Heat-seeking the invisible killers

"Antipersonnel land-mines affect 80 countries," says Brussels-based Professor Hichem Sahli. "But one should focus on the scourge’s economic aspect, which means recovering land as quickly as possible for local people."

Suspected areas are the main problem, adds the coordinator of IST project ClearFast. "They are harder to deal with than known mined areas. Land believed to be mined effectively becomes unusable."

With partners from three countries, Sahli carried out field trials on a live minefield in the United Nations Buffer Zone in Cyprus from 15 to 30 November 2004. The prototype system scans a 20mx30m area detecting suspected targets. It can produce an overview map, using the centimetre-accurate differential global positioning system that shows possible danger targets. "Deminers then decide where to enter the minefield," he says, "rather than waiting for mechanical clearance to create a narrow, random breach for them, using mine dogs and metal detectors as well."

Images taken by multispectral and thermal cameras are gathered and analysed by the ClearFast system. The cameras hang from a tall platform that stands outside the area to be surveyed. The system revealed that, in some soils and under some weather conditions, its thermal observations can find mines buried as deep as 10 cm.

Multispectral thermal imaging is not a new idea, admits Sahli: "It detects different thermal behaviours between the background and the target. For example, a stone and a landmine have different heat absorption and radiation signatures. Our research characterised these signatures."

When predicting the behaviour of each object type, the system takes into account the air and soil temperatures, and weather conditions. A computer compares these predictions with data gathered during the scans. Says the coordinator: "Our thermal images show the temperature on the top-soil. That temperature is obviously affected by the ground below. So we simplified the models, by assuming that the soil and vegetation are of the same type."

To improve mine detection, the system scans the suspected area several times a day. Deminers then get a better picture of the contrast between the background and targets.

Following trials in Belgium, the partners tested system upgrades in Germany, including a visible colour camera and the ability to pan/tilt from one position. "We can cover 20 by 20 metres with enough resolution to detect mines," notes Sahli. "We found you need an image of around five by five pixels to detect a five-centimetre mine."

The final trials, in Cyprus’ demilitarised zone, were supported by the United Nations Development Programme. "The goal was to demonstrate the system in a real minefield, where we surveyed three areas of 20 by 30 metres," says the coordinator. "We detected several mines which had not been mapped and which could not be easily seen."

Project partner Bactec will now exploit ClearFast. The Israeli mine-clearance firm will compare the system with other technologies, such as ground-penetration radar.

Sahli acknowledges that demining is a small market, comprising non-governmental bodies and private companies who may balk at the thermal camera’s high cost. On the other hand, he says, "Deminers want proven technology. Our tests highlighted how they could work more efficiently with multispectral thermal imaging."

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Contact: Tara Morris, +32-2-2861985, tmorris@gopa-cartermill.com