Radiometric Recalibration For The Reflective Solar Bands Of FengYun-3 Satellite Medium Resolution Spectral Imager And Its Applications

The medium resolution spectral imager(MERSI)on-board the FengYun-3 satellites(i.e.,FY-3A/3B/3C)are the main operational sensors in China at present that provide meteorological observation data about clouds,atmospheric precipitable water and aerosol.The FY-3 series of satellites provides continuous medium spatial resolution imagery dating back to the launch of FY-3A in 2008 and continues to operate today.The radiometric calibration of sensors is the prerequisite and foundation for information quantification of remote sensing.Dunhuang site vicarious calibration campaign is the main post-launch absolute radiometric calibration method for Fengyun series satellites.However,this campaign occurred only once a year and the limited frequency is not enough for effective on-orbit calibration coefficient updating,which could cause large uncertainties for remote sening data inversion accuracy.The radiometric response properties of FY-3A/3B/3C MERSI are different,the uniform radiometric calibration has not been sufficiently performed,causing the difficulty in linking the data from different sensors to acquire continuous and long-term remote sensing data.To ensure the consistency and accuracy steadiness of continuous long-term data of three sensors,this paper studies the uniform radiometric recalibration and demonstrates the application effect of recalibration.This paper provides the radiometric recalibration technology for FY-3A/3B/3C MERSI based on the processing results of approximately 6 TB remote sensing data.The main content is as follows:(1)For each radiometric calibration of one MERSI sensor,evaluates the impacts on radiometric response calculation resulting from different reflectivity values,atmospheric radiative transfer conditions and the changing solar angle in detail for each band.(2)For the long-term calibration of three sensors,this paper performed approximately 1100 calibrations based on the data since 2008 in Libya4 and Algeria5 desert sites.The consistencies between the results of recalibration are characterized by the gain difference acquired from the two sites.The cross-calibration gain coefficients of FY3A MERSI are determined by cross-calibration with MODIS;the differences are all less than 3%by comparing with recalibration results,which confirm the reliability of recalibration method.(3)This paper corrects the gains of FY-3 A and FY-3B MERSI by cross-comparison of the FY-3A/3B/3C MERSI sensors(FY-3C MERSI calibrated to FY-3A MERSI,FY-3A MERSI calibrated to FY-3B MERSI),which take the radiometric response of FY-3C MERSI as reference.On this basis,a consistent normalized apparent reflectance over Libya4 site of these systems was acquired;the difference is from-10%to +10%,which verifies that the consistency correction method is the feasible.This paper achieves the goal of correcting radiometric response differences between the FY-3A/3 B/3C MERSI sensors.(4)For the applications of the recalibration results,this paper determines the output change of the on-orbit calibration lamp based on the results of recalibration for FY-3B MERSI,which provides an independent and viable method to estimate the radiometric output change of the On-board Calibrator.The relibration gains are applied to generate ground reflectance at the Dunhuang test site when the satellite passed over,and the results are compared to the ground reflectance of synchronous satellite-ground measurements.With the recalibration method,the maximum reflectance measurement difference is reduced from 33.39%to 6.68%,which indicates that the recalibration method could effectively improve the accuracy of long-term remote sensing data.The technology project of recalibration proposed by this paper,can be used to realize the high frequency and high precision radiometric calibration,which helps to further understand the changes in the sensor system radiometric response,as well as improve the absolute calibration accuracy of remote sensing products.The recalibration data of FengYun series satellites provides data support for continuous and long-term study of the earth's land surfaces and climatic behaviour.