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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)

Title: A broadband signal processor for acoustic imaging using ambient noise.
Creator: Olivieri, Marc P., Florida Atlantic University, Glegg, Stewart A. L., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: Buckingham et al. (Nature Vol. 356, p 327) first introduced the concept of acoustic imaging using ambient noise as a method for passively detecting objects in the ocean. Several analytical studies followed, and it was shown that a two dimensional acoustic image could be obtained based on this approach, and that at least 900 pixels are necessary to restitute the details of spherical objects placed in an underwater sound channel. The alternative approach described in this paper is based on a...
Show moreBuckingham et al. (Nature Vol. 356, p 327) first introduced the concept of acoustic imaging using ambient noise as a method for passively detecting objects in the ocean. Several analytical studies followed, and it was shown that a two dimensional acoustic image could be obtained based on this approach, and that at least 900 pixels are necessary to restitute the details of spherical objects placed in an underwater sound channel. The alternative approach described in this paper is based on a signal processing which uses the broadband nature of the ambient noise in the ocean, and therefore, optimizes the use of available sound energy scattered by the object. Images with thousands of pixels can be obtained using a relatively small number of transducers. This method has been validated using simple experiments in air, scaled to represent an ocean application, and results showing images of various objects will be presented.
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Date Issued: 1994
PURL: http://purl.flvc.org/fcla/dt/15065
Subject Headings: Acoustic imaging, Signal processing, Underwater acoustics
Format: Document (PDF)

Title: Characterization of the acoustic signature of an Ocean Explorer class AUV.
Creator: Lambe, Frederic Lionel., Florida Atlantic University, Cuschieri, Joseph M., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: The radiated noise from Autonomous Underwater Vehicles (AUV's) can interfere with on-board sensors and with certain type of missions. It is thus important to understand the parameters controlling the AUV self noise. In this thesis, measurement techniques and analyses are developed to investigate the mechanisms contributing to the acoustic noise of an Ocean Explorer class AUV. Measurements of the AUV acoustic signature are performed in a reverberant tank, after the tank is qualified to...
Show moreThe radiated noise from Autonomous Underwater Vehicles (AUV's) can interfere with on-board sensors and with certain type of missions. It is thus important to understand the parameters controlling the AUV self noise. In this thesis, measurement techniques and analyses are developed to investigate the mechanisms contributing to the acoustic noise of an Ocean Explorer class AUV. Measurements of the AUV acoustic signature are performed in a reverberant tank, after the tank is qualified to establish a reliable procedure to measure the AUV source levels. The measurement results are compared that obtained in an anechoic tank and in open-water. Acoustic measurements are correlated with vibration measurements performed on various components of the AUV, in order to identify the dominant components. From the results, some preliminary mitigation procedures to reduce the AUV acoustic signature are developed.
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Date Issued: 1999
PURL: http://purl.flvc.org/fcla/dt/15618
Subject Headings: Oceanographic submersibles, Underwater acoustics
Format: Document (PDF)

Title: Characterizing magnetic noise of AUV for use in towed magnetometer study of internal waves.
Creator: Tilley, Dylan., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: As part of a project to study internal waves, FAU plans to utilize an AUV to tow a magnetometer to study electromagnetic signatures from internal waves. This research is focused on the electromagnetic noise issues related to using an AUV to tow the magnetic sensor package. There are active sources of electromagnetic noise caused by an AUV that are present in addition to those induced by the Earth's magnetic field and permanent magnets. To characterize the magnetic noise associated with the...
Show moreAs part of a project to study internal waves, FAU plans to utilize an AUV to tow a magnetometer to study electromagnetic signatures from internal waves. This research is focused on the electromagnetic noise issues related to using an AUV to tow the magnetic sensor package. There are active sources of electromagnetic noise caused by an AUV that are present in addition to those induced by the Earth's magnetic field and permanent magnets. To characterize the magnetic noise associated with the AUV magnetometer tow system, the various active source elements were identified, the orientation sensitivity of the sensors being used was determined, and the magnetic anomaly of a similar AUV which may be eventually be used in a magnetic sensing arrangement was measured. The results are used to show the proposed sensing arrangement will likely not achieve the necessary sensitivity to measure subtle internal wave signals.
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Date Issued: 2012
PURL: http://purl.flvc.org/FAU/3352881
Subject Headings: Automatic control, Mathematical models, Electromagnetic measurements, Fluctuations (Physics), Oceanographic submersibles, Underwater acoustics
Format: Document (PDF)

Title: Docking the Ocean Explorer Autonomous Underwater Vehicle using a low-cost acoustic positioning system and a fuzzy logic guidance algorithm.
Creator: Kronen, David Mitchell., Florida Atlantic University, Smith, Samuel M., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: Having the ability to dock an Autonomous Underwater Vehicle (AUV) can significantly enhance the operation of such vehicles. In order to dock an AUV, the vehicle's position must be known precisely and a guidance algorithm must be used to drive the AUV to its dock. This thesis will examine and implement a low cost acoustic positioning system to meet the positioning requirements. At-sea tests will be used as a method of verifying the systems specifications and proper incorporation into the AUV....
Show moreHaving the ability to dock an Autonomous Underwater Vehicle (AUV) can significantly enhance the operation of such vehicles. In order to dock an AUV, the vehicle's position must be known precisely and a guidance algorithm must be used to drive the AUV to its dock. This thesis will examine and implement a low cost acoustic positioning system to meet the positioning requirements. At-sea tests will be used as a method of verifying the systems specifications and proper incorporation into the AUV. Analyses will be run on the results using several methods of interpreting the data. The second portion of this thesis will develop and test a fuzzy logic docking algorithm which will guide the AUV from a location within the range of the sonar system to the docking station. A six degree of freedom simulation incorporating the Ocean Explorer's hydrodynamic coefficients will be used for the simulation.
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Date Issued: 1997
PURL: http://purl.flvc.org/fcla/dt/15502
Subject Headings: Oceanographic submersibles, Acoustical engineering, Underwater acoustics, Fuzzy algorithms
Format: Document (PDF)

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)

Title: Estimates of water turbine noise levels.
Creator: Guerra, Julian., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: This work seeks to understand water turbine noise generation and to make preliminary estimations of the noise levels. Any structure attached to a turbine upstream its blades will generate unsteady fluctuating loads on the blade's surface, which are proportional to the radiated acoustic pressure. The noise levels of a simplified turbine based on existing designs surpass the ambient noise levels of the ocean at low frequencies ( 30 Hz).
Show moreThis work seeks to understand water turbine noise generation and to make preliminary estimations of the noise levels. Any structure attached to a turbine upstream its blades will generate unsteady fluctuating loads on the blade's surface, which are proportional to the radiated acoustic pressure. The noise levels of a simplified turbine based on existing designs surpass the ambient noise levels of the ocean at low frequencies (< 20 Hz) by approximately 50 dB ref 1 μPa and stay under the ambient noise levels at higher frequencies for a blade-passing frequency of 0.83 Hz and point of observation (100 m, 45 degrees, 45 degrees) from the hub. Streamlining the cross-section of the upstream structure as well as reducing its width decrease the noise levels by approximately 40 dB ref 1 μPa, at low frequencies and moderately increase them at higher frequencies. Increasing the structure-rotor distance decreases the noise levels with increasing frequencies (> 30 Hz).
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Date Issued: 2011
PURL: http://purl.flvc.org/FAU/3170958
Subject Headings: Turbines, Vibration, Testing, Underwater acoustics, Fluid dynamics
Format: Document (PDF)

Title: Fatigue crack growth rate of short cracks for high strength steels in sea water.
Creator: Kim, Kijoon., Florida Atlantic University, Hartt, William H., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: Experiments have been performed which determined the fatigue crack growth rate (FCGR) of short cracks (a > 0.1mm) for five high strength steels (yield stress 370-570 MPa) in air and in natural seawater with and without cathodic protection. Attention was focused upon Regions I and Il of the classical FCGR-stress intensity range(Delta K) curve with particular consideration of the near-threshold behavior for short cracks. Single edge notch (SEN) three-point bend specimens and a direct current...
Show moreExperiments have been performed which determined the fatigue crack growth rate (FCGR) of short cracks (a > 0.1mm) for five high strength steels (yield stress 370-570 MPa) in air and in natural seawater with and without cathodic protection. Attention was focused upon Regions I and Il of the classical FCGR-stress intensity range(Delta K) curve with particular consideration of the near-threshold behavior for short cracks. Single edge notch (SEN) three-point bend specimens and a direct current potential drop (DCPD) crack monitoring system were employed, and test parameters simulated offshore structure conditions. The results indicated enhanced FCGR for short cracks compared to macrocracks by 3-20 times in air and 2-6 in seawater free-corroding(FC). Also, the Delta Kth for short cracks was apparently lower than for long ones in both environments. The transition from short to long crack behavior occurred at constant $\Delta$K in each environment (15.6 MPa m in air and 10.0 MPa m in seawater(FC)) irrespective of initial Delta K (Delta K(0)). The transition crack length ranged from 0.25 to 1.6 mm and was inversely proportional to $\Delta$K(0). Scanning electron microscope fractography showed that the mechanism of enhanced crack growth rate was associated with secondary crack (SC) formation in air and SC or inter-granular cracking (or both) in seawater (FC). The enhanced FCGR for short cracks was minimized by polarization to -950 mV(SCE). Through an elastic-plastic fracture mechanics analysis using the J-integral parameter it was found that the influence of plastic deformation at the crack tip was approximately independent of crack length (short versus long), and the linear-elastic fracture mechanics analysis gave a realistic representation for fatigue behavior.
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Date Issued: 1992
PURL: http://purl.flvc.org/fcla/dt/12313
Subject Headings: Steel--Fatigue--Environmental aspects, Underwater acoustics, Seawater--Acoustic properties
Format: Document (PDF)

Title: A feasibility study on using LonWorks Power Line Transceivers for underwater communications.
Creator: Powell, Jennifer Cairns., Florida Atlantic University, Smith, Samuel M., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: This project consisted of a feasibility study to ascertain whether or not an inexpensive acoustic modem for an Autonomous Underwater Vehicle (AUV) could be developed using low cost commercially available products. Our AUV's at Florida Atlantic University currently use LonWorks for their internal control networks, so we have plenty of experience with their parts. The LonWorks Power Line Transceivers are capable of generating a signal that can be sent to a transducer for communication through...
Show moreThis project consisted of a feasibility study to ascertain whether or not an inexpensive acoustic modem for an Autonomous Underwater Vehicle (AUV) could be developed using low cost commercially available products. Our AUV's at Florida Atlantic University currently use LonWorks for their internal control networks, so we have plenty of experience with their parts. The LonWorks Power Line Transceivers are capable of generating a signal that can be sent to a transducer for communication through the water. The PLT-30 Power Line Transceiver generates a direct sequence spread spectrum signal (DSSS) that offers many useful operating features; such as anti-jam, interference rejection and covert communications, low intercept probability, and most importantly, multipath protection. After numerous tests, however, the system was incapable of establishing reliable acoustic communications. We conclude that the PLT-30 Power Line Transceiver use as an underwater acoustic modem is not a viable approach. As an alternative method, communication through an electric current field was tested in a salt-water pool. The initial test produced a 100% success rate.
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Date Issued: 2000
PURL: http://purl.flvc.org/fcla/dt/12695
Subject Headings: Local area networks (Computer network), Underwater acoustics
Format: Document (PDF)

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)

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)

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)

Title: MODEL EXPERIMENTS FOR 3-DIMENSIONAL PROPAGATION CHARACTERISTICS IN A WEDGE-SHAPED OCEAN.
Creator: Yoon, Jong Rak, Florida Atlantic University, Glegg, Stewart A. L., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: The theoretical solution for acoustic propagation in a wedge-shaped ocean with ideal pressure-release boundaries predicts a well-defined beam which diverges as the energy propagates out towards deep water. Outside of the beam, shadow zones are formed, and the beam's spatial extent is determined by the lowest mode of propagation. The purpose of the experimental results presented here is to check the theoretical analyses, as part of an ongoing investigation into three dimensional propagation in...
Show moreThe theoretical solution for acoustic propagation in a wedge-shaped ocean with ideal pressure-release boundaries predicts a well-defined beam which diverges as the energy propagates out towards deep water. Outside of the beam, shadow zones are formed, and the beam's spatial extent is determined by the lowest mode of propagation. The purpose of the experimental results presented here is to check the theoretical analyses, as part of an ongoing investigation into three dimensional propagation in the ocean environment, and to investigate further the propagation characteristics of this type. It has been found that for downslope propagation, the spatial characteristics of the field in a direction parallel to the shore line are in good agreement with the theoretical solution and the azimuthal extent of the beam depends on the wedge angle and frequency.
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Date Issued: 1987
PURL: http://purl.flvc.org/fcla/dt/14387
Subject Headings: Underwater acoustics
Format: Document (PDF)

Title: Modeling the performance of a laser for tracking an underwater dynamic target.
Creator: Dill, Thomas J., von Ellenrieder, Karl, Florida Atlantic University, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: Options for tracking dynamic underwater targets using optical methods is currently limited. This thesis examines optical reflectance intensities utilizing Lambert’s Reflection Model and based on a proposed underwater laser tracking system. Numerical analysis is performed through simulation to determine the detectable light intensities based on relationships between varying inputs such as angle of illumination and target position. Attenuation, noise, and laser beam spreading are included in...
Show moreOptions for tracking dynamic underwater targets using optical methods is currently limited. This thesis examines optical reflectance intensities utilizing Lambert’s Reflection Model and based on a proposed underwater laser tracking system. Numerical analysis is performed through simulation to determine the detectable light intensities based on relationships between varying inputs such as angle of illumination and target position. Attenuation, noise, and laser beam spreading are included in the analysis. Simulation results suggest optical tracking exhibits complex relationships based on target location and illumination angle. Signal to Noise Ratios are a better indicator of system capabilities than received intensities. Signal reception does not necessarily confirm target capture in a multi-sensor network.
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Date Issued: 2014
PURL: http://purl.flvc.org/fau/fd/FA00004279, http://purl.flvc.org/fau/fd/FA00004279
Subject Headings: Acoustic velocity meters, Intelligent control systems, Optical instruments -- Design and construction, Roving vehicles (Astronautics), Target acquisition, Underwater acoustics
Format: Document (PDF)

Title: Numerical models to simulate underwater turbine noise levels.
Creator: Lippert, Renee'., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: This work incorporates previous work done by Guerra and the application of fluid dynamics. The structure attached to the turbine will cause unsteady fluctuations in the flow, and ultimately affect the acoustic pressure. The work of Guerra is based on a lot of assumptions and simplifications to the geometry of the turbine and structure. This work takes the geometry of the actual turbine, and uses computational fluid dynamic software to numerically model the flow around the turbine structure....
Show moreThis work incorporates previous work done by Guerra and the application of fluid dynamics. The structure attached to the turbine will cause unsteady fluctuations in the flow, and ultimately affect the acoustic pressure. The work of Guerra is based on a lot of assumptions and simplifications to the geometry of the turbine and structure. This work takes the geometry of the actual turbine, and uses computational fluid dynamic software to numerically model the flow around the turbine structure. Varying the angle of the attack altered the results, and as the angle increased the noise levels along with the sound pulse, and unsteady loading increased. Increasing the number of blades and reducing the chord length both reduced the unsteady loading.
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Date Issued: 2012
PURL: http://purl.flvc.org/FAU/3355622
Subject Headings: Underwater acoustics, Mathematical models, Turbines, Vibration, Mathematical models, Fluid dynamics
Format: Document (PDF)

Title: Source speed estimation using a pilot tone in a high-frequency acoustic modem.
Creator: Kathiroli, Poorani., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: This thesis proposes to estimate the speed of a moving acoustic source by either linear or non linear processing of the resulting Doppler shift present in a high-frequency pilot tone. The source is an acoustic modem (Hermes) which currently uses moving average to estimate and compensate for Doppler shift. A new auto regressive approach to Doppler estimation (labeled IIR method in the text) promises to give a better estimate. The results for a simulated peak velocity of 2 m/s in the presence...
Show moreThis thesis proposes to estimate the speed of a moving acoustic source by either linear or non linear processing of the resulting Doppler shift present in a high-frequency pilot tone. The source is an acoustic modem (Hermes) which currently uses moving average to estimate and compensate for Doppler shift. A new auto regressive approach to Doppler estimation (labeled IIR method in the text) promises to give a better estimate. The results for a simulated peak velocity of 2 m/s in the presence of additive noise showed an RMSE of 0.23 m/s using moving average vs. 0.00018 m/s for the auto regressive approach. The SNR was 75 dB. The next objective was to compare the estimated Doppler velocity obtained using the two algorithms with the experimental values recorded in real time. The setup consisted of a receiver hydrophone attached to a towing carriage that moved with a known velocity with respect to a stationary acoustic source. The source transmitted 375 kHz pilot tone. The received pilot tone data were preprocessed using the two algorithms to estimate both Doppler shift and Doppler velocity. The accuracy of the algorithms was compared against the true velocity values of the carriage. The RMSE for a message from experiments conducted indoor for constant velocity of 0.4 m/s was 0.6055 m/s using moving average, 0.0780 m/s using auto regressive approach. The SNIR was 6.3 dB.
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Date Issued: 2011
PURL: http://purl.flvc.org/FAU/3171396
Subject Headings: Underwater acoustics, Measurement, SIgnal processing, Digital techniques, Digital filters (Mathematics), Radio frequency, Mathematical models
Format: Document (PDF)

Title: A sparse volume array for imaging ocean ambient noise in the near-shore region.
Creator: Olivieri, Marc P., Florida Atlantic University, Glegg, Stewart A. L., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: Ocean ambient noise has been studied extensively in the past, and several models have been developed to predict its level and to characterize it in different ocean environments. However, most of these studies have been motivated by the need to reduce the negative effect of the ambient noise on measurements. Recently, several studies have used the ambient noise to obtain information about the ocean floor and to achieve passive target detection. This dissertation describes the development of an...
Show moreOcean ambient noise has been studied extensively in the past, and several models have been developed to predict its level and to characterize it in different ocean environments. However, most of these studies have been motivated by the need to reduce the negative effect of the ambient noise on measurements. Recently, several studies have used the ambient noise to obtain information about the ocean floor and to achieve passive target detection. This dissertation describes the development of an Ambient Noise Sonar (ANS) which can be used to measure ambient noise directivity to obtain information about the environment. The system was designed for use on an Autonomous Underwater Vehicle (AUV) and has been used to study the ambient noise in the near shore region by investigating different types of noise in shallow water, such as boat traffic, biological noise and naturally occurring noise up to 20 kHz. There are two advantages to the ANS. First, when mounted on an AUV its mobility will allow the ambient noise to be mapped over an extended area. Second, the very small number of transducers (6 total) used in the array, makes this system suitable for AUV operations because it uses a limited amount of space and power. This dissertation presents the theory of the array processing and preliminary results including examples of boat noise, and biological noise. It was found that the noise from biological sources such as snapping shrimp contributed to the anisotropic component of the acoustic field. These biological sources were found to be concentrated around artificial structures such as piers and groins, and also around natural reefs. Finally noise maps of coastal areas are presented to illustrate the potential of this system to measure the noise field in the coastal region and to evaluate acoustic propagation using passive sources such as the biological noise clusters found along the coast. In the future the ANS will be integrated onto the AUV 'Ocean Explorer II'.
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Date Issued: 1997
PURL: http://purl.flvc.org/fcla/dt/12534
Subject Headings: Underwater acoustics, Acoustic imaging
Format: Document (PDF)

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)

Title: Synchronous spatial array processing for underwater vehicle tracking.
Creator: Normand, Olivier., Florida Atlantic University, Schock, Steven G., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: Navigation of Unmanned Underwater Vehicles (UUVs) is commonly assisted in confined areas by acoustic positioning systems. The Department of Ocean Engineenng at Florida Atlantic University is developing an altemative system based on submerged modems. This thesis describes an optimal target location estimation technique using a multi-channel spatial receiver array (Millscross) used as a development tool combined with a synchronous modem and transponder network mounted on buoys and UUVs. The...
Show moreNavigation of Unmanned Underwater Vehicles (UUVs) is commonly assisted in confined areas by acoustic positioning systems. The Department of Ocean Engineenng at Florida Atlantic University is developing an altemative system based on submerged modems. This thesis describes an optimal target location estimation technique using a multi-channel spatial receiver array (Millscross) used as a development tool combined with a synchronous modem and transponder network mounted on buoys and UUVs. The Millscross provides a reference to evaluate the performance of the navigation estimator. Spatial array principles are used to develop decoding and beamforming techniques to process modem messages, enabling the end user (the UUV) to estimate in real-time its own position and navigate in space. A simulation was used to compare actual results with theory and determine the processing and decoding algorithms. These algorithms were then applied to real data to estimate the target position (direction of arrival and geodetic coordinates).
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Date Issued: 2002
PURL: http://purl.flvc.org/fcla/dt/12917
Subject Headings: Underwater navigation, Underwater acoustics, Signal processing--Digital techniques
Format: Document (PDF)

Title: Turbo-coded frequency division multiplexing for underwater acoustic communications between 60 kHz and 90 kHz.
Creator: Pajovic, Milutin., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: The Intermediate Frequency Acoustic Modem (IFAM), developed by Dr. Beaujean, is designed to transmit the command-and-control messages from the top-side to the wet-side unit in ports and very shallow waters. This research presents the design of the turbo coding scheme and its implementation in the IFAM modem with the purpose of meeting a strict requirement for the IFAM error rate performance. To simulate the coded IFAM, a channel simulator is developed. It is basically a multi-tap filter whose...
Show moreThe Intermediate Frequency Acoustic Modem (IFAM), developed by Dr. Beaujean, is designed to transmit the command-and-control messages from the top-side to the wet-side unit in ports and very shallow waters. This research presents the design of the turbo coding scheme and its implementation in the IFAM modem with the purpose of meeting a strict requirement for the IFAM error rate performance. To simulate the coded IFAM, a channel simulator is developed. It is basically a multi-tap filter whose parameters are set depending on the channel geometry and system specifics. The simulation results show that the turbo code is able to correct 89% of the messages received with errors in the hostile channel conditions. The Bose-Chadhuri-Hocquenghem (BCH) coding scheme corrects less that 15% of these messages. The other simulation results obtained for the system operation in different shallow water settings are presented.
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Date Issued: 2009
PURL: http://purl.flvc.org/FAU/215291
Subject Headings: Underwater acoustics, Measurement, Coding theory, Signal processing, Digital techniques
Format: Document (PDF)

Acoustic surface waves (4)	+ -
Digital techniques (3)	+ -
Fluid dynamics (3)	+ -
Mathematical models (3)	+ -
Oceanographic submersibles (3)	+ -

Signal processing (3)	+ -
Acoustic imaging (2)	+ -
Acoustical engineering (2)	+ -
Measurement (2)	+ -
Numerical solutions (2)	+ -
Turbines (2)	+ -
Vibration (2)	+ -
Wave equation (2)	+ -
Acoustic velocity meters (1)	+ -
Automatic control (1)	+ -
Coding theory (1)	+ -
Detection (1)	+ -
Digital filters (Mathematics) (1)	+ -
Electromagnetic measurements (1)	+ -
Electromagnetic waves (1)	+ -
Fluctuations (Physics) (1)	+ -
Fuzzy algorithms (1)	+ -
Green's functions (1)	+ -
Intelligent control systems (1)	+ -
Local area networks (Computer network) (1)	+ -
MIMO systems (1)	+ -
Marine sediments (1)	+ -
Marine sediments--Acoustic properties (1)	+ -
Mathematics (1)	+ -

College of Engineering and Computer Science (22)	+ -
Florida Atlantic University (13)	+ -
Glegg, Stewart A. L. (5)	+ -
Olivieri, Marc P. (2)	+ -
Schock, Steven G. (2)	+ -

Smith, Samuel M. (2)	+ -
Brisson, Lisa Nicole. (1)	+ -
Conrad, Alexander. (1)	+ -
Cuschieri, Joseph M. (1)	+ -
Dill, Thomas J. (1)	+ -
Guerra, Julian. (1)	+ -
Hartt, William H. (1)	+ -
Kathiroli, Poorani. (1)	+ -
Kim, Kijoon. (1)	+ -
Kronen, David Mitchell. (1)	+ -
Lambe, Frederic Lionel. (1)	+ -
LeBlanc, Lester R. (1)	+ -
Lippert, Renee'. (1)	+ -
Munro, Lachlan I. (1)	+ -
Normand, Olivier. (1)	+ -
Pajovic, Milutin. (1)	+ -
Pirie, Rachel Louise. (1)	+ -
Powell, Jennifer Cairns. (1)	+ -
Real, Gaultier. (1)	+ -
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Tilley, Dylan. (1)	+ -
Weeks, Rebecca. (1)	+ -
Yoon, Jong Rak (1)	+ -

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