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Articles 1 - 17 of 17
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Laser Intensity Scaling Through Stimulated Scattering In Optical Fibers, Timothy H. Russell
Laser Intensity Scaling Through Stimulated Scattering In Optical Fibers, Timothy H. Russell
Theses and Dissertations
The influence of stimulated scattering on laser intensity in fiber optic waveguides is examined. Stimulated Brillouin scattering (SBS) in long, multimode optical waveguides is found to generate a Stokes beam that propagates in the fiber LP01 mode. Additionally, the same process is found to combine multiple laser beams into a single spatially coherent source. Limitations in beam cleanup and combining are also investigated to identify ways to overcome them. The last portion of the dissertation theoretically examines suppression of stimulated Raman scattering in fibers to eliminate the restriction this imposes on the power of a fiber laser or amplifier. The …
Nonlinear Suppression Of Range Ambiguity In Pulse Doppler Radar, Jon M. Anderson
Nonlinear Suppression Of Range Ambiguity In Pulse Doppler Radar, Jon M. Anderson
Theses and Dissertations
Coherent pulse train processing is most commonly used in airborne pulse Doppler radar, achieving adequate transmitter/receiver isolation and excellent resolution properties while inherently inducing ambiguities in Doppler and range. First introduced by Palermo in 1962 using two conjugate LFM pulses, the primary nonlinear suppression objective involves reducing range ambiguity, given the waveform is nominally unambiguous in Doppler, by using interpulse and intrapulse coding (pulse compression) to discriminate received ambiguous pulse responses. By introducing a nonlinear operation on compressed (undesired) pulse responses within individual channels, ambiguous energy levels are reduced in channel outputs. This research expands the NLS concept using discrete …
Adaptive And Reconfigurable Flight Control, Yih Shiun Huang
Adaptive And Reconfigurable Flight Control, Yih Shiun Huang
Theses and Dissertations
An indirect adaptive and reconfigurable flight control system is developed. The three-module controller consists of: (1) a system identification module, (2) a parameter estimate smoother, and (3) a proportional and integral compensator for tracking control. Specifically: (1) The identification of a linear discrete-time control system's open-loop gain is addressed. The classical Kalman filter theory for linear control systems is extended and the control system's state and loop gain are jointly estimated on-line. Explicit formulae for the loop gain's estimate and estimation error covariance are derived. The estimate is unbiased and the predicted covariance is reliable. (2) An adaptive smoother is …
Optical And Etching Studies Of Native Aluminum Oxide Layers For Use In Microcavity Photonic Devices, William L. Bernhard
Optical And Etching Studies Of Native Aluminum Oxide Layers For Use In Microcavity Photonic Devices, William L. Bernhard
Theses and Dissertations
Optical communication and computing systems are required to meet future information transfer and processing needs. Microcavity devices serve as an enabling technology to implement and integrate optoelectronic systems. It is important to understand the optical and mechanical properties of materials utilize within microcavity devices. Only then is it possible to accurately model and analyze structures. Microcavity structures incorporating a high aluminum content AlGaAs layers are designed, grown, processed, and measured. The processing of these devices includes the conversion of high aluminum-content AlGaAs layers to native aluminum oxide (AlO) layers through the process of thermal oxidation. This selective conversion of microcavity …
The Calibration Of Bistatic Radar Cross Section Measurements, Christopher J. Bradley
The Calibration Of Bistatic Radar Cross Section Measurements, Christopher J. Bradley
Theses and Dissertations
Recent advances in signal processing and remote sensing have highlighted the importance of bistatic radar systems for the purposes of environmental monitoring, surveillance, and tracking radar. The calibration of such systems has been problematic-much more so than similar monostatic systems, primarily as a result of the lack of reference objects suitable for calibrating at any given bistatic angle. This research deals with the problems of calibrating full-polarimetric laboratory-environment bistatic radar systems, including the lack of suitable calibration targets and procedures, and operational considerations such as alignment and mounting. Several popular bistatic calibration techniques are classified, evaluated, and comparisons are made …
Using Gps As A Reference System To Hit A Moving Target, Daryl J. Burnette
Using Gps As A Reference System To Hit A Moving Target, Daryl J. Burnette
Theses and Dissertations
The Affordable Moving Surface Target Engagement (AMSTE) project attempts to develop affordable solutions to the precise moving target surface target engagement problem. Up to this point, most of the error analysis performed for the AMSTE project has been at the error variance level, generating root-sum-square (RSS) total errors from error budgets consisting of constant error variances. In reality, the level of error for both Global Positioning System (GPS) positioning and radar targeting systems is highly dependent upon the given situation (such as the distance between sensor and target, the altitude differences, etc.) This research generates a more comprehensive model of …
Characterization And Validation Of The Gp-3 Experimental Radar System, Benjamin L. Crossley
Characterization And Validation Of The Gp-3 Experimental Radar System, Benjamin L. Crossley
Theses and Dissertations
The experimental GP-3 radar system was originally designed and built under contract for the Air Force Research Laboratory (AFRL). AFRL sought AFIT's support in characterizing the as delivered' performance of the GP-3. This research effort focused exclusively on software modifications and hardware validations related to the GP-3 post-processing mode. As modified, tested, and validated, the GP-3's post-processing mode is now fully operational. The GP-3 is capable of transmitting and receiving bandlimited (3.5 MHz) waveforms at X-Band frequencies. System characterization tests included, noise performance and frequency response. System noise performance characterization permitted establishment of the receiver 'noise floor' and enabled determination …
Broadband Application Of High Impedance Ground Planes, Keven J. Golla
Broadband Application Of High Impedance Ground Planes, Keven J. Golla
Theses and Dissertations
Electrical conductors have long been the only materials available to antenna designers for reflecting structures. However, recently reported high impedance ground plane (HIGP) structures offer an alternative by creating image currents and reflections, within a limited frequency stop-band, that are in-phase with a source rather than out-of-phase as for a perfect electric conducting (PEC) surface. Also, the high impedance structures suppress surface waves while surface waves propagate on PEC surfaces. This research explores broadband antenna applications for HIGP structures. A broadband surface mount antenna is applied to both a homogeneous narrowband HIGP and a spatially varying broadband HIGP design. Measurements …
An Objective Evaluation Of Four Sar Image Segmentation Algorithms, Jason B. Gregga
An Objective Evaluation Of Four Sar Image Segmentation Algorithms, Jason B. Gregga
Theses and Dissertations
Because of the large number of SAR images the Air Force generates and the dwindling number of available human analysts, automated methods must be developed. A key step towards automated SAR image analysis is image segmentation. There are many segmentation algorithms, but they have not been tested on a common set of images, and there are no standard test methods. This thesis evaluates four SAR image segmentation algorithms by running them on a common set of data and objectively comparing them to each other and to human segmentors. This objective comparison uses a multi-metric a approach with a set of …
A Low Power Application-Specific Integrated Circuit (Asic) Implementation Of Wavelet Transform/Inverse Transform, Daniel N. Harvala
A Low Power Application-Specific Integrated Circuit (Asic) Implementation Of Wavelet Transform/Inverse Transform, Daniel N. Harvala
Theses and Dissertations
A unique ASIC was designed implementing the Haar Wavelet transform for image compression/decompression. ASIC operations include performing the Haar wavelet transform on a 512 by 512 square pixel image, preparing the image for transmission by quantizing and thresholding the transformed data, and performing the inverse Haar wavelet transform, returning the original image with only minor degradation. The ASIC is based on an existing four-chip FPGA implementation. Implementing the design using a dedicated ASIC enhances the speed, decreases chip count to a single die, and uses significantly less power compared to the FPGA implementation. A reduction of RAM accesses was realized …
Development And Testing Of A Multiple Filter Approach For Precise Dgps Positioning And Carrier-Phase Ambiguity Resolution, Paul E. Henderson
Development And Testing Of A Multiple Filter Approach For Precise Dgps Positioning And Carrier-Phase Ambiguity Resolution, Paul E. Henderson
Theses and Dissertations
The most precise relative positioning obtained using differential GPS depends on accurately determining carrier-phase integer ambiguities. To achieve high precision, many current static and kinematic algorithms use a floating-point solution until enough information becomes available to fix the carrier-phase ambiguities accurately. A mew method is presented that uses a multiple model Kalman filter to resolve the carrier-phase integer ambiguities. This method starts with the floating-point results, yet smoothly and rapidly attains the precision of the correct fixed-integer solution, eliminating the need to decide when to switch from the floating to the fixed-integer solution. This method is based on a theoretically …
Redundant Wavelet-Based Image Restoration Using A Prior Information, Mary K. Marcum
Redundant Wavelet-Based Image Restoration Using A Prior Information, Mary K. Marcum
Theses and Dissertations
Reconnaissance missions and satellites collect hundreds of images loaded with valuable information to be utilized by the Air Force. Intelligence operations must analyze these images to extract the information needed to help commanders make important decisions. No matter how obtained, images of this type are often degraded by noise due to disruptions such as atmospheric disturbances, optical system variations, motion, and large distance from the sensor to the source. This noise must be removed effectively to improve the quality of these images and ensure that the information contained in them can be correctly extracted. The Air Force relies on the …
Wavelet-Based Audio Embedding & Audio/Video Compression, Michael J. Mendenhall
Wavelet-Based Audio Embedding & Audio/Video Compression, Michael J. Mendenhall
Theses and Dissertations
With the decline in military spending, the United States relies heavily on state side support. Communications has never been more important. High-quality audio and video capabilities are a must. Watermarking, traditionally used for copyright protection, is used in a new and exciting way. An efficient wavelet-based watermarking technique embeds audio information into a video signal. Several highly effective compression techniques are applied to compress the resulting audio/video signal in an embedded fashion. This wavelet-based compression algorithm incorporates bit plane coding, first difference coding, and Huffman coding. To demonstrate the potential of this audio embedding audio/video compression system, an audio signal …
A Model To Predict Diffraction Attenuation Resulting From Signal Propagation Over Terrain In Low Earth Orbit Satellite Systems, Peter R. Pollock
A Model To Predict Diffraction Attenuation Resulting From Signal Propagation Over Terrain In Low Earth Orbit Satellite Systems, Peter R. Pollock
Theses and Dissertations
This study focused on multipath communication propagation impairments to the LEOSAT communications channel. Two terrain diffraction models, based on the geometric theory of diffraction (GTD), were developed and applied to the space-to-ground communications channel. These models were used to predict the impact of terrain on the performance of three LEOSAT communication systems with designs based on the Iridium, Globalstar and Orbcomm implementations. The study verified the feasibility of applying models based on the GTD rather than empirical or statistical models, to approximate the effect of propagating signals over terrain. Both models confirm that signal blockage and multipath propagation, due to …
Phugoid Damping Control, Nicolas J. Schindeler
Phugoid Damping Control, Nicolas J. Schindeler
Theses and Dissertations
A novel phugoid damping control design methodology is developed, based on the use of wind axes and a point-mass aircraft model. The state variables are air speed, flight path angle, and heading angle, the control variables are thrust setting, angle of attack, bank angle, and sideslip angle, and the command signals are airspeed, flight path angle, and heading angle or heading rate. All the variables and parameters are nondimensionalized. A multivariable set point controller is developed which consists of: (1) a trim calculation-based nonlinear feed-forward control computer; thus, given a commanded new trim state (air speed, flight path angle, and …
Microdot-A 4-Bit Synchronous Microcontroller For Space Applications, Kirby M. Watson
Microdot-A 4-Bit Synchronous Microcontroller For Space Applications, Kirby M. Watson
Theses and Dissertations
Satellites have limited power budgets due to the amount of power collected by the satellite's solar panels. The goal is to have a wide range of functionality, while running off a limited power source. Large microprocessors use large amounts of power to report back temperature and chemical sensor data to ground stations. By using small micro controllers to perform the data collection and minimizing the usage of the larger microprocessors, the satellites will save power. A prototype design of the Microdot 4-bit micro controller for space applications is presented. Requirements for the Microdot, such as microwatt power consumption and 23 …
Image Registration Using Redundant Wavelet Transforms, Richard K. Brown
Image Registration Using Redundant Wavelet Transforms, Richard K. Brown
Theses and Dissertations
Imagery is collected much faster and in significantly greater quantities today compared to a few years ago. Accurate registration of this imagery is vital for comparing the similarities and differences between multiple images. Since human analysis is tedious and error prone for large data sets, we require an automatic, efficient, robust, and accurate method to register images. Wavelet transforms have proven useful for a variety of signal and image processing tasks, including image registration. In our research, we present a fundamentally new wavelet-based registration algorithm utilizing redundant transforms and a masking process to suppress the adverse effects of noise and …