Glossary: P

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  1. Sensitive to all or most of the visible spectrum. Source: NASA (http://earthobservatory.nasa.gov/Glossary)
  2. A constant whose values determine the specific form or characteristics of an expression. Source: NASA (http://earthobservatory.nasa.gov/Glossary)
  3. A unit of measure used for very small quantities, it is equal to the ratio of the weight or volume of one component of a mixture to a billion weights or volumes of the mixture. When based on weight (ppbw), it is equal to the weight or mass of the...
  4. Unit of atmospheric pressure named in honor of Blaise Pascal (1632-1662), whose experiments greatly increased knowledge of the atmosphere. A pascal is the force of one newton acting on a surface area of one square meter. It is the unit of pressure...
  5. A system sensing only microwave radiation emitted by the object being viewed or reflected by the object from a source other than the system. Source: NASA (http://earthobservatory.nasa.gov/Glossary)
  6. A system sensing only radiation emitted by the object being viewed or reflected by the object from a source other than the system. See active system. Source: NASA (http://earthobservatory.nasa.gov/Glossary)
  7. The instruments that are accommodated on a spacecraft. Source: NASA (http://earthobservatory.nasa.gov/Glossary)
  8. On an elliptical orbit path, the point where a satellite is closest to the Earth. Source: NASA (http://earthobservatory.nasa.gov/Glossary)
  9. The point in the orbit of a planet or comet which is nearest the Sun (as opposed to the aphelion, which is the point in the orbit farthest from the Sun). Source: NASA (http://earthobservatory.nasa.gov/Glossary)
  10. pH
    A symbol for the degree of acidity or alkalinity of a solution. Expressed as a negative logarithm of the hydrogen ion concentration in a solution, pH = -log10[H+]. If the hydrogen ion concentration of a solution increases, the pH will decrease, and...
  11. Microscopic, plant-like marine organisms (mostly algae and diatoms), which are responsible for most of the photosynthetic activity in the oceans. Phytoplankton are the base of the ocean food web, and they absorb about as much carbon dioxide from the...
  12. Pixel, short for picture element, is the ground area corresponding to a single element of a digital image data set. Source: NASA (http://earthobservatory.nasa.gov/Glossary)
  13. The fraction of incident solar radiation that is reflected by a planet and returned to space. The planetary albedo of the Earth-atmosphere system is approximately 30 percent, most of which is due to backscatter from clouds in the atmosphere. Source...
  14. Concept that the Earth's crust is composed of rigid plates that move over a less rigid interior. Source: NASA (http://earthobservatory.nasa.gov/Glossary)
  15. A satellite that can carry instruments. See bus. The same term is applied to automatic weather data transmitters installed on buoys, balloons, ships, and planes, and mounted in remote areas. Source: NASA (http://earthobservatory.nasa.gov/Glossary)
  16. An orbit with an orbital inclination of near 90 degrees where the satellite ground track will cross both polar regions once during each orbit. The term is used to describe the near-polar orbits of spacecraft such as the USA's NOAA/TIROS and Landsat...
  17. Strictly, too much of any substance in the wrong place or at the wrong time is a pollutant. More specifically, atmospheric pollution may be defined as the presence of substances in the atmosphere, resulting from man-made activities or from natural...
  18. The comparatively slow torquing of the orbital planes of all satellites with respect to the Earth's axis, due to the bulge of the Earth at the equator which distorts the Earth's gravitational field. Precession is manifest by the slow rotation of the...
  19. Moisture that falls from clouds. Although clouds appear to float in the sky, they are always falling, their water droplets slowly being pulled down by gravity. Because their water droplets are so small and light, it can take 21 days to fall 1,000...
  20. The knowledge and capacities developed by governments, professional response and recovery organizations, communities and individuals to effectively anticipate, respond to, and recover from, the impacts of likely, imminent or current hazard events or...
  21. The outright avoidance of adverse impacts of hazards and related disasters. Comment: Prevention (i.e. disaster prevention) expresses the concept and intention to completely avoid potential adverse impacts through action taken in advance. Examples of...