Albedo
From Swikipedia
Introduction
The albedo of an object is the extent to which it diffusely reflects light from light sources such as the Sun. In simple words, it can be defined as surface reflectivity of sun’s radiation. The term has its origins from a Latin word albus, meaning “white”. Albedo is the ratio of diffusely reflected radiation to incident electromagnetic radiation. It is a unitless measure indicative of a surface's or body's diffuse reflectivity.
Brief Description
The range of possible values is from 0 (dark) to 1 (bright). An ideal white body has an albedo of 100% and an ideal black body, 0%. Albedo values can range between 3% for water at small zenith angles to over 95% for fresh snow. On average the Earth and its atmosphere typically reflect about 4% and 26%, respectively, of the sun’s incoming radiation back to space over the course of one year. As a result, the earth-atmosphere system has a combined albedo of about 30%, a number highly dependent on the local surface makeup, cover, and cloud distribution.
The proportion of absorbed, emitted, and reflected incoming solar radiation steers the Earth's climate system causing fluctuations in temperature, winds, ocean currents, and precipitation. The climate system remains in equilibrium as long as the amount of absorbed solar radiation is in balance with the amount of terrestrial radiation emitted back to space. Earth's albedo values are very important in shaping local and global climates through the radiation budget, determined as the difference between the amount of absorbed shortwave radiation (input) and the outgoing long-wave radiation (output). For instance, clouds control the amount of energy that may reach the Earth’s surface. Since mean cloudiness varies geographically with lowest values observed in the subtropics and highest values in the mid- to high-latitudes, the variation of surface reflectance has a significant impact on the distribution of absorbed solar radiation at the surface. Approximately half of the incident solar energy is absorbed by the Earth's surface. This energy is then used to heat the land and oceans and drive the hydrologic cycle.
Surface reflectance has been derived through the use of satellites and remote sensing technology. The International Satellite Cloud Climatology Project (ISCCP) established as part of the World Climate Research Programme (WCRP) has been collecting surface and atmospheric reflectance data since 1983. A traditional technique for estimating the Earth's albedo is observation of the moon's ashgrey light - earthlight reflected from its dark hemisphere.
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