Study On Hybrid SAR/ISAR Imaging Of Ship Target Based On Spotlight SAR

Spotlight SAR is an important mode in synthetic aperture radar imaging, mainly used for more detailed observations of sma ll specific area. Through regulating and controlling the beam direction, the spotlight SAR illuminate the target area with continuous long time to get more high azimuth resolution. But because of the longer residence time, the aircraft’s motion error flying in the residence time will cause more serious impact on the imaging result, which requires more detailed analysis for the aircraft motion error, just in order to further study the motion compensation problems. In addition, when imaging the moving target,like the ship on the sea, the traditional motion compensation and imaging algorithm are not enough, the target’s movement will lead to defocusing phenomenon in image. To solve these two problems, this paper has carried out the research on spotlight SAR imaging algorithm.The specific contents of the research are as follows:1. First is the introduction of the various motion errors of aircraft detailed, analysis of the impact caused by the errors, and then it’s formula derivation of the aircraft’s position errors for further compensation process.2. Secondly, before imaging of the static ship target, the aircraft’s inertial navigation data need to be preprocessed, including coordinate transformation of the GPS data and smoothing process of the displacement data.3. Thirdly, in the squint mode, Imaging the static ship target with PFA algorithm, and it includes rectification oblique azimuth direction and interpolation processing, to eliminate the coupling of distance and azimuth direction and so on. Then processing for PFA imaging results with phase compensation autofocus algorithm, using PGA algorithm to realize the correction of the high order phase error. The sub aperture adjustable frequency estimation is added, and the phase of distance direction is compen sated with MD-PGA autofocus processing. Using the procedures above to process the measured data, and the image result obtained shows that the method is correct.4. Finally, Consider about the problems of moving target spotlight SAR imaging, scattering point model was established to simulate the ship’s shape and motion equations, as the ship’s motion simulation. A spotlight SAR imaging algorithm based on hybrid SAR / ISAR processing of the moving target is proposed, first using traditional SAR compensation a lgorithm to compensate the motion errors of aircraft’s platform, and then using the ISAR motion compensation method to compensate for the moving target’s translational motion. The simulation results show the effectiveness of the proposed method.