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Improving Range Estimation of a 3D FLASH LADAR Via Blind Deconvolution Jason R

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Improving Range Estimation of a 3D FLASH LADAR Via Blind Deconvolution Jason R Air Force Institute of Technology AFIT Scholar Theses and Dissertations Student Graduate Works 9-10-2010 Improving Range Estimation of a 3D FLASH LADAR via Blind Deconvolution Jason R. McMahon Follow this and additional works at: https://scholar.afit.edu/etd Part of the Electrical and Electronics Commons, and the Electromagnetics and Photonics Commons Recommended Citation McMahon, Jason R., "Improving Range Estimation of a 3D FLASH LADAR via Blind Deconvolution" (2010). Theses and Dissertations. 1971. https://scholar.afit.edu/etd/1971 This Dissertation is brought to you for free and open access by the Student Graduate Works at AFIT Scholar. It has been accepted for inclusion in Theses and Dissertations by an authorized administrator of AFIT Scholar. For more information, please contact [email protected]. IMPROVING RANGE ESTIMATION OF A 3-DIMENSIONAL FLASH LADAR VIA BLIND DECONVOLUTION DISSERTATION Jason R. McMahon, Major, USAF AFIT/DEE/ENG/10-13 DEPARTMENT OF THE AIR FORCE AIR UNIVERSITY AIR FORCE INSTITUTE OF TECHNOLOGY Wright-Patterson Air Force Base, Ohio APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED. The views expressed in this dissertation are those of the author and do not reflect the official policy or position of the United States Air Force, Department of Defense, or the United States Government. AFIT/DEE/ENG/10-13 IMPROVING RANGE ESTIMATION OF A 3-DIMENSIONAL FLASH LADAR VIA BLIND DECONVOLUTION DISSERTATION Presented to the Faculty Graduate School of Engineering and Management Air Force Institute of Technology Air University Air Education and Training Command In Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy Jason R. McMahon, BSEE, MSEE Major, USAF September 2010 APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED. AFIT/DEE/ENG/10-13 Abstract The purpose of this research effort is to improve and characterize range estimation in a three-dimensional FLASH LAser Detection And Ranging (3D FLASH LADAR) by investigating spatial dimension blurring effects. The myriad of emerging applications for 3D FLASH LADAR both as primary and supplemental sensor necessitate superior per- formance including accurate range estimates. Along with range information, this sensor also provides an imaging or laser vision capability. Consequently, accurate range estimates would also greatly aid in image quality of a target or remote scene under interrogation. Unlike previous efforts, this research accounts for pixel coupling by defining the range image mathematical model as a 2D convolution between the system spatial impulse response and the object (target or remote scene) at a particular range slice. Using this model, improved range estimation is possible by object restoration from the data observations. Object estimation is principally performed by deriving a blind deconvolution Generalized Expectation Maximization (GEM) algorithm with the range determined from the estimated object by a normalized correlation method. Theoretical derivations and simulation results are verified with experimental data of a bar target taken from a 3D FLASH LADAR system in a laboratory environment. Simulation examples show that the GEM object restoration improves range estimation over the unprocessed data and a Wiener filter method by 75% and 26% respectively. In the laboratory experiment, the GEM object restoration improves range estimation by 34% and 18% over the unprocessed data and Wiener filter method respectively. This research also derives the Cramer-Rao bound (CRB) on range separation estima- tion of two point sources interrogated by a 3D FLASH LADAR system. Using an unbiased estimator, range separation estimation variance was attained through simulation and com- pared favorably to the range separation CRB theory. The results show that the CRB does indeed provide a lower bound on the range separation estimation variance and that the es- iv timator is nearly efficient. With respect to the estimator, traditional pixel-based estimators like peak detection and matched filtering are biased because they assume there is only one target in the pixel. Therefore, an unbiased estimator was derived accounting for the possi- bility of two targets within a single pixel. Additionally, among other factors, the range separation CRB is a function of two LADAR design parameters (range sampling interval and transmitted pulse-width), which can be optimized using the expected range resolution between two point sources. Typi- cally, a shorter transmitted pulse-width corresponds to better range resolution (the ability to resolve two targets in range). Given a particular range sampling capability determined by the receiver electronics, the CRB theory shows there is an optimal pulse-width where a shorter pulse-width would increase estimation variance due to the under-sampling of the pulse and a longer pulse-width would degrade the resolving capability. Using both CRB theory and simulation results, an investigation is accomplished that finds the optimal pulse- width for several range sampling scenarios. For example, given a Gaussian received pulse model sampled every 1.876 ns, both range separation CRB theory and simulation predict an optimal pulse-width standard deviation equal to 0.88 ns. As the speed of the optical re- ceiver is increased, the range resolution is improved with a corresponding narrower optimal pulse-width attained by the ability to sufficiently sample a shorter pulse-width. Conversely, the optimal pulse-width is wider with slower electronics with an associated negative impact on range resolution. v Acknowledgements I would like to thank my family and friends for supporting me through this academic journey which was filled with discovery, hard work, and laughter. Special thanks goes to my wife and children who provided love, support, positive distractions, and encour- agement. A substantial “thank you” also goes to my advisor, Dr. Richard Martin, whose guidance and advice was indispensable. Finally, I am most grateful to the giants whose shoulders I stood upon while completing my degree. Jason R. McMahon vi Table of Contents Page Abstract ...................................... iv Acknowledgements ................................ vi List of Figures ................................... x List of Tables ................................... xii I. Introduction ............................... 1 1.1 Motivation .......................... 2 1.2 3D FLASH LADAR Research Contributions ........ 4 1.2.1 Improving Range Estimation by Spatial Processing (Chapter V) .................... 4 1.2.2 Unbiased Two Point Target Temporal and Spatial Estimator (Chapter IV) ............... 4 1.2.3 LowerBound onRange Separation EstimationVari- ance (Chapter VI) ................. 4 1.2.4 Optimal Pulse-Width based on Range Resolution (Chapter VI) .................... 5 1.3 Organization ......................... 5 II. Background ............................... 7 2.1 LADAR Imaging Theory .................. 7 2.1.1 Description of Light ................ 8 2.1.2 Optical Field Propagation ............. 9 2.1.3 ImpulseResponseofanImagingSystemwithaThin Lens ........................ 12 2.1.4 Optical Imaging as a Linear and Nonlinear System 15 2.1.5 Coherence Theory and Laser Light Statistics ... 16 2.2 Deconvolution ........................ 23 2.2.1 Inverse Filtering .................. 24 2.2.2 Iterative Algorithms ................ 26 2.3 Maximum Likelihood .................... 29 2.4 Generalized Expectation Maximization ........... 31 2.5 3D FLASH LADAR Data Model .............. 33 2.6 Previous Research ...................... 42 2.6.1 3DFLASH LADAR ................ 43 2.6.2 3D FLASH LADAR Post-Processing ....... 47 2.6.3 Blind Deconvolution ................ 53 2.6.4 CRB and Parameter Optimization ......... 56 vii Page III. Laboratory Data Collection ....................... 58 3.1 3D FLASH LADAR Hardware Description ......... 58 3.2 Data Collection Details ................... 61 3.3 Spatial Aliasing ....................... 62 3.4 Data Pre-processing ..................... 63 3.5 Experimental PSF ...................... 66 3.6 Speckle Parameter Estimation – Incoherent Imaging .... 67 IV. RangeEstimation ............................ 71 4.1 Peak Detection ........................ 71 4.2 Maximum Likelihood .................... 72 4.3 Normalized Cross-Correlation ................ 74 4.4 Two Point Target Range and Spatial Separation Estimator . 76 4.4.1 Two Point Target Data Model ........... 76 4.4.2 Estimator Derivation ................ 79 4.5 Pixel-Dependent Two Surface Range Separation Estimator . 81 V. Improving3DFLASHLADARRangeEstimationviaObject Recovery 84 5.1 Theoretical Development .................. 86 5.1.1 Object Deconvolution ............... 87 5.1.2 Pulse-Shape Blind Deconvolution via the GEM Al- gorithm ....................... 88 5.1.3 Object Blind Deconvolution via the GEM Algorithm 96 5.2 Simulation .......................... 101 5.3 Experimental Results ..................... 108 5.4 Conclusions ......................... 110 VI. Range Separation Performance and Optimal Pulse-Width Prediction of a 3D FLASH LADAR using the Cramer-Rao Bound ......... 112 6.1 CRB on Range Separation Estimation ............ 113 6.2 Range Separation Estimation Results ............ 120 6.3 Optimal Pulse-width Investigation .............. 121 6.3.1 Optimal Pulse for Two Point Target ........ 124 6.3.2 Optimal Pulse for Complex Targets ........ 126 6.3.3 Optimal Pulse for a Two Point Target using Nor- malized Pulse Definition ............. 132 6.4 Conclusions ........................
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