Abstract
The Heliosat-II method was developed to process Meteosat satellite images in order to assess the solar irradiation at surface. It is modified for its use with GOES satellite images in order to estimate the solar irradiation over French Guiana. Modifications include a change in the calibration formula, in the calculation of the cloud albedo and in the values of the Linke turbidity factor. These modifications allow the improvement of t he performances of the Heliosat-II model in Intertropical z ones in French Guiana. The outcomes were compared to coincident measurements of hourly irradiation performed by ground stations. The res ults show that the use of the maximum apparent albedo as the cloud albedo (ρc max), along with a fixed value of the Linke turbidity factor produces the best results; the bias was less than 23.61 Wh/m² (5% of the mean value of the measurements) overall and the RMSE was less than 109.39 Wh/m² (24 %) overall when using hourly values. In the case of daily means, the RMSE drops down to less than 10.08 W/m² (10%) overall whereas the overall bias remains unchanged as expected. The model performs better in clear skies than in cloudy skies. The results suggest that the Linke turbidity factor used in the Heliosat-II method does not reproduce well the attenuation of the solar radiation in French Guiana. The results were compared to those obtained from Heliosat II method and Meteosat images (HelioClim-3 database) and we found a better accuracy for GOES satellite data which exhibits smaller viewing angle. The use of the Heliosat II method with GOES images allows assessment of the SSI with a good accuracy and high temporal and spatial resolutions.