Assessment and Correction of the On-Orbit Radiometric Calibration in FY-3D MERSI-2 Thermal Infrared Channels

Accurate radiometric calibration is fundamental to quantitative remote sensing. In this article, a thermal infrared radiative transfer model is first established, and then, the onorbit radiometric calibration of the thermal infrared channels 23 (8.55 mu m), 24 (10.8 mu m), and 25 (12.0 mu m) of the advanced MEdium Resolution Spectral Imager (MERSI-2) on the Chinese Fengyun 3D (FY-3D) satellite is evaluated and corrected against the channels of the Advanced Himawari Imager (AHI) on Himawari 8 satellite using the double difference (DD) method. The results indicate that the on-orbit radiometric calibrations in FY-3D MERSI-2 channels 23, 24, and 25 are slightly biased and certain variations exist between January and July 2020. In January 2020, the on-orbit calibration of MERSI-2 channel 23 is statistically consistent with that of AHI channel 11, and the calibration bias (mean f standard deviation at the mean) is 0.04 +/- 0.27 K, whereas they are 0.11 +/- 0.49 K and - 0.30 +/- 0.50 K in MERSI-2 channels 24 and 25, respectively. In July 2020, the on-orbit calibration of MERSI-2 channel 25 is very consistent with that of the AHI channels with a calibration bias of 0.06 +/- 0.31 K, while they are -0.18 +/- 0.23 K and - 0.27 +/- 030 K in MERSI-2 channels 23 and 24, respectively. The radiometric calibration biases are finally corrected by the linear fits on the matching observations.