MODIS observations of 3D radiative effects occurring in clouds

Most current algorithms used for cloud remote sensing rely on 1D radiative theory, which assumes no horizontal changes in cloud properties and radiation fields. While this approximation is highly advantageous from a practical standpoint, it can lead to errors for clouds that display significant horizontal variability. This study examined 3D radiative effects through a statistical analysis of MODIS Level 2 radiances and cloud products that considered liquid water clouds in virtually all daytime granules in a one year long period. The results indicate that 3D radiative effects change the angular and spatial patterns of cloud reflection, and that this affects the cloud optical thickness values retrieved using 1D theory. As a result, optical thicknesses retrieved for inhomogeneous clouds tend to be larger for oblique than for overhead views, and for cloud slopes that are tilted toward rather than away from the sun. The presentation will discuss these observations and their implications for satellite retrievals of cloud optical thickness.