Current Search:   LeBlanc, Lester R. (x)

View All Items

  • CSV Spreadsheet
(1 - 11 of 11)
Design and development of a high-speed underwater acoustic modem
Title
Design and development of a high-speed underwater acoustic modem.
Creator
Alleyne, Jochen Raoul, Florida Atlantic University, LeBlanc, Lester R.
Abstract/Description
The design, development and performance of an acoustic modem using spread spectrum modulation techniques in order to reduce multipath interference is detailed in this thesis. The design also includes a method to correct for Doppler shifts in the received data. Finally, error detection and correction are utilized in order to improve the robustness of the transmitted data. The results of field experiments with the modem are used to analyze the performance of the modem under a variety of...
Show moreThe design, development and performance of an acoustic modem using spread spectrum modulation techniques in order to reduce multipath interference is detailed in this thesis. The design also includes a method to correct for Doppler shifts in the received data. Finally, error detection and correction are utilized in order to improve the robustness of the transmitted data. The results of field experiments with the modem are used to analyze the performance of the modem under a variety of conditions. These results are then used as a basis from which to draw conclusions about the spread spectrum technique.
Show less
Date Issued
1997
PURL
http://purl.flvc.org/fcla/dt/15520
Subject Headings
Modems, Underwater acoustics
Format
Document (PDF)
Design of a frequency shift keying array receiver for the acoustic modem
Title
Design of a frequency shift keying array receiver for the acoustic modem.
Creator
Boubli, Cecile., Florida Atlantic University, LeBlanc, Lester R.
Abstract/Description
Currently, our acoustic modems are used to communicate underwater to Autonomous Underwater Vehicles AUVs. These modems have only one sensor and can transmit at low data rates (from 200 to 1200 bits per second) using Frequency Shift Keying (FSK) modulation. A two-dimensional array receiver (MillsCross) has been developed to receive underwater signals with more reliability, at a higher data rate (about 30,000 bits per second). This array has been designed to operate with Phase Shift Keying...
Show moreCurrently, our acoustic modems are used to communicate underwater to Autonomous Underwater Vehicles AUVs. These modems have only one sensor and can transmit at low data rates (from 200 to 1200 bits per second) using Frequency Shift Keying (FSK) modulation. A two-dimensional array receiver (MillsCross) has been developed to receive underwater signals with more reliability, at a higher data rate (about 30,000 bits per second). This array has been designed to operate with Phase Shift Keying modulated signals. The purpose of this thesis is to design and implement a signal processing software to demodulate and decode FSK signals acquired by the MillsCross. By taking advantage of the spatial gain of the MillsCross receiver array, higher reliability and longer ranges are expected using FSK, in addition to achieving compatibility between the two systems. This software includes a robust synchronization scheme, a spatial and an equalizing filter, a time-window self-adjusting process and the error control decoding.
Show less
Date Issued
2000
PURL
http://purl.flvc.org/fcla/dt/15788
Subject Headings
Underwater acoustics, Modems, Signal processing--Digital techniques
Format
Document (PDF)
Cross-correlation of phase centers to estimate direction-of-arrival for a 3-row bathymetric sidescan sonar
Title
Cross-correlation of phase centers to estimate direction-of-arrival for a 3-row bathymetric sidescan sonar.
Creator
Crenshaw, Edward T. G., Florida Atlantic University, LeBlanc, Lester R.
Abstract/Description
A new method for calculating the direction-of-arrival (DOA), and thus the bathymetry of the seafloor, is presented. This method will calculate the DOA directly from the phase difference between the phase centers of the array. In parallel, a bathymetric sidescan sonar system originally built at Woods Hole and now here at Florida Atlantic University's Department of Ocean Engineering, was completed. Once this system was working, the above mentioned signal analysis regime will be implemented on...
Show moreA new method for calculating the direction-of-arrival (DOA), and thus the bathymetry of the seafloor, is presented. This method will calculate the DOA directly from the phase difference between the phase centers of the array. In parallel, a bathymetric sidescan sonar system originally built at Woods Hole and now here at Florida Atlantic University's Department of Ocean Engineering, was completed. Once this system was working, the above mentioned signal analysis regime will be implemented on actual data to test its validity.
Show less
Date Issued
2001
PURL
http://purl.flvc.org/fcla/dt/12738
Subject Headings
Sidescan sonar, Bathymetric maps, Signal processing
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.
Show less
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)
Target signature for a periodic structure using a low-frequency broadband side-scan simulator
Title
Target signature for a periodic structure using a low-frequency broadband side-scan simulator.
Creator
Dietz, Jerrold Edward Gilbert., Florida Atlantic University, LeBlanc, Lester R.
Abstract/Description
Many acoustic targets of interest contain features that are periodic in space. This thesis demonstrates that a chirp waveform, 2 kHz to 12 kHz, can detect repetitive structures with periods in the range of 0.125 m to 0.75 m. As aspect angle increases from 0 deg to 90 deg, a frequency shift in the range of 830 Hz to 4800 Hz will occur as the period decreases from 0.75 to 0.125 m. It follows that, spectral analysis can aid in target identification. A sonar propagation model has been developed...
Show moreMany acoustic targets of interest contain features that are periodic in space. This thesis demonstrates that a chirp waveform, 2 kHz to 12 kHz, can detect repetitive structures with periods in the range of 0.125 m to 0.75 m. As aspect angle increases from 0 deg to 90 deg, a frequency shift in the range of 830 Hz to 4800 Hz will occur as the period decreases from 0.75 to 0.125 m. It follows that, spectral analysis can aid in target identification. A sonar propagation model has been developed to simulate the acoustic backscattered energy of a target with periodic characteristics in the presence of seafloor scattering. Examining the spectral components, with appropriate time gating, can achieve a gain of 7 dB at 3100 m.
Show less
Date Issued
2001
PURL
http://purl.flvc.org/fcla/dt/12788
Subject Headings
Sidescan sonar, Underwater acoustics, Scattering (Physics)
Format
Document (PDF)
volume scattering model for sediment classification through acoustic means
Title
A volume scattering model for sediment classification through acoustic means.
Creator
Jenkins, Michael Gerard., Florida Atlantic University, LeBlanc, Lester R.
Abstract/Description
A simple model is developed to evaluate the acoustic scattering environment of sediments based on the envelope function of digital sub-bottom sonar data. Scattering pressure and intensity histograms are produced from model results. These histograms are compared to the theoretical distributions expected for scattering event pressure and intensity. Sediment composition is inferred from the determined acoustic scattering environment. The model has been applied to X-Star digital sub-bottom data...
Show moreA simple model is developed to evaluate the acoustic scattering environment of sediments based on the envelope function of digital sub-bottom sonar data. Scattering pressure and intensity histograms are produced from model results. These histograms are compared to the theoretical distributions expected for scattering event pressure and intensity. Sediment composition is inferred from the determined acoustic scattering environment. The model has been applied to X-Star digital sub-bottom data taken in the vicinity of St. John's Harbor, New Brunswick. Model results are compared to ground truth (Borehole logs) taken within the survey area. This comparison indicates general trends within the sediment scattering environment which may be linked to sediment composition. Distinct differences in model results were noted over areas of differing sediment types.
Show less
Date Issued
1993
PURL
http://purl.flvc.org/fcla/dt/14945
Subject Headings
Sedimentation analysis, Underwater acoustics, Sound--Reverberation
Format
Document (PDF)
Transducer design for underwater acoustic communications using the finite element method
Title
Transducer design for underwater acoustic communications using the finite element method.
Creator
Jacquemin, Jean-Philippe M. J., Florida Atlantic University, LeBlanc, Lester R.
Abstract/Description
The behavior of radially polarized free-flooded ring (FFR) transducers is studied for application in underwater acoustic communications. Theoretical models are first presented. Then the finite element method (FEM) is introduced and a FEM model for the FFR transducer is proposed. Experimental data are collected and compared to the simulation results with good correspondence. A series of FEM simulations lead then to optimum geometrical parameters for a fine-tuned FFR transducer dedicated to...
Show moreThe behavior of radially polarized free-flooded ring (FFR) transducers is studied for application in underwater acoustic communications. Theoretical models are first presented. Then the finite element method (FEM) is introduced and a FEM model for the FFR transducer is proposed. Experimental data are collected and compared to the simulation results with good correspondence. A series of FEM simulations lead then to optimum geometrical parameters for a fine-tuned FFR transducer dedicated to underwater acoustic communications. Finally, stack transducers models and the piezocomposite technology are presented as possible improvement of the present transducer.
Show less
Date Issued
2001
PURL
http://purl.flvc.org/fcla/dt/12758
Subject Headings
Underwater acoustics, Finite element method, Transducers, Interdigital
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.
Show less
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)
Digital acoustic communications using decision directed learning
Title
Digital acoustic communications using decision directed learning.
Creator
Alleyne, Jochen Raoul, Florida Atlantic University, LeBlanc, Lester R., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
This document serves as a dissertation for the Doctor of Philosophy in Ocean Engineering degree at Florida Atlantic University's Department of Ocean Engineering. This dissertation documents the design, development, and performance analysis of an acoustic receiver system that incorporates a decision directed learning filter for acoustic multi-phase shift keying signals. The system makes use of advanced signal processing, inclusive of spatial diversity and decision directed learning techniques...
Show moreThis document serves as a dissertation for the Doctor of Philosophy in Ocean Engineering degree at Florida Atlantic University's Department of Ocean Engineering. This dissertation documents the design, development, and performance analysis of an acoustic receiver system that incorporates a decision directed learning filter for acoustic multi-phase shift keying signals. The system makes use of advanced signal processing, inclusive of spatial diversity and decision directed learning techniques in order to decode digital acoustic data. Error correcting techniques are also employed as well as methods of analyzing the efficiency of the system.
Show less
Date Issued
2001
PURL
http://purl.flvc.org/fcla/dt/11951
Subject Headings
Underwater acoustic telemetry, Digital communications, Acoustic filters
Format
Document (PDF)
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.
Show less
Date Issued
1999
PURL
http://purl.flvc.org/fcla/dt/15675
Subject Headings
Underwater acoustics, Acoustic surface waves
Format
Document (PDF)
High-speed acoustic communication in shallow water using spatio-temporal adaptive array processing
Title
High-speed acoustic communication in shallow water using spatio-temporal adaptive array processing.
Creator
Beaujean, Pierre-Philippe, Florida Atlantic University, LeBlanc, Lester R., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
A novel method of achieving stable high-speed underwater acoustic communication with a fairly low-complexity of implementation is proposed. The proposed approach is to split the space and time processing into two separate sub-optimal processes. As a result, processing complexity is significantly reduced and the instabilities associated with large tap vectors at large time-frequency spread products are reduced. The proposed space-time signal processing method utilizes a different beamformer...
Show moreA novel method of achieving stable high-speed underwater acoustic communication with a fairly low-complexity of implementation is proposed. The proposed approach is to split the space and time processing into two separate sub-optimal processes. As a result, processing complexity is significantly reduced and the instabilities associated with large tap vectors at large time-frequency spread products are reduced. The proposed space-time signal processing method utilizes a different beamformer optimization strategy compared to the time domain optimization strategy. This allows to separately adjust the adaptation parameters for the spatial and temporal characteristics of the signal, which have vastly different requirements. The time domain signal is subject to variations in phase that require rapid filter updates whereas the directional characteristics of the signal do not vary appreciably over the message length and do not require a rapid adaptation response. The proposed method allows for high-speed underwater acoustic communication in very shallow water using coherent modulation techniques, and offers a series of unique features: significant reduction of the signal-to-noise and interference ratio (SNIR), improvement of the bandwidth efficiency by reduction of the forward-error coding redundancy requirements, real-time evaluation of the time-spread by Doppler spread product (BL) and channel stability estimate. Experimental results demonstrate that stable acoustic communication can be achieved at rates of 32000 bits per second at a distance of 3 km, in 40 feet of water and in sea-state 2 conditions. Fast and slow fading properties of the channel are measured, as the BL product can vary by a decade in 116 ms, and by two decades within minutes, from 0.001 to 0.1. The real-time analysis shows a strong correlation between time spread, Doppler spread, spatial coherence of the acoustic channel and communication performance. Overall, this research provides more scientific and experimental ground to understand the limitations of multi-channel adaptive receiver techniques in terms of stability, hardware requirements and channel tracking capability.
Show less
Date Issued
2001
PURL
http://purl.flvc.org/fcla/dt/11952
Subject Headings
Underwater acoustic telemetry, Adaptive signal processing
Format
Document (PDF)