For nearly thirty years, the AVHRR has provided information on cloud heights and emissivity via the split-window observations (11 and 12 microns). This information continues to be provided by METOP with a global resolution of 1km. Once launched, VIIRS will provide an additional window channel (8.5 micron) that allows more information on the cloud microphysics. This work examines the potential impact of the 8.5 micron channel on the estimate of cloud height, emissivity and cloud microphysics for cirrus clouds. This work also presents our planned NPOESS/VIIRS cloud products validations methods.