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November 2002 |
GPS-Security and Restriction
N K Agrawal
Managing Director
Geodesy and GPS Services,
Hyderabad, India
nande@rediffmail.com
United States Department of Defense has given to the world GPS for navigation, positioning and time determination continuously. U. S. Government had put in place intentional restrictions on access to its signals so that accuracy of the system is limited for security considerations. Earlier there was anti-spoofing as well as selective availability (SA) to restrict accuracy of the system. Selective availability has been lifted since May 2, 2000. Anti- spoofing however continues. Accuracy of horizontal position in point positioning mode with a single receiver is limited to 15 to 20 metres, since P-code is not available to civil users. With P-code we can get accuracy of 3 to 5 metres. It is however possible to get better than 1 metre accuracy in position (latitude and longitude) by simultaneously using 2 receivers in relative or differential positioning.
If U.S.A., the most powerful nation, has put restrictions for security considerations, it is appropriate that India should also have some restrictions for dissemination of its geo-spatial data. Quote from R. Ramchandran’s “Public access to geographical data” is: “It only stands to reason that India devise appropriate restrictions to prevent national security-related risks. Of course any such restriction should have a rational basis. Unfortunately in the context of geographical data, the restrictions are perceived to be without much logical basis.”
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If the launching station and target coordinates are in WGS 84, the result will be precise and accurate whereas if we have Indian system coordinates the missile is not likely to hit the target
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