ALBEDO

The fraction of total incident solar radiation which is reflected by a surface. Albedo values are expressed using the ranges 0.01–1.00 or 0–100 per cent. Reflection does not change the wavelength of the incident radiation. Typical values of albedo include coniferous forests (5–15 per cent), crops (15–25 per cent), sand (20–30 per cent), grass (25 per cent), old snow (40–70 per cent) and freshly fallen snow (80–90 per cent). Water surfaces, such as a calm sea, normally have a very low albedo (around 5 per cent), but this increases to around 70 per cent when the elevation of the Sun is low and the waves are high. The albedo of clouds varies widely in relation to the type and thickness. The planetary albedo, measured at the top of the atmosphere and representing the Earth-atmosphere-ocean system as a whole, is 30–35 per cent. clouds are responsible for much of the planet’s brightness as seen from space. Venus and Mars have an albedo of around 75 per cent and 15 per cent, respectively.