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GPS is satellite-based radio navigation and surveying system. The technology was originally built for military use and the worldwide GPS system is funded by the U.S Department of Defense. GPS uses a constellation of a global network of 24-satellites that orbits the Earth to provide accurate navigational signals.
An Earth-based GPS antenna and receiver can track information from these satellites and compute the antenna's position accurately, in three dimensions1. Thus by using satellite technology, GPS identifies both military and civilian user location anywhere on Earth and at any time, within seconds. The atomic clocks on the GPS satellites also make the signals perfect for keeping highly accurate time. A few of the varied GPS applications are road, rail, air and marine navigation, surveying and mapping, agriculture and mining, asset management, avionics, oil exploration, environmental research, wireless communications, electronic data transfer, scientific applications, emergency response and others.
The growth of the worldwide GPS market is tremendous. As per the statement given by Executive Office of the U.S President (Office of Science and Technology Policy) Washington, there were more than 4 million global GPS users in 2000 and the market for GPS applications is expected to double from $8 billion to over $16 billion by 2003.
Significance of GPS signals
The accuracy of GPS signals plays a prominent role in obtaining quality data from GPS satellites, which is supplemented by pseudo range, carrier phase and the ephemeris data of the satellite. It is believed that the downing of Korean Flight 007 during 1980s, substantiated the need for timely access of better navigational signals to avoid any such disaster in future. It obligated the then U.S President Ronald Reagan to issue a directive on U.S GPS Policy.4 This directive assured the guarantee that GPS signals would be available free of cost to the GPS community. As a result, GPS burst into public awareness and many companies opened up their civilian and commercial GPS market. The deployment of GPS continued at a steady pace with a growing number of civilian and military users. In order to avoid the misuse of GPS data, the U.S employed a technique called 'Selective Availability' (SA) to globally degrade the quality of GPS signals available to civilians. The far-famed time in GPS history was the time when the U.S turned off SA in May 2000 followed by an executive order signed by President Clinton, due to the immense pressure on GPS markets.
Discontinuation of the use of SA improved the accuracy of GPS for civilian users from within 10m to within 20m, using capable receivers. This ensures attaining positional accuracy in autonomous (non-differential) mode. Further, the basic GPS "services" envisaged by the U.S. Department of Defense, are the Standard Positioning Service (SPS) and the Precise Positioning Service (PPS).7 SPS is available to all civilian GPS users whereas access to the PPS is controlled by US Department of Defence (DOD) by invoking SA and 'Anti-Spoofing', for its military use. With this discontinuation of SA, the accuracy of civil GPS receivers with SPS positioning must be more accurate, under normal circumstances. The Interagency GPS Executive Board is also revised 'SPS Signal Specification' by taking into account the new levels of performance achievable, without SA.
The September 11, 2001 terrorist attack on U.S took a new turn on the destructive usage of GPS. Reports say that the U.S Federal Bureau of Investigation (FBI) is suspecting terrorists' use of GPS as their lethal weapon to precisely locate the ill-fated sites.4 A week after that terrible attack, the FBI ordered the noted GPS company "Garmin" to hand over its sales records. The company's retailers and people who carried its aviation portable products were also browsed. It is suspected that at least three of the 19 terrorists could have purchased a GPS device during last year.8
On the other hand, since the Gulf War the U.S is using GPS in its military actions. In the ongoing military campaign against Afghanistan, the U.S Defense Department is trying to keep the GPS technology away from the Taliban forces. It is reported that SA has been replaced by selective deniability, which allows the U.S military forces to geographically locate areas and degrade GPS quality on a regional basis. It allows the worldwide GPS users to remain unaffected by regional GPS degradations and ensures GPS businesses will continue at a good level of competence. With this overall scenario, it is a hard-to-digest fact that such a constructive technology is used for destructive purposes, either as military action or as misuse by the anti-social elements.
Persian Gulf War: Era of GPS guided weapons
The Persian Gulf War in 1991 (from January 16 to February 28), which was headed by the U.S with international coalition against Iraq was the first combat to use GPS. During that 'Operation Desert Storm', soldiers tried to find their bearings in the desert landscape by using handheld GPS receivers. The U.S Defense acquired a number of civilian GPS receivers and temporarily allowed them to receive the high-accuracy military signals. That gave dramatic proof of the value of GPS data for military operations, and it also allowed civilians to recognize the value of the GPS system. Due to the immense demand, more than 9,000 commercial GPS receivers were used in the Gulf region before the end of the 'Gulf War'.
During the conflict, GPS receivers were carried by foot soldiers and attached to vehicles, helicopters, and aircraft instrument boards. The receivers were used in several aircraft, including F-16 fighters, KC-135 aerial refuelers, and B-2 bombers. Navy ships used them for aircraft operations, minesweeping and rendezvous. M1 Abrams tanks and Bradley Fighting Vehicles used GPS devices to get their exact position. Apart from the identification of precise location for the soldiers, GPS is used to bombard the specific targets in 'Desert Storm' and later, in the 1999 Kosovo conflict. They are 'SMART WEAPONS' and use a hi-tech network of satellites to find their targets at any time. It was reported that during the Gulf War, 10 percent of the ordnance dropped by U.S. forces were 'smart bombs'. By 1999, in the bombing of Serb targets in Yugoslavia, 90 percent of the ordnance had lasers and GPS guidance.
In the recent American attack against Afghanistan, U.S forces are preparing to extensively use GPS controlled smart bombs against terrorist camps and Taliban targets. GPS took over laser-guided bombs, as laser strikes were impossible during bad weather, as it couldn't penetrate cloud cover. Also, using the laser-guided system the targeted area had to be charted before the strike. Hence, the GPS system can reduce the preparation time for an officer who needs to coordinate the missile attack.
According to Tim Brown, a senior analyst with GlobalSecurity.org in Alexandria, Va., " GPS-guided munitions are much safer and more accurate than laser-guided bombs - they're accurate to within a few feet, and can be dropped from much higher, as laser-guided bombs require bomber crews to fly low enough to identify the target and illuminate it with a laser before dropping the bomb". If the laser encounters common battlefield conditions such as haze or smoke, "the bomb might lose signal on final approach and still miss the target," Brown added.
Of course, GPS is still a critical military technology. Soldiers on the ground use it to find their way, as do ships and planes. Precision-guided munitions like Tomahawk cruise missiles use GPS signals to zero in on non-moving targets like enemy airfields. After the Gulf War, GPS represents one of the critical military technologies whose civilian uses range far beyond what its planners could ever have envisioned.5
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