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Words begining with "G"
The hypothesis that the Earth's atmosphere,
biosphere, and its living
organisms behave as a single system striving to maintain a stability
that is conducive to the existence of life.
The increase in signal power produced by an amplifier, usually
expressed in decibels as the ratio of
the output to the input. A measure of the effectiveness of a
directional antenna as compared to a non-directional antenna. See
A branch of applied mathematics concerned with measuring the shape
of the Earth and describing variations in the Earth's gravity field.
Geographic Information System (GIS)
A system for archiving, retrieving, and manipulating data that has
been stored and indexed according to the geographic coordinates of
its elements. The system generally can utilize a variety of data
types, such as imagery, maps, tables, etc.
A surface of constant gravitational potential around the Earth -
an averaged surface perpendicular to the force of gravity.
The physical elements of the Earth's surface, crust, and interior.
Describes an orbit in which a satellite is always in the same
position (appears stationary) with respect to the rotating Earth. The
satellite travels around the Earth in the same direction, at an
altitude of approximately 35,790 km (22,240 statute miles) because
that produces an orbital period equal to the period of rotation of
the Earth (actually 23 hours, 56 minutes, 04.09 seconds). A worldwide
network of operational geostationary meteorological satellites
provides visible and infrared images of Earth's surface and
atmosphere. The satellite systems include the U.S. GEOS,
METOSAT (launched by the European
Space Agency and operated by the European Weather Satellite
Organization-EUMETSAT), the Japanese GMS, and most
commercial, telecommunications satellites. See Clarke
Geostationary Meteorological Satellite (GMS)
Japan's geostationary weather satellite.
Geostationary Operational Environmental Satellite (GOES)
NASA-developed, NOAA-operated series of satellites that:
- provide continuous day and night weather observations;
- monitor severe weather events such as hurricanes.
thunderstorms. and flash floods;
- relay environmental data from surface collection platforms to
a processing center;
- perform facsimile
transmissions of processed weather data to low-cost receiving
- monitor the Earths magnetic field, the energetic particle flux
in the satellite's vicinity, and x-ray emissions from the
- detect distress signals from downed aircraft and ships.
GOES observes the U.S. and adjacent ocean areas from vantage
points 35, 790 km (22,240 miles) above the equator at 75 degrees west
and 135 degrees west. GOES satellites have an equatorial,
Earth-synchronous orbit with a 24-hour period, a resolution of 8 km,
an IR resolution of 4 km, and a scan rate of 1864 statute miles in
about three minutes. See geostatinary.
The transmission of processed weather data (both visible and
infrared) by GOES is called weather facsimile (WEFAX).
GOES WEFAX transmits at 1691 + MHz and is accessible via a ground
station with a satellite dish antenna. GOES carries the following
five major sensor systems:
- The imager is a multispectral instrument capable of sweeping
simultaneously one visible and four infrared channels in a
north-to south swath across an east-to-west path, providing full
disk imaqery once every thirty minutes.
- The sounder has more spectral bands than the imager for
producing high-quality atmospheric profiles of temperature and
moisture. It is capable of stepping one visible and eighteen
infrared channels in a north-to-south swath across an east-to-west
- The Space Environment Monitor (SEM)
measures the condition of the Earths magnetic field, the solar
activity and radiation around the spacecraft, and transmits these
data to a central processing facility.
- The Data Collection System (DCS)
receives transmitted meteorological data from remotely - located
platforms and relays the data to the end users.
- The Search and
Rescue Transponder can relay distress signals at all times,
but cannot locate them. While only the polar-orbiting satellite
can locate distress signals, the two types of satellites work
together to create a comprehensive search and rescue system.
Geosynchronus (aka GEO)
Synchronous with respect to the rotation of the Earth. See
A multi-year surplus accumulation of snowfall in excess of
snowmelt on land and resulting in a mass of ice at least 0.1 square
kilometers in area that shows some evidence of movement in response
to gravity. A glacier may terminate on land or in water. Glacier ice
is the largest reservoir of fresh water on Earth, and second only to
the oceans as the largest reservoir of total water. Glaciers are
found on every continent except Australia.
Global Change Research Program (GCRP)
The USGCRP is a government-wide
program whose goal is "to establish a scientific basis for national
and international policy-making relating to natural and human-induced
changes in the global Earth
system." Mission to Planet Earth is NASAs central contribution to
Global Change Research Proqram. The Global Change Research Program
coordinates and guides the efforts of federal agencies. The program
examines such questions as, is the Earth experiencing global warming?
Is the depletion of the ozone layer expanding? How do we determine
and understand the causes of global climate changes? Are they
reversible? What are the implications for human needs and activities?
All of the activities required to specify a global variable, such
as ozone. These activities range from data acquisition to the
generation of a data-analysis product, and include estimates of the
uncertainties in that product. A global measurement often will
consist of a combination of observations from a spacecraft instrument
(required for global coverage) and measurements in situ (needed to
provide reference points for long-term accuracy).
Functions of space and time that describe the large scale state
and evolution of the Earth system. The Earth systems geosphere,
and biosphere and their
components are, or potentially are, global variables.
See Geostationary Meteorological Satellite.
See Geostationary Operational Environmental
GOES I/GOES 8
NOAA geostationary satellite launched in April 1994 (alphabetical
designators are used while on the ground and before geostationary
orbit, after it achieves geostationary orbit it became GOES 8). GOES
8 is the first in a series of five new geostationary satellites that
will ensure dual-satellite coverage of the U.S. into the next
century, and will provide better advanced warnings of thunderstorms,
flash floods, hurricanes, and other severe weather. GOES 8 will also
contribute important information to a new flood and water management
system which will assist decision-makers with the allocation of
precious western water resources.
The next generation of NOAA geostationary satellites, scheduled
for launch beginning sometime after 2003. Currently in the planning
phase, these satellites will follow the series of five geostationary
satellites which are being launched beginning in 1994. See GOES
Environmental satellite scanners, rather than photographing a
scene, scan a scene line-by-line measuring light or heat levels and
transmitting this information as a video image via an amplitude
modulated (AM) subcarrier contained in
the satellites FM signal. The video image a 2400 Hz tone - is
amplitude modulated to correspond to the light and dark areas sensed,
with the louder portion of the tone representing the lighter areas of
the image and the lower portion of the tone representing the darker
areas of the image. Intermediate volumes form the shades of the
grayscale (up to 256 shades) needed to complete the image. This is an
analog type of data transmission, and enables the assessment of such
features as heat, light, temperature, and cloud heights.
Process by which significant changes in the chemistry of Earths
atmosphere may enhance the natural process that warms our planet and
elevates temperatures. If the effect is intensified and Earth's
average temperatures change, a number of plant and animal species
could be threatened with extinction.
Certain gaseous components of the atmosphere, called greenhouse
gases, transmit the visible portion of solar radiation but absorb
specific spectral bands of thermal radiation emitted by the Earth.
The theory is that terrain absorbs radiation, heats up, and emits
longer wavelength thermal radiation that is prevented from escaping
into space by the blanket of carbon dioxide and other greenhouse
gases in the atmosphere. As a result, the climate warms.
Because atmospheric and oceanic circulations play a central role
in the climate of the Earth, improving our knowledge about their
interaction becomes essential.
A gaseous component of the atmosphere contributing to the
greenhouse effect. Greenhouse gases
are transparent to certain wavelengths of the suns radiant energy,
allowing them to penetrate deep into the atmosphere or all the way
into the Earths surface. Greenhouse gases and clouds prevent some of
infrared radiation from escaping, trapping the heat near the Earths
surface where it warms the lower atmosphere. Alteration of this
natural barrier of atmospheric gases can raise or lower the mean
global temperature of the Earth.
Greenhouse gases include carbon dioxide, methane, nitrous oxide,
chlorofluorocarbons, and water vapor. Carbon dioxide, methane, and
nitrous oxide have significant natural and human sources while only
industries produce chlorofluorocarbons. Water vapor has the largest
greenhouse effect, but its concentration in the troposphere is
determined within the climate system. Water vapor will increase in
response to global warming, which in turn may further enhance qlobal
Greenwich Mean Time (GMT)
See Coordinated Universal Time.
Gross Feature Map
Map that displays geographic characteristics rather than political
Ground Control (points)
Identifiable points on the ground whose locations on the surface
of the Earth are accurately known for use as geodetic references in
mapping, charting, and other related mensuration applications.
See Earth station.
The inclination of a satellite, together with its orbital altitude
and the period of its orbit, creates a track defined by an imaginary
line connecting the satellite and the Earths center. The intersection
on the line with the Earths surface is the subsatellite point. As the
Earth turns on its axis and the satellite orbits overhead, a line is
created by the satellite's apparent path over the ground (the series
of subsatellite points connected). A geostationary satellite has an
inclination of essentially zero, and, because its orbital period
exactly matches the Earths rotation, its ground track is reduced to
an apparent stationary point on the equator.
NASA Goddard Space Flight Center, located in Greenbelt, Maryland.
See NASA Centers
Electromagnetc or acoustic wave that is constrained within certain
boundaries, as in a wave guide (transmission line).
A large arm of an ocean or sea extending into a land mass.
A warm, swift ocean current that flows along the coast of the
Eastern United States and makes Ireland, Great Britain, and the
Scandinavian countries warmer than they would be otherwise.
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