of the NPAL 2004 experiment, LOAPEX (Long‐range Ocean Acoustic Propagation EXperiment), which was conducted between 10 September and 10 October 2004, was to better understand the roles of scattering and diffraction in general. The LOAPEX measurement provided Acoustic transmission data for ranges of 50, 250, 500, 1000, 1600, 2300, and 3200 km. By placing the source off‐axis in order to avoid exciting low‐order modes, we are able to study phenomena of the significant in‐filling of Acoustic energy into the finale region. Our focus will be on the transmissions for the off‐axis source location (nominally 350‐m depth), and the Acoustic receptions as recorded on the 1400‐m‐long axial receiving array. The observation of the mean intensity of the wavefront arrival pattern at each range will be compared to deterministic ray and parabolic equation calculations. The following questions will be addressed here: (1) How does high angle Acoustic energy from an off‐axis source transfer energy to low angles in the axial region of the waveguide? (2) What are the relative contributions from diffraction and scattering? (3) How does this energy transfer scale with range? [Work supported by ONR.]
Steven Finette - One of the best experts on this subject based on the ideXlab platform.
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a stochastic response surface formulation of Acoustic Propagation through an uncertain ocean waveguide environment
Journal of the Acoustical Society of America, 2009Co-Authors: Steven FinetteAbstract:Stochastic basis expansions are applied to formulate and solve the problem of including uncertainty in numerical models of Acoustic wave Propagation within ocean waveguides. As an example, a constrained least-squares approach is used to estimate the intensity of an Acoustic field whose waveguide environment has uncertainty in both source depth and sound speed. The mean intensity, a second moment of the field, and its probability distribution are computed and compared with independent Monte-Carlo computations of these quantities. Very good agreement is obtained, indicating the potential of stochastic basis expansions for describing multiple sources of uncertainty and their effect on Acoustic Propagation.
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Acoustic Propagation through anisotropic internal wave fields transmission loss cross range coherence and horizontal refraction
Journal of the Acoustical Society of America, 2002Co-Authors: Steven FinetteAbstract:Results of a computer simulation study are presented for Acoustic Propagation in a shallow water, anisotropic ocean environment. The water column is characterized by random volume fluctuations in the sound speed field that are induced by internal gravity waves, and this variability is superimposed on a dominant summer thermocline. Both the internal wave field and resulting sound speed perturbations are represented in three-dimensional (3D) space and evolve in time. The isopycnal displacements consist of two components: a spatially diffuse, horizontally isotropic component and a spatially localized contribution from an undular bore (i.e., a solitary wave packet or solibore) that exhibits horizontal (azimuthal) anisotropy. An Acoustic field is propagated through this waveguide using a 3D parabolic equation code based on differential operators representing wide-angle coverage in elevation and narrow-angle coverage in azimuth. Transmission loss is evaluated both for fixed time snapshots of the environment and...
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Acoustic Propagation through anisotropic internal wave fields transmission loss cross range coherence and horizontal refraction
Journal of the Acoustical Society of America, 2002Co-Authors: Roger M Oba, Steven FinetteAbstract:Results of a computer simulation study are presented for Acoustic Propagation in a shallow water, anisotropic ocean environment. The water column is characterized by random volume fluctuations in the sound speed field that are induced by internal gravity waves, and this variability is superimposed on a dominant summer thermocline. Both the internal wave field and resulting sound speed perturbations are represented in three-dimensional (3D) space and evolve in time. The isopycnal displacements consist of two components: a spatially diffuse, horizontally isotropic component and a spatially localized contribution from an undular bore (i.e., a solitary wave packet or solibore) that exhibits horizontal (azimuthal) anisotropy. An Acoustic field is propagated through this waveguide using a 3D parabolic equation code based on differential operators representing wide-angle coverage in elevation and narrow-angle coverage in azimuth. Transmission loss is evaluated both for fixed time snapshots of the environment and as a function of time over an ordered set of snapshots which represent the time-evolving sound speed distribution. Horizontal Acoustic coherence, also known as transverse or cross-range coherence, is estimated for horizontally separated points in the direction normal to the source–receiver orientation. Both transmission loss and spatial coherence are computed at Acoustic frequencies 200 and 400 Hz for ranges extending to 10 km, a cross-range of 1 km, and a water depth of 68 m. Azimuthal filtering of the propagated field occurs for this environment, with the strongest variations appearing when Propagation is parallel to the solitary wave depressions of the thermocline. A large anisotropic degradation in horizontal coherence occurs under the same conditions. Horizontal refraction of the Acoustic wave front is responsible for the degradation, as demonstrated by an energy gradient analysis of in-plane and out-of-plane energy transfer. The solitary wave packet is interpreted as a nonstationary oceanographic waveguide within the water column, preferentially funneling Acoustic energy between the thermocline depressions.
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Acoustic Propagation through an internal wave field in a shallow water waveguide
Journal of the Acoustical Society of America, 1997Co-Authors: Dirk Tielburger, Steven Finette, Stephen N WolfAbstract:This paper addresses the problem of predicting and interpreting Acoustic wave field properties in a stochastic ocean waveguide, for which the sound-speed variability within the water column is treated explicitly as a random process. It is assumed that the sound-speed distribution is composed of three components: a deterministic, time-independent profile and two stochastic components induced by internal wave activity. One random contribution represents a spatially diffuse Garrett–Munk field whose spectrum is constrained by the shallow water waveguide, while the second corresponds to spatially localized soliton packets. A high-angle elastic parabolic equation method is applied to compute single frequency realizations of the pressure field using this three-component representation of the sound-speed distribution. Ensemble-averaged transmission loss and scintillation index measures for the full pressure field and its modal components are estimated for different source depths and for both flat and sloping bott...
John A Goff - One of the best experts on this subject based on the ideXlab platform.
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shallow water 06 a joint Acoustic Propagation nonlinear internal wave physics experiment
Oceanography, 2007Co-Authors: Dajun Tang, Timothy F Duda, James F Lynch, Philip Abbot, Glen Gawarkiewicz, Scott Glenn, James N Moum, Ross Chapman, Peter H Dahl, John A GoffAbstract:Author Posting. © Oceanography Society, 2007. This article is posted here by permission of Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 20, 4 (2007): 156-167.
