Research Of Motion Compensation In Airborne UWB SAR With High Resolution

Airborne ultra-wideband synthetic aperture radar (UWB SAR) working in low frequency band can reconnoitre targets concealed by foliage or earth surface, which is very valuable for military purpose. But trajectory deviation of aircraft will introduce troublesome phase errors into radar echoes, which would influence badly SAR images quality without correction, and effective motion compensation method is crucial to UWB SAR with high resolution. Under the support by some National Defense Research Project, this dissertation researched the motion compensation (MoCo) for UWB SAR from the following subjects:Firstly, how to compensate the trajectory deviation error in line of sight (LOS) for UWB SAR was discussed in detail with the help of exact motion track. In this dissertation, the influence of error in LOS to range cell migration correction (RCMC) in UWB SAR imaging was analyzed with emphasis, and the spectrum formulation of a point target comprising the LOS error was derived under some approximation. On the basis of sub-aperture compensation method, a new MoCo method with sub-aperture in azimuth direction and sub-swath in range direction was detailedly derived, and computer simulation results validate the new method.Secondly, how to eliminate effectively errors in UWB SAR echoes was researched when inertial navigation system (INS) on board can not provide exact motion track, which is a universal fact for our country currently. A method combined the real time information from global position system(GPS )receiver with refined map drift(MD) was proposed in the dissertation, and based on the real UWB SAR data, some measurements were added into the refined MD to improve the precision of estimation. The processing results of two data segment validate the proposed method. Some questions in the method were discussed also.Thirdly, some autofocus algorithms for UWB SAR were deeply investigated, which were on the basis of imaging contrast. On the one hand, the widely used contrast optimization autofocus (COA) was mended to satisfy the demand of the real time MoCo onboard, and the real processing results prove the validation of the mended method. On the other hand, based on phase adjustment by Contrast enhancement(PACE), a new algorithm named as phase adjustment by contrast enhancement in time dimension (TD-PACE) was proposed, which can extract polynomial errors with high order from range compressed echoes, and the real results show that the method can get three order polynomial phase errors. Aimed the disadvantage of PACE algorithm with the huge computation load, an interpolated PACE (IPACE) was advanced also. The processing results of real UWB SAR data prove that the IPACE can greatly accelerate the run time of algorithm with the same quality. Furthermore, the images quality focused by IPACE was better than the images by phase gradient autofocus (PGA), which is considered to be standard nonparametric SAR autofocus algorithm.Finally, a low cost MoCo scheme for unmanned aerial vehicle (UAV) was designed. A GPS receiver with high sampling and a one-axis accelerometer mounted directly on the SAR antenna phase center (APC) and aligned in LOS were used to measure the motion of UAV in the scheme, and the information from complementary filter (CF), which was used to fuse the speed from GPS and the acceleration from accelerometer, was used to compensate SAR echoes roughly. The useful acceleration expression for accelerometer was derived, and the influence of SAR antenna platform stabilization's precision on the output of accelerometer was discussed also. The computer simulation results justify the scheme.