GAGAN, SIMRAN
What is the working mechanism for GAGAN and SIMRAN navigation system?
PIYUSH KR. PANDEY
GAGAN is GPS Aided Geo Augmented Navigation which improves the accuracy of Global Satellite Navigation System (GNSS) receivers. The normal GPS system does not provide the necessary accuracy, integrity etc. required for civil aviation. The GPS system is to be augmented for this.
Various countries have different Satellite Based Augmentation Systems (SBAS) and India is having GAGAN. This system consists of eight Reference Stations called Indian Reference stations, one master control centre, one Indian Uplinking Station and a geostationary satellite having GPS transponders namely L1 and L2. The reference stations receive GPS signals as well as signals from geostationary satellite.
The signals received at reference stations are sent to master control centre. The master control centre processes this data and computes the corrections for various errors. The corrected messages are formatted for GPS compatibility and sent to the uplinking station. The uplinking station transmits this to geosynchronous satellite for broadcast to user terminals.
The reference stations are located at widely distributed locations in India including at Port Blair.The geosynchronous satellite has GPS L1 compatible navigation transponder. Users like aircraft receive this satellite signal along with GPS signals and compute their improved position for navigation. The GAGAN system incorporates ionospheric corrections by studying the ionospheric behaviour and modelling and applying corrections. With this accuracy of less than 0.5metre will be provided by SBAS using GAGAN. GAGAN will offer high accuracies over wide geographical area like Indian airspace. GSAT-8 satellite has the GAGAN payload. This system will be used by the Airport Authority of India for air traffic management.
SIMRAN is Satellite Imaging for Rail Navigation. This provides real time information to people for accurate train tracking of trains. GPS receivers will be installed in trains to get the location of the trains and this information will be sent to a central server which can be accessed by public to find the train location. This system has been developed by the Research Designs and Standards Organisation (RDSO) in collaboration with IIT-Kanpur.
R. GOPALAKRISHNAN
Retired Scientist/Engineer
ISRO
