GAGAN MAKES GPS MORE ACCURATE

Phones that pick up signals from orbiting U.S. Global Positioning System (GPS) satellites are now common. The phone uses that information to work out the location and display it on a map. In a similar fashion, the GPS signals can be used to assist aircraft in determining position during landing and take off as well as in flying shorter routes to their destination. One important way to meet the demands of civil aviation has been through what is known as a Satellite-Based Augmentation System (SBAS). Satellites in geostationary orbit are used to supplement the GPS signals. The first SBAS was the U.S Wide Area Augmentation System (WAAS) that became operational in 2003. The European Geostationary Navigation Overlay Service (EGNOS) was officially declared available for aviation use March 2011. The Japanese have a system known by the acronym MSAS.

India is establishing its own system, the GPS Aided Geo Augmented Navigation (GAGAN), a joint effort by the ISRO and the Airports Authority of India. The ground segment for GAGAN, which has been put up by the U.S company Raytheon, has 15 reference stations scattered across the country. Two mission control centres have been set up at Kundalahalli in Bangalore. One more control centre and uplink station are to come up in Delhi. The space component for it will become available after the GAGAN payload on the GSAT-8 communication satellite, which was launched recently, is switched on. The reference stations pick up signals from the orbiting GPS satellites. These measurements are immediately passed on to the mission control centres that then work out the necessary corrections that must be made and send to satellites that have GAGAN payload. Those satellites then broadcast the messages. SBAS receivers are able to use those messages and apply the requisite corrections to the GPS signals that they receive, thereby establishing their position with considerable accuracy. Planes with SBAS receivers will be able to take shorter routes, saving both time and fuel. At present, to help pilots land their aircraft in bad weather and poor visibility, several airports use ground-based Instrument Landing System or ILS. Such ILS equipment is expensive. Consequently, even in airports that have it, only one runway and that too one end of a runway have the ILS capability. An SBAS, on the other hand, can provide guidance on both ends of all runways that fall within its coverage area. India’s GAGAN has a reach well beyond the country, from Africa and Middle East on one side to the Bay of Bengal and South-East Asia on the other. It will, therefore, fill a gap between Europe’s EGNOS and Japan’s MSAS systems.