For Immediate Release
Georgia Institute of Technology researchers are making progress with
a landmine detection system that could ultimately help prevent such losses.
The system uses high-frequency seismic waves to displace soil and objects
in it slightly (less than one ten-thousandth of an inch). A non-contacting
radar sensor then measures the results, creating a visual representation
of the displacement that reveals the buried mines.
This seismic-wave system presents potential advantages over existing electromagnetic-wave techniques used in metal detectors and ground-penetrating radars (GPR). Although metal detectors and GPRs can locate mines successfully, they have more trouble locating the small, plastic anti-personnel mines that have become more prevalent. Metal detectors and GPRs can also be confused by ground clutter -- rocks, sticks or scraps of metal - sometimes resulting in many false alarms.
Yet because plastic mines have very different mechanical properties from
soil and ground clutter, the seismic waves are capable of detecting and
distinguishing these mines from common ground clutter. This has been demonstrated
in laboratory and limited field tests.
"When a wave hits a land mine, resonance builds over the top of
the mine, triggering a vibration which is bigger than the wave that excited
it - and the vibration persists longer," says Waymond
R. Scott Jr., a professor in Georgia Tech's School
of Electrical and Computer Engineering (ECE) and principal investigator
on the project.
Sponsored by the U.S. Office of Naval Research, the U.S. Army Research
Office and the U.S. Army Night Vision & Electronic Sensors Systems
Directorate, the mine-detection project involves researchers from various
departments at Georgia Tech. This multidisciplinary team started work
in 1997 with computer modeling and lab experiments. Field testing began
in fall 2001, and during the past two years, the researchers have conducted
tests at six sites.
In November 2002, the researchers traveled to a government testing facility in a temperate climate where they detected six different anti-tank and anti-personnel mines. "Our results there were comparable to what we saw in the lab, which was very significant. That was a big hurdle for us," Scott says.
Field tests at government facilities give the researchers greater credibility
because conditions are more realistic, and they can compare results to
data from other research teams. What's more, the mines at government test
sites have been buried for several years, which complicates detection.
"It's much easier to detect a mine that's been buried recently because
you've disturbed the soil," says George McCall, a senior research
engineer in the Georgia Tech Research Institute's Electro-Optics,
Environment and Materials Laboratory. "After a land mine has
been in the ground for a while, the soil becomes weathered and more compact.
This makes it harder to find, so it's a better test for our detection
In February 2003, the researchers traveled to another government testing
facility where the ground was frozen. This test broadened the scope of
environmental conditions under which the mine detection system had been
Testing in a variety of sites is important because different environmental conditions affect how far and how fast seismic waves travel through the earth. That, in turn, affects how waves interact with buried mines and what kind of signal processing is required to image the mines.
The field tests have also given the researchers a chance to develop another
aspect of the seismic mine detector -- an audio representation of buried
"When the system passes over a mine, you hear a resonance that's
easy to distinguish from the incident signal - it's a hollow sound like
what you hear when you tap on a wall to find a stud," Scott explains,
adding that the operator would listen to this resonance via a headset,
or the unit would have a speaker. "In some cases, this audio representation
was clearer than the visual representation."
Because of this discovery, Georgia Tech will collaborate with CyTerra
Corp. to evaluate the feasibility of incorporating the Georgia Tech
seismic sensor into a handheld mine detector the company is producing
for the U.S. Army.
CyTerra's current handheld system combines a metal detector with ground-penetrating
radar. "Integrating the capability that Georgia Tech has developed
to acoustically measure vibrations will give us a triple-sensor device
that should increase our ability to detect mines and reduce false alarms,"
says William Steinway, executive vice president of CyTerra Corp. based
in Waltham, Mass.
"No single sensor has proven capable of detecting mines well with acceptable false alarms in all environmental conditions," Scott says, noting that what works best in a given situation depends on the type of mine and where it's buried. "A fusion of multiple sensors will most likely be necessary to get good performance in all conditions. Our seismic sensor is ideal to fuse with other types of sensors like GPRs and metal detectors."
In June 2003, researchers conducted their eighth field test, traveling
to Skidaway Island, Ga. This was the team's third visit to Skidaway, and
data derived from this field test was consistent with earlier measurements
-- an encouraging result.
Even more important, researchers were able to test techniques for making
the mine-detection system faster:
"The positioner we used was never intended to do this, so with different
hardware we should be able to get better results," says James
S. Martin, a senior research engineer from Georgia Tech's School
of Mechanical Engineering. "Even so, this was much better than
the snail's pace at which we had been working."
Two radar sensors have been used in the current system to demonstrate
that interactions between multiple sensors are not problematic. But adding
more sensors would make the system faster. "Anytime you increase
the number of sensors you're using, you can decrease the measurement time,"
Larson, another School of Mechanical Engineering researcher on the
Bottom line, researchers say the time required to measure a square meter
can be sliced from several hours to less than a minute. Faster measurements
are crucial as the team develops a prototype for more extensive field
"We need to measure larger areas and gather more information about
different mines, soil properties and environmental conditions," Scott
says, noting that data helps the researchers improve their numerical models
and signal-processing algorithms.
"Testing in different soil properties is important because the soil's complicated structure makes it to difficult to detect mines. You can't just look up the soil parameters we need in a book," he adds.
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