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Physics-based Near-field Microwave Imaging Algorithms for Dense Layered Media

出版	Ohio State University, 2017
URL	http://books.google.com.hk/books?id=SR9DvwEACAAJ&hl=&source=gbs_api

註釋It is of importance to understand the physics as electromagnetic (EM) waves propagate through stratified media, are scattered back from buried irregularities, and are received by an antenna in the near field. To generate better images, we need to incorporate the physics of the phenomena into the imaging algorithm, such as multiple reflections, refractions resulting from the existence of interfaces, and diffractions from embedded targets. A forward model is developed based on the spectral Green's function associated with layered media weighted by the antenna gain pattern, satisfying the near-field condition and incorporating all refraction effects. Thereby, the weak scattering from deeper layers and wide angles will be compensated in a model-based imaging algorithm with the consideration of the refraction coefficients and gain pattern, respectively. To form real-time continuous images of targets embedded in a layered structure, a near-field uniform diffraction tomographic (UDT) imaging algorithm is developed. Conventional diffraction tomography (DT) improperly applies the stationary phase method for stratified environments to evaluate the innermost spectral integral. In DT the large argument is assumed to be the depth, which is not appropriate for near-field imaging. This results in amplitude discontinuities occurring at the interfaces between adjacent layers. The correct dimensionless large argument is the product of the free space wavenumber and the depth, as used in high-frequency asymptotic solutions. UDT therefore yields uniformly continuous images across the interfaces. And like DT, UDT retains the fast Fourier transform (FFT) relation in the algorithm for generating images very efficiently. Both 2D and 3D cases are investigated to verify the efficacy of the proposed UDT algorithm.