Research On Airborne Bistatic Forward-Looking SAR Motion Compensation

Airborne bistatic Synthetic Aperture Radar(SAR)can achieve high resolution imaging in the forward-looking area of the receiver,which has an significant application value in the fields of autonomous landing,autonomous navigation,all-weather airdrop,ground attack target indication and so on.But for the reason that airborne bistatic forward-looking SAR has separated transmitter and receiver,dual platforms' independent motion and high radial velocity to the imaging scene,etc.,its motion errors are of high degree of freedom,non-linear,and strong spatially-variant.Correspondingly,the difficulty of motion compensation is significantly increased.Achieving high-efficiency and high-precision motion compensation is the key to realize high-resolution imaging of airborne bistatic forward-looking SAR.In this dissertation,the theoretical research,numerical simulation and experimental verification are carried out on the echo model,error characteristics and error estimation and compensation involved in airborne bistatic forward-looking SAR motion compensation.The main contents are as follows:1.The slow time-Doppler decoupling motion compensation method is proposed to compensate for the residual Doppler phase errors stemming from 2-dimensional spatially-variant motion errors,in the condition that motion errors can be precisely calculated from the motion measurement systems.2.The maximum imaging sharpness based back projection and rise dimensional for eliminating spatial-variance trajectory estimation methods are proposed to cope with the motion compensation problem in the condition that motion errors cannot be accurately calculated by the motion measurement systems.Both algorithms can precisely estimate the moving trajectories of the moving platforms and realize the Doppler phase error compensation with compensation error smaller than the wave length.They can significantly improve the motion compensation accuracy integrated with time-and frequency-domain imaging algorithms,respectively.3.In the situation that residual range cell migration is significant amplified by the range cell migration correction processing,the minimum waveform entropy based residual range cell migration correction algorithm is proposed to achieve an correction of residual range cell migration with accuracy smaller than a range resolution.4.In the condition that motion errors are strongly spatially-variant if the imaging scene is sparse,the inverse model based bistatic forward-looking SAR motion compensation with joint phase-amplitude corretion method is proposed to achieve the highly efficient and precise motion compensation.The effectiveness of the researches above are verified by both simulation experiment and the airborne bistatic flight experiment.The results demonstrate that the methods proposed above are able to meet the accuracy and efficiency requirement of the airborne bistatic forward-looking SAR,and improve the image quality and depth of field.