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Air Force Institute of Technology

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Articles 421 - 450 of 454

Full-Text Articles in Signal Processing

An Analytical And Experimental Investigation Of Fm-By-Noise Jamming, Charles J. Daly Dec 1992

An Analytical And Experimental Investigation Of Fm-By-Noise Jamming, Charles J. Daly

Theses and Dissertations

Among the jamming waveforms used in Electronic Warfare, FM-by-noise is the least understood, and no exhaustive analytical and experimental investigation of the subject exists. This investigation presents a thorough review, consolidation, and elucidation of the theory of FM-by-noise. To explain and predict the behavior of FM-by-noise at RF and IF, three useful ratios, namely the deviation-to-victim ratio, the noise-to-victim ratio, and the sweep- to-victim ratio, are developed. To complement the theory, results of FM-by-noise jamming experiments conducted using commercial test and measurement equipment are presented. Specifically, the time- and frequency-domain behavior of FM-by- noise at RF and IF is studied …

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Methods For Viewing Radar Cross Section Data In Three Dimensions, David J. Tisdale Dec 1992

Methods For Viewing Radar Cross Section Data In Three Dimensions, David J. Tisdale

Theses and Dissertations

Radar Cross Section data is an important factor in the design of modern fighter and bomber aircraft. Minimization of the reflected radar energy is one of the key issues when choosing shapes and materials in new aircraft. Visualization of the energy scattered back to a radar is neither intuitive nor easy. The mission planner and pilot need to gain an understanding of the vulnerabilities inherent in the design of the systems they use. The advent of relatively low cost graphics workstations has made their use affordable in applications inconceivable only a few short years ago. This thesis examines three graphics …

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A Radiosity Approach To Realistic Image Synthesis, Richard L. Remington Dec 1992

A Radiosity Approach To Realistic Image Synthesis, Richard L. Remington

Theses and Dissertations

The Air Force Institute of Technology (AFIT) has not had the capability to generate photorealistic images. This thesis is a research effort to implement such a system at AFIT, and to apply knowledge from the particle transport community to this problem. Investigation into various techniques for generating photorealistic images led to the conclusion that the radiosity method would serve as the foundation for development. This is because of the increased accuracy of the diffuse reflections with the radiosity method and the fact that the images produced with radiosity axe view-independent. Two distinct tools to generate photorealistic images axe described. The …

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Scientific Visualization Of Volumetric Radar Cross Section Data, Thomas G. Wojszynski Dec 1992

Scientific Visualization Of Volumetric Radar Cross Section Data, Thomas G. Wojszynski

Theses and Dissertations

For aircraft design and mission planning, designers, threat analysts, mission planners, and pilots require a Radar Cross Section (RCS) central tendency with its associated distribution about a specified aspect and its relation to a known threat, Historically, RCS data sets have been statically analyzed to evaluate a d profile. However, Scientific Visualization, the application of computer graphics techniques to produce pictures of complex physical phenomena. appears to be a more promising tool to interpret this data. This work describes data reduction techniques and a surface rendering algorithm to construct and display a complex polyhedron from adjacent contours of RCS data. …

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Cepstral And Auditory Model Features For Speaker Recognition, John M. Colombi Dec 1992

Cepstral And Auditory Model Features For Speaker Recognition, John M. Colombi

Theses and Dissertations

The TIMIT and KING databases, as well as a ten day AFIT speaker corpus, are used to compare proven spectral processing techniques to an auditory neural representation for speaker identification. The feature sets compared were Linear Predictive Coding (LPC) cepstral coefficients and auditory nerve firing rates using the Payton model. This auditory model provides for the mechanisms found in the human middle and inner auditory periphery as well as neural transduction. Clustering algorithms were used to generate speaker specific codebooks - one statistically based and the other a neural approach. These algorithms are the Linde-Buzo-Gray (LBG) algorithm and a Kohonen …

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Digital Signal Processing Using Lapped Transforms With Variable Parameter Windows And Orthonormal Bases, Brian D. Raduenz Dec 1992

Digital Signal Processing Using Lapped Transforms With Variable Parameter Windows And Orthonormal Bases, Brian D. Raduenz

Theses and Dissertations

This thesis develops and evaluates a number of new concepts and tools for the analysis of signals using variable overlapped windows and orthonormal bases. Windowing, often employed as a spectral estimation technique, can result in irreparable distortions in the transformed signal. By placing conditions on the window and incorporating it into the orthonormal representation, any signal distortion resulting from the transformation can be eliminated or cancelled in reconstruction. This concept is critical to the theory underpinning this thesis. As part of this evaluation, a tensor product based general N-point fast Fourier transform algorithm was implemented in the DOD standard language, …

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Radar Cross Section Models For Limited Aspect Angle Windows, Mark C. Robinson Dec 1992

Radar Cross Section Models For Limited Aspect Angle Windows, Mark C. Robinson

Theses and Dissertations

This thesis presents a method for building Radar Cross Section (RCS) models of aircraft based on static data taken from limited aspect angle windows. These models statistically characterize static RCS. This is done to show that a limited number of samples can be used to effectively characterize static aircraft RCS. The optimum models are determined by performing both a Kolmogorov and a Chi-Square goodness-of-fit test comparing the static RCS data with a variety of probability density functions (pdf) that are known to be effective at approximating the static RCS of aircraft. The optimum parameter estimator is also determined by the …

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Signal Approximation With A Wavelet Neural Network, Charles M. Westphal Dec 1992

Signal Approximation With A Wavelet Neural Network, Charles M. Westphal

Theses and Dissertations

This study investigated the use of Wavelet Neural Networks (WNN) for signal approximation. The particular wavelet function used in this analysis consisted of a summation of sigmoidal functions (a sigmoidal wavelet). The sigmoidal wavelet has the advantage of being easily implemented in hardware via specialized electronic devices like the Intel Electronically Trainable Analog Neural Network (ETANN) chip. The WNN representation allows the determination of the number of hidden-layer nodes required to achieve a desired level of approximation accuracy. Results show that a bandlimited signal can be accurately approximated with a WNN trained with irregularly sampled data. Signal approximation, Wavelet neural …

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High Range Resolution Radar Target Identification Using The Prony Model And Hidden Markov Models, Mark R. Dewitt Dec 1992

High Range Resolution Radar Target Identification Using The Prony Model And Hidden Markov Models, Mark R. Dewitt

Theses and Dissertations

Fully polarized Xpatch signatures are transformed to two left circularly polarized signals. These two signals are then filtered by a linear FM pulse compression ('chirp') transfer function, corrupted by AWGN, and filtered by a filter matched to the 'chirp' transfer function. The bandwidth of the 'chirp' radar is about 750 MHz. Range profile feature extraction is performed using the TLS Prony Model parameter estimation technique developed at Ohio State University. Using the Prony Model, each scattering center is described by a polarization ellipse, relative energy, frequency response, and range. This representation of the target is vector quantized using a K-means …

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Acquisition Of Direct Sequence Spread Spectrum Signals Using Digital Signal Processing Techniques, Ronald E. Schmitz Dec 1992

Acquisition Of Direct Sequence Spread Spectrum Signals Using Digital Signal Processing Techniques, Ronald E. Schmitz

Theses and Dissertations

This thesis investigates the use of digital signal processing (DSP) techniques to achieve initial synchronization with Global Positioning System (GPS) Pseudo-Noise (PN) signals. Synchronization with the transmitted PN signal is essential to the despreading of the transmitted Direct Sequence Spread Spectrum (DS/SS) signals and decoding of the transmitted satellite data. The use of DSP methods to decrease the time required to achieve initial synchronization is investigated. This thesis proposes an initial acquisition section of the GPS receiver and derives the equations to show the method is mathematically feasible. Computer simulations of the proposed receiver using received signals corrupted by Doppler …

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Detection Of Spoofing, Jamming, Or Failure Of A Global Positioning System (Gps), Juan R. Vasquez Dec 1992

Detection Of Spoofing, Jamming, Or Failure Of A Global Positioning System (Gps), Juan R. Vasquez

Theses and Dissertations

The Air Force has equipped its aircraft with avionic systems such as Global Positioning System (GPS) and Inertial Guidance Systems (INS) capable of providing accurate navigation solutions. The aircrews flying these aircraft require a system that can either survive the hostile environments encountered in combat or notify the aircrew that their performance has been significantly degraded. This research focuses on failure detection and isolation techniques using an extended Kalman filter and generalized likelihood ratios using matched filters. Analysis is conducted using a Kalman filter development package known as the Multimode Simulation for Optimal Filter Evaluation (MSOFE). Both a large order …

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The Detection And Correlation Modeling Of Rayleigh Distributed Radar Signals, Alan L. Buterbaugh Sep 1992

The Detection And Correlation Modeling Of Rayleigh Distributed Radar Signals, Alan L. Buterbaugh

Theses and Dissertations

This thesis provides a method for determining the detection of partially correlated Rayleigh distributed radar returns by a pulsed search radar. The receiver consists of a quadrature demodulator receiver, followed by a square law envelope detector and a linear post-detection integrator. In addition, a technique for determining the pulse-to-pulse correlation of a complex target is given using inverse Fourier transforms of the target scattering centers. An AIM-9 missile is used to illustrate how the partially correlated detection techniques and the pulse-to-pulse correlation predictions can be used to determine the probability of detection. The Detection and Correlation Modeling of Rayleigh Distributed …

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Speech Recognition Using Visible And Infrared Detectors, Patrick T. Marshall Sep 1992

Speech Recognition Using Visible And Infrared Detectors, Patrick T. Marshall

Theses and Dissertations

A system has been developed that tracks lip motion using infrared (IR) or visible detectors. The purpose of this study was to determine if the additional information obtained from the IR or visible detectors can be used to increase the recognition rate of audio Automatic Speech Recognition (ASR) systems. To accomplish this goal, several hardware analog prototypes had to be designed, built and tested. Different detectors (IR and visible) and modes of operation (active and passive) were tried before a reliable and useful signal was found. An analog-to-digital (A/D) board was then designed and built that digitized both the microphone …

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A Time-Dependent Adaptive Filter For Cochannel Interference Reduction, Matthew H. Foster Dec 1991

A Time-Dependent Adaptive Filter For Cochannel Interference Reduction, Matthew H. Foster

Theses and Dissertations

This thesis presents a Time Dependent Adaptive Filter (TDAF) which exploits the cyclostationarity of digitally modulated communications signals and seeks to improve the Signal to Interference Ratio (SIR) and Signal to Noise Ratio (SNR) of such signals. The TDAF is embedded in a computer simulation of a simple communication system consisting of a data source, data formatter, pulse shaping filter, BPSK modulator, and demodulator. In the simulation the TDAF and a Time Independent Adaptive Filter (TIAF) attempt to extract the Signal of Interest (SOI) from noise or interference. the criteria of Mean Squared Error (MSE) is used as the primary …

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Analysis Of Visual Illusions Using Multiresolution Wavelet Decomposition Based Models, John S. Laing Dec 1991

Analysis Of Visual Illusions Using Multiresolution Wavelet Decomposition Based Models, John S. Laing

Theses and Dissertations

This thesis provides alternatives to the explanation that spatial filtering is responsible for the perception of illusory contours in the Kanisza Triangle illusion. Specifically, we use a Multiresolution Wavelet Decomposition to divide an image into spatial-frequency bands that are used as inputs to three biologically motivated models. The thesis includes a brief tutorial of Wavelet theory and an in-depth explanation of our implementation of recently published algorithms for Multiresolution Wavelet Analysis. The first model is based on the saccadic movements of the human eye. It demonstrates the importance of the high spatial-frequency content of an image in the formulation of …

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Investigation Of The Effects Of Aeroelastic Deformations On The Radar Cross Section Of Aircraft, Samuel D. Mckenzie Dec 1991

Investigation Of The Effects Of Aeroelastic Deformations On The Radar Cross Section Of Aircraft, Samuel D. Mckenzie

Theses and Dissertations

The effects of aeroelastic deformations on the radar cross section (RCS) of a T-38 trainer jet and a C-5A transport aircraft are examined and characterized. Realistic representations of structural wing deformations are obtained from a mechanical/computer aided design software package called NASTRAN . NASTRAN is used to evaluate the structural parameters of the aircraft as well as the restraints and loads associated with realistic flight conditions. Geometries for both the non-deformed and deformed airframes are obtained from the NASTRAN models and translated into RCS models. The RCS is analyzed using a numerical modeling code called the Radar Cross Section - …

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Design Of A Fiber Optic Image Transmission Link, Justin D. Redd Dec 1991

Design Of A Fiber Optic Image Transmission Link, Justin D. Redd

Theses and Dissertations

An original design is presented for a fiber optic based digital image transmission link operating at a serial bit rate of 250 Mbits/Second. The link is designed as an integral part of an airborne infrared imaging system with particular emphasis on avoiding problems associated with aircraft electromagnetic interference (EMI). Unique features include simplicity (single PC board transmitter and receiver), low power, low cost (under $3,000), and use of the latest off-the-shelf components (including the Gazelle GA9011/GA9012 HOT ROD chip set). Theoretical modeling is used to predict a bit error rate of better than 10-15, while actual measurements include …

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Infrared Target Recognition, Brian D. Singstock Dec 1991

Infrared Target Recognition, Brian D. Singstock

Theses and Dissertations

In this thesis, three approaches were used for Automatic Target Recognition (ATR). These approaches were shape, moment and Fourier generated features, Karhunen-Loeve transform (KLT) generated features and Discrete Cosine Transform (DCT) generated features. The KLT approach was modelled after the face recognition research by Suarez, AFIT, and Turk and Pentland, MIT. A KLT is taken of a reduced covariance matrix, composed all three classes of targets, and the resulting eigenimages are used to reconstruct the original images. The reconstruction coefficients for each original image are found by taking the dot product of the original image with each eigenimage. These reconstruction …

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Verification And Validation Of The Simulated Radar Image (Srim) Code Radar Cross Section Predictions, Dale A. Stanley Dec 1991

Verification And Validation Of The Simulated Radar Image (Srim) Code Radar Cross Section Predictions, Dale A. Stanley

Theses and Dissertations

The objectives of this study were to verify and validate the Simulated Radar Image (SRIM) Code Version 4.0 monostatic radar cross section (RCS) predictions. SRIM, uses the theory of Physical Optics (PO) to predict backscatter for a user specified aspect angle. Target obscuration and multiple reflections are taken into account by sampling the target with ray tracing. The software verification and validation technique followed in this study entailed comparing the code predictions to closed from PO equations, other RCS prediction software packages, and measured data. The targets analyzed were a sphere, rectangular flat plate, circular flat plate, solid right circular …

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Performance Analysis Of The Speckle Holography Image Reconstruction Technique, Rudolf N. Vonniederhausern Dec 1991

Performance Analysis Of The Speckle Holography Image Reconstruction Technique, Rudolf N. Vonniederhausern

Theses and Dissertations

In speckle holography, short exposures frames along with wave front measurements allow post processing image reconstruction. With speckle holography the amplitude of high spatial frequencies is boosted to allow resolution out to the diffraction limit of the telescope. To provide system parameters for the wave front sensor design, a software analysis program has been developed that provides the system transfer function as a function of the number and size of sensor subapertures and sensor noise. Trends in the ratio of the atmospheric coherence diameter to wave front subaperture size and the effect on the system transfer function have been obtained. …

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Optical Image Segmentation Using Wavelet Correlation, Steven D. Pinski Dec 1991

Optical Image Segmentation Using Wavelet Correlation, Steven D. Pinski

Theses and Dissertations

This research introduces an optical method of segmenting potential targets using wavelet analysis. Implementation of an optical Harr wavelet is fulfilled using a magneto-optic spatial light modulator (MOSLM). Two methods of controlling wavelet dilation are explored: (1) spatial filtering of a ternary modulated MOSLM; (2) a single aperture positioned in front of a binary modulated MOSLM. Segmentation is performed through Vander Lugt correlation of a binarized image with a binarized optical wavelet. Three different image binarization methods are investigated for use in the correlation scheme: (1) average pixel value over an entire scene; (2) localized 4 x 4 pixel average …

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A Walsh-Domain Adaptive Filter, Larry J. Duvall Dec 1991

A Walsh-Domain Adaptive Filter, Larry J. Duvall

Theses and Dissertations

Two Walsh-domain dyadic convolution adaptive filters are developed using a circular convolution frequency-domain filter (FDF1) and the Fast LMS adaptive filter (FDF2): WDF1 and WDF2 respectively. General theory of time- domain adaptive filters and a theoretical analysis of the FDF1, FDF2, WDF1, and WDF2 filters are presented. WDF1 and WDF2 software implementation are shown to be error free. A time-domain filter (TDF) and a FDF2 frequency-domain filter (FDF) are implemented for comparison testing. The WDF1, WDF2, TDF, and FDF filters are tested using time-shifted sinusoidal and rectangular noisy and noiseless signals. WDF1 and WDF2 are shown to converge faster and …

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Kalman Filter Tracking Of A Reflective Target Using Forward Looking Infrared And Doppler Return Measurements, Theodore D. Herrera Dec 1991

Kalman Filter Tracking Of A Reflective Target Using Forward Looking Infrared And Doppler Return Measurements, Theodore D. Herrera

Theses and Dissertations

Plume phenomenology experiments conducted in 1990 uncovered the existence of plume speckle reflectance emanating from the exhaust of a solid- propellant rocket motor due to the presence of metallic particulates in the plume. This impeded attempts, that are dependent upon the speckle return of an actively illuminated target hardbody, to discern the plume/hardbody interface. This thesis investigates the feasibility of employing the Doppler return phenomenon in discerning the plume/hardbody interface and locating the hardbody center-of-mass. The potential of the Doppler phenomenon's utilization lies in the fact that the Doppler return frequency spectra of the plume and the hardbody respectively possess …

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Feature Extraction For Pose Estimation. A Comparison Between Synthetic And Real Ir Imagery, Donald J. Willis Dec 1991

Feature Extraction For Pose Estimation. A Comparison Between Synthetic And Real Ir Imagery, Donald J. Willis

Theses and Dissertations

This research addressed the problem of pose estimation of three- dimensional objects given their two-dimensional IR imagery and corresponding synthetic (computer-generated) IR imagery. Features and techniques were investigated to find those which may be extendable from computer models to real- world IR imagery. GTSIG and SCNGEN were used to create the synthetic imagery. Silhouette and outline shape moments were explored as optimum features for the comparison. Employing back-propagation with momentum as the training paradigm, a two-hidden-layer neural network was able to determine the base-plane orientation of the synthetic imagery to within 7.5 degrees with better than 90% accuracy. (No conclusive …

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Radar Scattering From Foamed Plastic Target Supports, Michael W. Chambers Dec 1991

Radar Scattering From Foamed Plastic Target Supports, Michael W. Chambers

Theses and Dissertations

This study investigates the scattering from foamed ranges to support all sizes of targets for radar cross section measurements. Two common foamed plastics, styrofoam and expanded bead polystyrene (EPS), are discussed. Two types of scattering are associated with foamed plastic, coherent and incoherent. The incoherent is normally the lowest, but has not been satisfactorily quantified. Coherent scattering is related to the shape of the target, and the emphasis of this study is on the coherent return. One goal was to predict the coherent RCS of an EPS column using the Uniform Theory of Diffraction (UTD). It was found that UTD …

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Simulation Of Finite-Precision Effects In Digital Filters, Perry L. Choate Dec 1991

Simulation Of Finite-Precision Effects In Digital Filters, Perry L. Choate

Theses and Dissertations

This thesis develops and demonstrates software that models finite- precision effects in digital filters. Coefficient quantization and internally generated roundoff noise effects are simulated by rounding coefficients and multiplier output values to (B+1) bits. Outputs include magnitude and phase responses that may be plotted to show results of coefficient quantization. The output noise power due to roundoff is calculated. Three types of digital filter structures are examined. The first type is direct form I implementation for FIR and IIR structures, second is direct form II, and third is cascading the canonic direct form II second-order sections for higher order filter …

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Determination Of Bistatic Radar Clutter Power From Topographic Data, Clyde R. Heddings Dec 1991

Determination Of Bistatic Radar Clutter Power From Topographic Data, Clyde R. Heddings

Theses and Dissertations

The purpose of this research was to develop a procedure for estimating the average bistatic radar clutter power from a topographic map using rough surface scattering theory. First, the terrain in the radar target area was divided into sub regions having homogeneous characteristics. A joint Gaussian distribution for the surface heights was fitted from the information contained in the topographic map contour lines for each homogeneous area. From these distributions, the normalized radar cross section for each terrain area was determined. The clutter power for each range cell was then determined via a modified radar range equation. The procedure was …

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Sensing Refractive Turbulence Profiles Using Wave Front Slope Measurements From Two Reference Sources, Michael D. Rejack Dec 1991

Sensing Refractive Turbulence Profiles Using Wave Front Slope Measurements From Two Reference Sources, Michael D. Rejack

Theses and Dissertations

This thesis examines a remote sensing technique for measuring the atmospheric structure constant as a function of altitude by performing spatial correlation or wavefront sensor measurements. Two point sources are used to irradiate two wavefront sensors in the aperture plane of an optical system. The geometric relationship between the sources and the sensors gives rise to crossed optical paths. At the point where the paths cross, the correlation value of the turbulence contributions will be at a peak. The correlation is shown to be mathematically related to the structure constant in terms of an integral of the structure constant multiplied …

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Image Segmentation Using Affine Wavelets, Steven E. Smiley Dec 1991

Image Segmentation Using Affine Wavelets, Steven E. Smiley

Theses and Dissertations

This thesis discusses the use of the multiresolution representation and Radial Basis Function (RBF) neural networks to segment both FLIR and SAR imagery. The multiresolution approximation coefficients are used as features into the RBF network which learns to distinguish between different cultural and natural regions or objects. The wavelets used are Mallat's spline wavelet and Daubechies' compactly supported wavelets. Additionally, this thesis provides an explanation of wavelets in a tutorial manner. It introduces wavelet theory and discusses two different approaches to generating the multiresolution or wavelet representation.

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Steady-State Production And Quenching Of Br(2P½), Ralph F. Tate Nov 1991

Steady-State Production And Quenching Of Br(2P½), Ralph F. Tate

Theses and Dissertations

The spin orbit relaxation of atoms has been investigated in a steady state infrared fluorescence experiment. A CW argon ion laser operating at 488 nm was used to photodissociate gas-phase Br into equal quantities of Bromine and Bromine atoms. The resulting 2.7 µm emission was observed as a function of added quenching gas. A steady-state analysis was used to determine quenching rates for SF6, N2, O2, He, Ne, Ar, Kr, and Xe, relative to quenching by the parent molecule. Limitations in the apparatus prevented determination of the quenching rate coefficient for Br2. …

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