Research On Synthetic Aperture Radar High-resolution Imaging Technology

High-resolution imaging is one of the key procedures in the synthetic aperture radar(SAR)manufacturing and application.High-resolutions detection and sensing characteristics of SAR system greatly improve the ability of situational awaness in the battlefield or the sensitive area,which makes radar an important information acquisition method in military and civil remote sensing field.High-precision and high-efficiency imaging algorithms,motion error compensation algorithms and wide continuous swath system design that are compatible with high-resolution SAR still encounter many problems and challenges.Based on SAR high-resolution application requirement,this paper studies on the signal processing technology and system parameters design are carried out in this paper.The major contents and innovations are summarized as follows:The researches of highly spatial resolution imaging algorithms are carried out in Chapter 2.The highly spatial resolution of SAR is usually realized with the wide bandwidth and wide scanning angle of system.The problem of basdband azimuth scaling(BAS)algorithm could not decouple the range-azimuth high order phase is analyzed in this paper.Combining with the generalized chirp scaling(GCS)algorithm,a GCS-BAS algorithm is proposed to process the sliding spotlight SAR data with wide bandwidth.Video SAR(ViSAR)operates in the wide continuous observation angle.Some aperture echo is acquired in the highly squint mode.The inaccuracy of the traditional nonlinear chirp scaling(NLCS)algorithm based on the principle of stationary phase(POSP)is analyzed.Then,a more accurate method based on the series reversion(MSR)is used to improve the traditional NLCS algorithm,and the scene focusing accuracy and depth are significantly impoved.The imaging algorithms proposed in this chapter supports the subsequent chapters.High-resolution motion error compensation algorithm based on motion measurement data and echo is studied in Chapter 3.The traditional two-step algorithm only compensates the envelope and phase error in the sight direction of beam center without considering the defocus effect of non-uniform sampling error along the track direction of the platform.Based on the two-step algorithm,motion measurement data is introduced to correct the non-uniform sampling error by the best linear unbiased estimation(BLUE)method.This method has no model and scenario assumptions.As the signal-noise-ratio(SNR)of sub-aperture image will affect the estimation accuracy of phase gradient autofocus(PGA)algorithm,it will limits the estimation accuracy and robustness of the traditional whole aperture phase error compensation by dividing the sub-aperture in the phase history domain.The proposed algorithm,named with full-aperture phase error compensation algorithm based on sliding window image PGA,can effectively avoid this problem by dividing image into apertures and time-frequency transformation,greatly improve the estimation accuracy of the full-aperture phase error and robustness in strip mode.ViSAR signal processing problem is researched in Chapter 4.The strict numerical coupling relationship between SAR system video frame rate and parameters is deduced from the definition of ViSAR frame rate.Based on fast factorized back projection(FFBP)algorithm,a fast generation method of SAR video stream is realized.The speed limitation of moving target shadow formation in SAR video is given through the theoretical derivation from the receiver SNR.This quantitative limitation condition can provide a theoretical basis for the parameter design and moving target detection of video SAR system.The system and signal processing problems of high-resolution wide swath(HRWS)based on staggered mode are performed in Chapter 5.The general principles for the design of pulse repetition interval(PRI)sequences are achieved from the performance analysis of single-channel Staggered SAR.Considering the wide application of the azimuth multichannel technology in HRWS systems,this paper studies and designs an azimuth multichannel phase center(AMPC)Staggered SAR system.The spatial sampling characteristics of signals in AMPC Staggered SAR system are analyzed,and an improved BLUE algorithm suitable for the imaging processing of AMPC Staggered SAR system is proposed based on the combination of characteristics and BLUE algorithm.In the end,the results of numerical simulation experiments and real data processing validate the accuracy and validity of the proposed high-resolution imaging algorithms and analysis above,which supports the foundation for the design and application of high-resolution SAR system.