Study On Airborne SAR/ISAR Imaging Of Ship

Synthetic aperture radar(SAR) is a kind of widely used high-resolution imaging radar.Imaging of the ship on the sea is an important one in the application of SAR imaging. The imaging of the ship on the sea can be used for monitoring and control of fishing vessels, cargo ships, etc., and it can also be used in the identification and tracking of warships. SAR imaging assumes that the target is stationary and the motion of the target causes the target to be defocused on the SAR image. Ship usually has a certain speed, and due to the role of surface waves, the ship will be swinging. The movement of the ship will ultimately cause its image can’t focus very well in the SAR image, Therefore, the resolution of the image of the ship is not high. Aiming at this problem, the following research is carried out in this paper:(1) Study of SAR imaging algorithm. Two classic algorithms RD algorithm, CS algorithm are analyzed. Then,the simulation and imaging based on measured data of the two methods is carried out.(2) Study of Doppler parameter estimation. Because of the error of motion parameters measured by the sensor in the measured data, the quality of the SAR image can be influenced when the parameters is used. In order to improve the quality of the image, the Doppler parameter estimation method is studied. Correlative function algorithm is studied to estimate Doppler center and Map Drift algorithm is studied to estimate the Doppler rate. Finally, the imaging results with the estimation of Doppler parameters are given, and the quality of the imaging results is improved.(3) Study of the refocusing method of defocused ship in SAR images. Aiming at the defocused problem of moving ship in SAR image, the SAR/ISAR hybrid algorithm was used to re image the ship. Firstly, the motion compensation method of ISAR is introduced. ISAR motion compensation method includes range alignment and phase compensation. In the method of range alignment Cross correlation method is introduced. In the method of phase compensation, Dominant scatterer algorithm, Doppler center tracking method, Phase gradient autofocus method is introduced. Secondly, the similarities and differences between SAR and ISAR are analyzed.Then,the feasibility of using ISAR method to deal with the moving targets in SAR data is analyzed and the simulation is carried out, The results show that the ISAR method can be used to get a clear image of the moving targets. Third, the SAR/ISAR hybrid algorithm is used for the imaging of the ship. The method of extracting ship data from SAR data and the imaging process are presented firstly.Then, the measured data are processed by the SAR/ISAR hybrid algorithm, and the results show that the SAR/ISAR hybrid algorithm can effectively improve the quality of image of the ship and results verify the validity of the algorithm.Finally, in view of the situation of non stationary motion of the ship, the Range instantaneous Doppler method is applied to the hybrid imaging method.