Advanced Synthetic Ape and Feature

Synthetic aperture radar (SAR) generates a range and cross-range image when radar is moving. Inverse synthetic aperture radar (ISAR) is a variation of the SAR that generates a range-Doppler image of targets by coherently processing radar returns at different target aspect angle due to relative motions between the radar and the target [1]. The distribution of radar reflectivity over a target can be measured through the Doppler spectrum at each range bin by taking the Fourier transform over the phase history time series. If the motion or rotations are accompanied by perturbations, the phase of the returned signal becomes nonlinear. Thus, the image of the target may be degraded when using the conventional imaging algorithms. Recent efforts in ISAR polar reformatting, super-resolution spectral analysis and time-frequency based image formation offer improvements in radar imagery over the commonly used Fourier transform approach. Study of the effect of motion perturbations on ISAR imaging is important. In this paper, commercial small craft accompanying with the GPS information is used to study this effect. For SAR, if there are moving objects in the scene, it cannot simultaneously produce clear images of stationary objects as well as moving objects. The moving object appears as defocused and spatially displaced one superimposed on the SAR scene. The important issue is how to detect and focus images of a moving target in SAR. Moreover, because of the additional Doppler caused by target’s motion, the detected and focused target may not be located in its true location in the SAR scene. Many algorithms have been proposed to re-locate the detected target to its true location: some uses a single channel antenna and some uses multiple antennas. ta sig fre ef