The influence of the albedo on the SSI varies with the solar zenith angle and the atmospheric turbidity. This influence is assessed by computing the difference between the SSIs obtained with the ground albedo equal to respectively 0 and 0.2 (Fig. 5).

The influence of the albedo on the SSI decreases as the wavelength increase because the intensity of diffusion decreases. It increases with increasing atmospheric turbidity and so, decreases also with increasing visibility. This influence decreases when the solar zenith angle is growing because of the decreasing of the SSI; this is also true for the relative deviation. Presence of clouds increases the relative influence of the albedo: the larger tc, the larger the relative deviation.