SHORTCASTING OF ONE HOUR MICRO SCALE CLOUD FRACTION TREND THROUGH CLOUD INFRARED RADIOMETER DATA

Since quite two decades, numerous instruments have been designed for automatic cloud cover monitoring. Through them, we can mention the Hemispherical Sky Imager HSI (Long and De Luisi) and the Cloud Infrared Radiometers range CIR (Besnard et al.). The aim of this communication will be particularly dedicated to the CIR-4V. This instrument is devoted to microscale observation (few square kilometers. Even if the profitability and the repeatability of these instruments versus human observers have been clearly demonstrated, the deployment of such instruments in Automatic Weather Observing Systems (AWOS) stays low. In parallel of pure weather activities, another filed moved up quickly during the same period. That's the field of renewable energies like photovoltaic energy. Few square meters of solar cells on the roof of private houses are not concerned by this talk. We speak about farms with several hundreds of Photovoltaic cells square meters and even several thousands for some recent projects. The goal of these investments is to highlight this type of renewable energy. Such a position in the electrical supply network implies a question which is the production trend during the coming hour. Along this period other electrical production means could be activated in order to match consumer's needs. The clear sky irradiance could be nowadays calculated very accurately but most of the time, we face to broken cloud conditions and the impact of clouds is significant. In this communication, we will show that the cloud fraction is linked to correlation and anti-correlations between cloud fraction and cloud height through data retrieved by CIR-4V and in a second time, the application of the algorithm that we designed for a period of several months. Through this campaign, statistical results will be presented, discussed and ways of improvement proposed.