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Articles 151 - 180 of 426
Full-Text Articles in Signal Processing
Local Histograms For Per-Pixel Classification, Melody L. Massar
Local Histograms For Per-Pixel Classification, Melody L. Massar
Theses and Dissertations
We introduce a rigorous mathematical theory for the analysis of local histograms, and study how they interact with textures that can be modeled as occlusions of simpler components. We first show how local histograms can be computed as a system of convolutions and discuss some basic local histogram properties. We then introduce a probabilistic, occlusion-based model for textures and formally demonstrate that local histogram transforms are natural tools for analyzing the textures produced by our model. Next, we characterize all nonlinear transforms which satisfy the three key properties of local histograms and consider the appropriateness of local histogram features in …
Dismount Threat Recognition Through Automatic Pose Identification, Andrew M. Freeman
Dismount Threat Recognition Through Automatic Pose Identification, Andrew M. Freeman
Theses and Dissertations
The U.S. military has an increased need to rapidly identify nonconventional adversaries. Dismount detection systems are being developed to provide more information on and identify any potential threats. Current work in this area utilizes multispectral imagery to exploit the spectral properties of exposed skin and clothing. These methods are useful in the location and tracking of dismounts, but they do not directly discern a dismount's level of threat. Analyzing the actions that precede hostile events yields information about how the event occurred and uncovers warning signs that are useful in the prediction and prevention of future events. A dismount's posturing, …
Ladar Range Image Interpolation Exploiting Pulse Width Expansion, Jeramy W. Motes
Ladar Range Image Interpolation Exploiting Pulse Width Expansion, Jeramy W. Motes
Theses and Dissertations
Laser Detection and Ranging (LADAR) systems produce both a range image and an intensity image by measuring the intensity of light reflected off a surface target. When the transmitted LADAR pulse strikes a sloped surface, the returned pulse is expanded temporally. This characteristic of the reflected laser pulse enables the possibility of estimating the gradient of a surface. This study estimates the gradient of the surface of an object from a modeled LADAR return pulse that includes accurate probabilistic noise models. The range and surface gradient estimations are incorporated into a novel interpolator that facilitates an effective three dimensional (3D) …
Passive Multistatic Radar Imaging Using An Ofdm Based Signal Of Opportunity, Matthew B. P. Rapson
Passive Multistatic Radar Imaging Using An Ofdm Based Signal Of Opportunity, Matthew B. P. Rapson
Theses and Dissertations
This paper demonstrates a proof of concept in using an OFDM-based signal of opportunity for SAR imaging purposes within a passive, multistatic radar construct. Two signal processing methods have been proposed to create phase history data. The same methods are applied in both a simulated software model and an experimental data collection environment to produce simulated SAR images using the CBP imaging algorithm. The images generated from both the experimental and simulated data were observed to be consistent with each other and with expectations in terms of resolution. Coherent addition of the images results in improved image resolution due to …
Ofdm-Based Signal Exploitation Using Quadrature Mirror Filter Bank (Qmfb) Processing, Felipe E. Garrido
Ofdm-Based Signal Exploitation Using Quadrature Mirror Filter Bank (Qmfb) Processing, Felipe E. Garrido
Theses and Dissertations
By performing QMFB processing with a given signal it is possible to obtain Frequency-Time (F-T) outputs that represent signal features such as bandwidth (W), center frequency (fc), signal duration (Ts), modulation type (AM, FM, BPSK, QAM, etc), frequency content and time allocation. Because of its unique structure, two widely used signals based on Orthogonal Frequency Division Multiplexing (OFDM) were chosen as signals of interest for demonstration. The general implementation of the QMFB process is described along with the basic structure of OFDM signals related to the physical layer perspective of 802.11a Wi-Fi and 802.16e WiMAX frame structures are described. The …
Spectral Detection Of Human Skin In Vis-Swir Hyperspectral Imagery Without Radiometric Calibration, Andrew P. Beisley
Spectral Detection Of Human Skin In Vis-Swir Hyperspectral Imagery Without Radiometric Calibration, Andrew P. Beisley
Theses and Dissertations
Many spectral detection algorithms require precise ground truth measurements that are hand-selected in the image to apply radiometric calibration, converting image pixels into estimated reflectance vectors. That process is impractical for mobile, real-time hyperspectral target detection systems, which cannot empirically derive a pixel-to-reflectance relationship from objects in the image. Implementing automatic target recognition on high-speed snapshot hyperspectral cameras requires the ability to spectrally detect targets without performing radiometric calibration. This thesis demonstrates human skin detection on hyperspectral data collected at a high frame rate without using calibration panels, even as the illumination in the scene changes. Compared to an established …
Optimized Hyperspectral Imagery Anomaly Detection Through Robust Parameter Design, Francis M. Mindrup
Optimized Hyperspectral Imagery Anomaly Detection Through Robust Parameter Design, Francis M. Mindrup
Theses and Dissertations
Anomaly detection algorithms for hyperspectral imagery (HSI) are an important first step in the analysis chain which can reduce the overall amount of data to be processed. The actual amount of data reduced depends greatly on the accuracy of the anomaly detection algorithm implemented. Most, if not all, anomaly detection algorithms require a user to identify some initial parameters. These parameters (or controls) affect overall algorithm performance. Regardless of the anomaly detector being utilized, algorithm performance is often negatively impacted by uncontrollable noise factors which introduce additional variance into the process. In the case of HSI, the noise variables are …
Targeting Breast Cancer Detection With Communications Technology, Hacer Varol
Targeting Breast Cancer Detection With Communications Technology, Hacer Varol
Theses and Dissertations
Breast cancer continues to be a significant public health problem in the United States: It is the second leading cause of female mortality, and, disturbingly, one out of eight women in the United States will be diagnosed with breast cancer in her life time. Until the cause of this disease is fully understood, early detection remains the only hope to improve prognosis and treatment. In this thesis, the tumor detection problem in breast images is formulated as a hypothesis testing problem, where the signal of interest is the tumor and the noise refers to the healthy tissue in the breast. …
Hyperspectral-Based Adaptive Matched Filter Detector Error As A Function Of Atmospheric Profile Estimation, Allan W. Yarbrough
Hyperspectral-Based Adaptive Matched Filter Detector Error As A Function Of Atmospheric Profile Estimation, Allan W. Yarbrough
Theses and Dissertations
Hyperspectral imagery is collected as radiance data. This data is a function of multiple variables: the radiation profile of the light source, the reflectance of the target, and the absorption and scattering profile of the medium through which the radiation travels as it reflects off the target and reaches the imager. Accurate target detection requires that the collected image matches as closely as possible the known "true" target in the classification database. Therefore, the effect of the radiation source and the atmosphere must be removed before detection is attempted. While the spectrum of solar light is relatively stable, the effect …
Characterizing Cyclostationary Features Of Digital Modulated Signals With Empirical Measurements Using Spectral Correlation Function, Mujun Song
Theses and Dissertations
Signal detection is widely used in many applications. Some examples include Cognitive Radio (CR) and military intelligence. CRs use signal detection to sense spectral occupancy. Without guaranteed signal detection, a CR cannot reliably perform its role. Similarly, signal detection is the first step for garnering an opponent's information. Wireless signal detection can be performed using many different techniques. Some of the most popular include matched filters, energy detectors (which use measurements such as the Power Spectral Density (PSD) of the signal), and Cyclostationary Feature Detectors (CFD). Among these techniques, CFD can be viewed as a compromise technique, in that it …
Blind Deconvolution Method Of Image Deblurring Using Convergence Of Variance, Quentin D. Macmanus
Blind Deconvolution Method Of Image Deblurring Using Convergence Of Variance, Quentin D. Macmanus
Theses and Dissertations
Images are used for both aerial and space imagery applications, including target detection and tracking. The current problem concerning objects in geosynchronous orbit is that they are dim and hard to resolve because of their distance. This work will further the combined effort of AFIT and AFRL to provide enhanced space situational awareness (SSA) and space surveillance. SSA is critical in a time when many countries possess the technology to put satellites into orbit. Enhanced imaging technology improves the Air Force's ability to see if foreign satellites or other space hardware are operating in the vicinity of our own assets …
Direction Finding With Mutually Orthogonal Antennas, David F. Chick
Direction Finding With Mutually Orthogonal Antennas, David F. Chick
Theses and Dissertations
Estimating the direction-of-arrival of incident electromagnetic plane waves (a.k.a. direction finding or DF) has typically been accomplished in the past using arrays of spatially separated antennas. The spatial separation produces a delay in each antenna's measured voltage due to the finite propagation time as the wave strikes each antenna in succession. In this thesis, we approach the problem differently by using three antennas that have been oriented in orthogonal directions but are co-located at the origin of a coordinate system. Being co-located, this mutually orthogonal arrangement of antennas cannot detect the propagation phase delay and must rely solely on the …
Characterization Of Noise Technology Radar Signal Detectability Using A Non-Cooperative Receiver, Daniel V. Atienza
Characterization Of Noise Technology Radar Signal Detectability Using A Non-Cooperative Receiver, Daniel V. Atienza
Theses and Dissertations
As Noise Technology Radar (NTR) systems emerge, there is a need for non-cooperative, non-matched filter detection and exploitation. This work is based on that need and AFIT's Noise Network (NoNET) radar system. These signals are associated with Low Probability of Detection/ Intercept (LPD/LPI) signals. Quadrature Mirror Filter Banks (QMFB) has been effectively used for non-cooperatively detecting structured LPD/LPI signals and extracting various waveform characteristics. However, the QMFB process performance with unstructured NTR signals was challenging and motivated a need for a transformed QMFB. This transform was based on AFIT research by Gronholz and Mims (G-M), who used a multi-channel receiver …
Effects Of Cyclic Prefix Jamming Versus Noise Jamming In Ofdm Signals, Amber L. Scott
Effects Of Cyclic Prefix Jamming Versus Noise Jamming In Ofdm Signals, Amber L. Scott
Theses and Dissertations
Signal jamming of an orthogonal frequency-division multiplexing (OFDM) signal is simulated in MATLAB. Two different means of jamming are used to see, which is a more efficient way to disrupt a signal using the same signal power. The first way is a basic additive white Gaussian noise (AWGN) jammer that equally jams the entire signal. The second way is an AWGN jammer that targets only the cyclic prefix (CP) of the signal. These two methods of jamming are simulated using different channel models and unknowns to get varying results. The three channel models used in the simulations are the no …
A Simple Non-Destructive Method For Characterizing Non-Dispersive, Low-Loss Dielectrics, Thomas S. Olney
A Simple Non-Destructive Method For Characterizing Non-Dispersive, Low-Loss Dielectrics, Thomas S. Olney
Theses and Dissertations
It is shown how permittivity can be extracted via time domain reflection data from a perfect electric conductor (PEC) backed planar sample of a low-loss, non-dispersive dielectric using two rectangular Ku-band waveguide aperture probes with attached PEC flange plates of the same geometry but different dimensions. Of critical importance is being able to identify the reflection from the edge of the flange plate in the parallel plate region created by the plate and the PEC backing of the sample. A signal processing method that takes advantage of physical insight into the geometry and superposition is developed for identifying this edge …
Signals Of Opportunity Navigation Using Wi-Fi Signals, Wilfred E. Noel
Signals Of Opportunity Navigation Using Wi-Fi Signals, Wilfred E. Noel
Theses and Dissertations
Since GPS is generally limited to areas with clear sky view, additional methods of navigation are currently being explored. This thesis explores navigation using Signals of Opportunity(SoOP). The signals chosen for evaluation in this thesis are the common Internet IEEE 802.11a/g signals, or Wi-Fi. This thesis presents SoOP navigation based on cross-correlations of received data from multiple Wi-Fi stations. It shows the effectiveness of the methods using collected Wi-Fi signals in a real-world environment. By using simple statistical representations of collected data in large groups, or windows, cross-correlation calculations can produce timing offsets between simulated stations. The timing offsets, or …
Simultaneous Range/Velocity Detection With An Ultra-Wideband Random Noise Radar Through Fully Digital Cross-Correlation In The Time Domain, James R. Lievsay
Simultaneous Range/Velocity Detection With An Ultra-Wideband Random Noise Radar Through Fully Digital Cross-Correlation In The Time Domain, James R. Lievsay
Theses and Dissertations
This research effort examines the theory, application, and results of applying two-dimensional cross-correlation in the time domain to ultra-wideband (UWB) random noise waveforms for simultaneous range and velocity estimation. When applying common Doppler processing techniques to random noise waveforms for the purpose of velocity estimation, the velocity resolution degrades as the signal bandwidth or the target speed increase. To mitigate the degradation, the Doppler approximation is not utilized, and instead, wideband signal processing theory is applied in the time domain. The results show that by accurately interpolating each sample in the digitized reference signal, a target's velocity and range can …
Bistatic 3d Electromagnetic Scattering From A Right-Angle Dihedral At Arbitrary Orientation And Position, Andreas Z. Tempelis
Bistatic 3d Electromagnetic Scattering From A Right-Angle Dihedral At Arbitrary Orientation And Position, Andreas Z. Tempelis
Theses and Dissertations
A method is created to extend a bistatic 3D electromagnetic scattering solution for a dihedral at a given orientation and position to the case of arbitrary orientation and position. Results produced using this method are compared to shooting and bouncing rays (SBR) and method of moments (MoM) predictions, as well as measured data for applicable cases. The model in this thesis shows excellent agreement in magnitude and phase with SBR predictions. It also shows good agreement in magnitude with MoM predictions. Small phase differences between model and MoM data occur due to differences in the underlying scattering solution and the …
Determining The Index Of Refraction Of An Unknown Object Using Passive Polarimetric Imagery Degraded By Atmospheric Turbulence, Milo W. Hyde Iv
Determining The Index Of Refraction Of An Unknown Object Using Passive Polarimetric Imagery Degraded By Atmospheric Turbulence, Milo W. Hyde Iv
Theses and Dissertations
In this research, an algorithm is developed to estimate the index of refraction of an unknown object using passive polarimetric images degraded by atmospheric turbulence. The algorithm uses a variant of the maximum-likelihood blind-deconvolution algorithm developed by LeMaster and Cain to recover the true object (i.e., the first Stokes parameter), the degree of linear polarization, and the polarimetric-image point spread functions. Nonlinear least squares is then used to find the value of the complex index of refraction which best fits the theoretical degree of linear polarization, derived using a polarimetric bidirectional reflectance distribution function, to the turbulence-corrected degree of linear …
Pulse Shape Correlation For Laser Detection And Ranging (Ladar), Brian T. Deas
Pulse Shape Correlation For Laser Detection And Ranging (Ladar), Brian T. Deas
Theses and Dissertations
Radar systems provide an important remote sensing capability, and are crucial to the layered sensing vision; a concept of operation that aims to apply the right number of the right types of sensors, in the right places, at the right times for superior battle space situational awareness. The layered sensing vision poses a range of technical challenges, including radar, that are yet to be addressed. To address the radar-specific design challenges, the research community responded with waveform diversity; a relatively new field of study which aims reduce the cost of remote sensing while improving performance. Early work suggests that the …
Development And Evaluation Of A Multistatic Ultrawideband Random Noise Radar, Matthew E. Nelms
Development And Evaluation Of A Multistatic Ultrawideband Random Noise Radar, Matthew E. Nelms
Theses and Dissertations
This research studies the AFIT noise network (NoNET) radar node design and the feasibility in processing the bistatic channel information of a cluster of widely distributed noise radar nodes. A system characterization is used to predict theoretical localization performance metrics. Design and integration of a distributed and central signal and data processing architecture enables the Matlab®-driven signal data acquisition, digital processing and multi-sensor image fusion. Experimental evaluation of the monostatic localization performance reveals its range measurement error standard deviation is 4.8 cm with a range resolution of 87.2(±5.9) cm. The 16-channel multistatic solution results in a 2-dimensional localization error of …
Spectrally-Temporally Adapted Spectrally Modulated Spectrally Encoded (Smse) Waveform Design For Coexistent Cr-Based Sdr Applications, Eric C. Like
Theses and Dissertations
This work expands the applicability of the Spectrally Modulated, Spectrally Encoded (SMSE) framework by developing a waveform optimization process that enables intelligent waveform design. The resultant waveforms are capable of adapting to a spectrally diverse transmission channel while meeting coexistent constraints. SMSE waveform design is investigated with respect to two different forms of coexisting signal constraints, including those based on resultant interference levels and those based on resultant power spectrum shape. As demonstrated, the SMSE framework is well-suited for waveform optimization given its ability to allow independent design of spectral parameters. This utility is greatly enhanced when soft decision selection …
Effects Of Channel Mismatches On Beamforming And Signal Detection, Christopher I. Allen
Effects Of Channel Mismatches On Beamforming And Signal Detection, Christopher I. Allen
Theses and Dissertations
Tuner gain measurements of a multichannel receiver are reported. A linear regression model is used to characterize the gain, as a function of channel number, tuner set-on frequency, and intermediate frequency. Residual errors of this model are characterized by a t distribution. Very strong autocorrelation of tuner gain at various frequencies is noted. Tuner performance from one channel to the next is diverse; several defects at specific frequencies are noted. The Wilcoxon signed rank test is used to test normality of tuner gain among devices; normality is rejected. Antenna directivity and phase pattern measurements are also reported. An antenna element …
An Approach To Large Scale Radar-Based Modeling And Simulation, Lester C. Long Iv
An Approach To Large Scale Radar-Based Modeling And Simulation, Lester C. Long Iv
Theses and Dissertations
This research presents a method of aggregating, or reducing the resolution, of a commonly available Department of Defense (DoD) simulation. It addresses the differences between varying levels of resolution and scope used in the DoD’s hierarchy of models pyramid. A data representation that aggregates engagement-level simulation data to use at a lower resolution level, the mission-level, is presented and analyzed. Two formats of implementing this data representation are developed and compared: the rigid cylinder format and the expanding tables format. The rigid cylinder format provides an intuitive way to visualize the data and is used to develop the theory. The …
The Effect Of Synthetic Aperture Radar Image Resolution On Target Discrimination, John E. Mcgowan
The Effect Of Synthetic Aperture Radar Image Resolution On Target Discrimination, John E. Mcgowan
Theses and Dissertations
This research details the effect of spatial resolution on target discrimination in Synthetic Aperture Radar (SAR) images. Multiple SAR image chips containing targets and non-targets are used to test a baseline Automatic Target Recognition (ATR) system with reduced spatial resolution. Spatial resolution is reduced by lowering the pixel count or synthesizing a degraded image by filtering and reducing the pixel count. A two-parameter Constant False Alarm Rate (CFAR) detector is tested, and three feature sets, size, contrast, and texture, are used to train a linear classifier and to estimate probability density functions for the two classes. The results are scored …
Aiding Gps With Additional Satellite Navigation Services, Yasin A. Mutlu
Aiding Gps With Additional Satellite Navigation Services, Yasin A. Mutlu
Theses and Dissertations
In modern warfare navigation services are very important. GPS is currently providing service for accurate navigation, except in some areas, especially urban areas, where GPS signals cannot always be tracked by users. In these cases some additional navigation support could be provided by other global navigation satellite systems. If GPS is combined with other navigation systems than the navigation gap will be minor. In this thesis, the effect of combining GPS with other satellite navigation systems, specifically GLONASS, Galileo and Compass, is evaluated in terms of availability and position dilution of precision (PDOP) values. First, satellite constellations are simulated in …
Design Of A Monocular Multi-Spectral Skin Detection, Melanin Estimation, And False-Alarm Suppression System, Keith R. Peskosky
Design Of A Monocular Multi-Spectral Skin Detection, Melanin Estimation, And False-Alarm Suppression System, Keith R. Peskosky
Theses and Dissertations
A real-time skin detection, false-alarm reduction, and melanin estimation system is designed targeting search and rescue (SAR) with application to special operations for manhunting and human measurement and signatures intelligence. A mathematical model of the system is developed and used to determine how the physical system performs under illumination, target-to-sensor distance, and target-type scenarios. This aspect is important to the SAR community to gain an understanding of the deployability in different operating environments. A multi-spectral approach is developed and consists of two short-wave infrared cameras and two visible cameras. Through an optical chain of lenses, custom designed and fabricated dichroic …
Phase Unwrapping In The Presence Of Strong Turbulence, Casey J. Pellizzari
Phase Unwrapping In The Presence Of Strong Turbulence, Casey J. Pellizzari
Theses and Dissertations
Phase unwrapping in the presence of branch points using a least-squares wave-front reconstructor requires the use of a Postprocessing Congruence Operation (PCO). Branch cuts in the unwrapped phase are altered by the addition of a constant parameter h to the rotational component when applying the PCO. Past research has shown that selecting a value of h which minimizes the proportion of irradiance in the pupil plane adjacent to branch cuts helps to maximize performance of adaptive-optics (AO) systems in strong turbulence. In continuation of this objective, this research focuses on optimizing the PCO while accounting for the cumulative effects of …
Frequency Diversity For Improving Synthetic Aperture Radar Imaging, Jawad L. Farooq
Frequency Diversity For Improving Synthetic Aperture Radar Imaging, Jawad L. Farooq
Theses and Dissertations
In this work, a novel theoretical framework is presented for using recent advances in frequency diversity arrays (FDAs). Unlike a conventional array, the FDA simultaneously transmits a unique frequency from each element in the array. As a result, special time and space properties of the radiation pattern are exploited to improve cross-range resolution. The idealized FDA radiation pattern is compared with and validated against a full-wave electromagnetic solver, and it is shown that the conventional array is a special case of the FDA. A new signal model, based on the FDA, is used to simulate SAR imagery of ideal point …
Application Of Time-Frequency Representation To Non-Stationary Radar Cross Section, John D. Mcshane
Application Of Time-Frequency Representation To Non-Stationary Radar Cross Section, John D. Mcshane
Theses and Dissertations
Radar Cross Section (RCS) imaging of a non-wide sense stationary signal poses significant problems in identifying scattering centers in the post processed radar- generated image. A non-wide sense stationary RCS is typically encountered when moving parts on the target impress a phase shift into the backscatter signal that is uncorrelated to the previous return pulse. When the Fourier transform of the phase shifted complex signal is taken, range and cross range information on scattering centers are misplaced. Time Frequency Representations (TFR) must be used to help locate these scattering centers so they can be properly treated to reduce the target’s …