5. Albedos

In a scene, the angular domain above the horizon or above the elements making up the terrestrial landscape has the apparent luminance of the sky, while the ground has the apparent luminance resulting from illumination modulated by the albedos or reflectivities of the materials making up the scene. The contrast between these albedos gives the image contrast. It is therefore advantageous to work in spectral domains where there are both high albedos and high contrasts, coinciding with the maxima of possible illuminances. These contributors are at the origin of the useful signal in the image.

Albedos can be grouped into three families: plant (figure 45 ), mineral (figure 46...