Secret tunnels can't hide from gravity.

• Author: Beidel, Eric
• Position: TECHWIRE - Battling subterranean threats - Brief article

* Sir Isaac Newton would be proud.

A project under way at the Defense Advanced Research Projects Agency will use gravity to battle subterranean threats. The program seeks to establish a way to detect tunnels from the air by using a special sensor that can find deficiencies in the Earth's surface.

"The explicit action of digging tunnels introduces a void into the subsurface geology," reads a DARPA document describing the program. The sensors can "measure tiny spatial variations in the pull of gravity caused by these underground voids."

The goal of the program is to find and define tunnels, bunkers and caches from a helicopter or unmanned aerial vehicle by measuring these distortions. DARPA has selected Lockheed Martin to...