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Daily downward shortwave 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 (see product manual for details).

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.

Basically the following steps are required to generate the surface solar irradiance from AVHRR input at pixel level (see product manual for details):

  1. Get input data
  2. Decide whether cloudy or cloud free
  3. Estimate clear sky irradiance
  4. If cloudy
    1. Narrowband to Broadband correction
    2. Anisotropy correction
    3. Estimation of cloud factor
    4. Estimation of cloudy sky irradiance

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 are at any time used in the validation as maintenance, other technical problems or characteristics of the station prevents it from being used at times. Recent validation results are presented at the bottom of the main product page.

Sample OSISAF SSI daily product
   
       
     

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