Impulse Pulse Sar Imaging Theories And Methods

The purpose of this thesis is to investigate the theory and algorithm of microwave target image formation with ultra-wideband(UWB) impulse SAR(ImpSAR). Projection reconstruction for the far field applications and wavefront reconstruction for the near field applications of the ImpSAR are addressed according to the target scattering center model. It is shown that the spectrum of the backward scattering signal of a rotating target is a slice of the spectrum of the scattering intensity function of the target in the corresponding aspect of the system, weighted by the spectrum of the incident signal. Based on this analysis, the ImpSAR projection reconstruction theory is presented. The corresponding image formation algorithms, both in tune domain and frequency domain, are introduced. Beginning with the projection reconstruction theory, Convolution-Backprojection and its approximated algorithm, Backprojection algorithm are given. Because of the equivalence of spotlight SAR and rotating target imaging, the ImpSAR projection reconstruction theory can be successfully used in spotlight ImpSAR. With Point Spread Function(PSF), the analytical expression of imaging resolution of the Ultra-Wideband (UWB) signal for both 360?and small angle rotating target are given. The ImpSAR wavefront reconstruction theory takes into account of the propagation property of spherical wave. Therefore, it can be used to interpret both the near field and far field ImpSAR applications. Based on this theory, the Fourier Transform based wavefront reconstruction algorithms, w-k and Soumekh algorithms, are discussed. Again, beginning with wavefront reconstruction theory, a time domain ImpSAR image formation algorithm, B-P algorithm, is derived. It is shown that the ImpSAR B-P algorithm in time domain is theoretically equivalent to Soumekh algorithm in frequency domain. In the far field ImpSAR application or if the relative bandwidth of the system is not very large, w - k is also equivalent to B-P. In this thesis, ImpSAR B-P is focused and modified with the considerations of the electromagnetic wave dispersion, synthetic aperture windowing and IQ channel realization in real time applications. The modified B-P, WB-P, is very efficient for the complicated application scenario, such as ImpSAR, GPR, where the imaging system moves along a fluctuated path. A WB-P fast algorithm, named Pure Backprojection (PB-P), is presented. This new algorithm speed up the image formation more significantly than the original one. Different from the other kinds of UWB signal, the radiation and picking up of the impulse signal has a very special property, time and space coupling. In this thesis, the effects of the coupling on ImpSAR image formation are analyzed quantitatively. A UWB time domain transient field measurement system, UWB-MCE, is used in the imaging experiments. The imaging results verify the correction of the theoretical analysis and efficiency of the algorithms presented in this thesis.