Lunar Phase Function Oversampling Correction Method for FY3D/MERSI On-Orbit Calibration

In order to further improve the accuracy of the lunar radiation correction, an oversampling correction method based on the lunar phase function was firstly proposed in this paper. This method avoided the dependence of the MODIS algorithm on the relative space position and velocity accuracy, and overcame the limitation of the classical SeaWIFS algorithm only applicable to low lunar phase angles, in order to realize the full lunar phase observation of the sky, earth and space. Based on the least square fitting of the actual image data together with the analytic solution of the lunar phase function, the exact expression of the oversampling correction coefficient was given, and the spatial resolution of the remote sensor was improved to the sub-pixel level by the numerical difference calculation. The effectiveness of the novel method was validated through the Terra MODIS freemoon data with the lunar phase angle range of [55°,80°], and the lunar phase fitting function was highly consistent with the lunar phase shape observed by the remote sensor, together with the normalized calibration coefficient calculated by the novel method coinciding basically with the results of the MODIS maneuver calibration data with the lunar phase angle range of about 55°, which demonstrated the competitive efficiency and accuracy of the novel method. To evaluate the on-orbit stability of the FY3D/MERSI satellite, the long time series of the normalized calibration coefficient was obtained by the oversampling correction method, and the calibration uncertainty of the effective data was analyzed, showing no significant change for the gain of the FY3D/MERSI in most bands. This research had significance for the lunar observation together with the on-orbit calibration and deep space detection.