Cloud phase classification using SLSTR measured brightness temperatures at 3.74, 10.85, 12.00 μm

This study investigates the sensitivity of satellite-based brightness temperature measurements at 3.74, 10.85, and 12.00 μ m with respect to the identification of water, ice, and mixed-phase clouds (MPC). Radiative transfer simulations computed by SCIATRAN reveal that the directional brightness temperature difference at 3.74 μ m ( Δ BT 3 . 74 ), which is dependent on scattering, enables water clouds and MPC separation from ice clouds. For water clouds and MPC, Δ BT 3 . 74 typically exceeds 2 K, whereas for ice clouds it remains below 2 K. To separate MPC from water clouds, we introduce the Liquid Cloud Probability Index (LCPI) based on cloud top temperature and absorption differences between water and ice at 10.85 and 12.00 μ m. LCPI values generally exceed 0.4 for water clouds but fall below 0.4 for many MPC cases. The Δ BT 3 . 74 and LCPI approach is validated using the Sea and Land Surface Temperature Radiometer (SLSTR) dual-view data collocated with the 2B-CLDCLASS-LIDAR cloud phase product, showing over 90% accuracy in water and ice phase classification, and approximately 60% for MPC. This dual-view, multi-channel method enhances the detection of cloud phases, offering improved results for brightness temperature measurements.