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Offline surface UV (solar noon UV index) from Metop-B

Description: Offline surface UV (OUV) products contain the most important quantities of the solar radiation that can be harmful to life and materials on the Earth. These quantities include daily doses and maximum dose rates of integrated UV-B and UV-A radiation together with values obtained by different biological weighting functions, solar noon UV index and quality control flags.

Type: Offline. The products are available to users in two weeks from sensing. Usual delay is 3 days.

Theoretical basis: The OUV products are derived from O3M SAF near real-time total ozone column product (NTO/O3) and Advanced Very High Resolution Radiometer (AVHRR) reflectances, therefore combining data from two different instruments onboard the Metop-B satellite. Sampling of the diurnal cloud cycle is improved by using additional AVHRR data from the NOAA satellites, available through the data exchange between EUMETSAT and NOAA.

Processing: At the FMI, OUV processor reads the look-up tables containing the radiative transfer results, calculated using the VLIDORT model. Then the files containing the extraterrestrial solar irradiance and list of the validation sites are read. Then the values of the biological weighting functions at the wavelengths of the extraterrestrial solar irradiance spectrum are calculated.

Validation: OUV product is validated by FMI. The validation is based on detailed comparison of existing satellite data with ground-based measurements. Visit AC SAF Offline surface UV validation site for further information.

Online quality monitoring: OUV product quality is constantly monitored by FMI. The online monitoring is based on a tracking value calculated from the daily product. Visit AC SAF Offline UV online quality monitoring page for further information.

Units and spatial resolution: Daily doses are given in (kJ/m2) and daily maximum dose rates in (mW/m2). The UV index is a unitless linear scale, with higher values representing the risk level of skin damage due to UV exposure. All offline UV products are calculated in a 0.5° x 0.5° grid.

Archiving and dissemination: This product is archived at the FMI and available via offline data access page.

File format: OUV product is delivered in HDF5 format, each file containing global coverage for one day. The size of a single product file is about 42.5 MB.

Algorithm version information:

Time period GOME-2 / Metop-A GOME-2 / Metop-B
02.06.2009 - 08.07.2013 1.13 N.A.
09.07.2013 - 28.02.2014 1.20 N.A.
01.03.2014 onwards N.A. 1.20

Important algorithm changes in 1.20: