Tapping space and spacing taps: Topics in radar-astronomy imaging and sparse filter design
Webb, Jennifer Lois Harmon
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https://hdl.handle.net/2142/21062
Description
Title
Tapping space and spacing taps: Topics in radar-astronomy imaging and sparse filter design
Author(s)
Webb, Jennifer Lois Harmon
Issue Date
1995
Doctoral Committee Chair(s)
Munson, David C., Jr.
Department of Study
Electrical and Computer Engineering
Discipline
Electrical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Electronics and Electrical
Language
eng
Abstract
This dissertation addresses topics in the areas of synthetic aperture radar (SAR) and finite impulse-response (FIR) digital filter design.
This investigation of SAR was based on a tomographic viewpoint. An existing form of spotlight-mode SAR processing was applied to a radar-astronomy application, forming images of the moon's surface from radar-astronomy data collected at Arecibo Observatory. In doing so, high-quality images were obtained while significantly reducing the number of computations required. It was found that a slight degradation was caused by arcing in the radar path.
This discovery led to a detailed investigation of the impact of radar maneuvers on SAR image formation. A method for improving image quality was developed, based on a piecewise-linear model for the radar path. To determine the number of segments required, and the appropriateness of this model, constraints were derived for the length of the linear path segments. The method was demonstrated for 1-D images with point scatterers and extended targets.
Another study, motivated by the problem of imaging asteroids, involved the formation of 3-D SAR images using limited data. When the surface reflectivity is known to be concentrated on the surface, it is possible to cast this problem into the framework of an angle-of-arrival or spectral-estimation problem. Thus, techniques such as ESPRIT and RELAX can be applied to form the sparse 3-D image. The image-formation method was demonstrated through simulation.
Other work deals with FIR digital filter design. These studies involved designing filters for which some of the tap weights are constrained to be zero. First, cases were considered where the locations of the zeroed tap weights are known; linear programming was used to optimize the remaining tap weights. If the goal is to reduce the number of multiplications, the locations of the zeroed tap weights must be determined first. For a class of filters, these locations were determined and a sparse direct-form filter was designed using linear programming. A second new design method was developed for filters implemented with cascades of sparse and nonsparse sections.
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