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Figure C 2.1. Penambra functions of diffusometers for 45 degrees solar elevation.

Comparing the calculated and measured sky functions it is seen, that the measured ones are much

larger then the calculated ones. This is illustrated by Figure C 2.2 where the measuredlargest, smallest

and mean function is seen altogether with ones calculated for different aerosol models, for 45 degrees

solar elevation. All calculated functions are below the measured mean one. The variability of the calculated

values is a factor of 5, while for the measured ones is about 10. The reason of difference between

the calculated and measured values is that, that the real cloudless atmosphere usually contains haze

particles too, while the model atmospheres are restricted to aerosol particles only. Figure C 2.3 shows

the smallest, mean and largest measured functions together with ones calculated for atmosphere including

haze particles too. Since the optical depth of haze contamination is very small, therefore the direct

and diffuse radiation changes slightly, but the circumsolar radiation might vary by several times.

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