OSI SAF central
Daily downward longwave irradiance
The processing of OSISAF HL radiative flux products are based upon processing the AVHRR data to Level 2 and predefined product areas by the EUMETSAT NWPSAF software package AAPP in combination with Meteo France/CMS software ANA and EUMETSAT NWCSAF software AHAMAP. The predefined product areas are also output from the NWCSAF PPS cloudmask/cloudtype processing. Whenever a new satellite passage is received, the NWCSAF PPS cloudtype is generated and OSISAF HL Flux processing is initiated.
All auxiliary data needed in the processing are remapped to these predefined areas which also are the high resolution products (1.5km nominal horizontal resolution) generated by the OSISAF HL FLUX processing. These product areas are, for each satellite passage, resampled onto 5 and 10km OSISAF HL grids (Polar stereographic, correct at 60°N, aligned along the Greenwich meridian. In the resampling only pixels with a confidence level of equal or better than bad are used.
The same procedure is used when the individual satellite passages at the OSISAF HL grid are averaged to get a daily estimate. Due to the poor coverage in time, no 3 hourly product is generated of the OSISAF HL Flux processing.
The algorithm is the same as the algorithm used by Meteo France/CMS for GOES/MSG data (see the product manual for details). It is essentially a hybrid method combining a bulk parameterization for the clear sky contribution and satellite derived cloud information according to the formula:
DLI = (e0 + (1 - e0) C ) S Ta4
AVHRR data both from NOAA and EUMETSAT satellites are used in the processing.
A sample product is provided below. The white dots in the image represents potential validation stations. All of these observe shortwave incoming irradiance, but not all observe longwave incoming irradiance. Please check the map of validation stations on the main information page for OSISAF radiative fluxes. Recent validation results are presented at the bottom of the main product page.