Study On Improved Frequency-Domain Imaging Algorithms For SAR Mounted On High Maneuvering Platforms With Curve Tracks

Synthetic Aperture Radar(SAR)imaging technology has been deeply studied by scholars all over the world.Due to its all-day,all-weather,long-range working characteristics and high resolution of space and radiation,the related achievements have been more and more widely used in military,civil and other fields.Due to the advantages of simple implementation,low computational complexity,high imaging efficiency and easy combination of motion compensation based on echo data,SAR frequency-domain imaging algorithms are always the first choice in engineering applications.Compared with the traditional algorithm,the frequency-domain SAR imaging algorithm for curve trajectory of high maneuvering platforms must have the characteristics of high precision,high real-time and strong adaptability,which makes conventional algorithms no longer meet the application requirements.Aiming at the application requirements and development prospects of SAR imaging technology for high-maneuvering platforms,this paper studies the key problems of SAR imaging model establishment,parameter optimization,space-variant correction and motion compensation in frequency domain for curve trajectory of high-maneuvering platforms,and proposes an improved sub-aperture frequency-domain imaging algorithm for high-maneuvering platforms based on high-order phase filtering in frequency domain and three-level motion compensation.The main contents of the paper are summarized as follows:Chapter 2: Firstly,the general slant model and sub-aperture SAR imaging model are established by SAR imaging geometry and motion characteristics of high-mobility platforms.At the same time,the applicability of the traditional "go-stop-go" approximation model for high-mobility platforms is discussed,and the improved motion model and imaging method are proposed.Finally,this chapter analyses the curve trajectory characteristics of high maneuvering platforms,the time-frequency characteristics of SAR echo signal and the influence of three-dimensional high acceleration on SAR signal.The correctness of the proposed imaging model is verified by the data processing experiments of mathematical simulation.Chapter 3: Firstly,based on the motion characteristics and imaging model of high maneuvering platforms,the characteristics of SAR beam coverage area are analyzed in detail,and a general and efficient calculation method is given.The design method of pulse repetition frequency for curve trajectory SAR of high maneuvering platform is given by establishing and analyzing the working time series constraint model.The design method of high repetition frequency which is not conducive to engineering application is discussed.The mathematical simulation results verify the applicability of the method.By analyzing the two-dimensional resolution characteristics of SAR ground-range plane,the elliptic model of ground-range plane resolution is established.Based on this,the analytical solution of arbitrary direction resolution of ground-range plane is deduced,and the optimal design method of SAR signal bandwidth and synthetic space time for curve trajectory of general high maneuvering platforms is given.Finally,the validity and applicability of the proposed method are verified by mathematical simulation and experimental data processing experiments.Chapter 4: Aiming at the problem of serious azimuth space-variance in wide-band and high-resolution imaging of large squint,but the traditional SAR frequency-domain imaging algorithms can not meet the requirement of wide-band and high-resolution SAR imaging of high maneuvering platforms because of its low focal depth,this chapter compensates azimuth space-variant phase by constructing high-order phase filter in azimuth frequency domain,and then synthesizes the SPECAN algorithm with the highest imaging efficiency to achieve azimuth frequency domain unification Focusing processing improves the imaging focusing accuracy and depth.In order to overcome the shortcomings of traditional oblique conversion algorithm such as large computation and low real-time performance,this chapter uses BP imaging algorithm for reference and adopts the method of "point-to-point" backward projection and local two-dimensional joint interpolation to realize fast oblique conversion.Finally,the validity and applicability of the proposed algorithm are verified by data processing experiments of mathematical simulation.Chapter 5: This chapter studies the improved three-step motion compensation methods: motion compensation based on INS measurement data,Doppler parameter estimation and Fast Weighted Phase Gradient Autofocus(FWPGA).Firstly,the INS measurement data are used to compensate most of the envelope errors,phase errors and attitude errors of non-space-variant and range-space-variant,and then the residual envelope errors of non-space-variant and range-space-variant,phase errors and attitude errors of non-space-variant and range-space-variant within second order are compensated based on Doppler center estimation and Doppler frequency modulation estimation.The envelope error has been corrected well.The third step is based on the FWPGA algorithm to compensate the residual non-space-variant and range-space-variant phase errors in arbitrary form.Finally,the precise and fast compensation of SAR motion errors for curve trajectories of high maneuvering platforms is realized,and the focusing quality of SAR images is improved.Finally,the correctness and applicability of the proposed algorithm are verified by mathematical simulation and outfield real-time measured data processing experiments.