How drones are hunting fires hidden beneath the Cairngorms

It is 06:00 and I'm meeting drone pilot Pete Short for a dawn patrol in the Cairngorms National Park.

It is a job he has been doing for almost three months, since a huge wildfire tore through this landscape in July.

The flames which swept across the hillsides are gone. From where we are standing, there is little to suggest there is still a fire here at all.

After a bumpy drive into the woodland, Pete launches a thermal drone into the early morning sky.

I am given a job too: keeping the aircraft in sight while he studies the images being sent back to his screen.

"Every week I hope that I find none," he tells me. "On the last thermal flight I did we found eight."

"We might have something here," Pete says, as a white glow appears on the thermal image beneath a tree.

Three months after the fire first ignited, heat is still being detected beneath the ground.

We make our way towards the coordinates identified by the drone, and at first, there is almost nothing to see.

The soil is warm. A rock Pete picks up from the ground is, too.

Nearby, after scraping away a thin layer of earth, smoke begins to rise.

"Without the thermal technology we would be totally blind to this."

The wildfire began in the middle of July and burned across about 3,300 hectares – 33 sq km – of land, according to the Cairngorms National Park Authority.

At the height of the emergency, five experienced drone pilots were brought together to provide aerial information to the agencies fighting the fire.

Pete describes it as one of the most challenging environments he has ever flown in, with "multiple walls of flame", personnel and vehicles moving around the site and helicopters operating overhead.

The dramatic flames have disappeared, but hot spots can continue to burn beneath the earth.

Each one found by the drones is reported to the land manager. They send teams who can dig into the ground and douse it with water.

For Ben Jones, senior site manager for the RSPB at Abernethy, knowing exactly where to send those teams has been crucial.

"So we really need to know where these specific hot spots are - where we should be sending people - so that they can be as efficient as possible."

And despite the arrival of colder, wetter weather, the remaining fires cannot simply be ignored.

"Each of these hot spots has got the potential to reignite a larger fire," Ben says.

Walking through the forest, the scale of what happened is almost haunting.

Tree trunks are blackened and charred. The acrid smell of fire still hangs around. Large areas of the forest floor have been scorched.

Green shoots are emerging. Fungi is growing. I even spot a small yellow flower shooting up from the blackened ground.

Dr Sarah Henshall, head of conservation at the Cairngorms National Park Authority, says it is too early to know the full ecological impact of the fire.

"Some of that will be incredibly quick, some of it will take years, decades, or even beyond our lifetime," she says.

"It will recover, but we just don't know what that's going to look like yet."

And the drones that helped during the fire - and are still searching for what remains of it - are being given another job.

Pete is programming them to repeatedly fly exactly the same routes over the damaged landscape.

Using predetermined waypoints, photographs and video can be taken from the same positions month after month and year after year, allowing conservationists to build up a picture of how the landscape changes.

"This standard drone route will have exactly the same route flown month by month, year by year and visually it's going to give us some amazing information about how it's recovering," Sarah says.

There could be another role for the tech too - spotting future fires before they have a chance to spread.

Pete believes getting a view above the tree canopy quickly could prove critical.

"It's those moments before a wildfire gets out of control that could be critical to stopping it before it gets out of hand," he says.

Again, there is almost nothing visible from a distance. But guided by the drone, we find the precise spot.

Beneath a thin layer of earth, it is hot and the smoke becomes obvious after we stoke the soil.

Another location to report. Another fire for the ground teams to extinguish.

Above us, the forest is already showing its first signs of life but below our feet, the last of the fire is still burning.

Last firefighters stood down from scene of Cairngorms wildfire

Sign of life as bright orange 'fire fungus' grows at park ravaged by wildfire