Research About Geometric Correction Method Of Bi-SAR Image

The unique slant range imaging mechanism of synthetic aperture radar(SAR)and the influence of relief of terrain make SAR images appear geometric distortion phenomena such as short-range compression,overlying,and high tower inversion.The geometric correction problem of SAR image becomes the bottleneck restricting its application.Focuses on the image simulation,image alignment and correction methods involved in the geometric correction of Bi-SAR images,the research content of this thesis mainly include:1.The improved SIFT algorithm is studied to address the problems of low correct alignment rate and many incorrect point pairs of the traditional SIFT algorithm.By introducing bilateral filtering pre-processing,feature point pairing angle constraint and bi-directional image alignment,the noise interference is reduced,the abnormal pairing is eliminated,and the correct alignment rate of SAR images is effectively improved.2.To address the problem of difficult alignment of heterogeneous source images in the traditional geometric correction scheme,a digital elevation map(DEM)-assisted geometric correction method for Bi-SAR images is investigated.Firstly,the simulation of SAR image based on DEM information is completed based on the Range Equation and the Doppler Equation of Bi-SAR,and then the alignment of the simulated image and the image to be corrected is realized based on the improved SIFT algorithm,and the geometric correction of the Bi-SAR image is realized according to the mapping relationship between the simulated image and the DEM.3.For the case of no DEM information or insufficient DEM resolution,a geometric correction scheme based on the alignment of ortho-optical images and Bi-SAR images is investigated.Firstly,the Bi-SAR image is filtered by noise reduction,and the skeleton extraction algorithm is used to reduce the range of feature points.Then,the improved SIFT algorithm is used to detect and align the feature points,which solves the problem of difficult alignment caused by the large difference of grey scale in the alignment of heterogeneous source images.Finally,based on the alignment and correction results,as well as the mapping relationship between the relative elevation of the terrain and the geometric correction offset,the inversion of the relative elevation of the terrain is completed.All the methods mentioned above have been verified by simulation and measured data.The results show that the geometric correction of Bi-SAR image can be realized effectively under different prior information conditions.