Doctor of Philosophy (Ph.D.), University of Dayton, 2017, Electro-Optics

This research describes a multi-static interferometric synthetic aperture ladar (IFSAL) for high resolution, high precision 3D imaging. Code division multiple access apertures are implemented using periodic, pseudorandom noise waveforms to create spatial aperture diversity and overcome the ambiguity limitations associated with the aperture separation requirements for interferometric synthetic aperture ladar. The theory and basic design requirements are developed for mapping relative aperture phase to a high precision elevation profile in a sparse, multi-static IFSAL system and subsequent processing steps are developed. An analytic signal model and computer simulation is developed for baseline validation of the theory and processing techniques. This research also presents the first-of laboratory demonstration of a sparse, multi-static ladar for IFSAL imaging. A preliminary sensitivity analysis is developed, system limitations are addressed and design considerations are discussed.

Committee: Matthew Dierking (Advisor); Bradley Duncan (Committee Member); David Rabb (Committee Member); Joseph Haus (Committee Member) Subjects: Optics

Doctor of Philosophy (Ph.D.), University of Dayton, 2017, Electro-Optics

Synthetic aperture LADAR (SAL) has been widely investigated over the last 15 years with many studies and experiments examining its performance. Comparatively little work has been done to investigate the effect of atmospheric turbulence on SAL performance. The turbulence work that has been accomplished is in related fields or under weak turbulence assumptions. This research investigates some of the fundamental limits of turbulence on SAL performance. Seven individual impact mechanisms of atmospheric turbulence are examined including: beam wander, beam growth, beam breakup, piston, coherence diameter/length, isoplanatic angle (anisoplanatism) and coherence time. Each component is investigated separately from the others through modeling to determine their respective effect on standard SAL image metrics. Analytic solutions were investigated for the SAL metrics of interest for each atmospheric impact mechanism. The isolation of each impact mechanism allows identification of mitigation techniques targeted at specific, and most dominant, sources of degradation. Results from this work will be critical in focusing future research on those effects which prove to be the most deleterious. Previous research proposed that the resolution of a SAL system was limited by the SAL coherence diameter/length r ~_0 which was derived from the average autocorrelation of the SAL phase history data. The present research confirms this through extensive wave optics simulations. A detailed study is conducted that shows, for long synthetic apertures, measuring the peak widths of individual phase histories may not accurately represent the true resolving power of the synthetic aperture. The SAL wave structure function and degree of coherence are investigated for individual turbulence mechanisms. Phase is shown to be an order of magnitude stronger than amplitude in its impact on imaging metrics. In all the analyses, piston variation and coherence diameter make up the majority o (open full item for complete abstract)

Committee: Matthew Dierking (Committee Chair); Joseph Haus (Committee Member); Eric Magee (Committee Member); Bradley Duncan (Committee Member) Subjects: Optics; Physics

Doctor of Philosophy (Ph.D.), University of Dayton, 2022, Electro-Optics

Coherent heterodyne lidar systems are used to indirectly measure the amplitude and phase of reflected optical waves. Photon-counting arrays (PCAs) are desirable for coherent sensing due to their high gain and bandwidth. However, coherent lidar systems using PCAs have extremely complex trade spaces to consider when designing a new sensor. System design tools are defined to enable performance optimization by maximizing the carrier-to-noise ratio (CNR) while also minimizing the data rates. These tools include the arm probability which is used to calculate the PCA CNR. Additionally, the output data rates are presented assuming a fire map readout architecture is implemented. The CNR and data rates of these unique systems are analyzed to demonstrate the tradeoffs for various detector parameters. Traditional coherent sensing design paradigms are reexamined using a frequency modulated continuous wave (FMCW) heterodyne lidar system as a baseline. The high gain and bandwidth of PCAs results in lower required local oscillator (LO) energies to increase performance. Using a newly defined ratio of CNR to data rate metric, analytic expressions for the LO flux which optimizes performance are presented. Ultimately, sparse coherent signals can be extracted from PCA outputs, using multiple orders of magnitude less recorded data than a traditional coherent detector.

Committee: Edward Watson (Committee Chair); Kevin Holman (Committee Member); Partha Banerjee (Committee Member); David Rabb (Committee Member) Subjects: Engineering; Optics

Doctor of Philosophy (PhD), Wright State University, 2022, Computer Science and Engineering PhD

Synthetic Aperture LADAR (SAL) has several phenomenology differences from Synthetic Aperture RADAR (SAR) making it a promising candidate for automatic target recognition (ATR) purposes. The diffuse nature of SAL results in more pixels on target. Optical wavelengths offers centimeter class resolution with an aperture baseline that is 10,000 times smaller than an SAR baseline. While diffuse scattering and optical wavelengths have several advantages, there are also a number of challenges. The diffuse nature of SAL leads to a more pronounced speckle effect than in the SAR case. Optical wavelengths are more susceptible to atmospheric noise, leading to distortions in formed imagery. While these advantages and disadvantages are studied and understood in theory, they have yet to be put into practice. This dissertation aims to quantify the impact switching from specular SAR to diffuse SAL has on algorithm design. In addition, a methodology for performance prediction and template generation is proposed given the geometric and physical properties of CAD models. This methodology does not rely on forming images, and alleviates the computational burden of generating multiple speckle fields and redundant ray-tracing. This dissertation intends to show that the performance of template matching ATRs on SAL imagery can be accurately and rapidly estimated by analyzing the physical and geometric properties of CAD models.

Committee: Michael Raymer Ph.D. (Advisor); Krishnaprasad Thirunarayan Ph.D. (Committee Member); Vincent Velten Ph.D. (Committee Member); Brian Rigling Ph.D. (Committee Member); Fred Garber Ph.D. (Committee Member); Mateen Rizki Ph.D. (Committee Member) Subjects: Computer Science

Doctor of Philosophy (Ph.D.), University of Dayton, 2021, Electro-Optics

This research presents methods and results of characterizing and correcting PIN photodiode 3D flash LiDAR cameras, with the goal of significantly simplifying and improving the calibration system design. 3D flash LiDAR detectors use time to digital conversion (TDC) circuits to estimate the time of flight of a pulse when a detection threshold is met. As the underlying time to digital conversion (TDC) circuits require more space and power, these circuits will cause, in high bus loading events, electronic crosstalk. These events are more likely to occur in situations where many detectors simultaneously trigger, something that can occur when viewing a flat object head-on with uniform illumination, thus limiting these sensors to image a full frame due to this simultaneous ranging crosstalk noise (SRCN). Solutions were devised including using a windowed region of interest to mitigate additional noise by preventing triggering on all of the focal plane array (FPA) except the windowed region, and methods using a checkerboard pattern for imaging the full frame, including using a physical target downrange and a spatial light modulator.

Committee: Paul McManamon (Committee Chair); Edward Watson (Committee Member); Russell Hardie (Committee Member); Andrew Huntington (Committee Member) Subjects: Optics

Doctor of Philosophy (PhD), Wright State University, 2020, Electrical Engineering

Synthetic aperture ladar (SAL) is an emerging remote sensing technology capable of providing high-resolution, interpretable, and timely imagery. SAL and synthetic aperture radar (SAR) are similar in that they provide high-resolution imagery suitable for a wide-variety of applications beyond the diffraction limit of the real aperture. Several advantages of SAL are; realistic imagery resulting from diffuse scattering of optically-rough objects, fine directionality of laser beam making the technology inherently low probability-of-detect, and shorter synthetic aperture collection times, all of which result from operating at optical as opposed to RF wavelengths. With the dramatic decrease in wavelength, SAL systems become more susceptible to phase errors induced by platform motion, vibration, and atmospheric turbulence. In this research effort, we focus on mitigating the detrimental effects of atmospheric turbulence on SAL image quality. We show that traditional autofocusing algorithms; Phase Gradient Autofocus (PGA), Sharpness-based Autofocus, and Sparsity Driven Autofocus (SDA), are unable to mitigate atmospheric phase errors due to their spatially-variant nature. We overcome the challenge imposed by spatially-variant atmospheric phase errors through the use of a model-based image reconstruction framework. Utilizing this framework we implement three different spatially-variant model error correction algorithms; Moving Target Autofocus (MTA), Spatially-variant Phase Correction (SVPC), and Model-based Atmospheric Phase Correction (MBAPC) algorithms. The MTA algorithm is a spatially-variant phase error estimation algorithm originally designed for focusing moving targets in SAR. We develop an image-quality metric (IQM) based parameter tuning algorithm that enables the success of the MTA algorithm for the unique challenges presented by atmospheric phase errors. Both SVPC and MBAPC are spatially-variant model error correction algorithms developed to handle atmospheric pha (open full item for complete abstract)

Committee: Arnab K. Shaw Ph.D. (Advisor); Brian D. Rigling Ph.D. (Committee Member); Michael A. Saville Ph.D. (Committee Member); Partha P. Banerjee Ph.D. (Committee Member); Matthew P. Dierking Ph.D. (Committee Member) Subjects: Electrical Engineering; Remote Sensing

Master of Science (M.S.), University of Dayton, 2020, Aerospace Engineering

Velocity measurement inside of a wind tunnel is an extremely useful quantitative data for a multitude of reasons. One major reason is that velocity has a mathematical relationship with dynamic pressure which in turn influences all the aerodynamic forces on the test model. Many devices and methods exist for measuring velocity inside wind tunnels. At the same time, Doppler wind lidar (light detection and ranging) has been used for decades to make air speed measurements outdoors at long ranges. Lidar has been proven effective for many applications, and it has the potential to solve many of the problems faced by current velocimetry techniques inside wind tunnels. Despite this, minimal research has been performed with Doppler wind lidars inside wind tunnels. While multiple commercial systems exist for making air speed measurements at longer ranges, there are currently no widely available commercial devices designed to work well inside wind tunnels. In this research, initial work is described for the design and development of a continuous wave (CW), coherent wind lidar system. The system is for use as an alternative non-intrusive velocimetry method inside wind tunnels relying on the Doppler effect. A scaled down wind lidar designed to operate at much shorter ranges than current commercial wind lidars can be simpler, less expensive, and require less power. A first iteration of the design was constructed for proof of concept testing with a small-scale wind tunnel at low speeds (7.5-9 m/s). Testing showed that the lidar system could take one-dimensional speed measurements of seeded flow that closely matched Pitot static tube data. When not adding tracer particles to the flow, the lidar return signal was not strong enough for the photodetector used to measure the beat frequency. This research is focused on the process for designing the Doppler wind lidar system, constructing the experimental setup, and studying methods for data analysis. Results of testing presente (open full item for complete abstract)

Committee: Sidaard Gunasekaran (Advisor); Aaron Altman (Committee Member); Paul McManamon (Committee Member) Subjects: Aerospace Engineering; Atmosphere; Atmospheric Sciences; Engineering; Optics; Technology

Doctor of Philosophy (Ph.D.), University of Dayton, 2019, Electro-Optics

This research demonstrates registration algorithms specific to multi-pixel imaging Inverse Synthetic Aperture LiDAR (ISAL) complex data volumes. Two registration approaches are considered, a mutual information registration algorithm (MIRA) and an enhanced, range bin-summed cross-correlation algorithm. For implementing these in the context of an ISAL signal, a theoretical mapping of the reflected target plane field to an aperture plane for multi-pixel detection is done. The theory for implementing both MIRA and cross-correlation enhancements is detailed and applied to a simulated sensitivity analysis that compares algorithm convergence and performance for different SNR, sub-aperture shift distances, and low pixel supports. To the best of the authors' knowledge, this is the first application of 3D complex volume mutual information registration to LiDAR aperture synthesis. The enhanced cross-correlation algorithm showed significant gain in registration operability with respect to SNR and sub-aperture shift, giving new options for potential ISAL system design. An experimental Flash LiDAR system was constructed utilizing a multi-pixel temporal heterodyne detection approach for simultaneous azimuth, elevation, range and phase ISAL imaging of a target and this system was used to benchmark registration sensitivity for real data volumes. This is the first known application of a fast focal plane array for low support flash temporal heterodyne LiDAR for aperture synthesis.

Committee: Matthew Dierking Ph.D. (Advisor); Partha Banerjee Ph.D. (Committee Member); David Rabb Ph.D. (Committee Member); Bryce Schumm Ph.D. (Committee Member); Edward Watson Ph.D. (Committee Member) Subjects: Electrical Engineering; Optics; Physics

Master of Science in Electrical Engineering (MSEE), Wright State University, 2018, Electrical Engineering

Synthetic aperture ladar (SAL) is similar to synthetic aperture radar (SAR) in that it can create range/cross-range slant plane images of the illuminated scatters; however, SAL has wavelengths 10,000x smaller than SAR enabling a relatively narrow real aperture, diffraction limited beam widths. The relatively narrow real aperture resolutions allow for multiple slant planes to be created for a single target with reasonable range/aperture combinations. These multiple slant planes can be projected into a single slant plane projections (as in SAR). It can also be displayed as a 3-D image with asymmetric resolutions, diffraction limited in the dimension orthogonal to the SAL baseline. Multiple images with diversity in angle orthogonal to SAL baselines can be used to synthesize resolution with tomographic techniques and enhance the diffraction limited resolution. The goal of this research is to explore methods to enhance the diffraction limited resolutions with multiple observations and/or multiple slant plane imaging with SAL systems. Specifically, metrics associated with the information content of the tomographic based 3 dimensional reconstructions of SAL intensity imagery will be investigated to see how it changes as a function of number of slant planes in the SAL images and number of elevation observations are varied. Approved for public release, distribution unlimited (APRS-RY-18-0785)

Committee: Arnab Shaw Ph.D. (Advisor); Lawrence Barnes M.S. (Committee Member); Joshua Ash Ph.D. (Committee Member) Subjects: Electrical Engineering

Master of Science (M.S.), University of Dayton, 2018, Electro-Optics

In this thesis, Electro-Optic (EO) range signatures are obtained with a Short-Wave Infrared Super-Continuum Laser (SWIR-SCL) source. 3D printed canonical targets of interest are illuminated by the SWIR-SCL pulsed laser. The scattered laser light from the target is directly detected in mono-static and bi-static configurations with a fast, high bandwidth Indium Gallium Arsenide (InGaAs) PIN photodiode. Temporal pulse returns provide target shape, orientation, and surface roughness information. Spatial and temporal analysis of the collected intensity distribution is performed in MATLAB. Macro and micro surface properties are identified from the collected data by correlating pulse amplitude variations with known range scenes. Finally, range resolution improvement is investigated by means of Tomographic Reconstruction using Radon Transforms and by image processing techniques such as Deconvolution.

Committee: Edward Watson Ph.D. (Advisor); Paul McManamon Ph.D. (Committee Member); Joe Haus Ph.D. (Committee Member) Subjects: Computer Engineering; Electrical Engineering; Engineering; Experiments; Optics; Physics; Scientific Imaging

Master of Science (M.S.), University of Dayton, 2018, Electro-Optics

Imaging through obscurants is a critical issue for lidars looking through clouds, or human tissue. Traditionally Spatial heterodyne imaging has been performed with a low-bandwidth laser source that exhibits good coherence length characteristics. One of the drawbacks of using a low-bandwidth source with long coherence length is that signal return from all objects within the coherence length of the source mix equally well on the camera imaging the system. Broadening the bandwidth of the source shortens the coherence length of the system. This thesis intends to show that through careful system design, spatial heterodyne imaging can be performed in the presence of a broadband source, allowing significantly improved imaging in the presence of obscurants such as clouds or human tissue. The method used will be phase modulating the source with a pseudo-random bit sequence and matching the optical path lengths of the signal and local oscillator branches of the system. By matching the path lengths for a pseudo-random coded source we can image objects at specific distances related to the modulation speed and code length, while isolating the power of signal return from objects at other distances as a factor of the autocorrelation coefficient of the code.

Committee: Paul McManamon Ph. D. (Advisor); Edward Watson Ph. D. (Committee Member); Partha Banerjee Ph. D. (Committee Member) Subjects: Electrical Engineering; Engineering; Optics; Remote Sensing

Doctor of Philosophy (Ph.D.), University of Dayton, 2016, Electro-Optics

3-D holographic ladar uses digital holography with frequency diversity to allow the ability to resolve targets in range. A key challenge is that since individual frequency samples are not recorded simultaneously, differential phase aberrations may exist between them making it difficult to achieve range compression. Specific steps for this modality are described so that phase gradient algorithms (PGA) can be applied to 3-D holographic ladar data for phase corrections across multiple temporal frequency samples. Substantial improvement of range compression is demonstrated in a laboratory experiment where our modified PGA technique is applied. Additionally, the PGA estimator is demonstrated to be efficient for this application and the maximum entropy saturation behavior of the estimator is analytically described. Simultaneous range-compression and aperture synthesis is experimentally demonstrated with a stepped linear frequency modulated waveform and holographic aperture ladar. The resultant 3D data has high resolution in the aperture synthesis dimension and is recorded using a conventional low bandwidth focal plane array. Individual cross-range field segments are coherently combined using data driven registration, while range-compression is performed without the benefit of a coherent waveform. Furthermore, a synergistically enhanced ability to discriminate image objects due to the coaction of range-compression and aperture synthesis is demonstrated. Two objects are then precisely located in 3D space, despite being unresolved in two directions, due to resolution gains in both the range and azimuth cross-range dimensions.

Committee: Bradley Duncan Ph.D. (Committee Chair); David Rabb Ph.D. (Advisor); Joseph Haus Ph.D. (Advisor); Matthew Dierking Ph.D. (Advisor) Subjects: Electrical Engineering; Optics; Physics; Remote Sensing

Master of Science in Engineering (MSEgr), Wright State University, 2014, Electrical Engineering

Classification algorithms trained using finite sets of target and confuser data are limited by the training set. These algorithms are trained under closed set assumptions and do not account for the infinite universe of confusers found in practice. In contrast, classification algorithms developed under open set assumptions label inputs not present in the training data as unknown instead of assigning the most likely class. We present an approach to open set recognition, the probabilistic open set SVM, that utilizes class posterior estimates to determine probability thresholds for classification. This is accomplished by first training an SVM in a 1-vs-all configuration on a training dataset containing only target classes. A validation set containing only class data belonging to the training set is used to iteratively determine appropriate posterior probability thresholds for each target class. The testing dataset, which contains targets present in the training data as well as several confuser classes, is first classified by the 1-vs-all SVM. If the estimated posterior for an input falls below the threshold, the target is labeled as unknown. Otherwise, it is labeled with the class resulting from the SVM decision. We apply our method to classification of synthetic ladar range images of civilian vehicles and measured infrared images of military vehicles. We show that the POS-SVM offers improved performance over other open set algorithms by allowing the use of nonlinear kernels, incorporating intuitive free parameters, and empirically determining good thresholds.

Committee: Brian Rigling Ph.D. (Advisor); Fred Garber Ph.D. (Committee Member); Arnab Shaw Ph.D. (Committee Member) Subjects: Electrical Engineering

Master of Science in Engineering (MSEgr), Wright State University, 2012, Electrical Engineering

We consider the problem of LADAR ATR classifier performance prediction in the presence of arbitrary nuisance parameters including but not limited to pose. We use several noise models for both range images and point clouds that are significantly more accurate and complex than the Gaussian models used by previous non-Monte Carlo prediction methods. Two accurate new methods of efficiently predicting the optimum Bayesian classification performance are then derived, and applied to the noise models. Advantages of these methods include significant gains in accuracy for medium to high noise levels and the ability to handle target near symmetry. Extensions are developed for multiple targets and predicting the performance of classifiers designed using incorrect noise models. We also derive several simple analytic approximations for the behavior of the probability of error as important sensor and noise parameters vary. Finally, we verify the accuracy of our predictions using Monte Carlo simulations.

Committee: Brian Rigling PhD (Advisor); Frederick Garber PhD (Committee Member); William Pierson PhD (Committee Member) Subjects: Electrical Engineering

Master of Science (MS), Ohio University, 2006, Electrical Engineering & Computer Science (Engineering and Technology)

Airborne Laser Scanning (ALS) has been used extensively to collect dense clouds of terrain and feature points to generate accurate Digital Elevation Models (DEMs) and feature databases. To enable the use of an ALS-based terrain navigation system for autonomous aircraft navigation, continuous availability of the system must be ensured. The most important factor affecting the availability and reliable operation of ALS-based systems are weather effects. Weather conditions like fog, cloud cover, rain, and snow affect the availability, continuity and accuracy of the system when used for navigation purposes. This thesis focuses on the scattering of light by atmospheric particulates and its effects on the ALS ranging and target detection. It discusses the phenomenon of light scattering, important relations concerning ALS and laser ranging, the theories and equations governing it. Data were collected under various weather conditions with an experimental ALS setup at the Ohio University airport, Albany, OH. The processed data helped us analyze the intensity variation with range, thus serving as a performance characterization tool for the ALS system, enabling performance analysis of ALS-based terrain navigators.

Committee: Maarten Uijt de Haag (Advisor) Subjects:

Doctor of Philosophy (PhD), Ohio University, 2006, Electrical Engineering & Computer Science (Engineering and Technology)

This dissertation explores the use of an Airborne Laser Scanner (ALS) for use in aircraft Terrain-Referenced Navigation (TRN). Position estimation techniques developed in this dissertation enable the use of large sets of high accuracy ALS measurements to solve for position in real-time. The explored techniques were then used to design, implement, and - for the first time ever - fly a real-time ALS-based TERRain Aided Inertial Navigator (TERRAIN) precision approach system. During the flight tests, the system provided meter-level horizontal and vertical positioning accuracies in real-time. The ALS-based TRN techniques discussed in the dissertation are constrained to the information found in the terrain shape domain. The data acquisition, pre-processing, and position estimation techniques of ALS TRN vary significantly from traditional radar altimeter-based TRN primarily due to differences in the measurement mechanism used in both TRN systems. First, traditional radar altimeter-based TRN senses the terrain contours traversed in the along-track direction, whereas ALS-based TRN makes measurements in the along-track and in the cross-track directions. The second difference is that the ALS laser's milli-radian beamwidth has sufficient resolution to identify not only the ground, but also objects on the ground such as buildings. A radar altimeter with a beamwidth of several degrees can not observe the same level of detail. These differences increase the spectral content of the ground measurement data in the ALS-based system thus permitting high-accuracy position estimates. The described ALS TRN navigation techniques include methods to estimate the position based on the best match between ALS data and a high resolution/accuracy terrain database. Finally, the dissertation explores the certification path for an ALS-based landing system.

Committee: Maarten Uijt de Haag (Advisor) Subjects:

Master of Science (M.S.), University of Dayton, 2012, Electro-Optics

The cross-range resolution of a laser radar (ladar) system can be improved by synthesizing a large aperture from multiple smaller sub-apertures. This aperture synthesis requires a coherent combination of the sub-apertures; that is, the sub-apertures must be properly phased and placed with respect to each other. One method that has been demonstrated in the literature to coherently combine the sub-apertures is to cross-correlate the speckle patterns imaged in overlapping regions. This work investigates the effect of low signal to noise ratio (SNR) on an efficient speckle cross-correlation registration algorithm with sub-pixel accuracy. Specifically, the algorithms ability to estimate relative piston and tilt errors between sub-apertures at low signal levels is modeled and measured. The effects of these errors on image quality are examined using the modulation transfer function (MTF) as a metric. The results demonstrate that in the shot noise limit, with signal levels as low as about 0.02 signal photoelectrons per pixel in a typical CCD, the registration algorithm estimates relative piston and tilt accurately to within 0.1 radians of true piston and 0.1 waves of true tilt. If the sub-apertures are not accurately aligned in the synthetic aperture, then the image quality degrades as the number of sub-apertures increases. The effect on the MTF is similar to the effects due to defocus aberrations.

Committee: Edward Watson PhD (Advisor); Matthew Dierking PhD (Committee Member); David Rabb PhD (Committee Member) Subjects: Engineering; Optics; Remote Sensing; Scientific Imaging

Doctor of Philosophy (Ph.D.), University of Dayton, 2012, Electro-Optics

The use of a saturated Semiconductor Optical Amplifier (SOA) as both a phase modulator and an amplifier for long range laser radar applications is explored. As will be discussed, this concept could reduce the hardware necessary to transmit high bandwidth pulses and allow for the transmission of shorter pulses that are less sensitive to the detrimental effects of target motion. After reviewing the concepts governing ranging, vibrometry, and synthetic aperture ladar, the nature of the phase and amplitude modulation from saturating an amplifier with a high peak power Gaussian pulse is explored. The key SOA parameters affecting the modulation of the output pulse are addressed and optimized, and their impact on the ideal pulse response of a laser radar system is explored. Proof of concept laboratory demonstrations using phase modulated pulses to interrogate stationary, vibrating, and translating targets are also presented. The concept of using a saturated SOA to enable short-pulse synthetic aperture ladar and vibrometry is also explored. This research will show that the range resolution of a ladar system can be optimized by saturating a SOA with a carrier lifetime that is one half the FWHM Gaussian input pulse duration, yielding a substantial improvement in range resolution that is highly insensitive to variations in the input pulse duration and energy.

Committee: Bradley D. Duncan PhD (Committee Chair); Matthew P. Dierking PhD (Committee Member); Peter E. Powers PhD (Committee Member); Robert P. Penno PhD (Committee Member) Subjects: Electrical Engineering; Optics

Master of Science (M.S.), University of Dayton, 2012, Electro-Optics

Holographic aperture ladar (HAL) is a variant of synthetic aperture ladar (SAL). The two processes are related in that they both seek to increase cross-range (i.e., the direction of the receiver translation) image resolution through the synthesis of a large effective aperture – which is in turn achieved via the translation of a receiver aperture and the subsequent coherent phasing and correlation of multiple received signals. However, while SAL imaging incorporates a translating point detector, HAL takes advantage of two-dimensional translating sensor arrays. For the research presented in this article, a side looking Stripmap HAL geometry was used to sequentially illuminate a set of Ronchi ruling targets. Prior to this, theoretical calculations were performed to determine the baseline, single sub-aperture resolution of our experimental, laboratory based system. Theoretical calculations were also performed to determine the ideal modulation transfer function (MTF) and expected cross-range HAL image sharpening ratio corresponding to the geometry of our apparatus. To verify our expectations, we first sequentially captured an over-sampled collection of pupil plane field segments for each Ronchi ruling. A HAL processing algorithm was then employed to phase correct and re-position the field segments after which they were properly aligned through a speckle field registration process. Relative piston and tilt phase errors were then removed prior to final synthetic image formation. By then taking the Fourier transform of the synthetic image intensity and examining the fundamental spatial frequency content, we were able to produce experimental modulation transfer function curves which we could then compare to our theoretical expectations. Our results show that we are able to achieve nearly diffraction limited results for image sharpening ratios as high as 6.43

Committee: Brad Duncan PhD (Committee Chair); Matt Dierking PhD (Committee Member); Joe Haus PhD (Committee Member) Subjects: Optics

Master of Science (M.S.), University of Dayton, 2011, Electro-Optics

In stretch processing (SP) both the local oscillator (LO) and the transmitted signal are linearly frequency modulated (LFM). A heterodyne detection process is performed using the LO and the received echo signal, which create a detected signal at a single difference-frequency. The frequency is proportional to the distance the received echo signal travels relative to the LO signal, and the range resolution is inversely proportional to the bandwidth making large bandwidth LFM chirps favorable. However, it is difficult to maintain linearity over a lager bandwidth LFM chirp. On the other hand small bandwidth LFM chirps can be easily produced, so the idea of segmenting the transmitted pulse into multiple small non-overlapping frequency LFM chirps was conceived. The extended frequency bandwidth is recovered in post processing. This technique is called multi-frequency stretch processing (MFSP). The procedure outlined is a practical method to achieve greater range resolution using less expensive technology. Another advantage of this technique is the similar modulation noise on each LFM chirp. The multiple signals are processed using an algorithm developed for extracting the additional bandwidth information. The range resolution is related to the time span and bandwidth of the LFM pulses. For n transmitted LFM chirped signals the range resolution is nearly n times longer. Moreover the required detection bandwidth of the echo signal is lower than for other LFM processing systems without a chirped LO signal.

Committee: Joseph Haus PhD (Advisor); Matthew Dierking PhD (Committee Chair); Peter Powers PhD (Committee Member) Subjects: Electrical Engineering; Optics; Physics