Prelaunch Performance Evaluation of MWTS-III Onboard FengYun-3F Using Thermal Vacuum Test Data

The third generation of microwave temperature sounder (MWTS-III) is a major payload of FengYun-3F (FY-3F) satellite, which was launched on August 3, 2023. It can provide valuable atmospheric temperature profiles in morning time for numerical weather prediction (NWP) applications. The prelaunch thermal vacuum (TVAC) calibration test was performed to examine the instrument quality. This article briefly describes of the instrument design of MWTS-III and details the TVAC tests' calibration methodology and radiometric performance, including sensitivity, striping, nonlinearity, and calibration accuracy. Channels 1 and 2, which are received by direct-detection receivers, have a noise-equivalent delta temperature (NEDT) of less than 0.2 K, weak correlations with other channels, striping indexes (SIs) of 1.0 and 1.2, small peak nonlinearity, and calibration residual errors within ±0.03 K. The NEDT for Channels 3-17 is 0.16-1.38 K. The interchannel correlation and striping phenomena are more significant for these 15 channels. Since the linear calibration deviations were well-mitigated by the nonlinear calibration, the calibration residual errors for channels 3-11 are within ±0.05 K and for channels 12-17 are within ±0.17 K. The predicted on- orbit calibration accuracy for all the channels is between 0.37 and 1.48 K. In summary, all the channels of FY-3 F MWTS-III meet the specifications, and the instrument has great application potential.