Global Navigation Satellite Systems

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Few tools have helped change and improve data collection within the field of Geographic Information Systems (GIS) more than the Global Positioning System (GPS). GPS has provided data collectors in the field with a simple and efficient means of highly accurate positioning. Before GPS, GIS data logging was not a precise science, as identifying exact positioning was reliant more on landmarks and map coordinates, leading to potential errors and broad estimations. Developments in GPS, however, have changed the use of GPS receivers for data collection.  Now, with a hand-held GPS receiver, a GIS data collector can tell within a few feet exactly where they are in the world. Most GPS systems can provide a precise location to within 10-50 feet, and advances and the development of new GNSS (Global Navigation Satellite Systems) means this precision will get ever more accurate.

Current and Future Global Navigation Satellite Systems

Currently, the American NAVSTAR GPS system and the Russian GLONASS are  the only fully functioning GNSS; however, several other systems are currently in development.

The Global Positioning System was developed by the U.S. Military in 1973 and became fully functional in 1995 with an original constellation of 24 satellites (there are now 24 satellites in continuous operation with additional spare satellites in orbit).  Each satellite circles the earth two times a day and there are four satellites in view from any point on the earth at any given time.  The GPS satellite constellation consists of six orbital planes encircling the Earth. The Expandable 24 constellation was completed in June of 2011 which optimized the geometry of the of orbital planes in order to increase the navigation data by GPS users worldwide.

The Enhanced 24 GPS satellite constellation.  Source: Schriever AFB.

The Enhanced 24 GPS satellite constellation. Source: Schriever AFB.

The Russians, who used to have a functioning GNSS called GLONASS during the Cold War only for it to fall into disrepair, fully restored the system in October of 2011 with 24 satellites in operation (21 operational and 3 spare satellites in orbit). The constellation has eight satellites on each of its three orbital planes.

Galileo is an effort by European Union (EU) and European Space Agency (ESA).  The Galileo constellation will consist of 30 satellites (27 active and 3 spares) organized into three orbital planes and each satellite will orbit the Earth once every 14 hours.  Like the U.S. GPS, there will be four satellites visible from any given point on earth.  Galileo will provide coverage reaching to the polar regions.    Galileo should be fully functional by 2020, and will not only act as a rival to the American GPS, but also complement it. Future satellite navigation receivers will be able to receive both GPS and Galileo signal, and by using both sets of information, provide positioning that is even more precise.

Galileo's constellation. Source: ESA.

Galileo’s constellation. Source: ESA.

The Europeans are not the only ones developing new GNSS. The Chinese are developing a new global system known as the Compass navigation system, which should also be fully functional by 2020.  The constellation will hold 35 satellites.

These next generation GNSS, combined with the GPS improvement plans currently in operation, mean the future of satellite navigation will result in increased accuracy, providing ever more precise GIS data logging.

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