Study On Multi-channel SAR High Resolution And Wide Swath Imaging And Ground Moving Target Indication Technology

Synthetic Aperture Radar(SAR)system is capable of performing high-resolution imaging all day long,and plays an important role in both military and civilian areas.Among them,the multi-channel SAR system has obtained many achievements in high-resolution wide swath imaging(HRWS),ground moving target indication(GMTI)and interference suppression,and has become a hot research topic in both domestic and overseas.This thesis focuses on key technologies such as Doppler spectrum reconstruction,channel-calibration,and GMTI in multi-channel HRWS-SAR signal processing.The main contents and innovations are as follows:1.The multi-channel HRWS-SAR spectrum reconstruction technique is studied.The relationship between azimuth and Doppler in the echo signal of ground scatter is analyzed under the assumption of under-sampling in slow-time domain.Followed by the construction of multi-channel HRWS-SAR echo signal model.The multi-channel SAR Doppler spectrum reconstruction algorithm based on spatial domain adaptive processing is studied,with the adaptive beam-forming and multi-Doppler-direction restriction ambiguity suppression algorithms investigated in detail.The performance of the two algorithms is then verified by simulation and measured data processing results.2.The multi-channel HRWS-SAR channel-calibration technique is investigated.The causes of channel mismatch in multi-channel receiving system are analyzed,and the multi-channel HRWS-SAR channel mismatch model is constructed based on that.The existing channel-calibration method based on signal subspace is studied,with the feasibility verified by the airborne three-channel SAR measured data.To address the problems of the existing channel-calibration method such as the dependence on the parametric model,is the difficulty in accurately correcting azimuth-variant channel mismatch,and the relatively weak robustness,a channel-calibration method based on isolated strong scattering points is proposed.In this algorithm,the sub-aperture signal processing technology is used to automatically extract the echo signal of isolated strong scattering point from the Doppler-ambiguity and reconstruct the unambiguous Doppler spectrum of them,which is then employed to directly estimate the channel-mismatch to accurately calibrate channels.Finally,the performance of the algorithm was verified by the results of airborne four-channel SAR measured data processing.3.Multi-channel SAR simultaneous HRWS imaging and GMTI techniques were investigated.The existing multi-channel SAR/GMTI processing methods are studied,including techniques of moving target detection and moving target parameter estimation.In the HRWS imaging mode(the Doppler spectrum is aliased),new problems emerge in multi-channel SAR/GMTI technology,especially in the procedure of ground clutter suppression and target radial velocity estimation.Aiming at the above problems,a complete multi-channel SAR simultaneous HRWS imaging and GMTI signal processing scheme is proposed.The scheme uses Doppler domain SAR-STAP technology to achieve clutter,and introduces digital spotlight imaging method into the target velocity estimation process to overcome the influence of velocity-ambiguity and achieves accurate estimation of the moving target motion parameters.Finally,the scheme can simultaneously acquire the ground high-resolution SAR image and the GMTI result,and mark the target real position and motion information on the image.The scheme is also verified by the airborne three-channel SAR measured data.