Study On Moving Target Indication Method For Synthetic Aperture Radar Mounted On High Speed And Maneuvering Platforms

Synthetic aperture radar(SAR)can achieve not only high-resolution imaging of the measured stationary scenes,but also achieve ground moving target indication(GMTI)of the interested moving targets in the detected area.With the improvement of application requirements,the optimization of system structures and the improvement of processing methods,the traditional low-speed uniform linear flight SAR can no longer meet the current demand.The problem determines that the platform of future SAR system is more diverse,the trajectory of future SAR platform is more complex,and the corresponding SAR signal processing method should be further explored.Among them,the high speed and maneuvering SAR with single-or three-dimensional acceleration(and even high-order acceleration vector)during the flight has recently received extensive attention.Due to the urgent and practical military civilian demand,independent and safe detecting environment,and flexible and timely revisiting capability,high speed and maneuvering SAR is more suitable for the practical environment of SAR.However,the differences between SAR imaging and GMTI in system restrict the direct expansion of existing SAR imaging methods.Besides,the direct application of traditional SAR-GMTI methods are restricted by the difference of echo signal characteristics and internal mechanism.Based on the establishment of echo signal model,this dissertation studies SAR-GMTI methods for high speed and maneuvering SAR from two aspects: moving target extraction and moving target processing.The main contribution of this dissertation including the following four parts:First,a vectorization signal model of the stationary/moving target for single-/multi-channel high speed and maneuvering SAR-GMTI is established.The three-dimensional acceleration introduced by the high speed and maneuvering flight of the radar platform will change its flight attitude,which will induce severe phase error for conventional instantaneous baseline model.Based on the kinematics principle,the proposed model takes into account the characteristics of the stationary/moving target and the rigid body characteristics of the radar antenna from the perspective of vector analysis,and subtly integrates the effects of high speed and maneuvering of the radar platform on the instantaneous baseline vector variation of multi-channel SAR.Simulation experiments show that the proposed model can effectively avoid the phase error introduced by the conventional constant instantaneous baseline model in high speed and maneuvering SAR signal processing.Second,a multi-channel non-adaptive moving target extraction method is proposed.Considering that the range compressed echo signal of low-orbit space-borne multi-channel SAR contains high-order coupling part,Doppler extension part,and traditional space-time part,the proposed method firstly eliminates the influence of high-order coupling part through non-space-variant phase compensation.Then,the influence of Doppler extension part is eliminated by Doppler extension compression.Finally,the clutter canceller is designed to process the traditional space-time part,so as to suppress the clutter and extract the moving target.Theoretical analysis shows that compared with the traditional SAR adaptive moving target extraction method,the proposed method effectively avoids the requirement of a large number of independent and identically distributed training samples,the prior information of the moving target information and the huge calculation.Meanwhile,the simulation experiments show that compared with the non-adaptive displaced phase center antenna method,the proposed method has fewer restrictions on radar system parameter design and can tolerate a small degree of radar system parameter measurement error.Third,a single-channel complex image domain moving target extraction method is proposed.Considering that the imaged background clutter of high speed and maneuvering single-channel SAR has the characteristics of symmetrical Doppler spectrum,the proposed method firstly complete SAR imaging through the back-projection algorithm to avoid the failure of conventional range Doppler algorithm.Then,the moving target extraction in the complex SAR image domain can be completed by the proposed symmetry Doppler pixel processing.Theoretical analysis shows that compared with the traditional raw-data domain moving target extraction method,the proposed method effectively avoids the problems of raw-data re-transform,failure of clutter-free assumption,and repetitive and redundancy processing.Meanwhile,the simulation experiments show that compared with the symmetric Doppler view cancellation method,the proposed method can avoid not only the phenomenon of moving target cancellation,but also realize the moving target extraction when there exist pixels' mismatch in the two symmetric Doppler views.Fourth,a single-channel efficient moving target processing method is proposed.Considering that the range compressed echo signal of near-space hypersonic vehicle-borne squint-looking single-channel SAR has severe Doppler center and spectrum ambiguity,range migration and azimuth migration,the method proposed in this dissertation firstly eliminates the influence of Doppler spectrum ambiguity and reduce the influence of Doppler center ambiguity through signal pre-processing.Then,the influence of range migration is eliminated by blur matching keystone transform.Finally,the high-efficiency chirp Fourier transform is processed for the azimuth migration.Theoretical analysis shows that the proposed method is not only suitable for the single/multi-moving target processing of the squint-looking single-channel SAR of the near-space hypersonic aircraft with ideal uniform linear flight,but also suitable for that of the near-space hypersonic aircraft of the actual maneuvering curve flight.Meanwhile,the simulation experiments show that the proposed method has a lower computational complexity compare to the similar methods under the case of achieving same moving target processing performance.In summary,this dissertation conducts a preliminary study on the high speed and maneuvering SAR-GMTI,and proposes some solutions or ideas in theory to explore new technical approaches for SAR in military and civilian applications,and promote the development of SAR theory,and the practical use of methods.