OPTIMAL METHODOLOGIES IN INVERSE SCATTERING UTILIZING WAVELENGTH, POLARIZATION AND ANGULAR DIVERSITY

Abstract

It is well-known that the scattered electromagnetic field produced by a scattering target subjected to coherent illumination obeys Maxwell\u27s equations. The scattered field is determined by the relative positions of scattering centers on the target. A scattering center is defined as target detail that contributes to the observed field. It has been of longstanding interest in electromagnetics to investigate and develop analytical methods and measurement systems that enable one to use the information in the measured scattered field to infer the target shape, size, orientation and material properties in the context of target identification and/or classification. This problem is described by the generic term inverse scattering which is to determine the boundary conditions at the scattering target given the received scattered wavefield over a range of aspect angles and frequencies that is normally determined by practical constraints. The aim of the work described in this dissertation is the study and development of an optimal data acquisition and processing scheme for use in microwave inverse scattering techniques employing trade-off between angular, frequency and polarization diversities to collect a maximum amount of information about the scattering target cost-effectively. Efficient data processing and terminal information presentation in the form of an image interpretable by the eye-brain system are also central to this study. The use of frequency diversity over an extremely broad spectrum in coherent scattering measurements as a means of acquiring more information about the scattering target has been the subject of vigorous study at the Electro-Optics and Microwave-Optics Laboratory of the University of Pennsylvania. This dissertation represents a continuation of this effort. A variety of methods aimed at making the data acquisition and processing more efficient and cost-effective are studied. In particular, methods of deriving a phase reference signal from the target being imaged (target derived reference--TDR concept) to affect coherent detection and imaging are studied and compared. The advantages of TDR are numerous such as simplification of data acquisition, allowing considerable thinning of the imaging aperture, and elimination of Doppler and atmospheric distortions. Also the role of polarization, a priori knowledge (such as target symmetry for example), and digital image processing in image enhancement are studied extensively in an approach based on close interaction of theoretical analysis and experimental verification. . . . (Author\u27s abstract exceeds stipulated maximum length. Discontinued here with permission of author.) UM