Heat signatures help track down old and still deadly land mines | Science News for Students

Heat signatures help track down old and still deadly land mines

A drone-mounted infrared camera could aid in locating the old explosives so they can be removed
Apr 30, 2019 — 6:45 am EST
Afghan minefield

This sign in English and Arabic warns pedestrians that live land mines still litter this field in Afghanistan.

manxman/iStock/Getty Images Plus

This is one in a series presenting news on technology and innovation, made possible with generous support from the Lemelson Foundation.

WASHINGTON, D.C. Even when a war is over, the killing can continue. Land mines left behind in former conflict zones can still claim casualties. Now, researchers have developed a technique that can help spot one type of plastic-based mine. It’s a type that is very hard to spot. One day, this new technique might be used to locate and eliminate those explosives — especially in fields where children now play.

In late 1979, troops from the Soviet Union invaded Afghanistan, a nation in south-central Asia. In the more than nine years the Soviet troops were there, they spread a lot of land mines, says Alex Nikulin. He’s a geophysicist at Binghamton University in New York. These weren’t big explosives, the types designed to target tanks. Instead, the soldiers’ intent was to hurt or kill people. Made largely of plastic, these mines can be quite difficult to find the usual way — walking around with metal detectors.

mines cassette
PFM-1 “butterfly” mines (a non-explosive example at right) were dropped from helicopters in Afghanistan by the millions in the 1980s. At left is a metallic rack filled with such mines. It was used to dispense the mines from helicopters. 
T. deSmet et al/Journal of Conventional Weapons Destruction 2018

Soviet helicopters dropped millions of these mines, each small enough to fit into the palm of an adult’s hand. Their official name is the PFM-1 mine. But owing to their shape, people often call them “butterfly mines,” notes Jasper Baur. He’s a geology student at Binghamton University. Baur was part of a team — one that included Nikulin — that developed the new mine-spotting technique. 

The Soviets often painted the butterfly mines with colors that helped them blend into the background. That helps the human eye miss them, explains Baur. His team’s innovation relies on thermal inertia, a trait that many materials have. Inertia is the tendency of an object to remain in place, even if something is pushing on it. Thermal inertia is the tendency of an object to remain at a constant temperature even as its environment is warming or cooling down. So when air temperatures are changing fairly rapidly, an object lying on the ground may tend to retain its temperature longer than the rocks and soil around it. And a special camera that senses heat — or infrared wavelengths — should be able to highlight objects that are cooler or warmer than the ground around them.

mines infrared
Land mines (three of them, labeled A) are hard to see at this site in visible light. They show up well, however, in this image taken at infrared wavelengths. The metallic racks used to dispense such mines (B and C) also show up well. This is the innovation behind a new technology that could be used in de-mining efforts in Afghanistan. (Scale bar at right shows the temperatures of objects in the image.)
T. deSmet et al/Journal of Conventional Weapons Destruction 2018

To test the idea, the team mounted an infrared camera on a drone. Then they flew the robotic craft back and forth over an area. They had already placed a few faux mines at the site — ones with no explosives. They also added a few of the small metal racks used to hold such mines before they are dropped from a copter. Finally, the researchers used computer software to create video images from the drone’s camera data.

When the team analyzed the infrared images, it was often easy to eyeball the mines. They had been cooler than the surrounding rocks, making them show up as a different color on the image. That color difference was often stark in images taken some 30 minutes to 2 hours after sunrise. That’s when the land was warming quickly. The technique also worked well when data had been collected soon after sunset, as the land was cooling. These are times when the temperature difference between the mines and the rocks was typically greatest.

In tests, the researchers could detect about eight out of every 10 faux mines. And they picked out the metallic racks in those images each and every time. Baur’s group shared its new findings here, last December, at the annual meeting of the American Geophysical Union.

Speeding the search for mines

Based on these data, the team estimates that its drone-based camera system can scan an area about 20 meters (66 feet) long and 10 meters (33 feet) wide in 10 minutes or less. That would greatly speed up the search for mines, Baur and Nikulin say. To carefully look for mines on foot in an area that size (about one-third the size of the infield in a baseball field) could easily take hours, they note.

drone images
In the infrared image at top, PFM-1 “butterfly” mines and metallic racks used to disperse them stand out clearly (red blobs and rectangles), but in the visible-light image at bottom the munitions (labeled) are largely invisible.
A. Nikulin et al./Remote Sensing (2018) 

Sayed Agha Atiq is a technical advisor to the United Nations’ de-mining operations in northeastern Afghanistan. There, he works out of the city of Kunduz. The Binghamton team’s technique is “interesting and somewhat promising,” Atiq says. Still, he cautions that it might be challenging to use in the mountainous areas where he works. 

Mohammad Wakil Jamshidi agrees and explains why. Based in Kabul, Afghanistan’s capital, he and his boss supervise United Nations de-mining efforts throughout Afghanistan. They also provide technical support for the country’s program to locate and remove mines. And here’s one potential problem, Jamshidi says: Sunlight may reach the valley floor for only a short time each day. Plus, trees and bushes may shade the ground. Such conditions would limit the amount of sunlight reaching the surface to heat it up. So many northeastern Afghan sites may not experience the rapid ground heating and cooling on which this technique relies. Jamshidi would expect, therefore, to see less thermal inertia of mines there than in regions where the terrain is flat. Vegetation would also make it difficult for a drone-mounted camera to see the ground.

Also, for much of the year snow covers the ground. That blanket, Jamshidi points out, will block the view of any mines it covers. Finally, mines on steep slopes can become buried over time. In that case, soil would block the view.

All of these factors might prevent detection of mines by the new technique, he suspects.

Fazel Rahman works in Kabul for Afghanistan’s de-mining agency, the National Mine Action Authority. He says that a field trial of the team’s mine-finding technique would help determine how useful this novel technology might be. 

Researchers explain and demonstrate their drone-based technique that uses an infrared camera to locate landmines that are made largely of plastic.
Binghamton University Geophysics

Power Words

(more about Power Words)

annual     Adjective for something that happens every year. (in botany) A plant that lives only one year, so it usually has a showy flower and produces many seeds.

drone     A remote-controlled, pilotless aircraft or missile.

environment     The sum of all of the things that exist around some organism or the process and the condition those things create. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature and humidity (or even the placement of things in the vicinity of an item of interest).

factor     Something that plays a role in a particular condition or event; a contributor.

faux     Meaning false or fake. Faux fur, for instance, would not be made from animal products but from some manufactured fibers.

field     An area of study, as in: Her field of research was biology. Also a term to describe a real-world environment in which some research is conducted, such as at sea, in a forest, on a mountaintop or on a city street. It is the opposite of an artificial setting, such as a research laboratory. 

geology     The study of Earth’s physical structure and substance, its history and the processes that act on it. People who work in this field are known as geologists. 

infrared     A type of electromagnetic radiation invisible to the human eye. The name incorporates a Latin term and means “below red.” Infrared light has wavelengths longer than those visible to humans. Other invisible wavelengths include X-rays, radio waves and microwaves. Infrared light tends to record the heat signature of an object or environment.

innovation     (v. to innovate; adj. innovative) An adaptation or improvement to an existing idea, process or product that is new, clever, more effective or more practical.

novel     Something that is clever or unusual and new, as in never seen before.

plastic     Any of a series of materials that are easily deformable; or synthetic materials that have been made from polymers (long strings of some building-block molecule) that tend to be lightweight, inexpensive and resistant to degradation.

slope     (in geology) The steeply pitched side of a cliff, hill or mountain. 

software     The mathematical instructions that direct a computer’s hardware, including its processor, to perform certain operations.

technology     The application of scientific knowledge for practical purposes, especially in industry — or the devices, processes and systems that result from those efforts.

terrain     The land in a particular area and whatever covers it. The term might refer to anything from a smooth, flat and dry landscape to a mountainous region covered with boulders, bogs and forest cover.

thermal     Of or relating to heat. (in meteorology) A relatively small-scale, rising air current produced when Earth’s surface is heated. Thermals are a common source of low level turbulence for aircraft.

thermal inertia     The concept that some materials do not change temperature (warm or cool) as quickly as their surroundings.

trait     A characteristic feature of something. (in genetics) A quality or characteristic that can be inherited.

wavelength     The distance between one peak and the next in a series of waves, or the distance between one trough and the next. It’s also one of the “yardsticks” used to measure radiation. Visible light — which, like all electromagnetic radiation, travels in waves — includes wavelengths between about 380 nanometers (violet) and about 740 nanometers (red). Radiation with wavelengths shorter than visible light includes gamma rays, X-rays and ultraviolet light. Longer-wavelength radiation includes infrared light, microwaves and radio waves.


Journal:​ ​​T. deSmet et al. Drones and “Butterflies”: A low-cost UAV system for rapid detection and identification of unconventional minefields. Journal of Conventional Weapons Destruction. Vol. 22, November 2018, p.50. 

Meeting:​​ J. Baur et al. Improved detection of plastic landmines with aerial polarized thermal imaging. American Geophysical Union Fall Meeting 2018. December 12, 2018. Washington, D.C. Poster/Presentation NS33B-0792.