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

Topographic features of the Earth’s surface play a strong role in the element of solar radiation. To observe this, Viewshed models can be used which are critical for calculating sky obstructions on any topographic surface wh8ch ideally finds the amount of solar radiation being exposed to a specific area. These Viewshed models follow along with an algorithm for rapid calculation of solar radiation interception, which is then compared to a lookup table of irradiance from each direction in the sky.

As displayed by Figure 1 and from the basic example in Figure 2 above, the angular distribution of any sky obstruction is calculated for the location of interest and stored in a hemispherical coordinate system to be used for later reference. Then, the lookup table values for all the unobstructed sky directions are summed to determine the total irradiance where the angle of incidence is accounted by a cosine correction. This process can continually be repeated across any topographic surface to thus in turn to calculate the spatial distribution of intercepted solar radiation. After all results are collected, they can be expressed as ether an energy flux or as sky view factors. As an added benefit, this same viewshed approach can be used for optimizing a previous calculation of reflected radiation from a specific topographic surface. This approach has the potential to be pivotal for studies of ecological processes as it permits the assessment of topographic influences on energy balance and microclimate.

In conclusion, solar radiation has and is still becoming the most prominent source of energy arising from the Earth’s surface. Topography itself has also become a significant factor in manipulating the radiation points for a specific spatial location. A general algorithm presented by the authors of this article allows for this tracking of topographic influences on solar radiation by factors of – but not limited to – sky obstruction, irradiance, and surface orientation. This algorithm also is very flexible and can be used easily by observers as it permits a choice in the level of resolution to use in simulations as they are derived from theories or noted data based on various first principles.

Rich, P.M., R. Dubayah, W.A. Hetrick, and S.C. Saving. 1994. Using viewshed models to calculate intercepted solar radiation: applications in ecology. American Society for Photogrammetry and Remote Sensing Technical Papers. pp 524–529.