WHILE diplomats work to restrict the manufacture, sale, and use of land mines worldwide, a massive cleanup effort is needed to find and destroy the estimated 100 million land mines still buried in 65 countries. Land mines left behind from wars worldwide are one of the century's main unsolved problems of war and remain the focus of humanitarian mine detection and removal primarily in Europe, Africa, Asia, and Central and South America.
A combination of technologies from Lawrence Livermore National Laboratory is being directed toward the most daunting challenge presented by land mines--quickly determining the location of each individual land mine in an area so all of them can be removed. The Laboratory's patented micropower impulse radar and advanced imaging technologies are being combined in a practical system called the Land-Mine Detection Advanced Radar Concept, or LANDMARC, that is making pivotal advances in meeting the challenge of land-mine detection.

The Detection Dilemma
Effective solution of the problem posed by land mines means that close to 100% of the mines in any area must be detected at the fastest rate possible and with few false alarms (i.e., mistaking a buried object, such as a rock, for a mine). The United Nations, for example, has set the detection goal at 99.6%, and the U.S. Army's allowable false-alarm rate is one false alarm in every 1.25 square meters. No existing land-mine detection system meets these criteria. And the reasons for this failure have as much to do with the mines themselves and the variety of environments in which they are buried as with the limits or flaws in the current technology.
Land mines are of two basic types--antitank and antipersonnel. Antitank mines are larger and more powerful than antipersonnel mines. However, antipersonnel mines are the most common type of mine, yet the most difficult to find because they are small and often made of plastic. Antitank mines generally contain more metal than do antipersonnel mines and are thus more easily detectable by simple metal detectors. Both types are buried as close to the surface as possible and are found in a variety of soils and terrain--rocky or sandy soil, open fields, forested areas, steep terrain, jungle. For both types of mines, detonation is typically caused by pressure, although some are activated by a trip-wire or other mechanisms. Thus, a land-mine detector must do its job without having direct contact with a mine. It also must be able to locate all types of mines individually in a variety of environments.

Other Detection Technologies
Various detection technologies are currently used, each with limits or flaws. Dogs and other "sniffers" have high ongoing expenses, are subject to fatigue, and can be fooled by masked scents. Metal detectors are sensitive to metal mines and firing pins but cannot reliably find plastic mines. Infrared detectors effectively detect recently placed mines, but they are expensive and limited to certain temperature conditions. Thermal neutron activation detectors are accurate but are large for field use, slow, and expensive.
In early attempts, ground-penetrating radar was sensitive to large mines, had good coverage rate at a distance, and with signal processing, could discriminate antitank mines from clutter such as rocks beneath the ground surface. This type of radar, however, remains expensive, cannot detect antipersonnel mines because its resolution is too low, and frequently records false alarms from clutter sources.
Livermore's ongoing LANDMARC project addresses all of these problems and stands a good chance of solving them, especially the problems of detecting small plastic antipersonnel mines and reducing the false-alarm rate.

Livermore's Systems Approach
The LANDMARC system's enabling technology is micropower impulse radar (MIR), which was invented at Livermore in 1993 as an outgrowth of the Nova laser program.1 The invention, which won an R&D 100 Award in 1993 and an Excellence in Technology Transfer award from the Federal Laboratory Consortium in 1996, led directly to a battery-operated pulsed radar that is remarkably small and inexpensive, has a wide frequency band, and works well at short ranges2--all necessary attributes of land-mine detection systems.
MIR's small size, light weight, and low power requirements make it superior to any previous attempts to use ground-penetrating radar to detect land mines. MIR's ultrawide bandwidth is the source of the high-resolution imaging capabilities that differentiate LANDMARC from similar land-mine-detection technologies. Furthermore, the ability to group individual MIR units in arrays increases the speed and coverage area of LANDMARC's detection work.
Livermore's LANDMARC team has combined MIR units with a high-performance imaging system that uses sophisticated computer algorithms to convert large amounts of raw waveform data from the MIR units to high-resolution two- and three-dimensional images of the subsurface. The prototype systems enable users to visualize both antitank and antipersonnel mines and to differentiate them from rocks and other clutter of similar size and shape by the reflected MIR signal. Once the mines can be "seen" and identified, they can be recovered and destroyed.
LANDMARC prototypes have multiple MIR units that are either configured in a hand-held wand, much like that used for simple metal detectors, or mounted on a small robotic cart (Figure 1). In either configuration, the MIR array is passed over the ground with the antennas of the units about 10 centimeters above the surface. The units rapidly emit microwave impulses with very short risetimes (100 trillionths of a second) that radiate from transmitting antennas and penetrate the ground. These impulses strike and penetrate buried objects, bounce back to a receiving antenna, and are sampled and processed by an onboard computer to measure changes in the dielectric and conductivity properties of the subsurface. In a few seconds, the data reconstruction algorithms convert the raw radar data into high-resolution two- and three-dimensional tomographic images of the subsurface (Figure 2). On the system currently under development, the images will appear on either a laptop computer or the operator's headset screen.






LANDMARC Innovations
One of LANDMARC's chief contributions to land-mine detection technology is combining MIR units with a high-performance imaging system.3 LANDMARC's MIR-based imaging software, which was originally developed for radar inspection of steel-reinforced concrete bridge decks, provides a great improvement over previous land-mine detection technology in sorting out clutter--the most difficult of the imaging tasks--and lowering the false-alarm rate.
Central to perfecting LANDMARC's imaging capabilities are the comprehensive signal and noise models being developed by the Livermore team. These models are based on the contributions from temperature differences, inhomogeneity in the soil, increased noise resulting from multiple reflections in MIR arrays, surface reflections, and subsurface clutter such as rocks, roots, and voids. They identify terrain and soil conditions where radar is likely to work well and other situations where different types of sensors would be more appropriate. More important, the models are used to design algorithms to help reduce the false-alarm rate and increase the positive identification rate in laboratory and field tests, both of which, in turn, improve LANDMARC's ability to discriminate between mines and clutter.

Results from Field Testing
Preliminary experiments identified the operational requirements of the prototype systems. The LANDMARC team developed the reconstruction algorithms that generate a three-dimensional image and is using them to investigate design trade-offs such as array size, sampling rate, and overall speed. In laboratory tests, the prototype clearly distinguished plastic antipersonnel mines from surrounding soils. In field tests at Fort Carson in Colorado and Fort A. P. Hill in Virginia, funded by the U.S. Defense Advanced Research Projects Agency (DARPA), the system performed well, though at a slow pace. The images it produced indicated that much progress has been made in removing the strong ground-surface reflection and other noise sources--that is, improving the signal-to-clutter ratio.
Field tests also indicated areas for additional refinement, among them using higher frequencies (that is, wider bandwidth) to improve resolution and better distinguish mines from clutter, and providing the system with a means of communicating a more accurate field position of the imaged mines.

Future Plans
When field tests with the prototypes are complete, the LANDMARC team plans to conduct blind tests at U.S. Army mine fields to measure detection probabilities under realistic conditions. In addition, plans to speed up the scan rate with advanced arrays are under way. Already experienced in industrial licensing of the MIR technology, the team will then direct LANDMARC toward external sponsorship for deployment in actual mine fields. The Department of Defense, U.S. industries, nongovernmental organizations such as Operation USA and the World Bank, and foreign governments have all shown interest in using Livermore's land-mine detection technology.
-Sue Stull

Key Words: antipersonnel mines, antitank mines, humanitarian land-mine detection, ground-penetrating radar, LANDMARC (Land-Mine Detection Advanced Radar Concept), micropower impulse radar (MIR), subsurface imaging, ultrawide bandwidth.

References
1. "World's Fastest Solid-State Digitizer," Energy & Technology Review, Lawrence Livermore National Laboratory, Livermore, California, UCRL-52000-94-4 (April 1994), pp. 1-6.
2. "Micropower Impulse Radar," Science & Technology Review, Lawrence Livermore National Laboratory, Livermore, California, UCRL-52000-96-1/2 (January/February 1996), pp. 16-29.
3. S. G. Azevedo et al., Statement of Capabilities: Micropower Impulse Radar (MIR) Technology Applied to Mine Detection and Imaging, Lawrence Livermore National Laboratory, Livermore, California, UCRL-ID-120801 (March 1995).

For further information contact Stephen Azevedo (510) 422-8538 (azevedo3@llnl.gov).
For licensing and MIR partnering information contact (510) 423-1077 (mir@llnl.gov).
Also see the MIR home page (http://www-lasers.llnl.gov/lasers/idp/mir/mir.html).


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