Implementation Of Airborne SAR Imaging And Geometric Distortion Correction Based On FPGA

As a kind of active imaging radar,Synthetic Aperture Radar(SAR),which has the ability to penetrate shelter to acquire target images,has all-time,all-weather work characteristics superior to traditional optical or infrared imaging,which has made it gradually occupied an important position in the field of both military and civilian applications such as battlefield reconnaissance and emergency rescue.The application of synthetic aperture technology makes SAR have a high resolution characteristic that is significantly different from traditional radar.The pursuit of resolution improvement is also one of long-term research topics in the field of SAR imaging.Considering the high algorithm complexity and huge data throughput of SAR imaging processing,Field Programmable Gate Array(FPGA)has been much more widely used in the hardware implementation of SAR imaging system due to its performance advantages in data rate,logic and storage resources.This paper mainly studies the FPGA implementation system for a kind of classic algorithm for airborne SAR imaging—Polar Format Algorithm(PFA)and its post-imaging geometric distortion correction processing.The full text consists of five chapters.The contents of each chapter can be summarized as follows:Chapter 1 introduces the background of SAR imaging research,and also reviews the development of airborne SAR imaging research.Considering the requirements of SAR signal processing,a comparison of technology and application characteristics between FPGA and DSP shows the advantages of applying FPGA to realize the hardware implementation of airborne SAR imaging system.Based on the constructed acquisition model of SAR signal,chapter 2 conducts the principle derivation of PFA after analyzing the geometric relationship.The improved PFA applying range scaling and azimuth SINC interpolation is used to realize the resampling of the echo data from polar coordinate format to rectangular coordinate format.Since the flat wavefront hypothesis has been applied in the PFA derivation process for approximate calculation,the imaged target has geometric distortion due to the wavefront curvature actually which can be corrected by the two-dimension resampling on image domain.Finally,the software simulation of imaging processing is carried out for simulated echo signal of point targets to verify the effectiveness of the algorithm.Chapter 3 analyses the design of the FPGA-based hardware system from the aspects of function division,processing flow and so on,realizing the module mapping from algorithm to hardwareimplementation of range processing,azimuth processing,time division multiplexing of FFT and geometric distortion correction.Considering the data characteristic of imaging processing,DDR3 SDRAM is used for the data storage of the hardware system,with the control design of the transposition read/write process under the demand of the algorithm.Chapter 4 introduces the construction of FPGA-based airborne SAR imaging processing system,and carried out system verification and performance evaluation.The Virtex7-XC7VX690 T board provided by Xilinx Corp.is used as the hardware platform of system implementation.In order to realize the data communication between the host and the processing board,a communication link has been designed based on Ethernet and the PCIe module on the processing board.The actual processing flow is introduced with a complete system structure,which process the PFA imaging and its geometric distortion correction.The comparison between FPGA and MATLAB results shows the processing ability of FPGA-based imaging processing system of airborne SAR.The analysis of quantified error,resource utilization and data processing rate shows the processing capabilities,performance and development value of this system.Chapter 5 proposed the follow-up direction and some viable promotion after summarizing the research content and achievements.