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CHAPTER 10. THEORETICAL BACKGROUND
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Figure 10.6: Solar illumination geometry and radiation components.
The illumination image cosβ(x, y) is calculated within ATCOR and stored as a separate map. The
diffuse solar flux on an inclined plane is calculated with Hay’s model (Hay and McKay 1985, also
see Richter 1998 for the enhancement with the binary factor b):
Ed∗ (x, y, z) = Ed (z)[bτs (z)cosβ(x, y)/cosΘs + {1 − bτs (z)}Vsky (x, y)]
(10.18)
The sky view factor can be computed from local information as Vsky (x, y) = cos2 (Θn (x, y)/2)
based on the local DEM slope angle Θn . ATCOR uses the horizon algorithm that provides a more
accurate value of the sky view factor by considering the terrain neighborhood of each pixel (Dozier
et al. 1981). Vsky and Vterrain are related by :
Vsky (x, y) = 1 − Vterrain (x, y)
(10.19)