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effect of sea surface motion on underwater communication systems
Title
The effect of sea surface motion on underwater communication systems.
Creator
Strutt, Guenael Thomas., Florida Atlantic University, LeBlanc, Lester R., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
Underwater acoustic communications are significantly affected by time-varying multipath. Time-delays induced by multiple reactors on boundaries can be compensated for through equalization, and good transmission can be achieved. However, soundwaves reflected from moving scatterers on the sea surface undergo slight variations in frequency that significantly degrade the performance of communication devices. Ocean data was collected to evaluate the amount of Doppler-spread induced by wind-driven...
Show moreUnderwater acoustic communications are significantly affected by time-varying multipath. Time-delays induced by multiple reactors on boundaries can be compensated for through equalization, and good transmission can be achieved. However, soundwaves reflected from moving scatterers on the sea surface undergo slight variations in frequency that significantly degrade the performance of communication devices. Ocean data was collected to evaluate the amount of Doppler-spread induced by wind-driven surface waves. A model for the shallow water acoustic channel is discussed and implemented using a simplified approach to the gaussian-beam ray-tracing algorithm. This leads to the definition of the spreading function, a convenient tool to describe fading channels. The spreading function serves as a reference for the simulation of a classic digital communication setup, using baseband antipodal equalization. It is shown how frequency-spreading, a consequence of sea surface motion, affects the resulting error rate.
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Date Issued
1999
PURL
http://purl.flvc.org/fcla/dt/15675
Subject Headings
Underwater acoustics, Acoustic surface waves
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)
Radius distribution of ocean near surface bubbles
Title
Radius distribution of ocean near surface bubbles.
Creator
Auffret, Yvan., Florida Atlantic University, Glegg, Stewart A. L.
Abstract/Description
This study proposed to determine an ocean surface bubble radius distribution using theoretical noise models, experimental noise spectral data and a theoretical model for the bubble size distribution. The obtained distribution was compared to previous experimental distributions. A good agreement was found for the radius upper cut-off but the shape and the peak radius of the distribution are different from experimental observations. The most probable reasons for these differences were given....
Show moreThis study proposed to determine an ocean surface bubble radius distribution using theoretical noise models, experimental noise spectral data and a theoretical model for the bubble size distribution. The obtained distribution was compared to previous experimental distributions. A good agreement was found for the radius upper cut-off but the shape and the peak radius of the distribution are different from experimental observations. The most probable reasons for these differences were given. Moreover, the validity of recent theoretical bubble noise models was checked. Eventually, the main limitations of the study were pointed out and directions for future works were given.
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Date Issued
1993
PURL
http://purl.flvc.org/fcla/dt/14922
Subject Headings
Underwater acoustics, Acoustic surface waves, Bubbles
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)
study of ambient noise in shallow water
Title
A study of ambient noise in shallow water.
Creator
Pirie, Rachel Louise., Florida Atlantic University, Glegg, Stewart A. L., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
This thesis describes a series of measurements that took place over the duration of one year on the South Florida Testing Facility (SFTF) range, Dania, in order to survey the shallow water ambient acoustic environment. Three groups of data sets were taken in December 1998, May 1999 and July 1999. The data was collected using the Ambient Noise Sonar (ANS) that was developed in the Ocean Engineering department at Florida Atlantic University. The ambient acoustic environment was found to be...
Show moreThis thesis describes a series of measurements that took place over the duration of one year on the South Florida Testing Facility (SFTF) range, Dania, in order to survey the shallow water ambient acoustic environment. Three groups of data sets were taken in December 1998, May 1999 and July 1999. The data was collected using the Ambient Noise Sonar (ANS) that was developed in the Ocean Engineering department at Florida Atlantic University. The ambient acoustic environment was found to be highly variable with two main components. Boat noise was found to primarily be associated with the inlet and a source of snapping shrimp situated on the shallow water 30ft reef became apparent through 24hr observation. The effects of adverse weather were not studied due to the absence of this source during the measurement periods.
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Date Issued
1999
PURL
http://purl.flvc.org/fcla/dt/15738
Subject Headings
Underwater acoustics, Noise--Measurement, Acoustic surface waves
Format
Document (PDF)
Boundary reflection coefficient estimation from depth dependence of the acoustic Green's function
Title
Boundary reflection coefficient estimation from depth dependence of the acoustic Green's function.
Creator
Conrad, Alexander., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
Sound propagation in a waveguide is greatly dependent on the acoustic properties of the boundaries. The effect of these properties can be described by a bottom reflection coefficient RB, and surface reflection coefficient RS. Two methods for estimating reflection coefficients are used in this research. The first, the ratio method, is based on the variations of the Green's function with depth utilizing the ratio of the wavenumber spectra at two depths. The second, the pole method, is based on...
Show moreSound propagation in a waveguide is greatly dependent on the acoustic properties of the boundaries. The effect of these properties can be described by a bottom reflection coefficient RB, and surface reflection coefficient RS. Two methods for estimating reflection coefficients are used in this research. The first, the ratio method, is based on the variations of the Green's function with depth utilizing the ratio of the wavenumber spectra at two depths. The second, the pole method, is based on the wavenumbers of the modal peaks in the spectrum at a particular depth. A method to invert for sound speed and density is also examined. Estimates of RB and RS based on synthetic data by the ratio method were very close to their predicted values, especially for higher frequencies and longer apertures. The pole method returned less precise estimates though with longer apertures, the estimates were better. Using experimental data, results of the pole method as well a geoacoustic inversion technique based on them were mixed. The ratio method was used to estimate RS based on the actual data and returned results close to the predicted phase of p.
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Date Issued
2010
PURL
http://purl.flvc.org/FAU/3164094
Subject Headings
Underwater acoustics, Acoustic surface waves, Green's functions, Electromagnetic waves, Mathematics, Wave equation, Numerical solutions
Format
Document (PDF)
Geoacoustic inversion of subbottom channels using mulitple frequency input parameters
Title
Geoacoustic inversion of subbottom channels using mulitple frequency input parameters.
Creator
Weeks, Rebecca., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
This thesis investigates inversion techniques used to determine the geoacoustic properties of a shallow-water waveguide. The data used were obtained in the Shallow Water '06 Modal Mapping Experiment in which four buoys drifted over a system of subbottom channels. The method used was perturbative inversion using modal eigenvalues as input parameters, which were found using an autoregressive spectral estimator. This work investigates the differences between a "channel" region and a "no channel"...
Show moreThis thesis investigates inversion techniques used to determine the geoacoustic properties of a shallow-water waveguide. The data used were obtained in the Shallow Water '06 Modal Mapping Experiment in which four buoys drifted over a system of subbottom channels. The method used was perturbative inversion using modal eigenvalues as input parameters, which were found using an autoregressive spectral estimator. This work investigates the differences between a "channel" region and a "no channel" region based on an inferred stratigraphic model. Inversions were performed on data from a single buoy both at individual frequencies and multiple frequencies simultaneously. Since the use of multiple frequencies and a certain set of constraints proved to be an effective method of inversion, the method was applied to data from the other three buoys as well. It is shown that the "channel" and "no channel" regions have significantly different sound speed profiles.
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Date Issued
2010
PURL
http://purl.flvc.org/FAU/1930486
Subject Headings
Oceanographic buoys, Stochastic processes, Acoustic surface waves, Underwater acoustics, Wave equation, Numerical solutions
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)