| Summary: | R.sun is a solar radiation model implemented in the OpenSource GRASS GIS. The model can be used to calculate spatial patterns of both instantaneous and daily sums of beam, diffused and reflected solar radiation. The input data are digital elevation model, needed to calculate slopes and their aspects, and the Linke turbidity factor, which describes the attenuation of the solar radiation in the atmosphere. Optionally, terrain-shadowing effects may be considered, which is important for areas with complex relief. Effects of cloudiness on the incoming solar radiation can also be parameterised, separately for the beam and diffused radiation. Here the r.sun model is applied to calculate the potential (i.e. for cloudless conditions) solar radiation for the Hornsund area (SW Spitsbergen). The shadowing effect is included, which is of special importance for the area because of the relief complexity and low solar altitudes. The results are shown on a series of maps and compared with measurements. The validation of the model shows a good agreement between the model results and the available measurements.
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