Research On The Moving Target Detection And Imaging Algorithm Of Airborne Multichannel SAR

Synthetic aperture radar(SAR),as an active microwave remote sensing equipment,has the ability to observe the earth at all times and all weather.SAR imaging algorithm obtains a focused SAR image by performing a two-dimensional matching filtering process on the echo signal of the stationary target in the range direction and azimuth direction.However,in practical applications,moving targets are often more valuable and meaningful.Whether in the field of military applications or civil applications,the detection and focus imaging of moving targets are very necessary.Although the structure of airborne single-channel SAR moving target processing system is simple and the cost of the system is low,it is difficult to suppress clutter and has no ability to process the moving target submerged in the clutter.The development of airborne multi-channel SAR system provides the possibility of multi-channel SAR moving target signal processing.Moreover,the airborne multi-channel SAR system can be flexibly assembled according to the mission requirements.It can not only construct along-track multi-channel system or cross-track multi-channel system,but also combine two of them to form a two-dimensional baseline distribution,which provides more spatial freedom for moving target processing,and is conducive to moving target detection and imaging.Therefore,the multi-channel SAR moving target processing system has become the development trend in the future.With the development of SAR moving target processing technology,the types of moving targets are constantly changing.Generally,the moving targets processed by SAR are ground moving targets with only two-dimensional velocities.However,with the popularity of low-altitude aircraft and the appearance of highly maneuverable targets,the moving targets have three-dimensional velocities,even three-dimensional accelerations.Therefore,SAR detection and imaging algorithm for three-dimensional moving targets is also worth studying.This dissertation focuses on a series of practical problems encountered in the process of airborne multi-channel SAR moving target detection and imaging processing.The main innovations are as follows:(1)Aiming at the problem of interferometric phase error in real along-track interferometric SAR data,this dissertation establishes a geometric model and analyzes the influence of aircraft attitude error on the along-track interferometric phase in detail.This dissertation proposes an along-track interferometric phase correction algorithm.The algorithm does not rely on the aircraft motion parameters and external data,but corrects the along-track interferometric phase through reasonable partitioning and appropriate iteration.The corrected along-track interferometric phase conforms to the distribution law of along-track interferometric phase,which is beneficial to the moving target detection.The effectiveness of the algorithm is verified by simulation experiments,and combined with actual SAR data,a comparative analysis with the existing algorithm is carried out,which reflects the advanced nature of the algorithm.(2)Aiming at the problem of the influence of three-dimensional velocities of moving target on SAR imaging,this dissertation establishes an airborne SAR three-dimensional moving target imaging model in the ?radial-azimuth-normal? coordinate system,and analyzes the influence of the three velocity components of the moving target on the SAR imaging results.Radial velocity affects SAR imaging through Doppler ambiguity,while azimuth velocity and normal velocity affects SAR imaging by changing Doppler modulation frequency.In this dissertation,the mathematical expressions of the influence of three velocity components on SAR imaging are given,and the theoretical model is verified by simulation experiment,which provides a theoretical basis for the subsequent research of three-dimensional moving targets.(3)Aiming at the problem that the normal velocity of three-dimensional moving target cannot be estimated,this dissertation constructs an airborne multi-channel SAR system with "L-shaped" baseline,and proposes a joint estimation algorithm of azimuth velocity and normal velocity of moving target.The algorithm extracts the moving target data of each channel in the range-Doppler domain,performs conjugate multiplication and extracts the phase.The first-order term coefficients are obtained by linear fitting.According to the coefficients,the azimuth velocity and normal velocity of the moving target can be estimated at the same time.The advantage of this algorithm is that processing moving target data in the range-Doppler domain can avoid the registration process between multi-channel SAR images and improve the operation efficiency.Moreover,the algorithm requires low signal-to-noise ratio and short signal extraction length,and has good robustness and stability.The algorithm is verified and analyzed by simulation and contrast experiments.(4)Aiming at the problem of three-dimensional moving target processing,this dissertation presents a complete three-dimensional moving target processing system for airborne multi-channel SAR,including multi-channel moving target detection,moving target three-dimensional velocities estimation and moving target imaging.Among them,the three-dimensional velocities estimation algorithm of moving target combines Doppler ambiguity resolution algorithm with joint estimation algorithm of azimuth and normal velocities,which can estimate three-dimensional velocities of moving target without the influence of Doppler ambiguity.The effectiveness of the system is verified by simulation experiments and real data.Based on the National Key Lab of Microwave Imaging Technology of AIRCAS,this dissertation uses the existing airborne SAR system and the rich SAR real data to study the problems encountered in the actual scientific research process,and achieves good results,which laid the foundation for further research in the future.