Atmospheric correction for the KNMI Cloud Physical Properties retrieval algorithm

A procedure is described to correct monochromatic reflectances simulated by a radiative transfer model to narrow-band reflectances measured by a satellite imager and affected by trace-gas absorption in the atmosphere. This atmospheric correction scheme has been implemented in the KNMI/CM-SAF Cloud Physical Properties (CPP) retrieval algorithm, version 3.0.
Correction factors have been calculated for three satellite instruments (SEVIRI, MODIS, and AVHRR) and five spectral bands (around wavelengths 0.6, 0.8, 1.6, 2.1, and 3.8 micrometer). The effect of atmospheric correction on CPP retrievals based on the 0.6- and 1.6-micron bands is illustrated using SEVIRI data over Europe. On average, the cloud optical thickness increases by about 3%, while the particle effective radius decreases by about 10%.