Augmentation of a global
navigation satellite system (GNSS) is a method of improving the navigation
system's attributes, such as accuracy, reliability, and availability, through
the integration of external information into the calculation process. There are
many such systems in place and they are generally named or described based on
how the GNSS sensor receives the external information.A satellite-based augmentation system (SBAS) is a system that supports wide-area or regional augmentation through the use of additional satellite-broadcast messages. Such systems are commonly composed of multiple ground stations, located at accurately-surveyed points. The ground stations take measurements of one or more of the GNSS satellites, the satellite signals, or other environmental factors which may impact the signal received by the users. Using these measurements, information messages are created and sent to one or more satellites for broadcast to the end users.
The GPS
Aided Geo-Augmented Navigation (GAGAN) is a planned implementation of a
regional satellite-based augmentation system (SBAS) by the Indian government. Jointly
developed by AAI and ISRO, the ground segment consists of eight reference
stations and a master control centre at Bangalore, 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. The
space segment will consist of one geo-navigation transponder.
As a part of the programme, a network of 18
total electron content (TEC) monitoring stations are 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 three-metre accuracy as against the requirement of 7.6 metres.
On deployment, GAGAN
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.
GAGAN will increase safety by using a three-dimensional approach
operation with course guidance to the runways which will improve airport and
airspace access in all weather conditions( especially those that have no ILS), with
enhanced ability to meet the environmental and obstacle clearance constraints Pilots can also expect greater flexibility in
the use of operator-preferred
trajectories, more precise terminal area procedures that
feature parallel routes and environmentally optimized airspace corridors.
This is fascinating. Thank you for the excellent explanation. Technology... we've got to love it.
ReplyDeleteThe error due to Ionospheric distortion was a challenge . Studies are currently underway to get more precise prediction of ionospeheric disturbances in the subcontinent region. Once completed the accuracies should improve even better. Indian subcontinent has a large number of airports without precision approach facilities. GAGAN will indeed be a great boon to the pilots operating in these areas.
ReplyDeleteMost GPS receivers usually have two or more expansion slots available where additional ECB cards can be inserted. One or more cards depending on the version and capabilities of the host receiver would be required to accept and process the additional information from the SBAS, GBAS or GRAS systems. GAGAN too is designed to be compatible with other SBAS systems. The next step in development is to work on ground based augmentation with VHF band radio messages. We might soon find accuracies better than one metre. Once the receiver is modified for including the update information, the approaches can be developed and programmed into the computer as for any other precision approach. In the first phase precision approaches to CAT I minimum can be flown. Future developments would be able to support Cat II or greater precision.
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