Fast Three-dimensional Imaging Algorithm For Circular Scanning Ground-based SAR In Frequency Domain

Circular scanning ground-based SAR(GBCSAR)is a new ground-based SAR system with three-dimensional imaging capability.It introduces the circular trace SAR mode into the ground-based platform.Different from the traditional linear orbit ground-based SAR,it collects data through circular motion to form a two-dimensional synthetic aperture,master the three-dimensional information of the scene,and has the advantages of convenient three-dimensional imaging and data acquisition.However,its special circular motion trajectory increases the difficulty of three-dimensional imaging.Although its three-dimensional resolution has been demonstrated theoretically in the world,the research on imaging algorithm for circular scan groundbased SAR is not mature.The time domain backward projection(BP)algorithm,which is suitable for the imaging of the system,has huge redundancy.With the expansion of the monitoring scene,the huge amount of computation makes the algorithm difficult to meet the needs of real-time monitoring imaging.There are obvious differences in imaging geometry and signal transmission mode between airborne circular trace SAR and circular scan ground-based SAR.The existing airborne circular trace SAR imaging frequency domain algorithms can not be directly applied to circular scan ground-based SAR.Therefore,in this paper,a fast threedimensional imaging algorithm in frequency domain is proposed to solve the problem that the imaging algorithm of circular scan ground-based SAR system is not perfect.Because of the great spatial variability of the circular scan ground-based SAR imaging at different distance positions,this paper divides the monitoring scene into regions and studies the imaging algorithm in blocks to achieve the fast frequency domain imaging of the whole scene.The main contents of this paper are as follows:(1)Based on the imaging geometric model and signal model of circular scanning ground-based SAR system,the echo of targets with the same distance and different angles is deduced,and the characteristic of "constant displacement along the angle dimension" of the signal is analyzed;The spectral characteristics of circular scanning ground-based SAR are analyzed,and the calculation method of threedimensional resolution is given;According to the imaging model of circular scanning ground-based SAR,the scene is divided into imaging areas for algorithm research.(2)According to the geometric characteristics of the long distance,the plane wave approximation method is used for two-dimensional matched filtering to achieve long-distance high-quality imaging;The target in close range has a large error when imaging with plane wave approximation method.Therefore,when designing the matched filter,the quadratic term compensation method of error and the matched filter method based on reference distance are proposed,which greatly expands the effective imaging area.The effectiveness of the algorithm is verified by simulation and actual scene data processing.(3)In view of the different imaging geometry between the front side view area and the oblique side view area,the above methods are not applicable to the imaging of the front side view area.The polar format algorithm(PFA)algorithm is introduced,and the algorithm is derived in combination with the geometric feature of the small radius of the rotation track of the circular scanning ground-based SAR.The polar coordinate algorithm of the circular scanning ground-based SAR is proposed.The effectiveness of the algorithm is verified by simulation and actual scene experimental data processing.