Quality Assessment of Cloud Detection and Cloud Top Height Products from FY-3D/MERSI-II in Polar Regions

The Medium Resolution Spectral Imager II (MERSI-II) is one of the primary payloads on the FY-3D satellite, capable of dynamically monitoring important atmospheric and environmental parameters such as cloud characteristics and aerosols. The study evaluated the cloud detection and cloud top height (CTH) retrieval accuracy of FY-3D/MERSI-II in polar regions (Arctic and Antarctic) using CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) cloud products as reference truth. The results demonstrated that MERSI-II-derived cloud coverage in the Arctic was 7.2% lower than CALIOP observations, while overestimating cloud cover in Antarctic summer but underestimating it in other seasons. Seasonal variations in cloud detection accuracy were notable, with Arctic accuracy reaching 90.4% in summer but declining to 51.3% in winter. Antarctic detection accuracy consistently underperformed compared to the Arctic, though MERSI-II showed significantly better detection capability over water surfaces than snow/ice-covered areas. For CTH retrievals, correlation coefficients between MERSI-II and CALIOP reached 0.70 (Arctic) and 0.71 (Antarctic), with systematic underestimations averaging -0.46 km (Arctic) and -1.52 km (Antarctic). Larger deviations occurred in multi-layer cloud systems and ice cloud conditions. Notably, MERSI-II tended to overestimate CTH for low-level clouds while underestimating high-level clouds, demonstrating superior retrieval accuracy for water clouds compared to ice clouds.