Albedo

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  • Albedo
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  • Albedo is the ratio of the radiation (radiant energy or luminous energy) reflected by a surface to that incident on it. Snow and cloud surfaces have a high albedo, because most of the energy of the visible solar spectrum is reflected. Vegetation and ocean surfaces have low albedo, because they absorb a large fraction of the energy. Clouds are the chief cause of variations in the Earth's albedo. 
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Abstract from DBPedia
    Albedo () (Latin: albedo, meaning 'whiteness') is the measure of the diffuse reflection of solar radiation out of the total solar radiation and measured on a scale from 0, corresponding to a black body that absorbs all incident radiation, to 1, corresponding to a body that reflects all incident radiation. Surface albedo is defined as the ratio of radiosity to the irradiance (flux per unit area) received by a surface. The proportion reflected is not only determined by properties of the surface itself, but also by the spectral and angular distribution of solar radiation reaching the Earth's surface. These factors vary with atmospheric composition, geographic location and time (see position of the Sun). While bi-hemispherical reflectance is calculated for a single angle of incidence (i.e., for a given position of the Sun), albedo is the directional integration of reflectance over all solar angles in a given period. The temporal resolution may range from seconds (as obtained from flux measurements) to daily, monthly, or annual averages. Unless given for a specific wavelength (spectral albedo), albedo refers to the entire spectrum of solar radiation. Due to measurement constraints, it is often given for the spectrum in which most solar energy reaches the surface (between 0.3 and 3 μm). This spectrum includes visible light (0.4–0.7 μm), which explains why surfaces with a low albedo appear dark (e.g., trees absorb most radiation), whereas surfaces with a high albedo appear bright (e.g., snow reflects most radiation). Albedo is an important concept in climatology, astronomy, and environmental management (e.g., as part of the Leadership in Energy and Environmental Design (LEED) program for sustainable rating of buildings). The average albedo of the Earth from the upper atmosphere, its planetary albedo, is 30–35% because of cloud cover, but widely varies locally across the surface because of different geological and environmental features. The term albedo was introduced into optics by Johann Heinrich Lambert in his 1760 work Photometria.

    アルベド(albedo)とは、天体の外部からの光に対する、反射光の比である。反射能(はんしゃのう)とも言う。アルベードとも表記する。 0以上、1前後以下(1を超えることもある)の無次元量であり、0 – 1の数値そのままか、0 % – 100 %の百分率で表す。

    (Source: http://dbpedia.org/resource/Albedo)

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