Evaluating the First Year On-Orbit Radiometric Calibration Performance of GIIRS Onboard Fengyun-4B

The geostationary interferometric infrared sounder (GIIRS) onboard the Fengyun-4B (FY-4B) is the first operational geostationary hyperspectral infrared (IR) sounder. This study analyzes the first-year FY-4B/GIIRS on-orbit calibration performance by comparing it to the collocated IR atmospheric sounder interferometer (IASI) observations and radiative transfer (RT) simulations. The results reveal that the mid-wave IR (MWIR) channels had a slightly larger calibration bias compared to the long-wave IR (LWIR) channels. However, the operational FY-4B/GIIRS showed improved performance compared to the experimental FY-4A/GIIRS. Furthermore, this study also found that most channels exhibited negligible annual and weak diurnal variations in calibration bias. However, there was a significant degradation in the LWIR channels (<850 cm1) and the weak diurnal variation in the MWIR channels. Finally, the calibration performance of FY-4B/GIIRS demonstrates a reduced dependence on brightness temperature (BT), except for the channel at wavenumber 703.125 cm1. Overall, it concluded that FY-4B/GIIRS demonstrated consistent calibration stability and high accuracy, highlighting its capability for precise quantitative applications.