LAUSR

This study mainly focuses on the diurnal and long-term variation characteristics of the calibration performance of the geostationary meteorological satellite Fengyun-4A/Advanced Geostationary Radiation Imager (FY-4A/AGRI) infrared channels from June 1, 2017 to December 31, 2020. An improved algorithm is developed in this research based on the in-situ observations from ocean drifters, which can capture the diurnal variations of the calibration performance of FY-4A/AGRI infrared channels. The results suggest that there are significant and non-negligible diurnal v-ariations of the uncertainties and biases for the brightness temperature (TB) observed by the FY-4A/AGRI, especially the infrared channels at 3.71 μm, 8.61 μm, 10.83 μm and 12.07 μm. Among them, the calibration performance from 16:00 UTC to 18:00 UTC (ar-ound the time of local midnight at the sub-satellite point of FY-4A) is worse at 3.71 μm, while TB biases from 04:00 UTC to 16:00 UTC are relatively large at 12.07 μm. Moreover, after the operational calibration and update in June 2020, the long-term TB biases at channel 08 (3.71 μm) obviously decrease from about 5 K to 2.5 K, and the TB biases at channel 14 (13.54 μm) increase from about 0.5 K to 3 K, implying a possible positive or negative impact of the calibration update on the calibration performance of infrared channels. Overall, this method based on the in-situ drifter data can well monitor the on-orbit calibration performance of geostationary satellite imaging sensor’s infrared channels such as the FY-4A/AGRI, allowing an objective assessment on the effect of calibration update events.