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Techniques to improve GPS accuracy
From Wikipedia, the free encyclopedia.
By: Wikipedia
The accuracy of GPS can be improved in a number of ways:
- Using a network of fixed ground based reference stations. These stations
broadcast the difference between the measured satellite pseudoranges and
actual (internally computed) pseudoranges, and receiver stations may correct
their pseudoranges by the same amount. This method is called Differential
GPS or DGPS. DGPS was especially useful when GPS was
still degraded (via the "Selective Availability" described below), since
DGPS could nevertheless provide 5-10 metre accuracy. The DGPS network has
been mainly developed by the Finnish and
Swedish maritime
administrations in order to improve safety in the archipelago between the
two countries.
- Exploitation of DGPS for Guidance Enhancement (EDGE) is
an effort to integrate DGPS into precision guided munitions such as the Joint
Direct Attack Munition (JDAM).
- The Wide-Area Augmentation System (WAAS).
This uses a series of ground reference stations to calculate GPS correction
messages, which are uploaded to a series of additional satellites in geosynchronous
orbit for transmission to GPS receivers, including information on ionospheric delays,
individual satellite clock drift, and suchlike. Although only a few WAAS
satellites are currently available as
of 2004, it is hoped that eventually WAAS will provide sufficient reliability
and accuracy that it can be used for critical applications such as GPS-based
instrument approaches in aviation (landing an airplane in conditions of little
or no visibility). The current WAAS system only works for North America (where
the reference stations are located), and due to the satellite location the
system is only generally usable in the eastern and western coastal regions.
However, variants of the WAAS system are being developed in Europe (EGNOS,
the Euro Geostationary Navigation Overlay Service), and Japan (MSAS,
the Multi-Functional Satellite Augmentation System), which are virtually
identical to WAAS.
- A Local-Area Augmentation System (LAAS). This is similar
to WAAS, in that similar correction data are used. But in this case, the
correction data are transmitted from a local source, typically at an airport
or another location where accurate positioning is needed. These correction
data are typically useful for only about a thirty to fifty kilometre radius
around the transmitter.
- Wide Area GPS Enhancement ([MORE]
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