This study introduces global cloud climatology derived from CALIPSO observations. The algorithm theoretical basis, algorithm performance, and global cloud statistics will be discussed. The theoretical studies include: 1) deriving a simple relation between multiple scattering and depolarization for cloud phase discrimination (Hu 2007, GRL); 2) estimating cloud droplet number concentration from combined MODIS/CALIPSO data sets (Hu et al. 2007, ACP); and 3) analyzing extinction to backscatter ratios for various clouds.

Based on the theoretical studies, cloud algorithms are developed to retrieve accurate cloud properties. The performance of the algorithm is verified against ground measurements. The global cloud statistics are obtained using the combined active/passive measurements and will be presented.