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Ground Moving Target Indicator [GMTI]

GMTI (Ground Moving Target Indicator) radar provides continuous wide area surveillance coverage of ground moving vehicles. Thousands of vehicles can be detected and tracked with each sweep of the radar. Ground Moving Target Indicator radars can be a source of signi?cant tactical,theater and even strategic intelligence answering fundamental Theater Commander questions such as: Is the enemy moving? Where? How fast? How many vehicles? When did they start? Where did they come from? Where are they going? What military units are involved? Are there air defense units involved? What are civilian traffic indicators?

The concept of airborne surveillance of enemy ground forces with a Ground Moving Target Indicator [now called GMTI] radar capable of detecting moving ground vehicles and helicopters was proposed in 1968 and resulted in DoD programs to realize its potential. The currently fielded Joint Surveillance and Target Attack System [JointSTARS], in prototype form, more than proved its worth in the 1991 Gulf War. JointSTARS permitted theater commanders and his air and ground component commanders to see not only "what was on the other side of the hill" but what was going on throughout the entire theater, and to attack selected targets. Thus a totally new and unique kind of information whose military value and signi?cance was equal to that of overhead imagery and signals intelligence was made available to US and coalition forces. It was a longtime coming; a very long time.

JointSTARS is a direct descendent of two programs: the Army's Stand Off Target Acquisition System (SOTAS) and the Air Force/DARPA Assault Breaker/Pave Mover. Bert Fowler conceived and initiated a program to put a Moving Target Indicator (MTI) ground surveillance radar in a helicopter in 1968 when he visited Vietnam and realized the potential value of such surveillance capability. To help sell the program, he pointed out the utility of the GMTI information in a NATO/PACT war and in other types of engagements. SOTAS ran into ?nancial and political troubles and was, unfortunately, canceled in 1981.

The Assault Breaker concept for attacking Soviet 2nd and 3rd echelon armored forces was based upona GMTI radar in a high ?ying aircraft with much longer range than SOTAS. The concept was originally proposed by a Defense ScienceBoard summer study in 1976 chaired by Bert Fowler. In 1978 it became a joint Air Force/DARPA program and the Rome Air Development Center (RADC) was given the job of de?ning the system and running the development. As they had done for several earlier difficult new development efforts, DARPA and the Air Force called upon John Entzminger to lead their GMTI efforts: RADC's GMTI research program with MIT Lincoln Labs; the demonstration (1975) of moving target location and attack using two SOTAS radars in a multilateration mode guiding a KMU-358HOBO missile launched from an F-4; and the new Assault Breaker radar called Pave Mover. Entzminger de?ned the required performance of Pave Mover, including the addition of a synthetic aperture radar (SAR) mode, managed the program throughout its development, and was an effective spokesman for GMTI during the crucial years.

The Pave Mover radar would locate the moving or stationary ground vehicles. Then, simultaneously and in real time, track and guide an Army surface-to-surface missile giving guidance corrections in ?ight to allow the missile to deploy aload of terminally guided sub-munitions to strike thetargets. Competing development programs for the new radar were awarded to Grumman Aerospace and Hughes Aircraft. In 1978, on-board digital processors were not as powerful or small as today, so the systems had wide-band data links to allow the processing of the radar information at the ground station. In additionto the GMTI modes the Pave Mover radars had SAR spot modes and were capable of switching between wide area MTI (l20-200 km), smaller area MTI (10 x lO km), precision moving target track, SAR spot image, and weapon guidance modes. Both contractors successfully demonstrated all these modes in tests at White Sands Missile Range in 1980-1982.

Currently, GMTI platforms include Joint Stars, U2, and ARLM (Air Reconnaissance Low MTI). Planned GMTI platforms sensors include U2-AIP, Discoverer II, Joint Stars - RTIP, and Global Hawk. The ability to perform multiple platform tracking will improve target location, track association and track correlation. The problem is that each sensor platform uses a unique coordinate system for locating targets on the surface of the earth and each platform also has a platform location error. In order to fuse the GMTI detections from multiple GMTI sensors, a common reference point must be used to register the GMTI detections and remove the platform location error. Geo-registration is needed to accurately determine target location by reducing tracking errors from different sensors by, but not limited to, registering detections to RF tags and/or images of fixed sites for example. It is also important to accurately locate GMTI detections from a single platform. Single platform location errors need to be eliminated to provide accurate target location. Approaches and techniques for single-platform geo-registration may include but not limited to using RF Tags (GPS, Unattended Sensor) and Image registration to known fixed sites.

As part of the effort to extract information from this wealth of data, techniques are being developed to automatically generate and maintain tracks that represent these ground moving vehicles. A track database maintains history and heading information of the ground-moving vehicles allowing for an algorithm to exploit the information to determine items like traffic flow, density, and convoys. To accomplish the necessary resource management, these GMTI tracks must be exchanged and shared among a large number of nodes allowing for hand-off between systems and exploitation at various command nodes.The track management challenge is to develop techniques for the efficient, but non-ambiguous sharing of this GMTI track data among a large number of distributed users.

In this distributed and potentially highly dense environment, it is critical to have only one track representing any given vehicle (or group of vehicles). As new information is obtained for a vehicle (or group of vehicles), this information needs to be associated with the track unique to that vehicle (or group of vehicles) and then shared among all interested users. Novel techniques in database management, data fusion and collaborative work environments need to be developed to ensure that only one unique track is generated and maintained for any given detected moving vehicle and that this same track in maintained over the entire life of the track.

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