Imaging Research Based On Hybrid SAR/ISAR

The transmittion of radar signals for target location is the primary step in Inverse synthetic aperture radar(ISAR) imaging, which also includes another procedure, which is to image with broadband radar signals. However, Synthetic Aperture Radar(SAR) can analyze and deal with the data echo scence within much bigger extendence relative to ISAR, which is called large-scence imaging capability. But severe dispersion is found in SAR when target moves despite this capability, making it difficult to detect or identify the moving target. SAR/ISAR hybrid imaging method is used in this paper to gain high resolution imaging of moving targets, which is to locate the target with SAR, to intercept the scence around the target and finally to image with ISAR.This paper describes the principles for high resolution in SAR and ISAR imaging, including the Range-Doppler(RD) algorithm of SAR, the Chrip sacling(CS) algorithm and the Range-Doppler(RD) algorithm of ISAR.After detailedly analyzing the echo signal processing procudure in SAR and ISAR, the impact of target movement on both two imaging methods is explained and verified with simulation data.In order to study ISAR image characteristics, a three axis rotation model of ship is set up with instructions and further imaging compensation. In this section, a variety of methods on range alignment and phase compensation are introduced. Besides, time-frequency analyzing method is introduced in case of complex ship movements, based on which a modified time-frequency analysis method is put forward, named as WV-SPWV filter approach.The double RD algorithm and CS-RD algorithm are interpreted respectively, with the former making it easier to eliminate platform effects via pre-treatments together with better focusing performance.There exist other target points except for the intereting target in the large-scale scence formed by SAR in the new SAR/ISAR hybrid imaging. And this will deteriorate target imaging performance when the unintereting ones are nearby. The imapcts of the nearby uninteresting points are analysed in different ways, with each one simulated and analysed. And the solution for each imapct is f inally deduced in the hybrid SAR/ISAR.Finally, the proposed hybrid algorithm is validated by real data, demonstrating the feasibility and effectiveness of the algorithm. During the study, it is also discovered that the target location and imaging performance varies greatly with different algorithms and compensation methods. At the same time, the intercepting area size and position affects the ISAR imaging consequences as well. To sovle this problem, an automatic target searching and intercepting algorithm is also proposed in this paper, which endows the hybrid SAR/ISAR algorithm with more certain practicability.