Faraday Rotation Angle Under The Influence Of Spaceborne Polarization Sar Calibration Method

Polarimetric calibration is one of the key technologys for PolarimetricSAR measurements and applications. Faraday rotation caused by theionosphere has considerable effects on Polarimetric SAR measurementsand calibration. So faraday rotation has to be corrected at the processof Polarimetric calibration. With the development of spacebornePolarimetric SAR technology and the increase of its applications,calibration of the spaceborne Polarimetric SAR subject to faradayrotation has recently become a "hotspot" of research from theworldwide. Therefore the research on this topic would have significanttheoretical and practical meanings.This paper firstly presents a brief introduction of the basic principles ofPolarimetirc SAR calibration, the physical mechanism of Faradayrotation(FR) and its effects on spaceborne Polarimetric SARmeasurements. Then a systematic analysis of the scatteringcharacteristics(including reciprocity, correlation and symmetry) ofseveral typical distributed targets with calibrated real SAR data iscarried out to set a foundation for the study of calibration methods forPolarimetric SAR. After that, this paper analyzes the current calibrationmethods for Polarimetric SAR subject to faraday rotation. Here R.Touzi'scalibration method is thoroughly studied and an error model of thetarget's symmetry concerning the estimation of faraday rotation andSAR system channel imbalance is developed through experiment withreal SAR data. Based on the analysis and study of the current methods,this paper proposes a new method for estimating faraday rotationand channel imbalance f, which improvesthe Polarimetric calibration precision. The new method only uses two different targets that satisfy reciprocity to estimateΩand f andovercomes the defects of current methods that require the deploymentof point targets or some preknowledge about the calibration targetsand thus can be more widely applied. Simulation experiment with realPolSAR data is also carried out to confirm the validity of this newmethod.