Fast Retrieval Scheme for Clouds from Oxygen absorption bands
The satellite UV-visible spectrometers, GOME, SCIAMACHY, GOME-2, and OMI provide continuous atmospheric composition data for air quality and climate monitoring. The new-generation satellite instruments Sentinel-5P, Sentinel-4, and Sentinel-5 are dedicated to monitoring the composition of the atmosphere for the Copernicus Atmosphere Monitoring Service. Clouds have a strong impact on atmospheric composition retrievals from satellite measurements. Therefore, we have developed cloud retrieval algorithms (FRESCO and O2-O2) for satellite spectrometers.
The Fast Retrieval Scheme for Clouds from the Oxygen A band (FRESCO) algorithm retrieves cloud parameters using oxygen A band (centered at 760 nm). The FRESCO cloud products include effective cloud fraction, cloud pressure (height), scene pressure (height), and scene albedo. The FRESCO effective cloud fraction and cloud pressure are included in the EUMETSAT GOME-2 L1b product. The FRESCO cloud products are also available on the TEMIS website (http://www.temis.nl/fresco). Figure 1 shows the multi-year mean FRESCO effective cloud fraction and cloud pressure maps from SCIAMACHY.
For OMI, the O2-O2 absorption close to 477 nm is used to derive cloud parameters. According to our recent studies, the FRESCO and O2-O2 cloud products are comparable. Furthermore, the broadband surface solar irradiance (SSI) is derived using the OMI O2-O2 effective cloud fraction and available at http://www.temis.nl/ssi/. Figure 2 illustrates the surface solar irradiance from the OMI SSI product.
Recently, KNMI has performed several projects from EUMETSAT, ESA, and NWO/NSO to improve and develop the FRESCO cloud retrieval algorithm. One of the new developments of the FRESCO algorithm is to retrieve cloud parameters using the oxygen B band (at 688 nm) and to derive scattering cloud parameters (NWO/GO FRESCO-B project, to be finished in 2019). Figure 3 shows an example of the GOME-2 O2 A and B bands spectra. We expect that the FRESCO algorithm will be run operationally for TROPOMI and Sentinel-5.