On-Orbit Radiometric Performance Assessment of FY-3F MERSI-III: A Cross-Platform Intercomparison Approach Based on Global Pseudo-Invariant Pixels

FengYun-3F, a new generation Chinese polar-orbiting meteorological satellite, is equipped with the advanced Medium Resolution Spectral Imager-3 (MERSI-III). Extensive validation tests are currently underway to characterize on-orbit capabilities of MERSI-III. We utilize global pseudo-invariant pixels (PIPs) for radiometric intercomparison between payloads on different satellite platforms to evaluate the radiometric performance of MERSI-III in the reflective solar bands. A total of 70 simultaneous nadir overpass cases from low latitudes (SNO-x) are utilized. The findings are cross validated with two alternative calibration methods and further confirmed based on three pseudo-invariant calibration sites: Dunhuang, Libya-4, and Railroad Valley. Validation results indicate that the true color, near-infrared, water vapor channels 16 and 18, and the ocean color channels below 0.490 µm demonstrate excellent radiometric performance, with intercomparison bias standard deviations (bias STDs) under 2.00% . Although Channel 6 (1.64 µm) showed fluctuations during its initial phase, it stabilized after late November (bias STD < 2.16% ). Channel 11 (0.490 µm) among the ocean color channels exhibited slightly lower performance, with a bias STD below 4%, necessitating targeted calibration efforts. Channel 17 (0.936 µm), marked by strong water vapor absorption, requires a comprehensive evaluation using various alternative calibration strategies. Site-specific validation reveals that the temporal radiometric variability of MERSI-III channels remains below 3.5%, aligning well with in situ data. The overall uncertainty of the radiation assessment based on PIPs is less than 3.38%; channel 17 has an uncertainty of 4.62% . This study establishes a theoretical foundation and evaluation framework for the quantitative application and long-term monitoring of the MERSI-III sensor, providing significant references for the dynamic updating of operational calibration coefficients.