The FRESCO+ cloud algorithm for GOME and SCIAMACHY: improvement and validation

The FRESCO algorithm (Fast Retrieval Scheme for Clouds from the Oxygen A-band) has been successfully used for GOME and SCIAMACHY cloud retrieval for several years. FRESCO simulates the measured reflectance at top-of-atmosphere at 15 wavelengths at about 758, 761, and 765 nm. In FRESCO only O2 absorption has been considered until now. In the
new version of the FRESCO algorithm, FRESCO+, single Rayleigh scattering has been added to the reflectance database and the retrieval. The new reflectance database has been compared with detailed radiative transfer model simulations of the O2 A-band using the DAK model (Doubling Adding KNMI).
The FRESCO algorithm will also be used in the GOME-2 data processing by EUMETSAT.

FRESCO+ has been applied to GOME and SCIAMACHY data. The improvements in the FRESCO+ cloud results are mostly important for the less cloudy pixels, which are most relevant for detection of tropospheric pollution.

The FRESCO+ cloud pressures have been validated at single pixel scale with SGP/ARM results of
cloud boundaries obtained by active remote sensing. Globally averaged ISCCP cloud fraction, cloud optical thickness and cloud top height have been
used for validation of FRESCO+ effective cloud fraction and cloud height.