Madhav N. Kulkarni
Civil Engineering Department, IIT, Mumbai
Email: [email protected]
With the launching of the National GPS programmes by DST and DOS, India is poised to play a significant role to the global GPS programmes.
The Global Positioning System (GPS) is a satellite-based navigation and surveying system, launched and controlled by the US Department of Defence (DOD), for determination of precise position and time, using radio signals from the satellites, in real-time or in post-processing mode. GPS is primarily a military navigation system for real-time positioning. However, with the transformation from ground-to-ground survey measurements to ground-to-space measurements made possible by GPS, this technique overcomes the numerous limitations of terrestrial surveying methods, like the requirement of inter-visibility of survey stations, dependability on weather, difficulties in night observations, etc. These advantages over the conventional techniques, the high accuracy achieved in three-dimensional positioning and the economy of operation make GPS the most promising surveying, positioning and navigation technique of the future. In India, GPS is being used for applications in diverse fields like navigation, surveying, geodetic control networks, crustal deformation studies, cadastral surveys, creation of GIS databases, time service etc. by various organisations. With the launching of the National GPS programmes by DST and DOS, India’s contribution to the global GPS programmes has become significant. However, many issues like sharing of data, co-ordination between the agencies involved and augmentation of resources and infrastructure etc. need to be addressed, in order to make the Indian presence felt on the global scenario.
Global GPS Programmes
Globally, many co-ordinated GPS programmes have been launched by government and non-government agencies for various applications. Some of the important applications are :
- Establishment of high precision zero order Geodetic National Survey Control Networks;
- Strengthening, densification and readjustment of existing Primary Control Networks;
- Connecting remote islands to mainland Geodetic Control Networks;
- Determination of a precise geoid;
- Earth rotation and Polar Motion Studies;
- Estimating gravity anomalies;
- Marine Geodesy: positioning of oceanic stations, platforms, etc.
- Earthquake monitoring: Crustal movement studies, continental drifts, neotectonic movements etc;
- GIS, Digital Mapping, Vertical Control Networks, DEM, etc;
- Geophysical positioning, mineral exploration and mining;
- Survey control for topographical and cadastral surveys;
- Ground control for photogrammetric surveys and mapping;
- Instantaneous time transfer over trans-continental distances with accuracy of a few nanoseconds;
- Space-craft tracking ;
- General aircraft navigation, approach to runways, navigation/ positioning in remote areas like deserts, dense jungles, precise sea navigation, approach to harbours, land navigation etc;
- Military: Improved weapon delivery accuracy i.e. for missile- launching etc., ranging in artillery, navigation for Defence;
- Scientific applications, like studies related to the ionosphere and troposphere, glaciology etc.
Many earthquake-affected countries in the world have undertaken GPS and other Geodetic Studies to monitor seismotectonic activities. International GPS Service for Geodynamic (IGS) is a co-ordinating agency for such studies.
International GPS Service (IGS)
The IGS Global network consists of about 200 permanent GPS stations, spanning across the continents. The 76 agencies implementing these stations contribute to the GPS global network, the backbone of the IGS. The IGS is organised into a Central Bureau, governing board, analysis centres and data centres. Most of the IGS analysis centres rely on a subset of the stations that are optimally distributed to produce the global rapid orbits.
There are a number of dense GPS arrays being implemented all over the world for geodynamic purpose, such as the 600-station Japanese Geographical Survey Institute (GSI) Array and the proposed 250-station Southern California Integrated GPS Network(SCIGN). Other countries are also implementing networks for their national mapping, land information and civil aviation purposes, such as the Continuously Operating Reference Stations(CORS) and Federal Aviation Administration (FAA) Networks in the US, the Canadian Active Control System(CACS), and networks in Australia, Sweden, Norway, Central Europe, etc., to name a few.
International DGPS Services
With Differential GPS (DGPS) becoming a very powerful tool for positioning, navigation and mapping, many types of DGPS services are operating in different parts of the world. These range from the global satellite-based DGPS services like LANDSTAR DGPS from RACAL NCS Inc., USA, OMNISTAR, to regional DGPS signals available commercially from many local DGPS companies on FM band radio. For specific purpose, dedicated DGPS services are also operating, like the beacons: master DGPS stations located on lighthouses, for oceanic navigation. In the near future, DGPS services are expected to become a major source for all navigational and positioning needs.
International Civil Aviation
The International civil aviation is already in the process of adopting GPS as its primary navigation system. This decision has been a great boon for global GPS activities and all the airlines and civil aviation agencies in the world are now in the process of changing over to GPS for their navigation. The Airport Authority of India (AAI) is also now involved in implementation of GPS-based navigation systems in India. In addition to civil aviation, most countries are also in the process of adopting GPS-based navigation systems for their military aircraft. This change-over will also lead to uniformity in the reference datum and use of DGPS for navigation.
Other Satellite Positioning Systems
In addition to GPS, the Russian system, Global Navigation Satellite System (GLONASS), which has been operative for several years, has assumed great importance, especially to achieve high integrity and reliability in aircraft navigation. GPS-GLONASS combined receivers are now available, which are capable of providing near 100% reliability. The European Commission (EC) and the European Space Agency (ESA) are also in the advanced stage of planning the launch of the all-European Global Navigation Satellite System (GNSS), called “Galileo”. The European Geostationary Navigation Overlay Service (EGNOS), being launched shortly, is the first step in this direction.
Indian GPS Programmes
Several organisations in India, including the Survey of India (SOI), the Wadia Institute of Himalayan Geology, Dehradun (WIHG), the Indian Institute of Geomagnetism, Mumbai (IIG), the Centre for Mathematical Modelling & Computer Simulation, Bangalore (CMMACS), the Geological Survey of India (GSI), the National Geophysical Research Institute, Hyderabad (NGRI), the Indian Institute of Technology, Bombay (IITB), the National Informatics Centre, New Delhi (NIC), the Department of Electronics (DOE), etc., have been actively involved in GPS-related activities. After the 1993 Latur earthquake, extensive GPS Control Network has been established in the Peninsular Shield, under the Maharashtra Earthquake Project. With the World Bank assisted DST Project on ‘Seismic Instrumentation in the Indian Peninsular Shield’, extensive GPS studies are being carried out by various government organisations in the Peninsular Shield. A National programme on GPS studies for Geodynamics, evolved by the GPS Expert Group set up by DST, the report of which was compiled by the author, is now being implemented.
The Department of Space (DOS), Government of India had constituted a National Committee for GPS Based Geodynamics Studies in 1995. The Report of the Committee, of which the author was a member, recommended establishment of a three-tier network of GPS stations, including two Permanent Reference Stations (PRS), four Permanent Monitoring Stations (PMS) and a number of Mobile Monitoring Stations (MMS). An Association of Indian Users of GPS (AIUG) and a Centralised Data Bank (CDB) are also recommended by the Committee. This programme is being implemented by DOS. Many other government and non-government agencies are also in the process of initiating GPS programmes for their specific needs. The National Informatics Centre (NIC) is establishing a nation-wide DGPS network. The Department of Light Houses, (DLH) Government of India, is operating a coastal DGPS network for oceanic navigation. In the private sector also, GPS activities, like GPS control for the National Highway Network and other projects, are gaining momentum.
Suggestions and Recommendations
As highlighted above, extensive GPS activities have been launched globally and in India, for a variety of applications of GPS. However, in order to make our contribution to the Global GPS programmes significant and to emerge as a major force in the world in this Information Technology area in the coming decade, the following suggestions are offered:
- The Indian GPS activities by government and non-government agencies need to be co-ordinated properly for achieving optimum progress through exchange of know-how. The GPS programmes initiated by DST, DOS, NIC, AAI, DLH, and other agencies will be cost-effective and efficient, if close interaction is achieved.
- A national policy on exchange of GPS data needs to be formulated, to ensure free flow of information for scientific and commercial applications of GPS.
- The AIUG should be made more active and powerful, by support from government and private sectors.
- A National GPS Data Centre, catering to the needs of all GPS users, should be established.
- Training of personnel in GPS and its applications needs to be taken up rigorously, to ensure adequate manpower development
- Development of software and hardware for a variety of applications of GPS is one area which requires priority.