Performances between the <scp>FY‐4A</scp>/<scp>GIIRS</scp> and <scp>FY‐4B</scp>/<scp>GIIRS</scp> Long‐Wave InfraRed (<scp>LWIR</scp>) channels under clear‐sky and all‐sky conditions

Abstract

Abstract The observation‐minus‐background (O − B) bias characteristics are compared for the Long‐Wave InfraRed (LWIR) channels of the Geostationary Interferometric Infrared Sounder (GIIRS) on board Fengyun‐4A (FY‐4A) and Fengyun‐4B (FY‐4B) satellites under clear‐sky and all‐sky conditions. Under the clear‐sky condition, the data quality of the FY‐4B/GIIRS is better than that of the FY‐4A/GIIRS. Specifically, the standard deviations (&lt;1 K) of the O − B values for FY‐4B/GIIRS LWIR channels are smaller than those (&gt;1 K) of the FY‐4A/GIIRS, especially in carbon dioxide (CO 2 ) and ozone (O 3 ) absorption bands. The diurnal variations of the mean O − B biases for the O 3 band of the FY‐4B/GIIRS are less than those of FY‐4A/GIIRS. To our surprise, the diurnal variations of O − B biases for the FY‐4B/GIIRS and FY‐4A/GIIRS channels show an obvious antiphase characteristic in the CO 2 band, which could be caused by diurnal environmental field variations from the different geostationary (GEO) platforms. In addition, the FY‐4B/GIIRS channel 7 (703.75 cm −1 ) has smaller pixel‐dependent biases than those of FY‐4A/GIIRS. Under the all‐sky condition, the observation and cloudy simulation () for channels 7 (703.75 cm −1 ), 36 (721.875 cm −1 ), and 320 (900 cm −1 ) of the FY‐4B/GIIRS are more consistent than those of FY‐4A/GIIRS with smaller root‐mean‐square errors (RMSEs), which also indicates a better observation quality in the cloudy area.