Christelle Rigollier

On the clear sky model of the ESRA - european solar radiation atlas - with respect to the heliosat method

Abstract This paper presents a clear-sky model, which has been developed in the framework of the new digital European Solar Radiation Atlas (ESRA). This ESRA model is described and analysed with the main objective of being used to estimate solar radiation at ground level from satellite images with the Heliosat method. Therefore it is compared to clear-sky models that have already been used in the Heliosat method. The diffuse clear-sky irradiation estimated by this ESRA model and by other models has been also checked against ground measurements, for different ranges of the Linke turbidity factor and solar elevation. The results show that the ESRA model is the best one with respect to robustness and accuracy. The r.m.s. error in the estimation of the hourly diffuse irradiation ranges from 11 Wh m −2 to 35 Wh m −2 for diffuse irradiation up to 250 Wh m −2 . The good results obtained with such a model are due to the fact that it takes into account the Linke turbidity factor and the elevation of the site, two factors that influence the incoming solar radiation. In return, it implies the knowledge of these factors at each pixel of the satellite image for the application of the Heliosat method.

The Operational Calibration of Images Taken in the Visible Channel of the Meteosat Series of Satellites

A method and its implementation are presented for the automatic calibration of the images taken in the visible channel of the Meteosat series of satellites. The method performs on a daily basis and is based on a statistical analysis of two images: one when the sun illuminates the entire field of view of Meteosat, the other during nighttime. This approach does not require any information about atmospheric and surface parameters, and therefore can be easily performed either on archived data, or in quasi-real time when receiving the images. Daily calibration coefficients were obtained since 1985 and are available on the Internet. The results are fully consistent with previous studies.