Image-based measurement of clear sky radiation distribution from 0 to 5000 meters above sea level

Field observations were carried out in the Pyrenees and the Andes to study the evolution of the distribution of solar radiation on clear sky conditions at high altitudes. We recorded measurements in increments of approximately 1000 m, from Anglet (France), at sea level (0 mamsl: meters above mean sea level), to the heights of Chimborazo (Ecuador), at nearly 5000 mamsl. In high-altitude cities, such as Quito, the sun is brighter and the sky is darker than at the foothills of the Pyrenees. The measurement of this radiation, necessary for thermal simulation by finite element methods, raises challenges due to the extreme differences between the sun and the sky. The measurement technique is based on flexible imaging techniques that allow obtaining, on a single image, the direct and diffuse irradiances of the sky. The results obtained are consistent with theoretical models and provide additional information on the color of the sky.