Atlantic High Latitude Surface Solar Irradiance
The high latitude radiative flux products developed at the Norwegian Meteorological Institute contains shortwave (SSI) and longwave (DLI) irradiance received at the surface. The Ocean and Sea Ice SAF radiative flux products are currently produced at 5km spatial resolution once daily. Input data are AVHRR and VIIRS data from NOAA POES and Eumetsat Polar System (EPS). Although each satellite passage is processed, the official radiative flux products from the EUMETSAT OSISAF are daily products which represents the mean daily irradiance received at the surface in Watt per square meter.
This page describes the SSI product.
The processing of OSISAF HL radiative flux products starts with processing the AVHRR and VIIRS data to Level 1C on the satellite swath and then generating cloud type products using the NWCSAF PPS v2021 processor. 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 the satellite swath by the OSISAF HL FLUX processor. These product areas are then, for each satellite passage, resampled onto 5km 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.
Basically the following steps are required to generate the surface solar irradiance from AVHRR and VIIRS input at pixel level (see the product user manual for details):
- Get input data
- Decide whether cloudy or cloud free
- Estimate clear sky irradiance
- If cloudy
- Narrowband to Broadband correction
- Anisotropy correction
- Estimation of cloud factor
- Estimation of cloudy sky irradiance
SSI and DLI validation
The estimates based on remote sensing data are routinely validated against available in situ measurements. Much effort has been dedicated to validation and gaining access to relevant validation data in recent years. In the map below validation stations where data are available for usage in the OSISAF validation scheme are indicated.