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Simulation of reflection tomographic images of underwater targets with the effect of vehicle motion sensing errors
Title
Simulation of reflection tomographic images of underwater targets with the effect of vehicle motion sensing errors.
Creator
Quentin, Gwendoline., Florida Atlantic University, Schock, Steven G., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
The Buried Object Scanning Sonar (BOSS) is being developed at Florida Atlantic University to image targets buried under the seabed. Tomographic images are constructed using a sequence of sonar transmissions while the vehicle is moving. This motion causes image distortion and should be measured and removed by mapping the echoes received to an absolute coordinate system. The aim of this thesis is to develop and simulate a technique for generating BOSS images that provide an accurate...
Show moreThe Buried Object Scanning Sonar (BOSS) is being developed at Florida Atlantic University to image targets buried under the seabed. Tomographic images are constructed using a sequence of sonar transmissions while the vehicle is moving. This motion causes image distortion and should be measured and removed by mapping the echoes received to an absolute coordinate system. The aim of this thesis is to develop and simulate a technique for generating BOSS images that provide an accurate representation of target shape and size, by removing vehicle motion while mapping the image pixels. Synthetic acoustic data sets are generated by convolving the auto-correlated FM transmission pulse with the impulse response of an elastic sphere. Synthetic outputs of a Doppler velocity log and a 3-axis inertial measurement unit are generated to simulate vehicle motion. Noise is added to the sensor data to show the effects of motion sensor errors on image quality.
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Date Issued
2003
PURL
http://purl.flvc.org/fcla/dt/13040
Subject Headings
Ocean tomography, Sonar, Underwater navigation
Format
Document (PDF)
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)
Three-Dimensional Inversion Technique in Ocean Acoustics Using the Parabolic Equation Method
Title
Three-Dimensional Inversion Technique in Ocean Acoustics Using the Parabolic Equation Method.
Creator
Roa, Camilo Carlos, Frisk, George V., Florida Atlantic University, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
A three-dimensional parabolic equation (PE) and perturbation approach is used to invert for the depth- and range-dependent geoacoustic characteristics of the seabed. The model assumes that the sound speed profile is the superposition of a known range-independent profile and an unknown depth- and range-dependent perturbation. Using a Green’s function approach, the total measured pressure field in the water column is decomposed into a background field, which is due to the range-independent...
Show moreA three-dimensional parabolic equation (PE) and perturbation approach is used to invert for the depth- and range-dependent geoacoustic characteristics of the seabed. The model assumes that the sound speed profile is the superposition of a known range-independent profile and an unknown depth- and range-dependent perturbation. Using a Green’s function approach, the total measured pressure field in the water column is decomposed into a background field, which is due to the range-independent profile, and a scattered field, which is due to the range-dependent perturbation. When the Born approximation is applied to the resulting integral equation, it can be solved for the range-dependent profile using linear inverse theory. Although the method is focused on inverting for the sound speed profile in the bottom, it can also invert for the sound speed profile in the water column. For simplicity, the sound speed profile in the water column was assumed to be known with a margin of error of ± 5 m/s. The range-dependent perturbation is added to the index of refraction squared n2(r), rather than the sound speed profile c(ro). The method is implemented in both Cartesian (x,y,z) and cylindrical (r,q,z) coordinates with the forward propagation of the field in x and r, respectively. Synthetic data are used to demonstrate the validity of the method [1]. Two inversion methods were combined, a Monte Carlo like algorithm, responsible for a starting approximation of the sound speed profile, and a steepest descent method, that fine-tuned the results. In simulations, the inversion algorithm is capable of inverting for the sound speed profile of a flat bottom. It was tested, for three different frequencies (50 Hz, 75 Hz, and 100 Hz), in a Pekeris waveguide, a range-independent layered medium, and a range-dependent medium, with errors in the inverted sound speed profile of less than 3%. Keywords: Three-dimensional parabolic equation method, geoacoustic inversion, range-dependent sound speed profile, linear inversion, Born approximation, Green’s functions.
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Date Issued
2017
PURL
http://purl.flvc.org/fau/fd/FA00004868, http://purl.flvc.org/fau/fd/FA00004868
Subject Headings
Ocean tomography., Ocean bottom., Born approximation., Green's functions.
Format
Document (PDF)
methodology to detect and classify underwater unexploded ordnance in DIDSON sonar images
Title
A methodology to detect and classify underwater unexploded ordnance in DIDSON sonar images.
Creator
Brisson, Lisa Nicole., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
High-resolution sonar systems are primarily used for ocean floor surveys and port security operations but produce images of limited resolution. In turn, a sonar-specific methodology is required to detect and classify underwater unexploded ordnance (UXO) using the low-resolution sonar data. After researching and reviewing numerous approaches the Multiple Aspect-Fixed Range Template Matching (MAFR-TM) algorithm was developed. The MAFR-TM algorithm is specifically designed to detect and classify...
Show moreHigh-resolution sonar systems are primarily used for ocean floor surveys and port security operations but produce images of limited resolution. In turn, a sonar-specific methodology is required to detect and classify underwater unexploded ordnance (UXO) using the low-resolution sonar data. After researching and reviewing numerous approaches the Multiple Aspect-Fixed Range Template Matching (MAFR-TM) algorithm was developed. The MAFR-TM algorithm is specifically designed to detect and classify a target of high characteristic impedance in an environment that contains similar shaped objects of low characteristic impedance. MAFR-TM is tested against a tank and field data set collected by the Sound Metrics Corp. DIDSON US300. This thesis document proves the MAFR-TM can detect, classify, orient, and locate a target in the sector-scan sonar images. This paper focuses on the MAFR-TM algorithm and its results.
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Date Issued
2010
PURL
http://purl.flvc.org/FAU/2683533
Subject Headings
Ocean tomography, Unexploded ordnance, Detection, Methodology, Underwater acoustics, Signal processing, Digital techniques
Format
Document (PDF)