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Module 2 – GPS (EDUSAT based Trg.)
Comparative study of NAVSTAR GPS/ GLONASS/GALILEO/ Augmented Positioning Systems P.L.N. Raju, Geoinformatics Division IIRS Email –
[email protected]
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Outline of my Talk
• Comparison of – GPS – GLONASS – GALILEO
• Augmented SBNS – – – – – – –
WAAS MSAS EGNOS GAGAN GBNS (NDGPS/LAAS) Chinese Beidou System IRNSS, India’s Navigation System
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GPS Constellation Plane F E D C B A
M
ea n
an om
a ly
160° 120° 80°
40°
320°
280° 240° 200°
Equator
0°
17° 137° 257° 77° 197° 317°
satellite operational spare
Right ascension of ascending node Inclination 55° Semi major axis 26561.75 km (altitude above Earth 20183,6 km) Eccentricity nominally e = 0, generally e < 0,02
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GNSS SYSTEM
GPS Modernization •
Improved code on the L2 frequency of GPS (called L2C) – •
ionospheric error,
•
more immune to RF interference and
•
multipath.
•
The first Block IIR-M during October 2005.
•
Under currently published plans, that is not expected to occur until 2013 or beyond.
•
A third civil frequency at 1176.45MHz (called L5) on the Block IIF satellites. Full operational capability is unlikely until 2015.
•
GPS-III, (extra L2 and L5 signals of the Block IIR-M and Block IIF satellites), Thirty GPS-III satellites are planned for launch from about 2013 until 2018.
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GLONASS Constellation
• 24 satellites (8 satellites in each of 3 planes) • e ~ 0 (circular orbit) • inclination 64.8° • altitude 19 100 km, • orbit period 11h 15m • angular spacing between orbits 120°
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About GLONASS
GLobal NAvigation Satellite System Beginning in 1982 Belongs to USSR (Now Russia) No onboard atomic clocks Precise timing on the ground 16 Satellites in orbit Three orbital planes 60% of time for position calculation
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About GLONASS
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About GALILEO
Galileo
Galileo Constellation
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About GALILEO
GIOVE - standing for 'Galileo In-Orbit Validation Element
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About Galileo
• Galileo is a global navigation satellite system currently being built by the European Union (EU) and European Space Agency (ESA) • €3.4 billion project • To be operational by 2013 with 30 total satellites • Position Accuracy down to the metre range • Also called as Galileo positioning system
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About Galileo
• orbital altitude: 23,222 km • 3 orbital planes, 56° inclination (9 operational satellites and one active spare per orbital plane) • Constellation of 30 satellites, increased altitude (approx. 3000km higher than GPS) which will enable better signal availability at high latitudes.
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iirs Different services and accuracy of position
iirs Satellite Based Augmented Systems • WAAS (Wide Area Augmentation System) • GAGAN (GPS Aided Geo Augmented Navigation) • EGNOS (European Geo-stationary Navigation Overlay Service ) • MSAS (Multi-Functional Satellite Augmentation System) • NDGPS (National level Differential Global Positioning System) • Chinese Beidou System • India’s IRNSS
iirs Satellite Based Augmented Systems
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How Position Accuracy improved with SBAS?
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How WAAS Works?
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How WAAS Works?
WAAS consists of approximately 25 ground reference stations positioned across the United States that monitor GPS satellite data. Two master stations, located on either coast, collect data from the reference stations and create a GPS correction message. This correction accounts for GPS satellite orbit and clock drift plus signal delays caused by the atmosphere and ionosphere. The corrected differential message is then broadcast through one of two geo-stationary satellites, or satellites with a fixed position over the equator. The information is compatible with the basic GPS signal structure, which means any WAASenabled GPS receiver can read the signal. Note: 1 – 3 m accuracy obtained with WAAS support
iirs Ground Based Augmented Systems
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NDGPS (USA)
• To ensure greater accuracy and improved integrity, the US Department of Transportation is deploying the Nationwide Differential Global Positioning System (NDGPS) service. This service uses ground reference stations to determine the differential between the GPS solution and the true solution. This differential is then broadcast on a low frequency carrier for users to access, free of direct user charge. • NDGPS provides accurate dynamic navigation information to travelers with 1- to 2- meter accuracy (and possibly better in the future).
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About GAGAN GPS Aided Geo Augmentation Navigation
• India and US cooperation to integrate GPS for ground based positioning • To improve air traffic and other civil navigation • Joint venture of ISRO and AAI for 760 cr • 8 reference stations • Master Control and Uplink facility • Operational by 2011 • Better than 3 m
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EGNOS EGNOS
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iirs Augmentations SBAS Constellation
EGNOS
GAGAN
MSAS MTSAT
WAAS
INMARSAT ARTEMIS
INMARSAT
GPS
iirs Local Area Augmentation System It is an all-weather aircraft landing system based on real-time differential correction of the GPS signal. Local reference receivers send data to a central location at the airport. This data is used to formulate a correction message, which is then transmitted to users via a VHF data link. A receiver on an aircraft uses this information to correct GPS signals, which then provides a standard ILS-style display to use while flying a precision approach.
iirs Chinese Beidou navigation system • • • • • •
Geostationary satellites Mainly for China Four satellites launched so Far (Total 35 No.) 10 m accuracy Open services by 2008 Covers North side 5° to 50° N Latitude and 70°E to 140°E • Receiver sends signal, satellite estimates based on time of it
iirs IRNSS – India’s own Navigation System • Indian Regional Navigation Satellite System (IRNSS) • With seven satellites • GEO/ elliptical orbit • To be Build and launch by ISRO • Costs 16 billion (1600 crore) rupees • First meeting held in July 2006 • First satellite in 2009 & Operational by 2012
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References
• Wikipedia the free online encyclopedia for GPS, EGNOS, WAAS, LAAS, NDGPS, Beidou Navigation System • Coordinates monthly Indian News Letter • GPS World Magazine
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