A GIS-based methodology for assigning experimental measurements of angular distribution of sky radiance and luminance to selected sky sectors

Mathematical models for the estimation of the angular distribution of diffuse radiance/luminance in the sky describe the anisotropic character of diffuse solar radiation and daylight in the sky vault. In most of these models the radiance/luminance of a sky point is determined by the product of the indicatrix function and the gradation function. When developing and/or calibrating these models, it is typical to consider separately the dispersion effects in the direction of the sun's rays and the gradation from the zenith towards the horizon. To do this, the sky is divided into a number of concentric spherical zones around the sun and a number of concentric spherical zones around the zenith. The intersection between both sets of zones delimits a series of sky elements. Unfortunately, these sky elements do not correspond to the 145 patches of sky vault recommended by the International Commission on Illumination (CIE), which are routinely scanned by the existing commercial sky scanners. The identification of the sky elements, geometrically different from those observed by commercial sky scanners, and the assignation of the radiance/luminance values registered by such sky scanners are not analytically trivial tasks. A GIS-based methodology is presented in this work to undertake these goals.