GPS Aided GEO Augmented Navigation

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Context

The government has exempted Boeing 787 aircraft in India from complying with the indigenously developed GAGAN navigation system until December 2025 as the aircraft manufacturer has said that it involves a major design change.

What is GAGAN?

GAGAN is an acronym for GPS Aided GEO Augmented Navigation.
It is a Space Based Augmentation System (SBAS) jointly developed by ISRO and AAI (Airport Authority of India) to provide the best possible navigational services over Indian FIR (Flight Information Region) with the capability of expanding to neighboring FIRs.

Background

GPS (Global Positioning System) signals are not always pin-point accurate.
GPS is susceptible to factors and disturbances such as ionospheric interference, the location of the moving vehicle, and even the functioning of the GPS satellite, signal availability, Many advanced countries have their own localised solutions to such problems and systems to perform this corrective action. Example: US-WAAS, European EGNOS, and Japanese MSAS etc.

GAGAN Technology

Using a technology known as the Satellite-Based Augmentation System (SBAS), GAGAN correct the errors in GPS signals and feed the corrected signals to the moving vehicle (GPS user), thus enabling precise navigation.
Thus, GAGAN is a system of satellites and ground stations that provide GPS signal corrections, giving better position accuracy.
GPS alone does not meet the ICAOs navigational requirements for accuracy, integrity and availability.
GAGAN corrects for GPS signal errors caused by Ionospheric disturbances, timing and satellite orbit errors and also it provides vital information regarding the health of each satellite.
The objective of GAGAN to establish, deploy and certify satellite based augmentation system for safety-of-life civil aviation applications in India has been successfully completed.
While the USA, Japan, Russia, China, etc., have had their own systems to perform this corrective action, India just tested its home-grown SBAS to aid the precise operation and landing of a passenger aircraft that uses GPS.
The system is inter-operable with other international SBAS systems like US-WAAS, European EGNOS, and Japanese MSAS etc.

Services Offered

Aviation, Forest management, Railways signalling, Scientific Research for Atmospheric Studies, Natural Resource and Land Management, Location based services, Mobile, Tourism.

Gagan applications

GAGAN system is being used for effective management of wildlife resources and monitoring of forests using GAGAN enabled GPS SXTREO-T51
It can provide navigational support to Indian railway for signalling when train approaches to no man crossing and also for alignment of railway tracks.
Road Asset Management System (RAMS) is likely to be developed for all National Highways in the country and a modern management system that will use GAGAN system.
GAGAN signals can also be used to manage traffic in real time to avoid traffic jams.
GAGAN provides the additional accuracy, availability, and integrity necessary for all phases of flight, from enroute through approach for all qualified airports within the GAGAN service volume.

How it works?

GAGAN consists of set of ground reference stations positioned across various locations in India called Indian Reference Station (INRES), which gathers GPS satellite data.
A master station, Indian Master Control Centre (INMCC) collects data from reference stations and creates GPS correction messages.
The corrected differential messages are uplinked via Indian Uplink Station (INLUS) and then broadcasted on a signal from three geostationary satellites (GSAT-8, GSAT-10 and GSAT-15).
The information on this signal is compatible with basic GPS signal structure, which means any SBAS enabled GPS receiver can read this signal.

Coverage Area

Two GEOs simultaneously transmit the GAGAN signal in space. GAGAN GEO footprint expands from Africa to Australia and GAGAN system has capability to cater 45 reference stations for expansion to neighboring countries.
GAGAN provides a civil aeronautical navigation signal consistent with International Civil Aviation Organization (ICAO) Standards and Recommended Practices (SARPs) as established by the Global Navigation Satellite System (GNSS) Panel.
The GAGAN system provides Non-precision approach (NPA) service accurate to within the radius of 1/10th of a nautical mile (Required Navigation Performance or RNP-0.1) over the Indian FIR .
It also provides precision approach service of APV-1.0 (Approach with Vertical guidance) over the Indian landmass on nominal days.