The Spatial distribution of diffuse solar radiation in the sky hemisphere

A technique was developed to produce maps of the distribution of diffuse solar radiation over the sky hemisphere for a variety of sky conditions. This procedure, by utilizing both actinometric and photographic information, overcomes the sampling problems of previous methods. Photographs were simultaneously exposed with actinometric measurements of diffuse solar radiance. The photographs were then digitized and the density values corresponding to the actinometric measurements correlated with the known radiances. The equation produced was then utilized to determine the radiance for each density value for the entire photograph. From this information, a map of diffuse solar radiation over the sky hemisphere was produced. To determine the quality of the radiance distributions, the estimated radiances were numerically integrated and compared with the diffuse irradiance incident on a horizontal surface. These were usually found to be within ±10% for the sky conditions examined. A further test, using this method to determine the diffuse irradiance, was performed to estimate the shortwave irradiance on several south-facing inclined surfaces. The results were found to be within ±5% of the measured values. The diffuse radiation distributions for clear skies were also compared with similar work and commented upon. This technique, although still not perfected, provides a superior means for instantaneously modelling diffuse energy and could also be utilized in the collection of the data base necessary for testing theoretical models of scattering in the atmosphere.Arts, Faculty ofGeography, Department ofGraduat