DAILY AND HOURLY GLOBAL IRRADIATIONS IN TUNISIA EXTRACTED FROM METEOSAT WEFAX IMAGES

To estimate solar irradiance at ground level, many satellite methods h ave been developed. The accuracy level and the performance of these me thods vary according to the complexity of the model used. The GISTEL m ethodology described by Ben Djemaa and Delorme (1992a,b) and Ben Djema a (1992) is based on a simple physical model with two components and u sed to assess the global irradiance from satellite images. It is descr ibed briefly in this paper. The treated images are of Wefax type of th e visible channel of Meteosat, regularly received in Carpentras. Our m ethod has been applied in Tunisia. The results obtained are compared t o the global, hourly and daily measurements done in three meteorologic al stations in the north of Tunisia. We have shown the possibility, fr om our images, to determine not only the daily irradiation but also th e evolution of solar irradiation during the day at whatever site situa ted in the field of view of the Meteosat satellite sensor. Thus two us eful pieces of information have been supplied by our model with suffic ient accuracy for the permanent control of an energetic solar system. Copyright (C) 1997 Elsevier Science Ltd.