Parameters - Geographical Coverage - Time Period - Units - Accuracy - Methodology - Acknowledgements -

Version 2.1 - 21 January 2005 ---- Version 3.0 since 4 March 2005

Warning. Known Defects (21 January 2005).
1. Spatial discontinuity of the radiation field off the coasts of Senegal (corrected)
2. Too low values for the Eastern half of the Arabian Peninsula (corrected)

Version 3.0 corrects for the defects mentioned above.

Parameters provided: time-series of global irradiation or irradiance

• daily values
• monthly mean of daily values
• 5- or 10-days (pentad) or monthly sums
• clearness index
• a reliability parameter

Approximately: 66 N - 66 S ; 66 E - 66 W. The field of view is restricted to the pixels belonging to the Earth and for which the elevation angle of Meteosat above horizon is larger than 12 degrees.

Clik on picture for magnification (copyright Eumetsat)

Data are regularly supplied by Eumetsat each month at the beginning of the following month.

Accuracy

Assessed by comparisons with measurements of the WMO radiometric network in Europe (55 sites) and Africa (35 sites) for the period 1994 - 1997.

	Mean value	Bias	RMSE
Daily Values	4848 Wh/m2 17453 kJ/ m2 202 W/m2	24 86 1	840 3024 35
Monthly Means of Daily Values	4848 Wh/m2 17453 kJ/ m2 202 W/m2	24 86 1	600 2160 25
5-days Sums	22.6 kWh/m2 81.5 MJ/ m2	0.1 0.4	3.2 11.6
10-days Sums (pentads)	45.4 kWh/m2 163.3 MJ/ m2	0.2 0.7	6.0 21.7
Monthly Sums	145 kWh/m2 497 MJ/ m2	0.7 2.6	17 60

Methodology

The images taken by the satellite Meteosat, in B2 format, are processed by the means of the method Heliosat-2. Hourly irradiations are computed every 3 hours, starting at 0000 UTC, and stored into a database (HelioClim). Upon request, daily values or other parameters are constructed. The reliability parameter ranges from 1 to 5. It indicates the number of valid elements used for the construction of the parameter. One may see it as a percentage once multiplied by 20. For example, a reliability parameter of 5 for a daily value means that all the possible hourly values for that day are valid and used for the construction of the parameter.

The database HelioClim comprises hourly values every 3 hours. The accuracy of these instantaneous assessments is about 107 W/m2 (RMSE) for a mean value of 339 W/m2 (approx. 32 %). As for monthly mean irradiance for a given hour, the RMSE is 52 W/m2 for the same mean value (approx. 15 %). These basic data are not presently distributed through this service. In case of strong interest, an access to these data can be envisioned. Please, contact Lucien Wald.

Acknowledgements

Eumetsat (and especially the Archive Facility) for their kind support in continuously supplying Meteosat data. WRDC and Met-Offices from Belgium, France, Germany, Hungary, South Africa, Spain, United Kingdom provided radiometric measurements for validation.