Albedo

Theoretically, the albedo's value may change from 0 of a blackbody until 1 of a 'white body' completely reflecting the solar radiation. It is natural that an albedo depends on spectrum of the radiation, since different surfaces reflect differently in different spectral bands.

Albedos of typical underlying surfaces in visible light range from 0.04 for charcoal, one of the darkest substances, up to 0.90-0.95 for fresh snow. Albedo of salt and sand deserts are 0.45-0.5, while the albedo of coniferous forest is 0.1. Note that the maximal albedo of a surface, covered by vegetation (meadow), is 0.25. Albedo of wet soils is usually less than the albedo of dry ones, for instance, the albedo of chernozem (~0.15) is reduced to 0.05 under moistening conditions.

The classic examples of albedo's effect are the snow-, vegetation-, and moisture-temperature feedbacks. If a snow-covered area warms and the snow melts, the albedo decreases down to 0.4-0.5, more sunlight is absorbed, and the temperature tends to increase. If a desert is covered by vegetation, then the albedo decreases, and the temperature has to increase. While the increase in plant biomass tends to slow down in the carbon dioxide concentration in the atmosphere that, in turn, tends to decrease the temperature, so that the balance of these feedbacks may become very complex. Similar considerations are valid also for 'soil moisture-temperature' feedback.

Albedo of water bodies differs from albedo of land surfaces, since the reflection of SWR from water depends on the angle of incidence. At small angles, most part of radiation is reflected from the surface, not penetrating deeply into water body. As a result the albedo increases up by a few tenths, while the albedo at the great angles, that is, when the Sun elevation is high, is equal to a few hundredths. For instance, if the angle of incidence @ <10°, then a >0.22; if @ >45°, then a < 0.05. Albedo of scattered radiation does not really depend on the angle of incidence, and it is almost constant, about 0.10.

The significant part of incoming radiation is reflected by clouds; their albedo, depending on the thickness of cloudiness, is equal on average to 0.4-0.5, so that the mean albedo of the Earth is about 0.29. This is far higher than for the ocean primarily.

The Earth's surface albedo is regularly estimated via 'Earth observation satellite sensors' such as NASA's MODIS instruments onboard the Terra and Aqua satellites.

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