Glossary: A

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  1. The process in which radiant energy is retained by a substance. A further process always results from absorption, that is, the irreversible conversion of the absorbed radiation into some other form of energy within and according to the nature of the...
  2. A remote-sensing system that transmits its own radiation to detect an object or area for observation and receives the reflected or transmitted radiation. Radar is an example of an active system. Compare with passive system. Source: NASA (http://...
  3. Particles of liquid or solid dispersed as a suspension in gas. Source: NASA (http://earthobservatory.nasa.gov/Glossary)
  4. The existence in the air of substances in concentrations that are determined unacceptable. Contaminants in the air we breathe come mainly from manufacturing industries, electric power plants, automobiles, buses, and trucks. Source: NASA (http://...
  5. The ratio of the outgoing solar radiation reflected by an object to the incoming solar radiation incident upon it. Source: NASA (http://earthobservatory.nasa.gov/Glossary)
  6. Sudden spurts of algal growth due to greatly increased amounts of phosphorus entering the aquatic ecosystem from sewage systems and agricultural fertilizers. Excessive growth of the algae causes destruction of many of the higher links of the food...
  7. The magnitude of the displacement of a wave from a mean value. For a simple harmonic wave, it is the maximum displacement from the mean. For more complex wave motion, amplitude is usually taken as one-half of the mean distance (or difference)...
  8. Made by people or resulting from human activities. Usually used in the context of emissions that are produced as a result of human activities. Source: NASA (http://earthobservatory.nasa.gov/Glossary)
  9. The point in its orbit when a planet is farthest from the sun. Source: NASA (http://earthobservatory.nasa.gov/Glossary)
  10. On an elliptical orbit path, the point at which a satellite is farthest from the Earth. Source: NASA (http://earthobservatory.nasa.gov/Glossary)
  11. Layer of water-bearing permeable rock, sand, or gravel capable of providing significant amounts of water. Source: NASA (http://earthobservatory.nasa.gov/Glossary)
  12. The point in an orbit (longitude) at which a satellite crosses the equatorial plane from south to north. Source: NASA (http://earthobservatory.nasa.gov/Glossary)
  13. The air surrounding the Earth, described as a series of shells or layers of different characteristics. The atmosphere, composed mainly of nitrogen and oxygen with traces of carbon dioxide, water vapor, and other gases, acts as a buffer between Earth...
  14. The range of wavelengths at which water vapor, carbon dioxide, or other atmospheric gases only slightly absorb radiation. Atmospheric windows allow the Earth's radiation to escape into space unless clouds absorb the radiation. See greenhouse effect...
  15. The direction, in degrees referenced to true north, that an antenna must be pointed to receive a satellite signal (compass direction). The angular distance is measured in a clockwise direction. Source: NASA (http://earthobservatory.nasa.gov/Glossary)