The National Satellite Meteorological Center (NSMC) has completed the upgrade of the radiometric calibration operational software for the Geostationary Interferometric Infrared Sounder (GIIRS) onboard the FY-4B satellite during the period from June 30 to July 15, 2026. Following a stability monitoring phase on the updated data from July 15 to August 20, 2026, the system has been verified to perform stably with satisfactory data quality. We hereby officially announce the operational upgrade.

The primary objective of this upgrade is to correct the scanmirrorinduced radiance bias in the longwave infrared (LWIR) band. With the updated radiometric calibration algorithm, the accuracy and longterm stability of the Level1 LWIR spectral radiance data products are improved.

As part of this upgrade, the version number of both the calibration software and the L1 data products has been revised from V1.1.0 to V1.2.0. The version change will be clearly indicated in the file attributes, while the data format and file naming conventions for L1 products remain unchanged.

This announcement is hereby issued.

National Satellite Meteorological Center

August 24, 2026