The orbital drift of the Fengyun-4B (FY-4B) satellite from 133°E to 105°E in early 2024 significantly altered its viewing geometry over China, providing a unique opportunity to evaluate the impact of satellite positioning on the accuracy of downward surface shortwave radiation (DSSR) retrievals. In this study, FY-4B DSSR products before and after the drift were systematically evaluated using a strictly matched common set of 141 first-order radiation stations from the China Meteorological Administration during the summer seasons of 2023 and 2024. The results show that the post-drift product achieved markedly improved satellite–ground consistency, with the correlation coefficient increasing from 0.93 to 0.95 and the RMSE decreasing by 11.8% from 111.5 to 99.58 W/m2, while the mean bias remained close to zero. Spatially, the historical east–west disparity in retrieval accuracy was substantially mitigated, mainly because the westward orbital shift reduced the viewing zenith angle over western China and thereby weakened geometric distortions and atmospheric path-length errors. Further analyses across longitude, latitude, land cover, elevation, cloud regime, and diurnal cycle consistently indicate that the optimized viewing geometry was the dominant driver of the post-drift improvement, although residual errors remain in complex terrain and heterogeneous cloud conditions. These results demonstrate that the orbital shift to 105°E fundamentally enhanced the reliability of FY-4B DSSR products over China and provide useful guidance for future geostationary satellite deployment and radiation product application in solar energy assessment and numerical weather prediction.
Wang et al. (Thu,) studied this question.