4. Albedos

In a terrestrial scene, the top, above the horizon, has the apparent luminance of the sky, and 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 both high albedos and high contrasts exist. These contributors will be at the origin of the useful signal in the image.

Albedos can be grouped into three families: plant: figure 12 , mineral: figure 13 and camouflage paints: figure