Five High-Tech Ways to Spot a Car Bomb

(May 3) -- When astute street vendors alerted police to smoke coming from an SUV parked in Times Square over the weekend, it was a lucky break. That's because car bombs remain one of the hardest to detect, and consequently deadliest, terrorist weapons.

Based on "the number of casualties and amount of property damage, VBIEDs [vehicle-born improvised explosive devices] have been the most successful means of terrorist attack both domestically and internationally, except for the Sept., 11, 2001, attacks," wrote Ruth Doherty of the U.S. Department of Homeland Security, Science and Technology Directorate, in a 2009 document.

There is no effective way to detect such bombs from a safe distance, government officials say, though a number of federal agencies have been seeking proposals to help develop one. Here are five of the technologies being pursued:

Neutron generator: A number of labs and companies have systems designed to bathe a car in neutrons, which cause materials inside to emit gamma rays that can then be measured. Those gamma rays can be used to identify specific chemicals associated with explosives. Though a number of systems have been developed, making devices "user friendly" is a long-standing issue. There also are problems associated with cost, size and radiation safety in neutron generators, and there have been concerns that such devices could be easily spoofed through shielding.

Laser Doppler vibrometry: Most people know that tapping on a wall and listening for the acoustic response can help identify where studs are. Laser Doppler vibrometry, which involves using optical instruments that can measure vibrating objects without touching them, takes this one step further. In the case of landmine detection, this technology works by using sound waves to excite the surface and then measuring the slight vibration to detect what lies beneath. This technique has been suggested for identifying objects, like explosives, inside a car. The advantage of laser Doppler vibrometry is that it would allow technicians to inspect for bombs without touching the suspected car. The drawback? It would not be able to definitively identify what's inside.

Robots: A robot was actually on duty this weekend in New York and was used to help identify the car bomb in Times Square. Law enforcement and military agencies would certainly like to see more and better robots replace the role of human bomb technicians, but so far they offer only a partial solution. New robots are in the works, however. A Pennsylvania-based company called Robotics Engineering Excellence, or RE2, has received funding to build a modular recon manipulator that would help technicians spot car bombs, and Massachusetts-based iRobot produces several robots designed to help spot and defuse bombs. Making them rugged and affordable remain major challenges.

X-rays: Improved X-ray systems could help spot car bombs. For example, Backscatter, made famous for revealing explicit images when used to screen people in airports, works by creating an image using reflected radiation. AS&E, the company that makes the Backscatter, is trying to make smaller machines that could peer into cars. Currently, the systems in place are large and costly. A major problem with X-ray systems is that they can provide images of objects, but they can't identify precisely what materials they are made from.

A chemical nose: Scientists readily admit that the state of the art in detecting chemical explosives is still a dog's nose, but they've been steadily working on something that can mimic, and possibly match, a canine's acute sense of smell. That's the idea behind an "electronic nose," which uses materials that react to chemical vapors. One method involves using a "nose" made out of polymer materials that can help detect and identify explosive vapors. The problem? Getting these sensors to work from a distance. So far, the dogs easily beat electronics.