Standoff explosive detection takes step backward

On August 8, portions of Dallas-Fort Worth International Airport’s Terminal A were evacuated when the airport received bomb threats made toward inbound flights. On July 17, dozens of police, security guards, and federal agents searched Comerica Park...

Onat says the system is factory calibrated and does not require extensive setup procedures in the field, and can be used in a variety of settings, including border patrol, airport security, IED detection, and military checkpoints. Unlike THz systems, there is no privacy issue, since the technology does not see body parts under clothing.

ChemImage in Pittsburgh is currently developing a stationary and mobile system using realtime hyperspectral imaging—a novel sensor concept for optical standoff detection of explosives that combines Raman hyperspectral imaging and laser induced breakdown spectroscopy. Raman spectroscopy is a tool for analyzing the properties of molecules. By incorporating specific algorithms into the system’s software, it can detect unique chemical markers found in materials commonly used to produce explosives and alert users of possible threats. According to a company spokesperson, ChemImage’s HSI system is capable of detecting explosives from up to 1,000 meters.

A key feature of the HSI system is the use of wide-field imaging, which allows realtime scanning of larger areas than those provided by traditional point detection systems. ChemImage says it is currently developing a multi-sensor vehicle screening system so military personnel can screen vehicle-born explosive threats.

Bad air day

One of the challenges with extending standoff detection distance is the impact of various atmospheric and environmental interferences, as well as screening threats that are in motion. Lasers seem to be particularly adept at overcoming many of these obstacles.

In March 2012, Australian researchers announced the use of deep Raman spectroscopy for standoff detection of concealed chemical agents from a distance of 15 meters under normal conditions. Raman spectroscopy relies on Raman scattering of monochromatic (single color) light, usually from a laser, to achieve rapid, non-destructive chemical analysis of solids, powders, liquids, and gases. The Australians reported they were able to non-invasively identify various explosive precursors hidden in opaque plastic containers within five seconds of data acquisition.

Laser research at Pranalytica in Santa Monica, California has resulted in even greater steps backward. A technique reported in 2010 claims detection and identification of trace quantities of explosives can now be achieved at standoff distances up to 1,000 meters. This method uses a rather bulky tunable CO2 laser that scans the absorption fingerprint of the target explosives. The technique involves illuminating (heating) the target object with laser radiation, then remotely monitoring the increased black-body (thermal) radiation from the sample.

CEO Kumar Patel says current company research is focusing on a smaller, shoulder-held technology using a new class of semiconductor lasers called quantum cascade lasers, that will yield detection standoff of 25 to 50 meters, a more practical distance from a first responder user standpoint. The current prototype is housed in what resembles a 5-inch Newtonian telescope aimed at the target by resting the device on the shoulder and peering through a small finder scope.

“This technology may play an important role in screening personnel and their belongings at short distances, such as in airports, and also for detecting and identifying explosives material residue on persons,” Patel says.


Douglas Page writes about science, technology and medicine from Pine Mountain, California. He can be reached at

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