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Low Frequency Acoustic Propagation In A Shallow Water Environment In The Presence Of Substantial Water Column Blockage
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Book Synopsis Low Frequency Acoustic Propagation in a Shallow Water Environment in the Presence of Substantial Water Column Blockage by : Michael L. Zucker
Download or read book Low Frequency Acoustic Propagation in a Shallow Water Environment in the Presence of Substantial Water Column Blockage written by Michael L. Zucker and published by . This book was released on 2011 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis The Role of the Seabed in Low-Frequency Shallow-Water Acoustic Propagation: Examples from Measurements and Modelling by : H. B. Ali
Download or read book The Role of the Seabed in Low-Frequency Shallow-Water Acoustic Propagation: Examples from Measurements and Modelling written by H. B. Ali and published by . This book was released on 1990 with total page 21 pages. Available in PDF, EPUB and Kindle. Book excerpt: Except in rather unusual circumstances, interaction with the seafloor is an inevitable accompaniment to the propagation of sound in the sea. In shallow water, especially at very low and low frequencies, the bottom interaction plays a significant, if not deterministic, role in acoustic propagation. From the results of numerous experiments and numerical modelling in recent years, it is evident that one must account for the geoacoustic properties in more than an ad hoc fashion. Some of the relevant research efforts, particularly those from the ongoing research program at the NOARL, are described in this paper. The results of the NOARL measurements in several geographical areas, coupled with numerical modelling, are used to demonstrate the significance of energy partitioning between waterborne and bottom paths, the role of Scholte interface waves, the efficacy and limitations of selected numerical models, and the significance of ambient noise. Keywords: Underwater sound transmission; Underwater acoustics interactions. (edc).
Book Synopsis Sound Propagation in the Sea by : Robert J. Urick
Download or read book Sound Propagation in the Sea written by Robert J. Urick and published by . This book was released on 1979 with total page 272 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Acoustic Attenuation in Ocean Sediments Found in Shallow Water Regions by : Karl Crawford Focke
Download or read book Acoustic Attenuation in Ocean Sediments Found in Shallow Water Regions written by Karl Crawford Focke and published by . This book was released on 1983 with total page 80 pages. Available in PDF, EPUB and Kindle. Book excerpt: The acoustic attenuation in ocean sediments is a major loss mechanism for low frequency acoustic propagation in shallow water regions. Analysis of measured propagation in these regions has generally included estimates of the attenuation in the sediment, without consideration of the variations in attenuation as a function of depth. It will be shown that these variations can have a significant impact on the standard estimates. A new procedure is then developed which provides estimates of the attenuation as a function of depth. This procedure is used to obtain attenuation depth profiles in three shallow water regions. These estimated profiles present characteristics observed in laboratory and in situ measurements
Book Synopsis Comparative Modeling and Analysis of Wideband Low Frequency Acoustic Propagation in the Shallow Water Environment by :
Download or read book Comparative Modeling and Analysis of Wideband Low Frequency Acoustic Propagation in the Shallow Water Environment written by and published by . This book was released on 2002 with total page 10 pages. Available in PDF, EPUB and Kindle. Book excerpt: This grant was supported by the Ocean Acoustics Program in the Sensors and Systems Division of the Ocean, Atmosphere and Space D
Book Synopsis Attenuation of Low Frequency Sound in the Sea by :
Download or read book Attenuation of Low Frequency Sound in the Sea written by and published by . This book was released on 1980 with total page 706 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Low Frequency Sound Propagation in Shallow Water by : John D. Nixon
Download or read book Low Frequency Sound Propagation in Shallow Water written by John D. Nixon and published by . This book was released on 1954 with total page 26 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Underwater Sound Propagation and Acoustic Communication in a Time-varying Shallow Estuarine Environment by : Zheguang Zou
Download or read book Underwater Sound Propagation and Acoustic Communication in a Time-varying Shallow Estuarine Environment written by Zheguang Zou and published by . This book was released on 2018 with total page 132 pages. Available in PDF, EPUB and Kindle. Book excerpt: Estuaries are water regions that connect rivers and oceans, which are very important due to heavy traffic, fishery and other coastal engineering activities. Underwater acoustic technology offers a series of effective applications and technical supports for real-time monitoring and long-term preservation of the nature environment and ecosystem in these regions. However, estuaries are shallow waters with complicated temporal and spatial environmental variability, involving a variety of physical oceanographic processes, such as tidal water mixing and ocean winds/waves, which can significantly influence the underwater sound propagation and moreover, underwater acoustic communications. In order to perform reliably and effectively in such complex time-varying shallow-water ocean environments, next-generation underwater acoustic communication systems need an all new design based on the environmental variability of the physical ocean, which takes the environmental physics and time-varying variability into account and is able to adapt and switch to the optimal mode as the environment evolves. Therefore, a deep, comprehensive and thorough understanding of the link between the time-varying ocean environment, underwater acoustic channel, and underwater acoustic communication systems is highly required. ☐ This dissertation investigated the relationship between the shallow-water, time-varying environment of estuaries, the underwater sound propagation and underwater acoustic communications, which can help the design of underwater acoustic systems so that they can adapt the time-varying environment with wiser parameter configurations. In this dissertation, field data analysis, joint numerical modeling, together with a controllable laboratory experiment were used to study acoustic channel variability of a shallow estuary and its influence on the performance of underwater acoustic communications. This dissertation included four aspects: (a) Effect of water-column variation due to the tidal dynamics in an estuary on the underwater acoustic direct path; (b) Effect of time-varying surface roughness due to the wind-driven waves on underwater acoustic surface paths; (c) Numerically modeling the effect of time-varying wind-driven shallow-water waves on coherent underwater acoustic communications using a combined model; (d) Conducting a controllable laboratory experiment to investigate the time-varying wind-driven water waves on the performance of coherent and non-coherent underwater acoustic communications. ☐ The first two aspects focused on the link between the time-varying environment of an estuary and the underwater acoustic wave propagation. With field data analysis and joint numerical modeling, the time-varying variability of acoustic direct paths and surface-bounced paths from a high-frequency acoustic experiment conducted in the Delaware Bay estuary was explored. On one hand, periodical acoustic direct path fading was found in the tidal-straining Delaware Bay estuary, with the fading period as same as the semi-diurnal tide. Based on physical oceanography and ocean acoustics, the mechanism that causes the direct path fading and its link to the water dynamics of an estuary was investigated. On the other hand, the relationship between the acoustic surface paths and the surface wind speed was investigated, and the wind-influenced shallow-water time-varying channel was studied using field data analysis and a joint model combining physical oceanography and ocean acoustics. The joint numerical model, including a wind-wave model, a surface generation algorithm and a parabolic equation acoustic model, reproduced the relationship between the wind speed and surface reflection signals. ☐ The last two aspects applied the knowledge of underwater sound propagation in shallow estuaries into analyzing the performance of underwater acoustic communication systems, i.e., investigating how the fast fluctuation of a shallow-water environment (wind-driven waves) influences different fundamental modulation schemes for underwater acoustic communications. To better analyze the effect of environmental variability of the physical ocean on underwater acoustic communications, the surface condition was set as the only variation in the numerical modeling and the controllable laboratory experiment. On one hand, a combined model including physical oceanography, ocean acoustics, and underwater acoustic communication was used to study the time-varying underwater acoustic channel under different wind speeds, and the performance of the coherent acoustic communication (QPSK) system. On the other hand, a controllable laboratory experiment was conducted to investigate bit-error-rate (BER) performance of the MFSK (representing the non-coherent acoustic communication) and the QPSK (representing the coherent acoustic communication) acoustic modulations. ☐ The main conclusions of the dissertation are as follows. For the time-varying variability of underwater acoustic channel: (a) Due to the tidal-straining water dynamics of an estuary, periodical water column exchange between the seawater and the freshwater, up-refracting sound speed profile is more likely to form by the end of ebb tide, which redirects sound signal away from the deep receivers and creates shadow zone for the sound direct path; (b) In an open estuary, the acoustic pressure of surface-bounced paths decreases with increased wind speed, as a result of increased acoustic scattering due to the wind-driven surface roughness. For underwater acoustic communications: (c) Coherent acoustic communications are sensitive to the fast time-varying variability, and performance decrease significantly with increased wind speed, as a result of increased channel variability and decreased temporal coherence; (d) Non-coherent acoustic communications are less sensitive to the channel variability, and the reduced multipath signals due to wind-wave surface may improve the system performance. ☐ The key novelties of this dissertation include: (a) Using a joint model involving physical oceanography and ocean acoustics to study the effect of time-varying estuarine environment (water-column variations and wind-driven surface waves) on underwater sound propagation and the underwater acoustic channels. (b) Using an integrated model involving physical oceanography, ocean acoustics, and underwater acoustic communications to study the effect of time-varying estuarine environment (wind-driven surface waves) on underwater acoustic communications. (c) Using field experimental data, numerical modeling and controllable laboratory experiment to study the underwater sound propagation and underwater acoustic communications in a time-varying ocean environment.
Book Synopsis Theory of Propagation of Explosive Sound in Shallow Water by : Chaim Leib Pekeris
Download or read book Theory of Propagation of Explosive Sound in Shallow Water written by Chaim Leib Pekeris and published by . This book was released on 1945 with total page 434 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Impacts of Short-time Scale Water Column Variability on Broadband High-frequency Acoustic Wave Propagation by : Justin Eickmeier
Download or read book Impacts of Short-time Scale Water Column Variability on Broadband High-frequency Acoustic Wave Propagation written by Justin Eickmeier and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Acoustical oceanography is one way to study the ocean, its internal layers, boundaries and all processes occurring within using underwater acoustics. Acoustical sensing techniques allows for the measurement of ocean processes from within that logistically or financially preclude traditional in-situ measurements. Acoustic signals propagate as pressure wavefronts from a source to a receiver through an ocean medium with variable physical parameters. The water column physical parameters that change acoustic wave propagation in the ocean include temperature, salinity, current, surface roughness, seafloor bathymetry, and vertical stratification over variable time scales. The impacts of short-time scale water column variability on acoustic wave propagation include coherent and incoherent surface reflections, wavefront arrival time delay, focusing or defocusing of the intensity of acoustic beams and refraction of acoustic rays. This study focuses on high-frequency broadband acoustic waves, and examines the influence of short-time scale water column variability on broadband high-frequency acoustics, wavefronts, from 7 to 28 kHz, in shallow water. Short-time scale variability is on the order of seconds to hours and the short-spatial scale variability is on the order of few centimeters. Experimental results were collected during an acoustic experiment along 100 m isobaths and data analysis was conducted using available acoustic wave propagation models. Three main topics are studied to show that acoustic waves are viable as a remote sensing tool to measure oceanographic parameters in shallow water. First, coherent surface reflections forming striation patterns, from multipath receptions, through rough surface interaction of broadband acoustic signals with the dynamic sea surface are analyzed. Matched filtered results of received acoustic waves are compared with a ray tracing numerical model using a sea surface boundary generated from measured water wave spectra at the time of signal propagation. It is determined that on a time scale of seconds, corresponding to typical periods of surface water waves, the arrival time of reflected acoustic signals from surface waves appear as striation patterns in measured data and can be accurately modelled by ray tracing. Second, changes in acoustic beam arrival angle and acoustic ray path influenced by isotherm depth oscillations are analyzed using an 8-element delay-sum beamformer. The results are compared with outputs from a two-dimensional (2-D) parabolic equation (PE) model using measured sound speed profiles (SSPs) in the water column. Using the method of beamforming on the received signal, the arrival time and angle of an acoustic beam was obtained for measured acoustic signals. It is determined that the acoustic ray path, acoustic beam intensity and angular spread are a function of vertical isotherm oscillations on a time scale of minutes and can be modeled accurately by a 2-D PE model. Third, a forward problem is introduced which uses acoustic wavefronts received on a vertical line array, 1.48 km from the source, in the lower part of the water column to infer range dependence or independence in the SSP. The matched filtering results of received acoustic wavefronts at all hydrophone depths are compared with a ray tracing routine augmented to calculate only direct path and bottom reflected signals. It is determined that the SSP range dependence can be inferred on a time scale of hours using an array of hydrophones spanning the water column. Sound speed profiles in the acoustic field were found to be range independent for 11 of the 23 hours in the measurements. A SSP cumulative reconstruction process, conducted from the seafloor to the sea surface, layer-by-layer, identifies critical segments in the SSP that define the ray path, arrival time and boundary interactions. Data-model comparison between matched filtered arrival time spread and arrival time output from the ray tracing was robust when the SSP measured at the receiver was input to the model. When the SSP measured nearest the source (at the same instant in time) was input to the ray tracing model, the data-model comparison was poor. It was determined that the cumulative sound speed change in the SSP near the source was 1.041 m/s greater than that of the SSP at the receiver and resulted in the poor data-model comparison. In this study, the influences on broadband acoustic wave propagation in the frequency range of 7 to 28 kHz of spatial and temporal changes in the oceanography of shallow water regions are addressed. Acoustic waves can be used as remote sensing tools to measure oceanographic parameters in shallow water and data-model comparison results show a direct relationship between the oceanographic variations and acoustic wave propagations.
Book Synopsis Spatial Coherence in a Shallow Water Waveguide by : Jie Yang
Download or read book Spatial Coherence in a Shallow Water Waveguide written by Jie Yang and published by . This book was released on 2007 with total page 160 pages. Available in PDF, EPUB and Kindle. Book excerpt: In shallow water environments, sound propagation experiences multiple interactions with the surface/bottom interfaces, with hydrodynamic disturbances such as internal waves, and with tides and fronts. It is thus very difficult to make satisfactory predictions of sound propagation in shallow water. Given that many of the ocean characteristics can be modeled as stochastic processes, the statistical measure, spatial coherence, is consequently an important quantity. Spatial coherence provides valuable information for array performance predictions. However, for the case of long-range, low frequency propagation, studies of spatial coherence influenced by various environmental parameters are limited insofar as having the appropriate environmental data with which to model and interpret the results.
Book Synopsis A Study of Low Frequency Sound Propagation in Shallow Water Ducts by :
Download or read book A Study of Low Frequency Sound Propagation in Shallow Water Ducts written by and published by . This book was released on 1992 with total page 14 pages. Available in PDF, EPUB and Kindle. Book excerpt: This paper presents results from a recent investigation of shallow water propagation loss for low frequencies (500-4000 Hz). Shallow water is defined in this context as a location where acoustic energy has numerous boundary interactions. This definition leads to both physically shallow and not- so-shallow sites. The objectives of this investigation are, first, to gain a quantitative understanding of propagation loss as a function of source/receiver placement and frequency for numerous shallow water environments, in this case, for 10 geographic areas across all four seasons; second, to gain quantitative information of surface duct versus downward refracting propagation by using a statistical approach, and third, to address questions concerning frequencies which are supported in ducting propagation, effects of duct transmission loss in shallow water, and the impact of source/receiver placement in shallow water.
Book Synopsis Effect of Solitary Waves on Low-frequency Acoustic Propagation [in] Shallow Water by : J.-X. Zhou
Download or read book Effect of Solitary Waves on Low-frequency Acoustic Propagation [in] Shallow Water written by J.-X. Zhou and published by . This book was released on 1991 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis An Efficient Multi-layer Boundary Element Method for Direct Computation of Sound Propagation in Shallow Water Environments by : Chengxi Li (Ph. D.)
Download or read book An Efficient Multi-layer Boundary Element Method for Direct Computation of Sound Propagation in Shallow Water Environments written by Chengxi Li (Ph. D.) and published by . This book was released on 2019 with total page 152 pages. Available in PDF, EPUB and Kindle. Book excerpt: The objective of this thesis is to develop and apply efficient three-dimensional (3D) direct simulation capabilities for underwater sound field predictions in shallow water environments. Despite the large number of theoretical and experimental studies, direct numerical simulation of the shallow water acoustic field is still challenging due to environmental complexities and large computation cost involved. In this thesis, we develop a highly efficient O(NlogN) multi-layer boundary-element method, PFFT-BEM, for direct numerical simulation of acoustic propagation and scattering in shallow water environment. This method utilizes a Pre-corrected Fast Fourier Transform (PFFT) approach to accelerate the boundary-element method and reduce the computational efforts from O(N2~3) to O(NlogN) where N is the total number of boundary unknowns. PFFT-BEM is capable of accounting for complex topography, inhomogeneity of water properties, and dynamic environments associated with realistic coastal conditions. With the O(NlogN) efficiency and linear scalability on massively parallel high-performance computing platforms, we first conduct multilayer 3D simulations benchmarking low-mid frequency acoustics over kilometer ranges against available theoretical results and field experiments. We then apply largescale PFFT-BEM simulations to investigate two underwater acoustics problems which are of scientific interest and practical importance: (1) 3D sound scattering from rough ocean surface; (2) 3D sound propagation and scattering around underwater seamount(s). For the 3D rough surface scattering problem, several approximation models have been proposed such as the perturbation theory and Kirchhoff approximation. These approximation models provide fast predictions of statistics for the acoustics scattering necessary for predicting the scattering effects and reverberations from the rough surfaces. The validities of these models need to be assessed by direct numerical methods. However, most existing direct numerical studies regarding the validity regions of the approximation models are limited to the 2D rough surface scattering problem. We apply direct PFFT-BEM computations to study the 3D rough surface scattering problem with a Gaussian roughness spectrum. We examine the accuracy of the approximation model results through comparisons with direct numerical simulation results by 3D PFFT-BEM with a Monte Carlo technique. We identify and quantify the 3D validity regions of the approximation models as a function of the surface roughness and correlation length. We characterize and quantify the importance of 3D scattering effects on the validities of different approximation models. Moreover, we find that both perturbation theory and Kirchhoff approximation become inaccurate for 3D scattering problems with low grazing angles. For the problem of 3D sound propagation/scattering around underwater seamount(s), we investigate the effects of seamount geometry and sound source frequencies on the sound scatterings by the seamount using 3D PFFT-BEM simulations. In particular, we investigate the backscattering, blocking and 3D scattering effects due to the presence of the seamount. We find that the acoustics scattering effects by the seamount have a strong dependence on the source frequency, and small variations in seamount geometry (such as seamount height and cross section shape) can induce significant changes in the acoustics scattering field.
Book Synopsis High-Resolution, Three-Dimensional Measurements of Low-Frequency Sound Propagation in Shallow Water by :
Download or read book High-Resolution, Three-Dimensional Measurements of Low-Frequency Sound Propagation in Shallow Water written by and published by . This book was released on 1998 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: An overview is presented of the Model Mapping Experiment (MOMAX), in which both fixed and moving source configurations were used to transmit several pure tones in the frequency range 50 - 300 Hz in shallow water. The magnitudes and phases of these signals were recorded on several freely drifting buoys, each containing a hydrophone, GPS and acoustic navigation, and radio telemetry. High-resolution, three-dimensional measurements of the sound field were made out to ranges of 10 km and illustrate the influence of the laterally varying seabed in both the space and wavenumber domains. In addition, the phases of the measured signals show a remarkably high level of stability and regularity which can be exploited to make accurate estimates of the relative source/receiver speed from measurements of the time rate-of-change of the phase.
Book Synopsis Measurement and Modeling of Low Frequency Acoustic Wave Propagation and Scattering in Shallow Water with Comprehensive Subbottom Structure Measurements by :
Download or read book Measurement and Modeling of Low Frequency Acoustic Wave Propagation and Scattering in Shallow Water with Comprehensive Subbottom Structure Measurements written by and published by . This book was released on 1996 with total page 84 pages. Available in PDF, EPUB and Kindle. Book excerpt: A high resolution acoustic crosswell tomography technique was developed for accurate measurements of variabilities of density, velocity, shear strength and permeability within the sediments. An analytical expression for the three dimensional wave number spectra of these sediment properties has been obtained. Acoustics scattering from sediment volume has been obtained as a function of the three dimensional spectra of velocity and density variabilities. Work continues to quantify the relation between the variabilities of sediment properties and acoustic bottom scattering. A method to measure the ocean wave directional spectra using a single buried ocean bottom seismometer and a pressure senser has been developed and sea tested successfully.
Book Synopsis Propagation of Sound in a Layered Laboratory Model by : Tariq Kakar
Download or read book Propagation of Sound in a Layered Laboratory Model written by Tariq Kakar and published by . This book was released on 1984 with total page 88 pages. Available in PDF, EPUB and Kindle. Book excerpt: The propagation of sound in a laboratory model consisting of a surface layer of water overlying a thick bottom layer of sand was experimentally investigated. The variations of pressure amplitude as a function of receiver depth, range, and transverse location were measured for the source at constant depth in the surface layer of water. Three frequencies for which only the lowest mode propagates were used in this investigation. The measurements of pressure amplitude as a function of depth and range were found in good agreement with normal mode theory, when absorption in the bottom was taken into consideration. Keywords include: Sound propagation, Shallow water, Normal modes, Shallow water facility, Theses.
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