The GPS Aided Geo Augmented Navigation or GPS and Geo Augmented Navigation system (GAGAN) is a planned implementation of a regional Satellite Based Augmentation System (SBAS) by the Indian government. It is a system to improve the accuracy of a GNSS receiver by providing reference signals.

The $18 million project is being implemented in three phases through 2008 by the Airport Authority of India with the help of the Indian Space Research Organization's (ISRO) technology and space support. The goal is to provide navigation system for all phases of flight over the Indian airspace and in the adjoining area.

It is applicable to safety-to-life operations, and meets the performance requirements of international civil aviation regulatory bodies. The final, operational phase of GAGAN is likely to be completed by May 2011. Gagan is a Hindi word of Sanskrit origin for the sky.

To begin implementing an SBAS over the Indian airspace, Wide Area Augmentation System (WAAS) codes for L1 frequency and L5 frequency were obtained from the United States Air Force and U.S Department of Defense on November 2001 and March 2005. The system will use eight reference stations located in Delhi, Guwahati, Kolkata, Ahmedabad, Thiruvananthapuram, Bangalore, Jammu and Port Blair, and a master control center at Bangalore. U.S. defense contractor Raytheon has stated they will bid to build the system.

As a part of the programme, a network of 18 total electron content (TEC) monitoring stations were installed at various locations in India to study and analyse the behaviour of the ionosphere over the Indian region. GAGAN's Technology Demonstration System (TDS) signal in space provides a three-metre accuracy as against the requirement of 7.6 metres.

Flight inspection of GAGAN signal is being carried out at Kozhikode, Hyderabad, Nagpur and Bangalore airports and the results have been satisfactory so far. To study the ionospheric behavior more effectively over entire Indian Airspace, Indian universities and R and D labs, which are involved in the development of regional based IONO-TROP model for GAGAN, have suggested nine more TEC stations.

The AAI's efforts towards implementation of operational SBAS can be viewed as the first step towards introduction of modern CNS/ATM system over Indian airspace.

GAGAN, after its final operational phase completion, will be compatible with other SBAS systems such as the Wide Area Augmentation System (WAAS), the European Geostationary Navigation Overlay Service (EGNOS) and the Multi-functional Satellite Augmentation System (MSAS) and will provide seamless air navigation service across regional boundaries.

While the ground segment consists of eight reference stations and a master control centre, which will have sub systems such as data communication network, SBAS correction and verification system, operations and maintenance system, performance monitoring display and payload simulator, Indian land uplinking stations will have dish antenna assembly. The space segment will consist of one geo-navigation transponder.

The Indian government has stated that it intends to use the experience of creating the GAGAN system to enable the creation of an autonomous regional navigation system called the Indian Regional Navigational Satellite System (IRNSS) and that it might use the GSAT-4 satellite as a technology demonstration system phase of the proposed navigational system.

Flight Management System based on GAGAN will then be poised to save operators time and money by managing climb, descent and engine performance profiles. The FMS will improve the efficiency and flexibility by increasing the use of operator-preferred trajectories.

It will improve airport and airspace access in all weather conditions, and the ability to meet the environmental and obstacle clearance constraints. It will also enhance reliability and reduce delays by defining more precise terminal area procedures that feature parallel routes and environmentally optimised airspace corridors.

GAGAN will increase safety by using a three-diemensional approach operation with course guidance to the runway, which will reduce the risk of controlled flight into terrain i.e, an accident whereby an airworthy aircraft, under pilot control, inadvertently flies into terrain, an obstacle, or water.

GAGAN will also offer high position accuracies over a wide geographical area like the Indian airspace. These positions accuracies will be simultaneously available to 80 civilian and more than 200 non-civilian airports and airfields and will facilitate an increase in the number of airports to 500 as planned. These position accuracies can be further enhanced with ground based augmentation system.

The first GAGAN transmitter was integrated into the GSAT-4 geostationary satellite, and had a goal of being operational in 2008. Following a series of delays, GSAT-4 was launched on 15 April 2010, however it failed to reach orbit after the third stage of the Geosynchronous Satellite Launch Vehicle Mk.II that was carrying it malfunctioned.

The project involves establishment of 15 Indian Reference Stations, three Indian Navigation Land Uplink Stations, three Indian Mission Control Centers and installation of all associated softwares and communication links. GAGAN is planned to get into operation by the year 2014.

It will be able to help pilots to navigate in the indian airspace by an accuracy of 3 Mts. This will be helpful for landing aircrafts in tough weather and terrain like Managalore airport and Leh.

Source: Wikipedia.