Research On Imaging Processing For One-stationary Bistatic SAR

One stationary bistatic SAR with a stationary platform and a moving one is a configuration of variant bistatic SAR.This system has the advantages of simple configuration and easy implementation.Besides,it can obtain rich information about ground targets.Moreover the fact that the receiver does not transmit signals makes the system stealthy and secure.Different from the invariant bistatic SAR,one component of point target's bistatic slant range is stationary while the other is formed by the moving platform which determines its slant range history during imaging.However,this bistatic slant range history changes with the positions of the point targets.That change creates two-dimensional spatial variances of the slant range history,which will bring difficulties to image processing.Like other SAR systems,OS-BSAR system is also affected by motion errors.These motion errors are not only come from the non-ideal motion of the platform,but also from the non-uniformity and time-varying of the propagation medium.If they are not compensated,the phase coherence of the signal will be weakened and the azimuth resolution will be reduced.Therefore,the imaging algorithms taking into account motion errors compensation must be studied in OS-BSAR system.This thesis focuses on the image processing algorithms of OS-BSAR with a stationary receiver and a moving transmitter.An improved nonlinear chirp scaling(NLCS)algorithm which can compensate the translation error of line of sight is studied after deeply analyzing the echo model of OS-BSAR system.The range spatial variance for different range bins and azimuth spatial variance for the same range bin but different azimuth positions can be made in this algorithm,leading to the improvement of the focused image quality.For the constant acceleration motion error of moving platform,a new range scaling function is derived in the range Doppler domain.Then an improved chirp scaling algorithm is used to compensate the motion error based on the new range scaling function.The main content of this thesis is as follows:1.The system properties are analyzed.The echo signal model is established according to the observation geometry of the system.Then the time domain and two-dimensional frequency domain analytical expressions of the echo are derived,whereby the spatial variances of the slant range history,the cross coupling between the range and azimuth and the spatial resolution of the system are analyzed.Those analyses provide a theoretical basis for the study of imaging algorithm and error compensation.2.An improved NLCS imaging algorithm with translation error compensation is carried out.The motion errors compensation of SAR system is indispensable because of its inevitable motion errors.The NLCS algorithm based on local data fitting is a basic imaging algorithm for OS-BSAR system.In this algorithm,the NLCS operation on the range is used to correct the range spatial variance of range migration for the position adjustment of the signal and the azimuth NLCS perturbation function is used to equalize the azimuth FM rate.In order to compensate the translation error of line-of-sight,an improved NLCS algorithm is studied.The simulation experiments of point targets and the process of real data verify the effectiveness of the algorithm.3.An imaging algorithm for constant acceleration motion error compensation is studied.For constant acceleration motion errors of moving platform,a new range scaling function is obtained after deriving the echo expression in range Doppler domain.Then an improved CSA is studied to compensate the constant acceleration motion errors.The simulated point targets experiments have been performed to verify the algorithm successfully.