The NAVSTAR Global Positioning System (GPS) is a constellation of 24 satellites developed, launched, and maintained by the U.S Air Force that provides positioning, timing, and navigation signals free-of charge to both military and civilian uses worldwide.
A second civil frequency will allow receivers to measure the time of arrival for two signals that have passed through the Earth's atmosphere and correct for the distortion introduced by passage from space to earth.
An improved location calculation will allow safety-critical uses requiring dynamic, reliable capability to be more reliant on the GPS signal, improve the overall accuracy of the system for the average user, and allow the high-accuracy users (surveying, geodesy, weather forecasters, etc.) to determine their data in a faster, more reliable manner. In addition, the second civil signal will allow the safety-critical users to have a backup signal in the event of inadvertent disruption of the current civil signal.
The Interagency GPS Executive Board(IGEB) has selected the 1227.6 MHZ band(currently known as the L2 signal) for the addition of new civil capability. A third civil signal will also be added with a decision on the frequency to be made in August of this year. The decision on which of these two new signals the Government will pursue to become the safety-of-life service signal will also be made in August.
One of the key factors in deciding which frequency to pursue as the safety-of-life signal is a commitment by all members of the IGEB to have a safety-of-life service signal available by 2005.
The new signals are intended to be added to the GPS Block IIF satellites.
The new signals will be available to all civil users worldwide.
Internationally, interest has been expressed via the International Civil Aviation Organization (ICAO) in the use of a second GPS civil signal in conjunction with the Japanese MSAS and the European EGNOS augmentation programs.
Currently the GPS system is used by a wide range of users： from cars and trucks on the nation's highways to ships at sea and on inland waterways; from civil aviation to satellites in space, from earthquake monitoring equipment to surveyors to backpackers; new industries such as precision farming; and the electrical power companies and long-distance phone systems which derive timing and synchronization from the signals.
