MS, University of Cincinnati, 2001, Arts and Sciences : Physics

Radio astronomy is the science of collecting extra-terrestrial radiation in the range of 15 MHz to 600 GHz to gain understanding of celestial objects. In this thesis I discuss both the single parabolic reflector radio telescope and the two-telescope radio interferometer used in radio astronomy. The total power received by a parabolic reflector is dependent on the size of the antenna, the efficiency of the reflector, the wavelength of light under observation, and the angular response of the antenna, called the "normalized power pattern". Diffraction effects limit the resolution of the single parabolic reflector. The two-telescope interferometer has increased resolution because the main beam that would be created by a single antenna is split into multiple beams through interference, with the width of one beam corresponding to the angular resolution of the interferometer. A commonly used typed of interferometer is the correlating interferometer that integrates the product of the voltages received at each telescope. The correlating interferometer does not measure the received power directly, but rather the Fourier transform of it called the visibility function. By taking many measurements with different baselines, the visibility function can be sampled over the Fourier transform (or u-v plane) space. The visibility function can then be inverted to create a radio map of the brightness distribution of the source.

Committee: Randy Johnson (Advisor) Subjects: Physics, Astronomy and Astrophysics

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

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 (M.S.), University of Dayton, 2015, Electro-Optics

Sparse aperture image synthesis requires proper phasing between sub-apertures. Phasing can be difficult due to hardware misalignments, atmospheric turbulence, and many other causes of optical path differences (OPD). Common synthesis techniques include incoherent and coherent methods. Incoherent methods utilize passive illumination and adaptive optics while coherent methods rely on active illumination and phase reconstruction approaches such as phase retrieval or spatial heterodyne. In this thesis, we present a partially coherent technique with the capability to use either active or passive illumination to digitally correct for piston phase errors. This technique requires an anamorphic pupil relay system and a piston correction algorithm. The anamorphic pupil relay causes two closely spaced sub-apertures in the entrance pupil to appear to be shifted further apart in the exit pupil. Analytic and numerical wave optics models demonstrate the effectiveness of this relay system, matching with experimental results. An analytic model shows that the higher frequency terms are equivalent to scaled cross-correlations of the two sub-apertures, which are shifted due to the anamorphic separation. The constant shifts due to the separation are found experimentally using a registration algorithm with a calibration target. The cross-correlations are dependent on the piston phase errors between sub-apertures. We show that a piston correction algorithm can be used to shift the cross-correlations to their original positions dictated by the entrance pupil, multiply a cross-correlation with the complex conjugate of the auto-correlation, use the summation of this product to calculate the piston, and correct the phase error in each cross-correlation before recombining them with the auto-correlation. Examples show diffraction limited results for both simulated and experimental images that are supported by analytical, numerical, and experimental analysis of the system's modulation (open full item for complete abstract)

Committee: David Rabb Ph. D (Advisor); Matthew Dierking Ph. D (Committee Member); Edward Watson Ph. D (Committee Member) Subjects: Electrical Engineering; Optics; Physics; Remote Sensing