Research On Interference Baseline Constant Error Calibration Method Of Distributed Spaceborne InSAR

Distributed spaceborne InSAR is currently the most popular ground-observing radar system.It has the characteristics of all-weather,all-day,high penetration,and high resolution.With the formation configuration,it can greatly reduce the temporal decoherence and its baseline can be flexibly adjusted with the task to achieve higher terrain mapping accuracy and better deformation monitoring effect,which is the main direction of spaceborne InSAR technology development in the future.Precise determination of interference baseline parameters is the basis for distributed InSAR to realize high-precision ground observation tasks.This thesis focuses on the theoretical basis and implementation method to improve the distributed InSAR interferometry target positioning accuracy through the GNSS initial interference baseline constant error calibration.The main work of this thesis includes four aspects:1.The principle of calibrating the constant error in GNSS initial interference baseline is studied.According to the existing methods for determining the inter-satellite baseline of the distributed spaceborne InSAR system,the errors involved in the process of converting GNSS orbit determination information to interference baseline parameters are analyzed.The mathematical model between the interference baseline constant error and the elevation measurement error is derived in classical InSAR imaging configuration.The error sources that may be introduced in the process of interference baseline constant error calibration are analyzed,and the influence formulas of various errors on the baseline calibration are derived.2.The target positioning model based on bistatic imaging of master and slave satellites is established.With reference to the existing research results of distributed InSAR target positioning algorithms,the Mora equation is improved based on the bistatic imaging model of the master and salve satellites.The target positioning model and data processing strategy are given according to the changes in the position and velocity vector of the satellite platform at the time of transmission and reception.We use this target positioning model to perform positioning accuracy experiments without control points.The experimental results prove the accuracy of the positioning model and data processing strategy.3.The correction scheme for the slant-range measurement error and the Doppler center frequency is designed.Aiming at the problem that system errors exist in the positioning experimental results without ground control points,according to the bstatic imaging model,we have designed a method to calibrate the slant-range measurement error and Doppler center frequency using a few number of ground control points,and detected the existence of slant-range measurement error successfully.Subsequently,the correction formula of the slant-range measurement error linearly related to the slant-range length and the calculation formula of the Doppler center frequency linearly related to the range direction coordinates are given to eliminate the interference factors during the interference baseline calibration.4.The algorithm for calibrating the interference baseline constant error is implemented and the interferometric positioning accuracy is improved.Based on the established target positioning model and slant-range measurement error correction method,this thesis combines three theories innovatively to solve the problem that the classical InSAR baseline calibration model cannot be directly applied to distributed InSAR,which is equivalent phase center,establishing the local coordinate system on master radar antenna phase center and projection onto the master imaging plane.Through this method,the interference baseline constant error calibration algorithm can be implemented,and the interference baseline constant error can be calibrated successfully.The positioning experiment results show that after completing the calibration of the interference baseline constant error,the positioning accuracy of distributed InSAR system can be improved effectively.