Home Articles GPS – The different arguments..?

GPS – The different arguments..?

Yogendran S
GIS Analyst of ENC Division, IIC Technologies Pvt Ltd
[email protected]

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
Age of JDAM Technology
‘JDAM’ (Joint Direct Attack Munition), is equipment that turns a simple iron bomb or so-called dumb bomb into a satellite-guided weapon capable of falling within 10 feet of its target.2 It extensively uses GPS to help pinpoint locations anywhere on Earth and at anytime. The Pentagon, the topmost defense authority of the U.S confirmed that JDAMs have been used in the opening phase of operation against worldwide terrorism in Afghanistan.

The functioning of JDAM using GPS technology is interesting. The $19,000 (approximate) worth JDAM contains a miniature size GPS receiver and can be programmed with the exact coordinates (latitude, longitude and altitude) of an intended target. Once freed from the aircraft, a JDAM collects data from the GPS satellites to position where the bomb is, relative to the target coordinates. The tail of ‘JDAM’ also contains small control fins that regulate and direct it as it falls.

U.S F/A-18 dropping JDAM guided bomb3 Source: BBC

The successful strike of JDAMs, mainly depends on the accurate set of pre-programmed co-ordinates in it. Hence, due to inaccurate coordinate programming by the pilots, the bombs still miss their targets. The US military uses the WGS co-ordinates, similar to the latitude and longitude shown on maps. The accurate co-ordinates of the target have to be loaded into a GPS-guided weapon and as a result there are chances of ‘human error’ in manipulating the coordinates. Also, in practice, errors of more than 10m can creep in, due to atmospheric conditions and electronic “noise”. If a GPS-guided weapon loses touch with the guiding satellite signals, it falls back on inertial navigation – calculating where it is, in relation to its last fixed position. If that happens with a JDAM, its “circular error probable” rises to 30 m (98 ft).6

The errant JDAM-guided missile launched by American B-2 stealth bombers struck the Chinese Embassy in Belgrade, Yugoslavia on 7 May 1999, killed three people. Their target was supposed to have been a Yugoslav arms procurement office. The mistake was put down due to faulty map data. Also, during the strike against Afghanistan, the US Navy jet dropped a 2,000lb (900-kg) JDAM in a residential area near Kabul airport in Afghanistan instead of the intended ‘military helicopter’, which is about a kilometer-and-a-half away.6 It was reported that the accident occurred from a targeting process error.

Dithering and Jamming GPS Signals
GPS is considered as a dominant global standard satellite navigation and U.S. policy makes both the GPS signal and the receiver design specification as an open standard and completely free of charge to the public. This lack of restriction results in the complimentary usage of GPS devices, as there are no controls on who can build/buy a GPS receiver. It is suspected that the terrorists attempted to use GPS technology built by the U.S, against the US itself. Hence, as the GPS signals from the satellites are freely available all over the planet, the U.S is willing to do ‘selective deniability’ to degrade GPS quality on a regional basis. Evidence confirms that there is a significant dithering of the GPS signals over Afghanistan and other areas where there are military operations. This created a buzz in the GPS industry worldwide, over the stringent policy action on GPS and the possible return of SA by the U.S. However, on Sept. 17, 2001, the Interagency GPS Executive Board, which governs the system, posted a statement on its Web site by saying ‘SA” will never be reinstated.

As JDAMs mainly rely on satellite signals, enemies could develop a jammer that would spoof the GPS signals. On the other hand, the U.S military is trying to ‘jam’ GPS signals to avoid misuse by terrorists. The Pentagon has developed the capability to jam civilian GPS signals within a specific targeted area and could easily deny the 36-meter-accuracy civilian signal to the Taliban forces, without interfering with users in other areas of the world.

Depending on whether the Pentagon, which developed and operates the 28-satellite GPS constellation – uses airborne or ground jammers – this could deny the signal to the Taliban over a wide area, with some of the jamming potentially spilling over neighboring nations like Pakistan and Uzbekistan. Hence, a new “navigational war” is here to stay, in which forces play a cat-and-mouse game of trying to jam each other’s ability to receive GPS signals, and also counteract jamming attempts made by others.4

The world is fast moving ahead, with day-to-day technological advancements. At the same time, terrorism is threatening humanity using the same technologies. The suspicion of destructive usage of GPS technology against the U.S is an inopportune one. Though the U.S declared that it would not restore the SA, it would not be surprising if the US turns the entire system off! However the affirmation given by U.S of not reinstating SA again ensures us that there is no such serious issue being contemplated around.

If we backtrack in history, it is the Pentagon that allotted millions of dollars in the research and development of smart GPS guided bombs to hit the specified target with higher accuracy. This was due to the poor performance of first phase of GPS guided weapons during Gulf War and failure of laser guided bombs due to bad weather during Kosova conflict. The supplementary issue of removal of SA will explode this technology to public with much more simplicity.

Necessary steps have to be taken for the effective usage of GPS and stringent rules have to be made to keep away this technology from terrorists. There could be different accuracy limits and restrictions, depending on the end use of GPS. Also it is definitely the need of the hour to prepare a proper ‘code of conduct’ even for the military use of GPS, by involving worldwide GPS communities. It will serve to create security and confidentiality for the geo-spatial community, ensuring constructive usage of GPS technology for a better tomorrow.


  1. Dr. Madhav Kulkarni, “GPS from an Indian Perspective”, GIM International, October 2000.
  2. Tom Infield, “Smart weapons are smarter now, evidence suggests”, Silicon Valley, October 9, 2001
  3. David Shukman, “Guide to military strength”, BBC, October 7, 2001
    (https://news.bbc.co.uk/hi/english/world/americas/newsid_1557000/1557140.stm#gps )
  4. Arik Hesseldahl, “After The Attacks, New Attention On GPS”, Forbes.com, October 2, 2001
    (https://www.forbes.com/technology/2001/10/02/1002gps.html )
  5. Hugh Dougherty, “KEY U.S. AIM ‘WILL BE TO TAKE PRISONERS'”, The Liverpool Daily Post & Echo Ltd, September 28, 2001
    (https://www.globalsecurity.org/org/news/2001/010928-attack02.htm )
  6. Gary Eason, “Why bombing can go wrong”, BBC, October 16, 2001
    (https://news.bbc.co.uk/hi/english/world/americas/newsid_1603000/1603181.stm )
  7. Tiwari, R.S, et al, “An Appraisal of GPS Related Errors “, GIS @development, September 2000
  8. Sue Kwon, “GPS Technology Could Help Taliban Fight U.S”, KPIX Channel 5, U.S