The Angular Distribution of Diffuse Sky Radiance: An Assessment of the Effects of Haze

Abstract

The effects of haze on the angular distribution of the diffuse sky radiance are investigated by examining and comparing data for individual clear skies with and without haze, and for other selected sky types, and by modeling and comparing data for such skies. It is found that haze appears to affect the radiance distributions only for clear, partly cloudy, and lightly overcast skies, and that for clear skies, increasing haze increases the absolute sky radiance values. In addition, the radiance distributions for clear skies with haze are found to exhibit characteristics generally similar to those for the nonopaque overcast skies. However, it is also found that the normalized radiance distributions for clear skies with haze, which generally provide clearer illustrations of distribution shape than the absolute radiance distributions, exhibit slightly less intense circumsolar and horizon brightening components than do the normalized distributions for clear skies without haze. In general, a systematic, but complex, relationship appears to exist between haze and the distribution of the diffuse sky radiance. The results may prove useful to several disciplines, including the design of solar technologies.