Millions of unexploded bombs made in America remain a dangerous worldwide threat waiting to be defused. In the most extreme case, Laos became the most bombed country in the world per capita when U.S. planes dropped more than 2 million tons of explosives on it during the Vietnam War — and as many as 30 percent of the bombs did not explode. Now the U.S. military has funded new technology that can better track buried threats from past wars.
Any battlefield cleanup using metal detectors faces the problem of detecting any old buried metallic object, rather than just unexploded bombs. Even the U.S. military has found itself spending 90 to 95 percent of efforts digging up nonexplosive metals during cleanups of test ranges. As a solution, it has invested in electromagnetic induction technology that detects magnetic field signatures from buried explosives.
"They started thinking about using more sophisticated technology to eliminate the problem," said Fridon Shubitidze, an engineer at Dartmouth College. "The goal is to dig up all the explosives — 100 percent — and leave behind 75 percent of the clutter."
The hidden dangers of unexploded ordnance stretch far beyond Southeast Asia to include explosives fired or dropped by militaries everywhere. German bomb experts defused two of the largest unexploded bombs ever found from World War II after evacuating 45,000 citizens last week. Almost 12 million unexploded artillery shells remain buried in the World War I killing grounds near Verdun, France. The U.S. itself has about 11 million acres, including military practice ranges, holding possible buried threats.
To tackle the problem, Shubitidze and his Dartmouth colleagues have created computer algorithms capable of sorting through the low-frequency electromagnetic signatures of buried explosives — making use of even weak signals. They also plan to help upgrade the electromagnetic induction (EMI) detectors being rolled out by companies such as Geometrics, based in Silicon Valley.
An EMI detector works by first creating its own magnetic field. That first magnetic field changes the magnetic properties of buried explosives so that the bombs or projectiles create their own unique magnetic field signatures. The detectors can then sense those magnetic field signatures.
"The EMI's transmitter pumps energy inside an object: the object accepts and holds the energy, changes its properties, and then releases the energy," Shubitidze told InnovationNewsDaily. "When it releases the energy, it's detected by the [EMI] sensors."
The U.S. Department of Defense gave a Project-of-the-Year award to the Dartmouth researchers for their detection efforts during the 2011 Partners in Environmental Technology Technical Symposium & Workshop held in Washington, D.C., on Nov. 29. It also gave the team a $1.4 million grant for a new three-year effort to boost detection of smaller and deeper-buried explosives.
Such reward comes because the Dartmouth team proved the only one capable of finding all unexploded threats during live-site studies. Its detection efforts can currently find 37-mm projectiles — fired by small cannons or grenade launchers — at 1.6 feet (half a meter) below the surface.
As a next step, the researchers want to figure out how to extract better signals from even deeper objects.
"We can detect small objects close to the surface, but when objects are far away then it's a problem," Shubitidze said. "Even if you have big objects very deep, detecting them is a challenge."