Using Viewshed Models to Calculate Intercepted Solar Radiation: Applications in Ecology

The solar radiation intercepted at a given location on the earth's surface is influenced by surface orientation and sky obstruction by surrounding topographic features. Viewshed models can be used to calculate sky obstruction for any given location on or above a complex topographic surface. We have developed an algorithm for rapid calculation of intercepted solar radiation using a combination of viewshed analysis and a lookup table of irradiance from each sky direction. First, the angular distribution of sky obstruction is calculated for the location of interest and stored in a hemispherical coordinate system. Then lookup table values for all unobstructed sky directions are summed to determine total irradiance. Angle of incidence is accounted for using a cosine correction. The process can be repeated across a topographic surface to determine the /Spatial distribution of intercepted solar radiation. The results can be expressed as energy flux or as sky view factors. This lookup table approach accounts for anisotropic irradiance distributions and can treat different spectral bands separately. The same viewshed approach can be used for optimizing calculation of reflected radiation from topographic surfaces. This approach will be especially valuable for studies of ecological processes, by permitting assessment of topographic influences on energy balance and microclimate.