Gagan: India's Eye in the Sky

Indian Space Research Organisation (ISRO) and Airports Authority of India (AAI) are at work to provide a modern navigation system over the Indian airspace.

The system, christened GAGAN or GPS and Geo Augmented Navigation, will be a Satellite Based Augmentation System (SBAS).

GAGAN will be operational by end 2007. For Delhi Airport it would mean less delays during the winter months when fog throws air traffic out of gear. GAGAN will operate like Category IIIA Instrument Landing System, helping flights land in near zero visibility conditions. Its accuracy will be within 1 metre. It will provide both lateral and vertical guidance.

Worldwide, ships and aircraft use two core constellations to determine their position - the GPS system of the US and a similar Russian system.

These set of satellites send a time-stamped message to the aircraft and ship, helping it fix its location and route. The position accuracy achievable with these core constellations (GPS and GLONASS) is 30 metres and not good enough for precision approach and landing requirements of civil aviation in India. These need to be augmented. GAGAN, with its satellites and ground-based transmitters will fill this gap over the Indian airspace.

There are three types of augmentation systems - Ground Based (GBAS), Aircraft Based (ABAS) Space/Satellite Based (SBAS). The ground and aircraft based systems have several handicaps - not available over the oceanic (Indian Ocean) airspace, unable to cover India's territorial airspace, performance dependent on terrain conditions, expensive to maintain and require periodic calibration.

GAGAN is being implemented in three stages:

Stage I: Technology Demonstration System — is complete.

Stage II: Initial Experimentation Phase — year-long, under process.

Stage III: Final Operational Phase — scheduled for 2007.[HT]