Intercalibration of FY-3D MWRI Against AMSR2.

The Fengyun (FY)-3D satellite launched in November 2017, provides the latest multi-frequency brightness temperature (TB) of Chinese FY-3 series satellites. In this study, the FY-3D TB at five frequencies from 10.7 to 89 GHz during 2019 to 2020 were intercalibrated against AMSR2 TB using two intercalibration methods, i.e., the commonly used global linear regression method and the global per-pixel linear regression method proposed in the study. The effects of different environmental variables (e.g., land cover and its heterogeneity, climate types, water body fraction, terrain and vegetation coverage) on the calibration accuracy were investigated. The results reveal the global per-pixel linear regression method performs much better than global linear regression method with an averaged root mean square difference (RMSD) of 2.93 K at ascending overpass and 2.34 K at descending overpass. The water body fraction has the greatest influence on calibration accuracy, followed by terrain, land cover heterogeneity, and vegetation coverage. The RMSD is relatively lower in savannas and barren lands as well as in arid, cold and tropical climatic zones than that in other land cover and climate types.