Calibration of Microwave Humidity Sounder-II Onboard FengYun-3F in Pre/Postlaunch Phases

FengYun-3F (FY-3F) is a sun-synchronous satellite launched on August 3, 2023. It crosses the equator at a local time of 10:15 a.m. and will be a substitute for FY-3C. This study introduces the preflight and in-orbit calibration of microwave humidity sounder-II (MWHS-II) onboard FY-3F. The instrument nonlinearity and radiometric sensitivity are characterized in the ground thermal vacuum chamber (TVAC) tests. The residual of nonlinearity correction is within 0.5 K, depending on viewing scenes and channels. As a substitute for its predecessor FY-3C, the performance of MWHS-II onboard FY-3F is compliant with requirements. The in-orbit radiometric sensitivity of the sensor is consistent with the prediction of the TVAC test results, with margins of 20%-60% relative to the requirements. The in-orbit behavior of the sensor is further evaluated by simultaneous nadir overpass (SNO) with the advanced technology microwave sounder (ATMS) and the difference between observation-background (O-B). The results confirm that the radiometric performance of MWHS-II onboard FY-3F is improved, compared to FY-3C. With stable and consistent observations, MWHS-II onboard FY-3F will benefit numerical weather predictions by providing accurate temperature and humidity information at the 118- and 183-GHz bands.