Translational motion compensation and instantaneous Imaging of ISAR maneuvering target

Inverse Synthetic Aperture Radar (ISAR) imaging of maneuvering target has received much attention in recent years. In the paper, we first discuss translational motion compensation (TMC), which can be decomposed into two step: envelope alignment and autofocus. There are many effective algorithms for these two step, but most of algorithms are only suitable to steadily flying targets. The analysis of the paper shows that the envelope alignment algorithms for steadily flying targets are still effective for maneuvering targets, but most of autofocus algorithms are not work very well, especially when the maneuverability is great, so this paper also presents a new autofocus algorithm based on coherent intergation to solve this problem. Then after TMC, we discuss imaging problem of maneuvering target, in fact, it is a instantaneous spectrum estimation problem, most of instantaneous ISAR imaging methods of maneuvering target are based on time-frequency distribution, and suppose scatterer echo has constant amplitude and linear frequency modulation. In fact, when target has dihedrals and trihedrals component, or scatterer' migration through resolution cells (MTRC) exists, these situation all will cause the amplitude is not a constant. For maneuvering target, scatterer echo's Doppler is time varying, usually, its time-frequency distribution can be regard as linear or part linear. So we propose a instantaneous ISAR imaging method based on multicomponent amplitude modulation and linear frequency modulation(AM-LFM) signal's parameter estimation, this method first estimates the chirp rate of one component by dechirping, then demodulates this component to a sinusoidal signal, separates and cleans this component in Fourier domain, and estimates instantaneous amplitude, then for next component, finally we get all the scattterers instantaneous amplitudes and frequencies, and the instantaneous ISAR images are obtained now.