Research On Block Adjustment Method Of High Precision Geometric For Spaceborne SAR Images

As an active microwave imaging remote sensor,Synthetic ApertureRadar(SAR)is an indispensable tool in the field of earth observation.In recent years,as SAR image plays an increasingly important role in various fields,the requirements of SAR image geolocation accuracy have becoming higher and higher.Geometric calibration technology can achieve high-precision geographic positioning of spaceborne SAR images,but due to the observation errors in SAR imagery imaging and orbital parameters,the positioning accuracy of SAR images is seriously affected.It is feasible to improve the positioning accuracy of SAR images by using appropriate and well-distributed ground control points.However,due to the imaging characteristics of SAR images and the influence of complex terrain and other factors,it is difficult to quickly and efficiently complete the geometric calibration of all SAR images in the wide area when the wide-range DOM and national radar remote sensing orthophoto images are obtained.Therefore,the Block adjustment technology of spaceborne SAR image is the key technology to obtain wide-area SAR image products,and it is also the current research hotspot in the field of geometric calibration of spaceborne SAR images.In this paper,aiming at the the technical problems of wide-area geometric calibration of spaceborne SAR images,the key techniques of Block adjustment of spaceborne SAR images are studied.For the imaging characteristics and complex terrain of GF-3 SAR images,the geometric calibration model of spaceborne SAR image based on range Doppler(R-D)model,a wide-area joint geometric calibration technology and Block adjustment technology are proposed.Moreover,the feasibility,effectiveness and stability of this methods are verified by the GF-3 SAR images with multiple orbits and multiple imaging modes.The main contents and work include:(1)A geometric calibration model of SAR images is established based on the R-D model,which takes into account the effects of atmospheric delays.GF-3 SAR images are used to verify that the model can achieve high-precision positioning of spaceborne SAR images.Based on the R-D model,the influence of atmospheric delays during the geometric calibration of SAR images is analyzed,and an atmospheric delay model is established to improve the positioning accuracy of spaceborne SAR images.(2)A wide-area joint geometric calibration method is proposed and its core algorithm is described in detail.A joint geometric calibration model is constructed based on the geometric calibration model of the SAR images and the processing flow of joint geometric calibration is designed.The wide-area joint geometric calibration is completed using the GF-3 SAR images with a few ground control points,which provides an idea for the geometric positioning of SAR images without control points or rare control points.(3)A Block adjustment method based on Strict Imaging Geometric Model is proposed to solve the problem of geometric calibration of spaceborne SAR images under large area.The basic principles and key technologies of the block adjustment method based on the geometric calibration model of SAR images are researched in depth.The Block adjustment model is constructed and the corresponding processing flow is designed in detail.The adjustment test of GF-3 SAR image verifies the feasibility and effectiveness of the block adjustment method proposed in this paper.