Reasearch On In-flight Calibration Method Of Satellite Polarization Sensor

In recent years,several kinds of spaceborne polarization sensors have been developed domestically and abroad.The Directional Polarimetric Camera(DPC)made in China is the only multi-angle polarization instrument operated in orbit at present.Due to the technical difficulty,it cannot be equipped with an onboard calibrator,so it is urgent to develop an in-flight alternative calibration method for high-precision calibration of DPC data.Based on the above research background and objectives,the radiation and polarization calibration methods based on Rayleigh scattering of an ocean scene,sunglint of an ocean scene and cross-calibration of a desert scene are developed in this study.Based on systematic theoretical accuracy analysis,they are applied to on-orbit calibration of domestic DPC sensors.Finally,the above calibration method was used to successfully monitor the radiation performance of DPC in long time series.The specific contents in this research are as follows:According to the characteristics of spaceborne polarization sensor,Rayleigh scattering calibration of an ocean scene,sunglint calibration of an ocean scene and cross-calibration of a desert scene are developed in this study.Compared with previous studies,a complete set of data source acquisition approaches and data screening methods were established for each method.On the basis of theoretical analysis,it is innovatively applied to the study of relative radiation calibration and polarization radiation calibration.Based on introducing the algorithm principle of each calibration method,the precision of different calibration parameters corresponding to each calibration method is systematically analyzed based on the parameter perturbation method and vector atmospheric radiative transfer model.The results show that the accuracy of the three calibration methods for DPC is better than 4.6%,4.5% and 6%,respectively;the relative radiative calibration accuracy of the three methods is better than 7%,8% and 5.5%,respectively;the polarization calibration accuracy is better than0.03,0.014 and 0.007,respectively.The accuracy of each calibration method can meet the requirements of DPC absolute radiative calibration of 7% and polarization calibration of 0.02.The calibration method is applied to the actual in-flight calibration of Gao Fen-5 DPC and Gao Fen-5(02)DPC,respectively,and the calibration results of the in-flight absolute radiation response,relative radiation response and polarization radiation response are obtained.By comparing the characteristics of the above three calibration methods,it is found that the three calibration methods can be completed and verified each other at different bands of DPC.The relative difference of radiation calibration results at the common band is less than 7%,and the relative difference of polarization calibration is less than 0.02.According to the principles and steps of the above three calibration methods,the in-flight radiation and polarization parameter calibration system for the spaceborne polarization sensor is developed in this study,and the long time series radiation performance monitoring research of Gao Fen-5 DPC is carried out by using this system.The results show that there is no significant radiation drift after the launch of DPC,but the maximum average decay of DPC’s 443,490,565,670,765,865 nm optical systems is about 26%,25%,21%,17%,21% and 22% from March 2019 to April 2021.Based on this,the decay correction model based on Gao Fen-5 DPC data is proposed,and a new validation method based on the physical model is proposed to verify the calibration coefficient accuracy from the inversion results.The test results show that the corrected data AOD inversion results are optimized with the comparison slope and root mean square error with foundation products.In general,this study provides a theoretical and methodological reference for the subsequent in-flight calibration of similar type sensors,which is significant for improving the detection data quality of domestic polarization sensors and will provide high-quality basic observation data support for global PM2.5detection and aerosol climate effect research.