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Words begining with "U"
Ultraviolet Radiation
The energy range just beyond the violet end of the visible
spectrum. Although ultraviolet radiation constitutes only about 5
percent of the total energy emitted from the sun, it is the major
energy source for the stratosphere
and mesosphere, playing a
dominant role in both energy balance and chemical composition.
Most ultraviolet radiation is blocked by Earth's atmosphere, but
some solar ultraviolet penetrates and aids in plant photosynthesis
and helps produce vitamin D in humans. Too much ultraviolet radiation
can burn the skin, cause skin cancer and cataracts, and damage
vegetation.
UARS
See Upper Atmosphere Research Satellite.
United States Geological Survey (USGS)
A bureau of the Department of the Interior. USGS was established
in 1879 following several Federally-sponsored independent natural
resource surveys of the West and Midwest. The Department of the
Interior has responsibility for most of our nationally owned public
lands and natural resources. The USGS monitors resources such as
energy, minerals, water, land, agriculture, and irrigation. The
resulting scientific information contributes to environmental-policy
decision making and public safety. For example, USGS identifies
flood- and landslide-prone areas and maintains maps of the United
States.
United States Global Change Research Program (USGCRP)
The USGCRP addresses significant uncertainties concerning the
natural and human-induced changes to Earth's environment. The USGCRP
has a comprehensive and multidisciplinary scientific research agenda.
See Global Change Research Proqram.
Upper Atmosphere Research Satellite (UARS)
UARS is part of a long-term, international program of space
research into global atmospheric change. Beginning in 1991, NASA's
UARS program began to carry out the first systematic, detailed
satellite study of the Earth's stratosphere,
mesosphere, and lower
thermosphere; establish the comprehensive data base needed for an
understanding of stratospheric ozone
depletion; and bring together scientists and governments around the
world to assess the role of human activities in atmospheric change.
Launched on September 12, 1991, UARS became the first official space
component of Mission to Planet
Earth.
USGCRP
See United States Global Change Research
Program.
UTC
See Coordinated Universal Time.
UV
Ultraviolet. See ultraviolet
radiation.
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