Underground Security System
Wednesday, December 15, 2010 @ 05:12 PM gHale
An underground surveillance system could watch the entire US-Mexico border continuously.
The border-monitoring system, known as Helios, consists of laser pulses transmitted through fiber-optic cables buried in the ground that respond to movements on the surface above. A detector at one or both ends of the cable analyzes these responses.
Helios is sensitive enough to detect a dog and can discriminate between people, horses and trucks. The system can avoid being triggered by small animals, and can also tell if people are running or walking, or digging, and in which direction, said researchers at The University of Arizona College of Engineering.
Zonge, a geophysical engineering company based in Tucson, Ariz., installed a Helios test system in the desert near Tucson.
This is not new technology. These smart sensor systems already see use to monitor large engineering works such as dams, pipelines, bridges, and highways for cracks or seismic damage and other unseen strain forces at work deep within structures.
The Helios system consists of fiber-optic cables, lasers and detectors, and is more accurately described as a “distributed acoustic sensor.” It relies on the physics phenomenon of “optical backscattering” for its operation. British fibre optic sensing systems provider Fotech Solutions makes the system.
“It’s all a matter of scale,” said Scott Urquhart, Zonge president and senior geophysicist, talking about the shift from detecting seismic events to measuring tiny subsurface vibrations caused by desert wildlife, both two- and four-legged.
“When very small vibrations hit the fiber-optic cables, the cables are slightly distorted,” Urquhart said. “This distortion creates a unique signature change in the laser pulses, which can be detected by the Helios unit.”
Urquhart said the Zonge team buried several types of cable at the desert test location. “Each had different properties in terms of flexibility or type of shielding,” he said. “The advantage of a Kevlar cable, of course, versus a steel cable, is that the Kevlar cable cannot be found with a metal detector.”
Nor does digging up the cable and cutting it clean through stop the system working, provided a Helios unit connects to both ends of the cable, Urquhart said. “We can detect people digging up the cable, and even if they cut it the signal doesn’t stop flowing from the cut back to the Helios unit,” he said.
The resolution of the cable can be set to one-meter intervals, which means that the location of a cut cable, or people, or vehicles, can be pinpointed instantly to within one meter along a section of cable up to 50 kilometers long.
“We can install cables up to 50 kilometers in length with only one Helios detector,” said Moe Momayez, associate professor of mining and geological engineering at the UA Lowell Institute for Mineral Resources and co-author of a report detailing the Helios tests. “Because the 50-nanosecond laser pulses travel at the speed of light, we can detect any event virtually instantaneously and deploy the appropriate resources to that location.”
These 50-kilometer cable lengths, each with a Helios detector, can be strung together indefinitely to cover vast distances. For example, the border between the United States and Mexico is 1,969 miles, or 3,169 kilometers. Although the extreme topography of some border areas would make cable deployment difficult, dividing the border length into 50-kilometer segments equates to approximately 64 cable sections and detector units.
Helios might integrate into a larger system that includes mobile surveillance vehicles, such as those used by border patrol agents.
Fotech is already working on automating Helios operation. Once a database of signals builds up over an extended period of time, advanced pattern-recognition software could automatically identify events detected by the Helios system. The system would generate an alert if the software detected a border crosser.
Zonge and Fotech signed a 2-year agreement to develop a border security application. The next step, according to the report, is a deployment along a stretch of border with a known high volume of border-crossing traffic. Zonge is seeking funding for this extended field trial.
Because Helios can detect if people are digging in or moving through underground tunnels, the system has great potential for mine safety. If such a system were installed in a network of mine shafts and tunnels, a trapped miner could just tap on the rock wall and the system could pinpoint his location to within a couple of feet.