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Model experiments for the acoustic field in a water column which includes the effects of shear in marine sediments
Title
Model experiments for the acoustic field in a water column which includes the effects of shear in marine sediments.
Creator
Hundley, Allen John., Florida Atlantic University, Glegg, Stewart A. L.
Abstract/Description
A scaled, horizontally stratified shallow water marine acoustic model is constructed for the purpose of investigating the sound field resulting from long range propagation. The characteristics of this sound field in the water column are strongly dependent upon properties of the surficial sediment. One effect is the conversion from compressional waves in the water column to shear waves in the sediment at grazing angles less than the critical. To model a shallow marine environment, concrete is...
Show moreA scaled, horizontally stratified shallow water marine acoustic model is constructed for the purpose of investigating the sound field resulting from long range propagation. The characteristics of this sound field in the water column are strongly dependent upon properties of the surficial sediment. One effect is the conversion from compressional waves in the water column to shear waves in the sediment at grazing angles less than the critical. To model a shallow marine environment, concrete is used as a substrate rock and laminating epoxy is used to model a surficial sediment. Preliminary tests of the effects of the model's environment are performed, and the range dependent sound field as a function of depth is measured for several CW frequencies. These sound field profiles are compared with an approximate predictive theory, and with a numerical solution which treats the sediment properties exactly.
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Date Issued
1990
PURL
http://purl.flvc.org/fcla/dt/14618
Subject Headings
Underwater acoustics, Marine sediments--Acoustic properties
Format
Document (PDF)
Impact of noise on seafloor property estimation using Biot model parameters obtained through an inversion of chirp sonar data
Title
Impact of noise on seafloor property estimation using Biot model parameters obtained through an inversion of chirp sonar data.
Creator
Munro, Lachlan I., Florida Atlantic University, Schock, Steven G., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
This thesis describes the development and testing of an inversion method, based on the Biot-Stoll acoustic wave propagation model, for estimating sediments properties from acoustic reflection measurements of the seabed. The Biot-Stoll model is a physics-based model which describes the propagation of compressional and shear waves through porous media. Given the physical sediment properties of the seabed, the pressure reflection coefficient of the seabed is calculated using the Biot-Stoll model...
Show moreThis thesis describes the development and testing of an inversion method, based on the Biot-Stoll acoustic wave propagation model, for estimating sediments properties from acoustic reflection measurements of the seabed. The Biot-Stoll model is a physics-based model which describes the propagation of compressional and shear waves through porous media. Given the physical sediment properties of the seabed, the pressure reflection coefficient of the seabed is calculated using the Biot-Stoll model. The proposed inversion procedure varies sediment properties until a least squares fit is obtained between the output of the model and the measured reflection coefficient. Random errors are introduced into the reflection coefficient measurement to determine the effect of measurement error in the estimation of seabed properties such as permeability, porosity, mean grain diameter, and sediment type.
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Date Issued
2003
PURL
http://purl.flvc.org/fcla/dt/13084
Subject Headings
Underwater acoustics, Marine sediments--Acoustic properties
Format
Document (PDF)
Broadband measurements of compressional wave attenuation
Title
Broadband measurements of compressional wave attenuation.
Creator
Reeder, Angela Christine., Florida Atlantic University, Schock, Steven G., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
An in situ acoustic measurement system was developed to estimate the compressional wave attenuation of marine sediments. The system uses acoustic probes to measure a wideband acoustic pulse traveling horizontally though various sediments. The system transmits a 20 millisecond frequency-modulated (FM) pulse swept from 3 to 50 kHz and match filters the received signals. A special ratio of data collected at two horizontal ranges from the source is used to estimate attenuation as a function of...
Show moreAn in situ acoustic measurement system was developed to estimate the compressional wave attenuation of marine sediments. The system uses acoustic probes to measure a wideband acoustic pulse traveling horizontally though various sediments. The system transmits a 20 millisecond frequency-modulated (FM) pulse swept from 3 to 50 kHz and match filters the received signals. A special ratio of data collected at two horizontal ranges from the source is used to estimate attenuation as a function of frequency. Data is collected with the in situ system and a chirp subbottom profiling sonar at two offshore sites to compare the attenuation of horizontally and vertically traveling waves in sediment. The collected data is also used to determine the feasibility of remotely estimating in situ attenuation using a chirp sonar. In situ and chirp sonar estimates agree and fall within the range of attenuation measurements made by other investigators in similar sediments.
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Date Issued
1996
PURL
http://purl.flvc.org/fcla/dt/15327
Subject Headings
Marine sediments--Acoustic properties--Measurement, Signal processing
Format
Document (PDF)
Real time method for remote measurement of compressional wave attenuation
Title
Real time method for remote measurement of compressional wave attenuation.
Creator
DeBruin, Darryl L., Florida Atlantic University, Schock, Steven G.
Abstract/Description
An acoustic measurement system is developed to estimate the compressional wave attenuation of marine sediments in real time. A chirp sonar transmits filtered digital reflection data to a signal processing computer that processes the data on an AT&T DSP32C chip. The signal processing computer estimates and displays the center frequency of the processed pulse as it is attenuated by the ocean sediments. Wavelet modelling establishes the relationship between the center frequency shift and...
Show moreAn acoustic measurement system is developed to estimate the compressional wave attenuation of marine sediments in real time. A chirp sonar transmits filtered digital reflection data to a signal processing computer that processes the data on an AT&T DSP32C chip. The signal processing computer estimates and displays the center frequency of the processed pulse as it is attenuated by the ocean sediments. Wavelet modelling establishes the relationship between the center frequency shift and relaxation time, from which the sediment type and compressional wave attenuation are determined. Frequency contours from two different data sites demonstrate that the system is able to reliably estimate sediment type and compressional wave attenuation. Error introduced by noise is below 1% for noise levels less than 0.1 of the normalized processed signal. Random error in the estimates is minimized by determining reliable frequency values and by ensemble averaging the values.
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Date Issued
1992
PURL
http://purl.flvc.org/fcla/dt/14824
Subject Headings
Marine sediments--Acoustic properties, Signal processing--Computer simulation
Format
Document (PDF)
Sediment layer tracking using neural networks
Title
Sediment layer tracking using neural networks.
Creator
Freyermuth, Vincent Nicolas., Florida Atlantic University, Schock, Steven G.
Abstract/Description
The detection of sediment layer interfaces in normal incidence acoustic reflection data is a requirement for automatic classification and geologic mapping of subsurface layers. The detection is difficult because of the constructive and destructive interference caused by the impedance changes in the sediment column and high scattering noise levels. The purpose of this work is to implement a procedure using neural networks that automatically detects the sediment layers from the envelope of...
Show moreThe detection of sediment layer interfaces in normal incidence acoustic reflection data is a requirement for automatic classification and geologic mapping of subsurface layers. The detection is difficult because of the constructive and destructive interference caused by the impedance changes in the sediment column and high scattering noise levels. The purpose of this work is to implement a procedure using neural networks that automatically detects the sediment layers from the envelope of acoustic reflections. The data was collected using a sub-bottom profiler that transmits a 2 to 10 kHz FM pulse. The detection procedure is a three step method: a first neural network removes most of the reflections due to random scatterers, a second neural network tracks the layers and a third algorithm recognizes the segments of detected layers corresponding to the same sediment interface Applied on different sub-bottom images, the procedure detects more than 80% of the layers correctly.
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Date Issued
1998
PURL
http://purl.flvc.org/fcla/dt/15561
Subject Headings
Neural networks (Computer science), Marine sediments--Acoustic properties
Format
Document (PDF)
development and application of a numerical model for predicting the frequency response of the seabed from vertical profiles of sediment impedance
Title
The development and application of a numerical model for predicting the frequency response of the seabed from vertical profiles of sediment impedance.
Creator
Zhang, Jian Long., Florida Atlantic University, Schock, Steven G., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
Interaction of normal incidence, wideband acoustic pulses with seabed is investigated to determine the acoustic frequency ranges that provide the most information about the sediment structure. An exact numerical model is developed for calculating the frequency response and impulse response of the seabed from an impedance profile of a sediment core. A database of impedance profiles from several ocean environments were studied to describe the shapes of commonly found impedance changes. The...
Show moreInteraction of normal incidence, wideband acoustic pulses with seabed is investigated to determine the acoustic frequency ranges that provide the most information about the sediment structure. An exact numerical model is developed for calculating the frequency response and impulse response of the seabed from an impedance profile of a sediment core. A database of impedance profiles from several ocean environments were studied to describe the shapes of commonly found impedance changes. The impulse response of the seabed is convolved with acoustic pulses to generate synthetic acoustic returns. The synthetic profiles are studied to determine the effect of operating frequency and bandwidth on resolution and on the accuracy of measuring impedance changes. This thesis explains why inversion procedures have failed to generate vertical impedance profiles of the seabed from normal incidence reflection data. The results of this work provide guidelines for selecting subbottom profiler array sizes and operating frequencies for quantitative sediment studies, and for subsampling cores.
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Date Issued
1996
PURL
http://purl.flvc.org/fcla/dt/15293
Subject Headings
Marine sediments--Acoustic properties, Seismic reflection method
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)
Classification of marine sediments using a fuzzy logic impedance inversion model
Title
Classification of marine sediments using a fuzzy logic impedance inversion model.
Creator
DeBruin, Darryl L., Florida Atlantic University, LeBlanc, Lester R., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
In this dissertation, a fuzzy logic impedance inversion model is developed to classify marine sediments. Expert knowledge and fuzzy decision making constrain the inversion procedures to the resolving ability of the transmitted. The model is validated by comparing the estimated impedance profile with the measured impedance profile. A coherent surface scattering and incoherent volume scattering model are incorporated into a single geoacoustic scattering model that is applied to acoustic...
Show moreIn this dissertation, a fuzzy logic impedance inversion model is developed to classify marine sediments. Expert knowledge and fuzzy decision making constrain the inversion procedures to the resolving ability of the transmitted. The model is validated by comparing the estimated impedance profile with the measured impedance profile. A coherent surface scattering and incoherent volume scattering model are incorporated into a single geoacoustic scattering model that is applied to acoustic subbottom measurements. The reflected signal is modeled as the convolution of the transmitted processed wavelet and the impulse response of the sea bottom. The impedance of the acoustic return is inverted at the layer interfaces and the volume scattering strength is measured between layer interfaces. The model is applied to acoustic subbottom measurements obtained by an X-STAR subbottom profiler sonar system. The inversion techniques are developed for a 2-10 kHz 20 msec swept FM pulse. A fuzzy logic layer tracking procedure identifies the coherent surface scattering layer interfaces in a subbottom profile image. The peak amplitudes and locations are used as fuzzy inputs in the layer tracking rule base. The rule base determines which peak is assigned to the layer when two peaks compete for assignment or which layer is assigned to the peak when two layers compete for assignment. The fuzzy event detection algorithm estimates the impulse response of the acoustic return by complex least squares fitting parts of the transmitted wavelet with sections of the acoustic return. Reflectors are iteratively identified and removed from the return and the residual return is reprocessed. The detection procedure is constrained by the resolving ability of the matching signals and the peak envelope shape of the acoustic return. A genetic algorithm allows up to five low error reflector estimates to be processed until converging on the correct estimated impulse response (the tree branch whose summed error is minimized). The impedance is correlated with sediment bulk density by empirical relation. Experimental results validate that the fuzzy logic impedance inversion model reliably estimates the impedance of the sea bottom. The estimated impedance profiles of fifty acoustic returns are averaged and compared with measured impedance values.
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Date Issued
1995
PURL
http://purl.flvc.org/fcla/dt/12415
Subject Headings
Fuzzy logic, Marine sediments, Acoustic impedance, Marine sediments--Acoustic properties
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)
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)