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Honey bees sniff-out landmines

11 Aug 2005

Researchers in the US are combining LIDAR and a honey bee's finely tuned sense of smell to locate buried land mines.

Honey bees could soon take the human risk out of finding landmines thanks to research being carried out in the US. The team trains the bees to sniff-out the explosives found in landmines and uses LIDAR to track their progress in-flight. (Optics Express 13 5853)

Dogs are currently used to locate mines but the animal and its handler are heavy enough to explode a mine placing them in constant danger. Bees on the other hand do not explode the mines, do not require a handler and can be trained in a couple of days to pick up the scent of the explosive in the landmine.

Jerry Bromenshenk and his colleagues from the University of Montana at Missoula are responsible for training the bees. "By injecting trace amounts of target chemical into feeders, the foraging bees seek sources of food with the same smell," explain the team in its paper. "Bees can be trained in one or two days to seek out buried explosives because of their high odor sensitivity in the low parts per trillion range."

When the trained bees locate vapors from a landmine, they fly along the plume until they reach its source, where they pause before continuing. The next part of the puzzle was how to track the bees and this is where Joe Shaw and colleagues from Montana State University come in with their horizontal scanning LIDAR system.

The co-polarised LIDAR system uses a frequency-doubled 532 nm Nd:YAG emitting 100 mJ pulses at a repetition rate of 30 Hz. The back-scattered light is passed through a receiver with a linear polarisation parallel to that of the emitted light.

To test the feasibility of the approach, the team carried out an experiment on a live mine field. Using tens of thousands of bees, the researchers conclude that the scanning LIDAR consistently detected a higher bee density near most of the significant chemical plumes. But there is still a lot of work to do.

"A bee hovers over a potential mine site for a few seconds at the most," Shaw told Optics.org. "This is a sufficiently long time for LIDAR detection if the laser beam is pointed in that direction at that time. This short dwell time really places a requirement on our sensors to use fast scanning or fast beams."

Another problem is that the bees fly close to the ground and direct-detection LIDAR cannot distinguish between scattered signals from the bees and vegetation. "The primary limitation was identifying bee-specific signatures from grass and other interfering objects," said Shaw. "We have already developed some new sensors and are in the process of characterizing them in the field. We want to end up with a compact, portable system that is flexible but effective."

Jacqueline Hewett is technology editor on Optics.org and Opto & Laser Europe magazine.

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