Research On Imaging Algorithm For Squint SAR

Synthetic aperture radar(SAR)is a high-resolution imaging system by means of pulse compression technique and synthetic aperture principle.Environment has little influence to the accuracy of image.So SAR has been widely used in civil application and military fields.Compared to side-glance SAR,Squint SAR imaging is more changeable.Squint SAR can detect the target of the ground area in advance and return to the desired area again.Squint SAR with curved trajectory and constant acceleration can accurately strike the ground target as missile leader,so it has a high practical significance.Based on the basic principles of SAR imaging,this article has conducted a depth study of Squint SAR with curved trajectory and constant acceleration.The main contents of arrangements are as follows:(1)In the squint SAR mode,due to the squint angle and constant acceleration,the impact of range cell migration on imaging is more serious.In the algorithm processing,the impact of range cell migration on imaging cannot be ignored.meanwhile,in order to make the formula more concise and improve the accuracy,this paper proposes a new slant range model to replace the real slant range process.The model is derived from Taylor's high-order approximation which can satisfy high-precision imaging.Moreover,the slanting distance model and the RD algorithm which increase range walking correction are used to analyze the imaging results,which proved the validity of the slant range model.(2)In view of the problems existing in the use of the traditional NLCS algorithm in the curved trajectory and constant acceleration scene,this paper proposes two points optimization: The first is that when the acceleration is considered,the position of the echo target point will shift.The article will analyze the position of the ground point target more deeply and correct the target to the correct position.The second is the use of a higher-order approximation of the azimuth FM rate,thereby improving the accuracy of the imaging in the curvilinear trajectory scene.(3)Based on the previous analysis,considering that acceleration has caused greater distance migration,Therefore,this article first used the Keystone transform to perform linear walk correction operation.Next,the residual range cell migration after Keystone are eliminated and the range focus is achieved by compensating for the residual range cell migration and the second range compression.Next,A modified NLCS algorithm is carried out to complete azimuth focusing.Finally,we get the focused SAR image.The simulation results show the effectiveness of the algorithm.