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Digital Holography Efficiency Experiments For Tactical Applications, Douglas E. Thornton
Digital Holography Efficiency Experiments For Tactical Applications, Douglas E. Thornton
Theses and Dissertations
Digital holography (DH) uses coherent detection and offers direct access to the complex-optical field to sense and correct image aberrations in low signal-to-noise environments, which is critical for tactical applications. The performance of DH is compared to a similar, well studied deep-turbulence wavefront sensor, the self-referencing interferometer (SRI), with known efficiency losses. Wave optics simulations with deep-turbulence conditions and noise were conducted and the results show that DH outperforms the SRI by 10's of dB due to DH's strong reference. Additionally, efficiency experiments were conducted to investigate DH system losses. The experimental results show that the mixing efficiency (37%) is …
Near Earth Space Object Detection Using Parallax As Multi-Hypothesis Test Criterion, Joseph C. Tompkins, Stephen C. Cain, David J. Becker
Near Earth Space Object Detection Using Parallax As Multi-Hypothesis Test Criterion, Joseph C. Tompkins, Stephen C. Cain, David J. Becker
Faculty Publications
The US Strategic Command (USSTRATCOM) operated Space Surveillance Network (SSN) is tasked with Space Situational Awareness (SSA) for the U.S. military. This system is made up of Electro-Optic sensors, such as the Ground-based Electro-Optical Deep Space Surveillance (GEODSS) and RADAR based sensors, such as the Space Fence Gaps. They remain in the tracking of Resident Space Objects (RSO’s) in Geosynchronous Orbits (GEO), due to limitations of SST and GEODSS system implementation. This research explores a reliable, ground-based technique used to quickly determine an RSO’s altitude from a single or limited set of observations. Implementation of such sensors into the SSN …
Target-Based Coherent Beam Combining Of An Optical Phased Array Fed By A Broadband Laser Source, Milo W. Hyde Iv, Jack E. Mccrae, Glenn A. Tyler
Target-Based Coherent Beam Combining Of An Optical Phased Array Fed By A Broadband Laser Source, Milo W. Hyde Iv, Jack E. Mccrae, Glenn A. Tyler
Faculty Publications
The target-based phasing of an optical phased array (OPA) fed by a broadband master oscillator laser source is investigated. The specific scenario examined here considers an OPA phasing through atmospheric turbulence on a rough curved object. An analytical expression for the detected or received intensity is derived. Gleaned from this expression are the conditions under which target-based phasing is possible. A detailed OPA wave optics simulation is performed to validate the theoretical findings. Key aspects of the simulation set-up as well as the results are thoroughly discussed.
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 …
Numerical Investigation Of Statistical Turbulence Effects On Beam Propagation Through 2-D Shear Mixing Layer, James C. Bowers
Numerical Investigation Of Statistical Turbulence Effects On Beam Propagation Through 2-D Shear Mixing Layer, James C. Bowers
Theses and Dissertations
A methodology is developed for determining the validity of making a statistical turbulent approach using Kolmogorov theory to an aero-optical turbulent ow. Kolmogorov theory provides a stochastic method that has a greatly simplified and robust method for calculating atmospheric turbulence effects on optical beam propagation, which could simplify similar approaches to chaotic aero-optical flows. A 2-D laminar Navier-Stokes CFD Solver (AVUS) is run over a splitter plate type geometry to create an aero-optical like shear mixing layer turbulence field. A Matlab algorithm is developed to import the flow data and calculates the structure functions, structure constant, and Fried Parameter ( …
Optical Phase Unwrapping In The Presence Of Branch Points, Todd M. Venema [*], Jason D. Schmidt
Optical Phase Unwrapping In The Presence Of Branch Points, Todd M. Venema [*], Jason D. Schmidt
Faculty Publications
Strong turbulence causes phase discontinuities known as branch points in an optical field. These discontinuities complicate the phase unwrapping necessary to apply phase corrections onto a deformable mirror in an adaptive optics (AO) system. This paper proposes a non-optimal but effective and implementable phase unwrapping method for optical fields containing branch points. This method first applies a least-squares (LS) unwrapper to the field which isolates and unwraps the LS component of the field. Four modulo-2π-equivalent non-LS components are created by subtracting the LS component from the original field and then restricting the result to differing ranges. 2π phase jumps known …
Polar Phase Screens: A Comparison With Other Methods Of Random Phase Screen Generation, Rebecca J. Eckert
Polar Phase Screens: A Comparison With Other Methods Of Random Phase Screen Generation, Rebecca J. Eckert
Theses and Dissertations
This research provides the first organized comparison of random phase screen generation methods, including logarithmic polar Fourier series, using structure functions. Random phase screens are essential elements of simulating light propagation through turbulent media. In order to be effective, they must accurately reflect theory and be practical to implement. This research explains and evaluates three methods of generating random phase screens: using a Fourier series upon a polar frequency grid with logarithmic spacing; using the fast Fourier transform, with its Cartesian frequency grid; and using Zernike polynomials. It provides a comparison of the Polar Fourier Series technique with the two …
Forecasting Advective Sea Fog With The Use Of Classification And Regression Tree Analyses For Kunsan Air Base, Danielle M. Lewis
Forecasting Advective Sea Fog With The Use Of Classification And Regression Tree Analyses For Kunsan Air Base, Danielle M. Lewis
Theses and Dissertations
Advective sea fog frequently plagues Kunsan Air Base (AB), Republic of Korea, in the spring and summer seasons. It is responsible for a variety of impacts on military operations, the greatest being to aviation. To date, there are no suitable methods developed for forecasting advective sea fog at Kunsan, primarily due to a lack of understanding of sea fog formation under various synoptic situations over the Yellow Sea. This work explored the feasibility of predicting sea fog development with a 24-hour forecast lead time. Before exploratory data analysis was performed, a geographical introduction to the region was provided along with …
Verification Of The Mountain Wave Forecast Model's Stratospheric Turbulence Forecasts Using Sounding Data And Pilot Reports, Scott M. Miller
Verification Of The Mountain Wave Forecast Model's Stratospheric Turbulence Forecasts Using Sounding Data And Pilot Reports, Scott M. Miller
Theses and Dissertations
Since stratospheric turbulence (Stratoturb) is becoming an increased concern to the Air Force, the threat of damage to aircraft must be addressed. Therefore, the Air Force Weather Agency (AFWA) requests an accurate Stratoturb forecast model. In 2002, The Mountain Wave Forecast Model (MWFM) was modified in order to develop a Stratoturb forecast tool. Turbulence forecasts generated twice daily by the MWFM for locations over East Asia over a period of thirty days were compared to output from the Rawindsonde Observation (RAOB) program to determine if the model agreed with the program output. Although the results were promising, verification by aircraft …
Atmospheric Simulation Using A Liquid Crystal Wavefront Controlling Device, Matthew R. Brooks
Atmospheric Simulation Using A Liquid Crystal Wavefront Controlling Device, Matthew R. Brooks
Theses and Dissertations
Test and evaluation of laser warning devices is important due to the increased use of laser devices in aerial applications. In this thesis, an atmospheric aberrating system is deve1oped to enable in-1ab testing of laser warning devices. This system employs laser 1ight at 632.8nm from a He1ium-Neon source and a spatial light modulator (SLM) to cause phase changes using a birefringent liquid crystaJ material. Before the system can be used, the SLM phase response must be quantified to ensure proper manipulation of index of refrnction. Additionally, diffraction from the SLM and rea1-world system scaling are addressed. Once completed, the atmospheric …
An Automated Method Of Predicting Clear-Air Turbulence, Brian L. Belson
An Automated Method Of Predicting Clear-Air Turbulence, Brian L. Belson
Theses and Dissertations
Clear-air turbulence (CAT) prediction is vitally important to military aviation and the successful completion of Department of Defense (DoD) operations such as air to air refueling and new national defensive weapon systems such as directed energy platforms. The unique mission requirements of military aircraft often require strict avoidance of turbulent regions. Traditionally, weather forecasters have found it difficult to accurately predict CAT. In order to forecast regions where CAT might occur, forecasters must first determine the location of breaking waves caused by either Kelvin-Helmholtz instabilities or topographically forced internal gravity waves (mountain waves) in the atmosphere. The United States Air …
Evaluation Of The Mountain Wave Forecast Model's Stratospheric Turbulence Simulations, Mark S. Allen
Evaluation Of The Mountain Wave Forecast Model's Stratospheric Turbulence Simulations, Mark S. Allen
Theses and Dissertations
Stratospheric turbulence (Stratoturb) is a well-known hazard to aircraft in flight. Forecasting mountain waves, specifically the breaking of these waves, is necessary to accurately predict the presence of Stratoturb. The Air Force Weather Agency (AFWA) requested a product with the capability of forecasting Stratoturb at 30, 50, and 70 mb using model data currently available, To facilitate their request, the Mountain Wave Forecast Model (MWFM) was acquired from the Naval Research Laboratory. MWFM turbulence forecasts generated twice daily over East Asia, using the AVN and MM5 models for initialization, were compared to S' layer turbulence analyses from the Rawinsonde Observation …
High Energy Laser Pointing Through Extended Turbulence, Jason A. Tellez
High Energy Laser Pointing Through Extended Turbulence, Jason A. Tellez
Theses and Dissertations
The airborne laser (ABL) uses adaptive optics to compensate the atmospheric turbulence between the ABL and the target. The primary purpose of this compensation is to increase the energy density of the energy laser at the target. However, the specifics of the engagement scenario require the tracking point of reference and the adaptive optics point of reference to be located at different points on the target. This research considers the effects of tracking a target in one direction while compensating for atmospheric turbulence in a different directions. The target references used are a point source and a rectangle, while a …
Distributed Beacon Requirements For Branch Point Tolerant Laser Beam Compensation In Extended Atmospheric Turbulence, Virgil E. Zetterlind Iii
Distributed Beacon Requirements For Branch Point Tolerant Laser Beam Compensation In Extended Atmospheric Turbulence, Virgil E. Zetterlind Iii
Theses and Dissertations
Branch point tolerant phase reconstructors can vastly improve adaptive optic system performance in extended atmospheric turbulence. This thesis explores the performance bounds of two such reconstructors Goldstein's algorithm and hidden phase. A least squares reconstructor is implemented for comparison. System performance is presented for various scenarios, including correction time-delays, wave-front sensor noise, and extended beacons. These scenarios are of interest for laser communication and directed energy systems such as Airborne Laser. Performance bounds are obtained through wave-optics simulation. The extended beacon propagation geometry approximates the USAF AFRL-DE North Oscura Peak range. Results show that branch point tolerant reconstructors outperform least …
Analyzing The Effects Of Meteorology On Radar Measured Index Of Refraction Structure Parameter, Jeffrey W. Budai
Analyzing The Effects Of Meteorology On Radar Measured Index Of Refraction Structure Parameter, Jeffrey W. Budai
Theses and Dissertations
Forecasting optical turbulence is essential for the Air Force's Airborne Laser program to optimize placement of aircraft. To find bow meteorology affects Cn2, the intensity of turbulence in the index of refraction, case studies of synoptically interesting times are first chosen. Correlation coefficients are then computed between radar measured Cn2 and meteorological quantities. The potential for mechanically turbulent activity is looked at. In the analysis of this work, six meteorological features were found likely to affect Cn2. Two features associated with affecting potential refractivity, and thus Cn2, are jets …
Performance Analysis Of A Hartman Wavefront Sensor Used For Sensing Atmospheric Turbulence Statistics, Toby D. Reeves
Performance Analysis Of A Hartman Wavefront Sensor Used For Sensing Atmospheric Turbulence Statistics, Toby D. Reeves
Theses and Dissertations
Atmospheric turbulence parameters, such as Fried's coherence diameter, the outer scale of turbulence, and the turbulence power law, are related to the wavefront slope structure function (SSF). The SSF is defined as the second moment of the wavefront slope difference as a function of both time and position. Knowledge of the SSF allows turbulence parameters to be estimated. Hartmann wavefront sensor (H-WFS) slope measurements composed of both signal and noise, allow the SSF to be estimated by computing a mean square difference of H-WFS slope measurements. The quality of the SSF estimate is quantified by the signal-to-noise ratio (SNR) of …
The Role Of Frame Selection And Bispectrum Phase Reconstruction For Speckle Imaging Through Atmospheric Turbulence, Elizabeth A. Harpold
The Role Of Frame Selection And Bispectrum Phase Reconstruction For Speckle Imaging Through Atmospheric Turbulence, Elizabeth A. Harpold
Theses and Dissertations
Frame selection using quality sharpness metrics have been shown in previous AFIT theses, to be effective in improving the final product of images obtained using adaptive optics. This thesis extends this idea to noncompensated speckle image data. Speckle image reconstruction is simulated with and without frame selection. Speckle images require the processing of hundreds of data frames. Frame selection is a method of reducing the amount of data required to reconstruct the image. A collection of short exposure image data frames of a single object are sorted based on sharpness metrics. Only the highest quality frames are retained and processed …
Maximum Likelihood Estimation Of Wave Front Slopes Using A Hartmann-Type Sensor, Scott A. Sallberg
Maximum Likelihood Estimation Of Wave Front Slopes Using A Hartmann-Type Sensor, Scott A. Sallberg
Theses and Dissertations
Current methods for estimating the wave front slope at the pupil of a telescope equipped with a Hartmann-type wave front sensor (H-WFS) are based on a simple centroid calculation of the intensity distributions (spots) recorded in each subaperture of the H-WFS. The centroid method does not include any knowledge concerning correlation properties of the slopes over the subapertures or the amount of light collected by the telescope and diverted to the H-WFS for wave front reconstruction purposes. This thesis devises a maximum likelihood (ML) estimation of the spot centroids by incorporating statistical knowledge of the spot shifts. The light level …
Characterization Of Atmospheric Turbulence Over Long Horizontal Paths Using Optical Slope Measurements, Eric E. Silbaugh
Characterization Of Atmospheric Turbulence Over Long Horizontal Paths Using Optical Slope Measurements, Eric E. Silbaugh
Theses and Dissertations
Atmospheric turbulence has long been recognized as one of the fundamental factors affecting optical systems operating through the atmosphere. Turbulence over vertical paths has been well characterized, both theoretically and experimentally. Much less is known about turbulence over long, horizontal paths. Perturbations of the wave front phase can be measured using a Hartmann wave front sensor (H-WFS). Theoretical expressions for the tilt removed structure function of the H-WFS slope measurements were derived and evaluated using quadrature. These slope structure functions are functions of the phase structure function. The Kolmogorov turbulence model was assumed. Simulated H-WFS slope measurements were generated using …
Laser Beam Propagation In Non-Kolmogorov Atmospheric Turbulence, Bruce E. Stribling
Laser Beam Propagation In Non-Kolmogorov Atmospheric Turbulence, Bruce E. Stribling
Theses and Dissertations
Several observations of atmospheric turbulence statistics have been reported which do not obey Kolmogorov's power spectral density model. These observations have prompted the study of optical propagation through turbulence described by non-classical power spectra. This thesis presents an analysis of optical propagation through turbulence which causes index of refraction fluctuations to have spatial power spectra that obey arbitrary power laws. The spherical and plane wave structure functions are derived using Mellin transform techniques and are applied to the field mutual coherence function (MCF) using the extended Huygens-Fresnel principle. The MCF is used to compute the Strehl ratio of a focused, …
Experimental Verification Of Tomographic Reconstruction Of Turbulent Air Flow Structure Using Optical Wavefront Measurements, Bryon L. Pedersen
Experimental Verification Of Tomographic Reconstruction Of Turbulent Air Flow Structure Using Optical Wavefront Measurements, Bryon L. Pedersen
Theses and Dissertations
The performance of an aircraft based optical system is degraded by aero-optic turbulence. The varying index of refraction within the turbulent field causes phase perturbation in an optical wave. In order to compensate for aero-optic turbulence effects, the nature of the turbulence must be understood. Large scale, organized structure within the turbulence has been found to contribute significantly to the overall phase perturbation caused by a turbulent field. A unique approach was devised to determine the turbulence structure using tomographic reconstruction techniques. Tomography provides an excellent means to determine the underlying structure within a turbulent field. The tomographic reconstruction produces …
Performance Impacts For Actuator Misalignments And Failures In Large- Aperture Adaptive-Optic Telescopes, Timothy D. Hogan
Performance Impacts For Actuator Misalignments And Failures In Large- Aperture Adaptive-Optic Telescopes, Timothy D. Hogan
Theses and Dissertations
Large-aperture telescopes require adaptive optics in order to compensate for atmospheric turbulence which would otherwise negate the resolution advantages of using large apertures. This investigation analyzes the impacts of misalignments and failures, in the deformable mirror actuators, upon the performance of such systems. A numerical simulation of a standard adaptive optics system is used to generate characteristic optical transfer function OTF and signal-to-noise ratio SNR performance metrics. The performance impacts of the misalignments are shown to be dependent upon the Fried parameter effective telescope diameter, the source object brightness, and the control system time delay. The degree of performance degradation …