Research Of Fast Imaging Method For UAV Swarm SAR

Synthetic Aperture Radar(SAR)can work full-time and all-weather to provide highresolution images through the movement of the platform to synthesize a virtual long aperture in three-dimensional space.Traditional monostatic SAR and bistatic SAR require longer synthetic aperture time or electromagnetic waves in higher frequency bands to realize high-resolution imaging.But the former will increase the echo acquisition time and cannot capture the dynamic information of the target area,while the latter is seriously attenuated in the atmosphere and cannot achieve long-distance detection.Unmanned Aerial Vehicle(UAV)swarm SAR use the cluster transceivers to move simultaneously in space to form a cluster distributed short apertures,and synthesize a large aperture through orderly sequential connection,so as to obtain high-resolution SAR images in a short time.UAV swarm SAR can realize dynamic real-time monitoring of key scene targets.The time-frequency synchronization problem and imaging method are two key problems in UAV swarm SAR.In this thesis,theoretical research and method verification are carried out from three aspects: echo modeling,error analysis and imaging method.The main work and innovation points are as follows:1.The echo model of UAV swarm SAR is established and the range history of UAV swarm SAR is derived.Then the echo characteristic is analyzed.The back-projection algorithm is introduced to image for UAV swarm SAR under different configurations and the influence of configuration differences on imaging is analyzed.These work lays a theoretical foundation for UAV swarm SAR.2.The effect of frequency source error on UAV swarm SAR imaging is studied and an error threshold is set for the frequency source error within an acceptable range of image quality.As for time-frequency synchronization error caused by frequency source errors that exceed threshold,a time-frequency synchronous compensation method based on direct wave is proposed to guaranteed the image quality of UAV swarm SAR.3.Due to the disadvantages of slow and inefficient imaging of traditional timedomain imaging methods,a rapid imaging method based on sub-aperture image domain sequential connection is proposed.In this method,coarse imaging results of sub-apertures are got at first,then the imaging results are fused through interpolation in image domain.In this way,sub-apertures are sequentially connected to a large aperture and rapid imaging of UAV swarm SAR is realized.4.In imaging method based on sub-aperture image domain sequential connection,the fusion of coarse imaging results by interpolation will introduce inevitable errors.Thus,a fast imaging method based on sub-aperture spectral domain sequential connection is proposed.The coarse imaging results of sub-apertures are fused by spectral sequential,which reduces the error introduced by interpolation and realizes fast and high-precision imaging of UAV swarm SAR.The above research work has been verified in the simulation experiment of UAV swarm SAR,which proves that the proposed method can be used to achieve rapid imaging of UAV swarm SAR.