Investigation of the validity of the TDRC model for the distribution of diffuse sky radiance

Abstract

The validity is investigated of the three discrete radiance components (TDRC) model, which was introduced by the author as a model for the instantaneous and time-averaged distribution of diffuse sky radiance. The TDRC model incorporates the cloudy sky geometry (CSG) model, a model proposed by the author for the distribution of clouds across the sky dome in which clouds are modelled as upright vertical cylinders of variable diameter and height, and in which the distribution of clouds is modelled as cylinders randomly spaced, but having an average separation distance in any azimuthal direction. The investigation involves a calibration of the TDRC model for the case of cumulus clouds, followed by a validation under time-averaged conditions of the calibrated model, in which predictions of the model are compared with luminance observations, for a wide range of cloudiness. This comparison showed good agreement, and supports the validity of the TDRC model. It is anticipated that the TDRC model will be of significance to researchers in several fields, particularly those in solar engineering.