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The surface of the earth has been mapped and mastered, with lidar, photography, infrared and other now-familiar systems, on satellites, manned aircraft and drones. Thermal imagers can even penetrate thin layers of soil. But go just a bit deeper, and you reach one of the last frontiers of ISR. How do you see into solid ground, below the roads, the rocks and the desert sand?
Israel is following very closely the American efforts to develop techniques to detect tunnels.
It’s a hot topic in U.S. government research. Tunnels have bedeviled prisons, security forces and border agents for years. Last summer, authorities discovered a 240-yard drug tunnel, fitted with electricity and lights and a ventilation system, under Arizona’s border with Mexico. The year before, there was embarrassing news from Kandahar: Almost 500 prisoners, including Taliban fighters, escaped from an Afghan prison via a 1,000-foot tunnel.
According to Defense News one of the focal points for research is the Rapid Reaction Tunnel Detection, a joint effort between the U.S. Defense Department’s Northern Command and the Department of Homeland Security’s Science and Technology Directorate. Along with prime contractor The Mitre Corp., program officials may be closing in on a possible solution.
There is actually one borefinder system already deployed. Called Border Tunneling Activity Detection System, it was developed by Raytheon BBN under contract with the Army Corps of Engineers. But the name may be a bit optimistic.
It’s an array of geophones — microphones that can detect noise in the earth — connected to advanced processors. Though it is still a research and development project, it has been tested and even deployed in the U.S., in Customs and Border Protection’s San Diego sector, according to congressional testimony. But the system is really just detecting noises from the ground: drills, chisels, people pushing carts full of drugs. The idea is a vast refinement to holding one’s ear to the ground, and it doesn’t help find the tunnels that are there. And on the southeast border with Mexico, where geology is complex, there is a lot of clutter to confuse the sensors.
You might think that the technology used to find oil and mineral deposits for decades could solve the problem. After all, geologists can find salt domes on top of oil deposits, or seams of coal.
Senior program adviser David Masters oversees the effort at DHS, and he said that in some ways the miner’s tools have proved almost useless in the search for tunnels.
“The miner is looking for gold, the oilman’s looking for oil, and the rescuer is looking for trapped miners,” Masters said. “So what they end up doing is excluding everything else except the specific thing they are interested in. And that particular thing does not have anything to do with a tunnel.”
The way border agents find tunnels now is basically luck. “They find tunnels through intelligence or by accident,” Masters said. “A dog goes and sniffs an area and everyone goes there and they find a tunnel. Or a truck full of equipment or water is driving across the desert and all of a sudden it sinks. Or they are paying snitches.”
A former executive at Hughes Aircraft, where he worked on electro-optical programs, Masters is today employed to examine the technology that might work to actively search for tunnels underground — to find the hollow spaces.
“Nobody’s done it before,” he said. “The physics of it is absolutely fascinating.”
Finding what’s under the surface of the earth is like trying to use an MRI or ultrasound to learn what’s under the skin. In theory, it should be pretty simple: Shoot mechanical or electromagnetic waves and the distortions to the return and the waves’ propagation could help find things like a tunnel. But in an underground world, teaming with unknown boulders, water tables and cracks, it doesn’t work that way.
“If you don’t understand the geophysics associated with the different type of sensor you are using and the earth you are actually standing on,” Masters said, “then you won’t be able to discriminate between targets and clutter.”
He said the solution is to first build computer simulations of the actual geology one wants to probe. Then you build models of how various sensors, seismic or ground-penetrating radar perform there.
During an interview in his office, Masters demonstrated a computer simulation of a section of ground. The simulated chunk of earth is colored blue, and a red translucent tunnel is modeled through it. In slow motion, the simulation of the wave return of “ground-penetrating radar” surges through the image screen.
“If you have a uniform geology,” Masters said, “and a single tunnel, you get a beautiful return. Looks great. And everyone says: ‘Look, there’s a tunnel!’”
But then he showed off another computer model, and this one, of an actual piece of terrain at the border, has rocks and boulders spread throughout on the screen.
He showed off a simulated seismic “thump” running through it. The returns and the wave returns were scattered and unpredictable.
Still, there has been success, at least on the computer. In small areas, where the actual geology has been adequately mapped, the simulations, theoretically, show that a tunnel can be found.
He said so far the chief interest in the U.S. government comes from Customs and Border Protection, the Army and “some agencies that prefer to be unnamed.”
That’s a long way to go before technology can be deployed in the real world, chiefly because there is little room for error. “We can’t go check if every rock or boulder is a tunnel,” Masters said.