Performance validation of MURAC, a cloudless sky radiance model proposal

The behaviour of a new model, previously proposed, for the directional distribution of the clear sky diffuse radiance is presented in this work. This new model, called MURAC, includes two parameters for which simple expressions without local dependence were proposed. In this way MURAC claims to be a general applicability model for the angular distribution of cloudless sky radiance. We present the model performance analysis by means of the well-known SKYSCAN 83/84 DATA SET, which involves angular sky radiance distributions recorded at Toronto, Canada. This analysis indicates that MURAC is able to estimate instantaneous sky radiance values with a mean bias error of −3.7% and a root mean square error of 63.6%. These results, in the same order of magnitude as other sky radiance models, seem to confirm our expectation.