Global Positioning System Reference
In-Depth Information
12.9.3 Space Applications
In the early 1980s, GPS receivers were flying on NASA's LANDSAT. This marked
the beginning of the use of GPS in a spacecraft. Pictures from LANDSAT of the
Yucatan peninsula, coupled with a GPS-equipped airborne survey, enabled a
National Geographic expedition to find ruins of several heretofore unknown
Mayan cities. Space use of GPS expanded on the Shuttle and the Space Station and
on many other civilian and military low- to mid-orbital satellites. GPS receivers are
quite useful on spacecraft in orbit up to about 10,000 nmi, although some visibility
is still present at synchronous altitudes. Typically, GPS receivers are used in LEO
and MEO satellites, where attitude determination is required. Further discussion on
this topic is contained in [22].
12.9.4 Other Government Applications
Within the United States, many government agencies make use of GPS. The Depart-
ment of Agriculture funds some research in precision farming, and both the Depart-
ment of the Interior and the Bureau of Land Management routinely use GPS in our
national forests. NASA looks after civilian space applications. The Department of
Homeland Security uses GPS in its law enforcement role to covertly track the move-
ments of suspects and through the Coast Guard's efforts to control our shores.
NGS and NOAA are heavy users of GPS reference stations' data and compute
high-accuracy, postprocessed orbital data for use by GPS surveyors and others.
One major supplier/user of this data is IGS. A major IGS center is located at the JPL
in Pasadena, California, but IGS is international in scope with other centers in
Europe.
Numerous law enforcement agencies rely on GPS for tracking applications,
especially for surveillance on suspected criminals or for recovering GPS-equipped
stolen vehicles. More and more accident investigators from the National Transpor-
tation Safety Board are incorporating GPS data into their findings. Automobiles
and trucks are being equipped with “black box” recorders such as those required on
commercial aircraft in order to have information about all vehicle systems as well as
the speed and location at the time of an accident.
The Department of Transportation in Minnesota ran an experimental program
that showed that a DGPS-equipped snow remover could accurately plow roads
completely obscured by several feet of snow.
12.10
User Equipment Needs for Specific Markets
On a system level, civil GNSS users have different priorities than military users. The
civil community expects high accuracy, availability, coverage, integrity, and robust-
ness. The latter will be obtained from redundant signals and more power than in the
premodernized GPS. These same users have been the drivers to require second and
third civil signals in the modernized GPS and in GALILEO. For SOL applications,
they clamor for spectrum protection from other systems such as ultrawideband and
telecommunications that covet GNSS bandwidths.
 
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