Abstract : The goals of the Heliosat project of Ecole Nationale Supérieure des Mines de Paris are: (i) to design a system for the estimation of incident solar radiation at ground level from images of the Earth acquired by geostationnary satellites, (ii) to produce detailed maps of the spatial distribution of the global radiation, and (iii) to improve the system depending upon the results and progress in science. Among the numerous methods already developed, one of them has been selected for its accuracy as well as its simplicity. It has been tested during 30 consecutive months starting from January 1983. Operations were performed in a completely automatic, unmanned fashion and trades-off between routine and accuracy have been adopted. Areas under concern were Europe and Central-Western Africa (1984 only). This paper presents the results of the tests conducted during 1983. Measurements of sixteen pyranometers were compared three times a day to the estimates of the selected method. Different comparisons are presented. The errors in the reconstruction of both the instantaneous hourly global radiation Gh and the monthly average of Gh is less than 0.06 kWh/m2. When compared to other methods, Heliosat ranks as one of the most accurate.