ESA and the EU are building the European GNNS Galileo, which will be the world's first civil satellite navigation system. Galileo should be operational in 2019, delivering an open service with higher accuracy and larger coverage than today's GPS and GLONASS.
In 1978, the American Ministry of Defense started to launch the NAVSTAR GPS (Navigation Signal Timing and Ranging Global Positioning System), better known as GPS. In the mean time, today's society can hardly be imagined without the use of Global Navigation Satellite Systems.
Satellite navigation is in fact radio navigation from satellites. These are send at Ultra High Frequency (UHF, 1575.42 MHz for GPS). Signals can only be received with satellites 'in sight'. For accurate positioning, a minimum of 4 satellites in sight is required.
GPS has an accuray around 15 m. Satellite navigation signals are improved by Satellite-Based Augmentation Systems. In preparation of Galileo, Europe also developed its own Satellite-Based Augmentation System (SBAS) called EGNOS (European Geostationary Navigation Overlay Service). EGNOS covers Europea and beyond, and makes use of three Inmarsat geostationary satellites and a number of ground stations. It improves the accuracy received from GPS up to 5 meter.
To improve the position accuracy even further, ground stations are used to compare the received positions with the true position. An improved signal is submitted by the ground stations, leading to higher position accuracies (differential corrections). Different methods exist like Real Time Kinematic (RTK) or Real-Time-On-The-Fly (RTOTF) which can lead to accuracies up to millimeters.
AIS (Automatic Identification System) is an automatic tracking system for identifying and locating vessels by electronically exchanging data with other nearby ships. When Vessels are fitted with AIS transceivers and transponders, ship information like unique identification, position, course, and speed can be tracked by AIS base stations located along coast lines and visualised on a screen. Marine traffic coordinators use AIS and radar to manage vessel traffic.
Satellite AIS (S-AIS) is a supplement which allows to monitor vessels beyond coastal regions, including the oceans. AIS empowered satellites are fitted with special AIS receivers which are capable of deconflicting a large number of signatures.
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