Research On Model And Method Of Geometric Calibration For Space-borne SAR

Since 2006,high resolution SAR remote sensing satellites,including five types and ten satellites,have been successfully designed and launched from China.It is possible for our country to realize the global mapping quickly.Over the years,with the break of many key technologies for domestic SAR satellite,the performance of SAR remote sensing satellite in China is gradually reached the international advanced level,such as the implementation of sub-meter resolution.However,the contradiction with the strong ability of data acquisition is that most of domestic SAR satellite image have not been fully utilized,resulting in a large number of satellite data waste.However,due to the limitation of the hardware level of the domestic SAR satellite,the positioning accuracy of domestic high resolution SAR satellite images is poor,which limits the wide application of domestic SAR satellite image products.The reason is that the geometric quality of domestic SAR satellite images is an important factor which affects its application.In order to solve the problem of poor positioning precision of SAR satellite in China,the key factors affecting the positioning accuracy of SAR satellite are analyzed in detail.By means of high precision geometry model,ground control point and geometric calibration method,the system errors of domestic SAR satellite are eliminated,and the positioning accuracy of domestic SAR satellite is improved.Taking this as the theme,the following topics are researched in this paper.(1)The high precision geometric model of domestic SAR satellite is constructed.Firstly,based on the analysis of influence factors of geometric positioning error for spaceborne SAR,a rigorous geometric model and a general geometric model of spaceborne SAR satellite are constructed.Secondly,an improved ASF numerical method is proposed to solve the problem of ASF numerical solution without solution under the condition of large squint imaging by considering the influence of squint angle.Then,the virtual re-imaging method of spaceborne SAR satellite is studied,which improves the fitting precision of rational polynomial coefficient(RPC)model in azimuth.(2)The acquisition method of high precision ground control points is studied.Firstly,Aiming at the problem of artificial corner reflector with high cost and low efficiency,this paper proposed a design method of automatic corner reflector equipment with an advantage of normalization,high precision,remote control and unattended operation.Secondly,according to the imaging characteristics of corner reflector on SAR image,a semi-automatic high-precision corner reflector point extraction method is proposed based on artificial initial judgment and centroid algorithm.Then,in view of the spaceborne SAR images which can not be taken in the field of geometric calibration,according to the imaging mechanism and imaging texture between optical image and SAR image,an acquisition method of control point is proposed based on optical remote sensing image,which is the effectively supplement for the control points acquirement of spaceborne SAR image.(3)High precision geometric calibration method for domestic SAR satellite is proposed.Firstly,based on the analysis of the relationship between radar signal characteristics and geometric positioning accuracy,this paper presents a multi-mode hybrid geometric calibration method of SAR satellite considering atmospheric propagation delay,and compares the advantages and disadvantages with classical methods.According to the pulse-width and bandwidth of radar signal,the geometric calibration scheme is determined,and the time-varying atmospheric propagation delay is eliminated by using the global atmospheric environment reference data.Then,based on the slant range imaging characteristics of spaceborne SAR,a cross geometric calibration method is proposed based on the constraint of the same name point.With the same incidence angle,the projection difference caused by elevation error can be eliminated,and the high-precision calibration of spaceborne SAR system can be realized without high-precision ground control data.(4)The geometric positioning accuracy of domestic SAR satellite is analyzed and verified.Taking the Yaogan-13 satellite and Gaofen-3 satellite as an example,this paper carries out a series of experiment and analysis for the proposed two geometric calibration methods by using the normalization calibration equipment placed in Songshan Remote Sensing Satellite Calibration Field.Combined with the ground control data in Taiyuan Shanxi,Xianning Hebei,Anping Hubei,Tianjin and other regions,the geometric positioning accuracy of YG-13 after calibration is verified without control points.By using the RPC model,which is constructed by the virtual reimaging method,the correctness and effectiveness of the proposed algorithm are verified by evaluating the plane and height accuracy of Yaogan-7 satellite.