Solar radiation enters the Earth's atmosphere with a portion being scattered by clouds and aerosols.

Processing, archiving and distributing Earth science data
at the NASA Langley Research Center

What is ISCCP?

ISCCP is the International Satellite Cloud Climatology Project, established in 1982 as part of the World Climate Research Programme (WCRP), to collect and analyze satellite radiance measurements to determine the global distribution of clouds, their properties, and their diurnal, synoptic, seasonal and interannual variations.

http://isccp.giss.nasa.gov/overview.html