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The albedo is the report/ratio of the solar energy reflected by a surface on incidental solar energy. One uses a scale graduated from 0 to 1, with 0 correspondent with the black, for a body with any reflection, and 1 with the perfect mirror, for a body which diffuses in all the directions and without absorption of all the visible Rayonnement electromagnetic that it receives.

Measurements

In practice, a body is perceived as white as soon as it reflects at least 80% of the light of a white source of light. Contrary any body reflecting less 3 % of the incidental light appears black.

Certain matters have a very variable albedo, like the Nuage S. On the other hand, the solid bodies very often have fixed albedos, which characterize to them Chemical composition. For example, the Lave has an albedo of 0,04, the Sable between 0,25 and 0,30, the ice between 0,30 and 0,50, snow (thick and fresh) up to 0,90. The terrestrial average albedo is of 0,39 all confused surfaces.

An important climatic indicator

The albedo is one of the indicators preventing of the temperature of the surface of the ground. It is a " baromètre" climatic variations which influences the knowledge of the amplitude of the greenhouse effect by opposing a positive feedback on the temperature on the surface and of the oceans, according to the variation of the volume of the ices.

The astronomical cooling of origin involves an extension of the continental ices, Inlandsis, Glacier S, and thus an increase in the albedo; the planet reflects the solar Rayonnement more, absorbs some less, which amplifies its cooling. The warming has opposite effects. What poses problem today: the warming of planet dissolves the polar icecap, which increases the warming of planet.

In astronomy

The albedo is used in Astronomie to have an idea of the composition of a too cold body to emit its own light, by measuring the reflection of an external source of light, like the Sun. One can thus easily differentiate the gas Planet S, which have a strong albedo, telluric planets which have they, a weak albedo.

For solar energy

Before installing equipment using the solar energy, it is important to know brightness on the ground, i.e. the quantity of solar light received on the ground. For that, one of the most effective techniques is the use of satellite of ground observation. The satellite of Meteosat of the second generation is thus able to provide precise measurements every 15 minutes on brightness on the ground of the continent of Europe.

The calculation of brightness on the ground also interests many other fields, like:

the Agriculture;
the Architecture;
the industry of the plastic , eager to adapt the guarantee of its products according to the place where they will be used;
the Medicine, to study the impact of solar light on health, via in particular the Luminothérapie.

Internal bond

"Albedo 0.39" is an album of music of Vangelis

External bond

"Why is the weather cold with the Poles? " An animation of the international polar Foundation which explains the influence of the albedo on the terrestrial temperature.

Simple: Albedo

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