FY-3C/MERSI TEB On-orbit Calibration And Uncertainty Assessments

The Medium Resolution Spectral Imager(MERSI)on the Fengyun-3C(FY-3C)satellite has been operated steadily for more than six years since it was launched in September 2013.As the core instrument of FY-3C,MERSI provides a large number of science data for studying the global climate change and natural disaster monitoring.In order to monitor the on-orbit performance of instrument and ensure the accuracy of satellite data,the calibration should be conducted on a regular basis.As an important means of real-time monitoring after satellite launch,on-orbit calibration is the most effective method.This paper mainly focuses on analysis of FY-3C/MERSI thermal emission bands(TEB)on-orbit calibration and uncertainty assessments.Based on the calibration principle,the on-orbit calibration equation of FY-3C/MERSI TEB is improved and the new calibration equation is provided.Combining it with the inversion calculation of the brightness of the earth's field of view,the 11 error factors of FY-3C/MERSI TEB are analyzed,which affect the accuracy of FY-3C/MERSI TEB measurements.By analyzing these error factors one by one using the satellite data,the error caused by each factor and the total error are quantified.The results show that the main error factors are the temperature of black body(BB),wavelength and the digital number response to Earth view,and that their relative errors for the radiance measurements of Earth view are 0.14%,0.47% and 0.2%-0.3%,respectively.The errors caused by other error factors are less than 0.07%.The total relative error of the Earth view radiance is about 0.56%,and the total absolute error of the equivalent brightness temperature is 0.35 K.In addition,due to different properties of each detector,the influence degrees of error factor on individual detectors are different,but the error variation trends of all detectors are consistent and their differences are very small.The accuracy of satellite-borne instruments and the errors of on-orbit calibration directly affect the observed radiance from the Earth view,which is an important part of meteorological data.Therefore,it is of great significance to carry out on-orbit calibration and quantify the measurement error on a regular basis for the research and application of the data in meteorological field.