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GPS: A military perspective
Navigation For a soldier operating under cover of darkness in enemy territory the biggest challenge is navigation due to unfamiliar territory and lack of easily identifiable landmarks on ground. Soldiers have been using night skies for ages to find out direction but their location on ground cannot be determined. The necessity of knowing their own position by troops during war was very clearly highlighted during the Gulf War (1990) and the Kargil conflict (1999). This can be judged from the fact that initially about 1000 GPS receivers were issued for use during the Gulf war but by the end nearly 9000 handheld devices were in use (Fig 2). Similarly, during the Kargil conflict, Indian patrols operating in rugged terrain along the line of control, initially strayed into enemy held areas with disastrous consequences but later on the availability of handheld GPS receivers proved to be invaluable to them. In fact, these GPS receivers are fast replacing the conventional compasses in a soldiers rug sack. Special forces and crack teams also use these to reach and destroy vital enemy installations. Such teams can draw air and artillery fire accurately by providing the accurate positional data. Further, gun positions can be occupied quickly using GPS, as in modern warfare, artillery batteries must move often to keep pace with assault troops and to avoid being hit by counter fire. Convoy movements can also be tracked and planned effectively using GPS devices. Tracking In a military scenario, potential targets need to be constantly tracked before they are declared hostile and engaged by various weapon systems. This tracking data is fed as input to modern weapon systems such as missiles and smart bombs etc. Just to site an example, the US Army has developed a GPS Truth Data Acquisition, Recording, and Display System (TDARDS). It is a compact, lightweight, low-cost, and easily transportable or mobile GPS-based tracking system that uses up-to-date GPS data, radio data link, and computer technology to provide highly accurate, real-time time-space position information (TSPI) on up to ten test objects, such as ground vehicles, helicopters, and fixed-wing aircraft. The system is highly modular, built with commercial off-the-shelf hardware, and easily modifiable to meet any special needs of individual testing and tracking applications (Gilkey et al., 1994). Bomb and Missile guidance Modern day weapon systems are designed to use GPS data as input for targeting and guidance. Cruise missiles commonly used by US to accurately hit targets from large standoff distances use multichannel GPS receivers to accurately determine their location constantly while in flight. The Multiple Launched Rocket System (MLRS) vehicle uses GPS based inertial guidance to position itself and aim the launch box at the target in a very short time (Fig 3). This reduces the chances of detection and counter bombardment. The Exploitation of DGPS for Guidance Enhancement (EDGE) program of the US army has developed a 2000 lb glide bomb, which uses a GPS seeker rather than a Laser for guidance. This bomb could accurately hit its target 11 miles from its drop point guided by four DGPS base stations about 1000 nautical miles away (Anonymous(a), 2001). Rescue Rescue and emergency response is another area where GPS can prove invaluable to the military. Determining the location of a casualty during operations, emergency response teams can use the GPS to reduce response time. For example, the US Air Force is already taking advantage of GPS based technology and is developing a Combat Survivor Evader Locator (CSEL) system. The new system integrates the GPS receiver with a communications radio so that search and rescue teams can locate downed aircrew members faster and more accurately than before (Anonymous(b), 2001). Map Updation To carry out planning at various military headquarter levels, the defence forces need accurate and updated maps at various scales  Fig. 2 : Image showing use of GPS receivers by US soldiers during Gulf War (Source: http://www.aero.org/publications/GPSPRIMER) depending upon the level of the commander for planning operations, administrative planning and training. The availability of GPS shall augment the collection of precise data necessary for quick and accurate map updation. The GPS can also be used effectively for the establishment of grid control locations for the placement of various weapons and other assets, location of targets etc. For example, the modern mapping techniques such as remote sensing and GIS will now constantly use the DGPS technology to register the images into absolute geocoordinates (Kelly, 2001). This would enable the military personnel to utilize modern map products to accurately determine the locations of target points for use by the new generation of weapons.  Fig.3: Image showing Multiple Launched Rocket System (Source: http://www.aero.org/publications/GPSPRIMER/) Facility Management In almost all countries of the world, the military manages and operates large bases which cover extensive areas. To manage these facilities effectively, it is essential to prepare an accurate base map. Here GPS/DGPS can be of immense help, as existing maps are not updated regularly. GPS co-opted with Geographic Information System (GIS) can effectively tackle this task. For example, at Yokosuka US Naval Base in Japan, Arc View GIS software was used to evaluate three different components for the GPS implementation. First, for modeling the optimum location for a GPS base station, secondly for selecting benchmark locations to fix the base station location and thirdly evaluating accuracy of survey by GPS (Dunham, 1999). Conclusions With war clouds looming large over the west Asian region, the world is likely to witness the state of the art weaponry being used by the US led forces. Most of these, either directly or indirectly shall be using GPS to accurately target and achieve the desired results. This paper has demonstrated the capabilities of GPS receivers for various kinds of military activities both during war and peace. Depending upon the nature of activity (i.e., navigation or precise target location), a particular kind of GPS may be used. It may thus be summarized that the GPS based weapon systems are here to stay and will form the backbone for the future development of better, more accurate and lethal munitions. References
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