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Acoustic propagation over a range-dependent bathymetry
Title
Acoustic propagation over a range-dependent bathymetry.
Creator
Riley, Joseph M., Florida Atlantic University, Glegg, Stewart A. L., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
Experimental measurements have been conducted to investigate the effects of a three dimensional bathymetry on ocean acoustic propagation and our abilities to use array processing for localizing sources. This work is unique because it uses laboratory scale measurements to isolate the effects of the bottom bathymetry. Previous investigations using laboratory scale measurements have only used simplistic bottom profiles. In addition, experiments which have investigated the effects of the bottom...
Show moreExperimental measurements have been conducted to investigate the effects of a three dimensional bathymetry on ocean acoustic propagation and our abilities to use array processing for localizing sources. This work is unique because it uses laboratory scale measurements to isolate the effects of the bottom bathymetry. Previous investigations using laboratory scale measurements have only used simplistic bottom profiles. In addition, experiments which have investigated the effects of the bottom bathymetry at sea have encountered difficulties isolating these effects due to range dependent sound speed profiles and the uncertainties of ocean acoustic experiments. The first part of this dissertation investigates the tracking of an acoustic source in a three dimensional shallow water environment. This work is comprised of two studies. The first study uses matched field processing for identifying the trajectory of a source. The second investigation uses experimental measurements and theoretical predictions to evaluate the beating angle bias caused by the use of plane-wave beamforming in the presence of bathymetric refraction. The second part of this dissertation uses laboratory scale measurements to analyze two and three dimensional propagation over a realistic bottom bathymetry. This series of investigations uses an inverse approach based on normal mode theory. The inversion algorithm is used to extract the normal mode amplitudes for the purpose of analyzing the measurements for two dimensional mode coupling and bathymetric refraction. The results of this investigation show that the bathymetry has a strong influence on the three dimensional acoustic field. Analysis of the experimental measurements identify that mode coupling and bathymetric refraction are important for propagation over the laboratory scale model and these effects adversely influence our abilities to localize sources in three dimensional shallow water environments. It is also shown that by incorporating three dimensional propagation models into the signal replica used by the array processor a significant improvement in performance can be achieved.
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Date Issued
1999
PURL
http://purl.flvc.org/fcla/dt/12618
Subject Headings
Underwater acoustics--Measurement, Ocean tomography
Format
Document (PDF)
Modelling of underwater ambient noise due to whitecaps
Title
Modelling of underwater ambient noise due to whitecaps.
Creator
Elisseeff, Pierre., Florida Atlantic University, Glegg, Stewart A. L.
Abstract/Description
A theoretical model accounting for underwater ambient noise due to whitecap-generated bubbles and drop-impacts is developed to investigate the possible mechanisms of ocean noise generation. A general analysis is laid down, leading to expressions of the noise spectrum in an undefined environment. Subsequently the cases of isovelocity and stratified deep oceans are considered, and specific expressions are derived. The stratified deep ocean estimations of the directional spectrum are then...
Show moreA theoretical model accounting for underwater ambient noise due to whitecap-generated bubbles and drop-impacts is developed to investigate the possible mechanisms of ocean noise generation. A general analysis is laid down, leading to expressions of the noise spectrum in an undefined environment. Subsequently the cases of isovelocity and stratified deep oceans are considered, and specific expressions are derived. The stratified deep ocean estimations of the directional spectrum are then compared to experimental data and a good agreement is found. Finally the absolute noise levels due to bubbles and drop impacts are discussed, and bubble noise is found to be larger than drop impact noise. The collective bubble oscillation hypothesis is also discussed, and although clues are given for and against this hypothesis no rigorous justification for this has been found.
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Date Issued
1992
PURL
http://purl.flvc.org/fcla/dt/14784
Subject Headings
Underwater acoustics--Measurement, Acoustic surface waves
Format
Document (PDF)
Modeling of shallow water ambient noise directionality using the effective depth approximation
Title
Modeling of shallow water ambient noise directionality using the effective depth approximation.
Creator
Galletta, Frank Anton., Florida Atlantic University, Glegg, Stewart A. L.
Abstract/Description
A theoretical model has been developed to compute the vertical array directional response for surface generated ambient noise in a shallow water environment. The cross spectrum function is based on a normal mode solution to the wave equation in which the effective depth approximation is used to yield closed form solutions for two distinct mode types. The effective depth modes encompass the shallowest grazing angles where the bottom reacts as a pressure release surface to the incident plane...
Show moreA theoretical model has been developed to compute the vertical array directional response for surface generated ambient noise in a shallow water environment. The cross spectrum function is based on a normal mode solution to the wave equation in which the effective depth approximation is used to yield closed form solutions for two distinct mode types. The effective depth modes encompass the shallowest grazing angles where the bottom reacts as a pressure release surface to the incident plane waves. The rigid bottom solution takes over as the grazing angle increases and attenuation becomes significant. The computed vertical array beam output was compared to other models including a fast field wavenumber integration method and a multipath eigenray method with mixed results. The results indicated good agreement for both comparisons with the realization that the effective depth model is sensitive to the approximation discontinuity at the mode transition point.
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Date Issued
1996
PURL
http://purl.flvc.org/fcla/dt/15237
Subject Headings
Underwater acoustics--Measurement, Noise--Measurement, Acoustic surface waves
Format
Document (PDF)
investigation of the acoustic field in wedge-shaped scale models of continental shelf regions
Title
An investigation of the acoustic field in wedge-shaped scale models of continental shelf regions.
Creator
House, Ian Geoffrey., Florida Atlantic University, Glegg, Stewart A. L., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
The acoustic field in the ocean is difficult to model theoretically, due to the complexity of the environment. This is particularly true if the water depth is range dependent, such as in the coastal region, where a fully three dimensional description is required. Propagation effects result in horizontal refraction, shadow zones, and the existence of regions with strong interference patterns. As a result, all of the existing theoretical models are based on significant simplifying assumptions....
Show moreThe acoustic field in the ocean is difficult to model theoretically, due to the complexity of the environment. This is particularly true if the water depth is range dependent, such as in the coastal region, where a fully three dimensional description is required. Propagation effects result in horizontal refraction, shadow zones, and the existence of regions with strong interference patterns. As a result, all of the existing theoretical models are based on significant simplifying assumptions. One such assumption is to model a region of the ocean as a water column overlying a planar sloping bottom. To test the accuracy of these theories model scale measurements of the acoustic field under highly controlled conditions have been undertaken in this study. Two experiments were performed on models with a sloping bottom. The first model consisted of a fast fluid bottom, and the second model consisted of a thin epoxy layer, to model a sediment, overlying a concrete layer, which modelled the substrate rock. The measurements performed included pulse, CW traverse, and depth profile measurements in both the across slope and down slope directions, in order to demonstrate the three dimensional features of the field. The features of the results are discussed and where possible are compared with existing theories. The results indicated that the three dimensional propagation effects in a fluid bottom wedge are described accurately by a theoretical model which uses an effective depth correction. No three dimensional theory was available for the shear wave supporting bottom case but the fluid bottom theory was found to provide accurate predictions. Down slope propagation over a shear wave supporting bottom was also shown to be accurately predicted using a two dimensional finite element parabolic equation code.
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Date Issued
1991
PURL
http://purl.flvc.org/fcla/dt/12284
Subject Headings
Underwater acoustics--Measurement, Ocean bottom, Continental shelf
Format
Document (PDF)
The Comprehensive Evaluation of Performance and Environmental Influence on MPSK Modulated High-Speed Acoustic Communications in Shallow Water
Title
The Comprehensive Evaluation of Performance and Environmental Influence on MPSK Modulated High-Speed Acoustic Communications in Shallow Water.
Creator
Proteau, Joshua C., Beaujean, Pierre-Philippe, Florida Atlantic University, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
A daily study spanning a month of the shallow water acoustic channel was conducted to estimate the environmental influence on performance of an underwater acoustic communications system. An automated acoustic modem transmitted phase-coherent modulated sequences of identical data with 186 dB re IpPa source level, at coded rates from 4000 to 16000 bits/s with 4 or 8 kHz symbol bandwidth, three times daily for a month. A 64 channel Mills-Cross receiver array was used with horizontal and vertical...
Show moreA daily study spanning a month of the shallow water acoustic channel was conducted to estimate the environmental influence on performance of an underwater acoustic communications system. An automated acoustic modem transmitted phase-coherent modulated sequences of identical data with 186 dB re IpPa source level, at coded rates from 4000 to 16000 bits/s with 4 or 8 kHz symbol bandwidth, three times daily for a month. A 64 channel Mills-Cross receiver array was used with horizontal and vertical beams each containing 32 and 33 elements respectively, spaced 0.03 meters apart, with a sampling frequency of 72 kHz. Source and receiver were deployed at depths of 20 meters respectively, with a 720 meter separation range. Environmental measurements of wind velocity and direction, surface wave activity, current and sound velocity profiles, and tidal measurements were performed. Results demonstrate reliable achievement of high data-rate shallow water acoustic communications using phase-coherent modulation techniques.
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Date Issued
2006
PURL
http://purl.flvc.org/fau/fd/FA00012541
Subject Headings
Underwater acoustics--Measurement, Artificial satellites in telecommunication, Underwater acoustic telemetry, Signal processing--Digital techniques
Format
Document (PDF)
Sediment classification of the sea floor using the Chirp Sonar and the Biot model
Title
Sediment classification of the sea floor using the Chirp Sonar and the Biot model.
Creator
Beaujean, Pierre-Philippe, Florida Atlantic University, LeBlanc, Lester R.
Abstract/Description
A new method is proposed to infer the geotechnical properties of the sea floor from its response to the frequency-modulated pulses emitted by the subbottom profiler called Chirp Sonar. The environment is assumed to be a multilayered medium, composed of homogeneous layers, or an inhomogeneous half-space with depth-dependent properties. The acoustic response of the sediment is computed using the Biot-Stoll theory. The Levenberg-Marquardt method is applied to fit the synthetic response to the...
Show moreA new method is proposed to infer the geotechnical properties of the sea floor from its response to the frequency-modulated pulses emitted by the subbottom profiler called Chirp Sonar. The environment is assumed to be a multilayered medium, composed of homogeneous layers, or an inhomogeneous half-space with depth-dependent properties. The acoustic response of the sediment is computed using the Biot-Stoll theory. The Levenberg-Marquardt method is applied to fit the synthetic response to the experimental response of an homogeneous layer overlying the sea floor. The porosity, the permeability, the mean grain diameter, the mass density, the bulk modulus and the shear modulus within this sediment layer can be estimated. A multilayered medium with depth-dependent properties could be applied to this inversion technique in the future.
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Date Issued
1995
PURL
http://purl.flvc.org/fcla/dt/15208
Subject Headings
Marine sediments--Acoustic properties, Underwater acoustics--Measurement, Ocean bottom, Sonar
Format
Document (PDF)
investigation of the influence of surface roughness on reflection coefficients measured by a chirp sonar using a laser profiling of the seafloor
Title
An investigation of the influence of surface roughness on reflection coefficients measured by a chirp sonar using a laser profiling of the seafloor.
Creator
Hache, Nicolas., Florida Atlantic University, Beaujean, Pierre-Philippe, Schock, Steven G.
Abstract/Description
This research investigates the validity of an acoustic propagation model by comparing theoretical reflection coefficients, function of frequency, to FAU chirp sonar measurements (chirp sub-bottom profiler). An acoustic model has been implemented to estimate the spectrum of energy reflected from sandy sediments in the presence of surface scattering. The surface roughness being the dominant reverberation part, the volume scattering has been neglected in this model. A laser scanning system...
Show moreThis research investigates the validity of an acoustic propagation model by comparing theoretical reflection coefficients, function of frequency, to FAU chirp sonar measurements (chirp sub-bottom profiler). An acoustic model has been implemented to estimate the spectrum of energy reflected from sandy sediments in the presence of surface scattering. The surface roughness being the dominant reverberation part, the volume scattering has been neglected in this model. A laser scanning system involving an image-processing algorithm has been designed to measure the seafloor bottom roughness using 1D Fourier transforms. In the case of anisotropic roughness, an estimation of the sand ripples dominant direction is provided involving 2D Fourier transforms. Measurements of acoustic data using a chirp sonar and estimation of bottom roughness from video data of the scanner over an artificial bottom are provided to compare the reflection coefficients obtained from the data actually measured with those from the acoustical model.
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Date Issued
2005
PURL
http://purl.flvc.org/fcla/dt/13212
Subject Headings
Underwater acoustics--Measurement, Marine sediments--Acoustic properties, Oceanography, Seawater--Acoustic properties
Format
Document (PDF)
normal incidence reflection coefficient of a sandy seabed as a function of frequency
Title
The normal incidence reflection coefficient of a sandy seabed as a function of frequency.
Creator
Arizzi, Ernest Allen., Florida Atlantic University, Schock, Steven G.
Abstract/Description
A thesis investigates the measured and theoretical pressure reflection coefficients of the seabed at normal incidence. The theoretical reflection coefficient is calculated using a physics-based model developed by Maurice Biot. The model describes sound propagation in saturated porous media and interrelationships between the acoustic properties of the media and the physical properties of the pore fluid and the porous solid. Stoll modified the Biot model for the case of ocean sediments and...
Show moreA thesis investigates the measured and theoretical pressure reflection coefficients of the seabed at normal incidence. The theoretical reflection coefficient is calculated using a physics-based model developed by Maurice Biot. The model describes sound propagation in saturated porous media and interrelationships between the acoustic properties of the media and the physical properties of the pore fluid and the porous solid. Stoll modified the Biot model for the case of ocean sediments and developed an expression for calculating the reflection coefficient as a function of frequency. This thesis tests the model by comparing the reflection coefficient measured with chirp sonar to the reflection coefficient calculated using the Biot model. An experiment was conducted off Fort Walton Beach, Florida where chirp sonar transmitted FM pulses at normal incidence to a sandy seabed. Sediment properties measured during SAX-99 are used to calculate the theoretical reflection coefficient using the Biot-Stoll model. The agreement of the measured reflection coefficients with the theoretical calculations over the band of 1500 to 16000 Hz varies as much as 70%. The plotted results show a reduction of the reflection coefficient with frequency but the large deviations from the trend prevent any further conclusions.
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Date Issued
2004
PURL
http://purl.flvc.org/fcla/dt/13191
Subject Headings
Marine sediments--Acoustic properties, Underwater acoustics--Measurement, Sedimentation analysis
Format
Document (PDF)
Influence of depth-dependent sediment properties on the pressure reflection coefficient at normal incidence using the Biot-Stoll model
Title
Influence of depth-dependent sediment properties on the pressure reflection coefficient at normal incidence using the Biot-Stoll model.
Creator
Joussein, Marianne., Florida Atlantic University, Beaujean, Pierre-Philippe
Abstract/Description
The impact of depth-dependent geophysical parameters on the acoustic pressure reflection coefficient is studied at normal incidence using the Biot-Stoll theory in porous marine sediments. The seabed is modeled as a sediment layer with depth-dependent properties on top of a homogeneous half-space, as originally proposed by Stern. There is no discontinuity in sediment properties between the layer and the half-space. The reflection coefficient is determined by the evaluation of boundary...
Show moreThe impact of depth-dependent geophysical parameters on the acoustic pressure reflection coefficient is studied at normal incidence using the Biot-Stoll theory in porous marine sediments. The seabed is modeled as a sediment layer with depth-dependent properties on top of a homogeneous half-space, as originally proposed by Stern. There is no discontinuity in sediment properties between the layer and the half-space. The reflection coefficient is determined by the evaluation of boundary conditions at the water-sediment layer interface and the sediment layer-half-space interface. Results are obtained for different types of sediment, from medium size sands to silty clay, and different porosity profiles vs. depth.
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Date Issued
2004
PURL
http://purl.flvc.org/fcla/dt/13168
Subject Headings
Marine sediments--Acoustic properties, Underwater acoustics--Measurement, Sediments (Geology), Environmental geology
Format
Document (PDF)
A Study of the Underwater Acoustic Propagation in a Turning Basin Modeled as a Three-Dimensional Duct Closed at One End Using the Method of Images
Title
A Study of the Underwater Acoustic Propagation in a Turning Basin Modeled as a Three-Dimensional Duct Closed at One End Using the Method of Images.
Creator
Staska, Matthew D., Beaujean, Pierre-Philippe, Florida Atlantic University, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
A computer-efficient model of the underwater acoustic propagation m a shallow, three-dimensional duct closed at one end has been developed using the method of images. Presented in this research is the development of this three-dimensional method of images analysis for a rectangular duct. Using this analysis, a model of the impulse response of the acoustic channel is constructed. Also presented in this work is the actual impulse response collected during field experimentation in the south...
Show moreA computer-efficient model of the underwater acoustic propagation m a shallow, three-dimensional duct closed at one end has been developed using the method of images. Presented in this research is the development of this three-dimensional method of images analysis for a rectangular duct. Using this analysis, a model of the impulse response of the acoustic channel is constructed. Also presented in this work is the actual impulse response collected during field experimentation in the south turning basin of Port Everglades in Fort Lauderdale, Florida. The results demonstrate that the impulse response is modeled with a relative echo magnitude error of 1.62 dB at worst, and a relative echo location error varying between 0% and 4% when averaged across multiple measurements and sensor locations.
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Date Issued
2007
PURL
http://purl.flvc.org/fau/fd/FA00012557
Subject Headings
Underwater acoustics--Measurement, Wave motion, Theory of, Wave equation--Numerical solutions, Sound-waves--Transmission--Mathematical models
Format
Document (PDF)
An Investigation into the Acoustic Variability and the Attenuation of an Acoustic Signal within a Port Environment Focusing on Port Everglades, Florida
Title
An Investigation into the Acoustic Variability and the Attenuation of an Acoustic Signal within a Port Environment Focusing on Port Everglades, Florida.
Creator
Sheahan, Daniel, Frisk, George V., Florida Atlantic University, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
A methodology for characterizing the acoustical properties of a port environment, namely Port Everglades, has been proposed and carried out. This approach includes both a port-wide analysis of how the basic oceanographic features within the port impact the acoustic properties, and also a more focused sampling methodology within a small region of Port Everglades, allowing for the acoustic characteristics, including ambient noise, and an approximate signal absorption to be computed. The results...
Show moreA methodology for characterizing the acoustical properties of a port environment, namely Port Everglades, has been proposed and carried out. This approach includes both a port-wide analysis of how the basic oceanographic features within the port impact the acoustic properties, and also a more focused sampling methodology within a small region of Port Everglades, allowing for the acoustic characteristics, including ambient noise, and an approximate signal absorption to be computed. The results documented through the duration of this research indicate that the temperature variation throughout the port is the principal contributor to the characteristics of the sound velocity profile. Ambient noise measurements have revealed high levels of background noise within the sub-5 kHz region, owing likely to consistent port traffic. The calculation of absorption indicates that high frequency systems, i.e. > 100 kHz, may encounter problems when transmitting over a considerable distance. These are important factors for consideration when implementing a successful underwater acoustic system.
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Date Issued
2007
PURL
http://purl.flvc.org/fau/fd/FA00012553
Subject Headings
Underwater acoustics--Measurement, Port Everglades (Fort Lauderdale, Fla), Harbors--Environmental aspects--Florida--Fort Lauderdale, Acoustic surface waves--Measurement
Format
Document (PDF)