Months after a massive wildfire swept across the Cairngorms National Park in Scotland, the surface flames are gone and the hillsides look quiet. However, fires are still burning invisibly beneath the ground. To find them, drone pilot Pete Short carries out dawn patrols using thermal drones—aircraft fitted with heat-sensing cameras—to search the forest floor before the morning air warms up.
The thermal cameras detect heat that human eyes cannot see from a distance. On Short's screen, an underground fire shows up as a bright white glow under the trees. When the drone guides searchers to the exact location, the surface seems normal at first. But just under a thin layer of soil, the ground is hot, and smoke rises as soon as the earth is moved. Ground teams can then step in to extinguish the hidden fire.
These underground hotspots can quietly burn for months if nobody finds them. Short has been flying over the area for nearly three months, since the main wildfire burned through the landscape in July. Finding every hotspot is difficult; on a recent flight alone, his drone discovered eight separate fires burning beneath the earth.
The drones are also taking on new roles in the park. Short is programming them to fly the exact same routes over the damaged forest month after month. By taking photos from the same positions, conservationists can monitor how the land slowly recovers over the coming years. In the future, teams hope the same drone technology can spot rising heat above the tree canopy early, stopping wildfires before they get out of control.