Study On The Calibration Of Solar Channel Radiation Of Fengyun Satellite Spectroradiometer Based On Cloud Targe

Absolute radiometric calibration of satellite radiometer plays an essential role in meteorological and environmental applications,in order to guarantee the accuracy of satellite data,all satellites must be strictly calibrated before they are launched,but due to the influence by space environment and their instruments aging during the on-orbit operation,the radiation characteristics of the satellite instruments will inevitably change,resulting in lower measured values,which is called sensor degradation.To solve this problem,some satellites are equipped with onboard calibration system to conduct on-orbit calibration correction.However,due to the limitation of the space and weight of the platform,calibration system method is not available for all the satellites.Therefore,vicarious calibration methods were proposed to solve the onboard calibration problem of satellite.The second-generation Medium Resolution Spectral Imager(MERSI-Ⅱ)is an important instrument onboard Fengyun-3D(FY-3D),one of Chinese polar orbit meteorological satellite,but its calibration performance is still not clearly reported.New on-orbit calibration methods are needed to carry out the stability analysis of signal,and compared to other calibration methods to complete the calibration system and improve the calibration accuracy.This research proposed a new on-orbit vicarious calibration method,which used general cloud targets as the vicarious targets,utilizing the Moderate Resolution Imaging Spectroradiometer(MODIS)onboard Aqua as reference sensor to obtain cloud products,establishing radiative transfer model for MERSI-Ⅱ,simulating top of atmosphere(TOA)reflectance of six solar reflective bands of MERSI-Ⅱ.Then,this research analyzing the sensor’s signal tendency of MERSI-Ⅱ in 2019–2021 period.The results show that visible and near-infrared channels of MERSI-Ⅱ are relative stable,with annual degradation of less than 2%.the maximum is in band 1,reaching 1.82%,while two shortwave-infrared bands are relatively unstable,the annual degradation of band 6 is over 5%.By establishing fitting model,fitting the signal tendency of MERSI-Ⅱ in three years period,this research further corrects the signal of MERSI-Ⅱ.After correcting,the signal’s stability can be improved to within 3% uncertainty range,which suggesting that cloud target calibration simulation method has well performance and has potential to be applied in subsequent calibration work.In addition,this research also extends the cloud target calibration method to Advanced Geosynchronous Radiation Imager(AGRI)onboard geostationary meteorological satellite Fengyun-4A(FY-4A),the results show that cloud target method is feasible,and can characterize the signal change of AGRI in 2020.