C-DRONE GUIDE · 18 JULY 2026
Post-wildfire hot spot detection with a thermal drone
A wildfire declared "under control" is not necessarily out: embers can smoulder 30 to 40 centimetres under the ash, inside a root system or a stump, invisible to the naked eye and capable of restarting a fire days after the fire crews have left. Until now, spotting these residual hot spots before they flare up meant slow, uncertain ground patrols across dozens of hectares of scorched land. A drone fitted with a thermal camera changes the scale of the problem: a flight of a few dozen minutes maps an entire burnt area and finds what the eye cannot see. Here is how these missions are prepared, under exactly which legal framework, and what they cost in 2026 — well after the water bombers have left, never during.
Published on 18 July 2026, reviewed on 27 July 2026 — regulations in force as of July 2026.
The real risk after a wildfire: reignition, not the fire itself
Once the flame front is knocked down, fire services speak of "damping down" and monitoring the burnt area rather than total extinction: heat built up in organic matter — forest litter, peat, stumps, deep roots — can smoulder with no visible flame for several days. These pockets of latent heat, which foresters and firefighters call residual hot spots, typically sit 30 to 40 centimetres below the surface, exactly where water sprayed from above fails to penetrate effectively. A gust of wind or a rise in temperature can be enough to turn a smouldering pocket into a full reignition, sometimes tens of metres from where it was expected.
The risk is not theoretical: a meaningful share of wildfire reignitions in France trace back to residual hot spots missed during the surveillance rounds that follow an apparent extinction. For a private forest, a forested municipality or the national forestry office managing state woodland, the period after a fire — often 24 to 72 hours of reinforced monitoring required by the authorities — is therefore as critical as the firefighting itself, usually with far fewer people available than at the height of the intervention.
How a thermal camera sees an ember under the ash
The principle is the same as for a flat-roof leak or a faulty power line: the onboard thermal camera does not "see" matter, it measures the infrared radiation each surface emits and renders it as an image where temperature differences show up in false colour. An ember smouldering 40 centimetres under still-warm surface ash produces a characteristic thermal gradient, often visible even when the naked eye can make out nothing but uniform grey ground.
The flight is organised as a systematic low-altitude grid over the whole burnt area, with enough overlap to leave no blind spot. The pilot almost always pairs the thermal layer with a visual one: overlaying the two images makes it possible to tell a genuine residual hot spot from a false positive — a stone still warm from the sun, a piece of sheet metal, a hollow trunk that burned through cleanly with nothing left smouldering. The most effective flight window is early morning, when the gap between ambient temperature and the still-hot subsoil is largest; a night flight, where regulations allow it, sharpens the contrast further by removing the sun's warming of the surface ash. Every anomaly is geolocated to centimetre-level precision and plotted on a map delivered in near real time to ground teams, who can then go straight to the suspect points instead of combing the whole area.
How a mission unfolds for a forestry office, a town or an insurer
This kind of mission is never launched during active firefighting: it starts once the incident has been officially declared under control by the fire commander, in direct coordination with the fire brigade or the forestry office on state-owned woodland. The drone provider works alongside the firefighters' people and equipment, never in their place or on their slot — a point that any mission of this kind should clarify from the first contact, to avoid any confusion with the rescue operation itself.
On site, the flight starts with a briefing from the liaison officer or forest manager to define the perimeter to cover and the areas judged highest risk — forest edges, valley bottoms where heat lingers, peaty ground. The report, delivered within a few hours to stay useful to ongoing surveillance, combines a map of numbered hot spots, an orthophoto of the burnt area and, if a second pass is requested the next day, a comparison showing how the hot spots evolved between flights. For a forest operator or an insurer, that same work also serves, in the following days, to document the real extent of the damage for the claim file — a use that connects with what our guide to forestry drone management covers for post-storm mapping.
The regulatory framework: never during the fire, tightly framed afterwards
The single most important point is also the strictest: while a wildfire is still being fought, the airspace above the incident is off-limits to any aircraft, drones included, that is not involved in managing the event. The French civil aviation authority (DGAC) regularly reminds pilots of this in its safety bulletins: a "curious" remote pilot approaching an active fire can force a water bomber or a firefighting helicopter to break off its run, with a collision risk that is far from hypothetical. Flying over a disaster site outside the rescue operation is an offence, whatever the flight category.
Only once the incident has been declared under control, at the request or with the explicit agreement of the fire brigade, the fire commander or the forest manager, can a hot-spot detection mission begin — most often in the open category, subcategory A3, since the area is by nature far from any assembly of people. Night flying, which improves detection, remains subject to the waiver regime detailed in our guide to night drone flights and what the law says; for urgent needs, an accelerated procedure exists with the authorities to obtain a specific-category authorisation within 48 hours. Before any flight, the pilot checks the Géoportail drone map — updated in real time — to confirm no temporary zone tied to the incident is still active, as detailed in our guide to reading the Géoportail drone zone map. The operator otherwise stays registered on AlphaTango, with an FRA number on the aircraft and aerial liability insurance compliant with Regulation (EC) No 785/2004.
What a hot-spot detection mission costs in 2026
The price depends mainly on the burnt area to cover, how urgent the request is, and how many passes are needed to track how the hot spots evolve. Ranges observed in France in 2026:
| Mission | Observed price (excl. VAT) |
|---|---|
| Emergency flight over a small area (up to 10 ha, hot-spot map within hours) | €500 to €850 |
| Full mapping of a medium burnt area (10 to 50 ha) | €900 to €1,500 |
| Large forest tract, or repeated passes over several days of monitoring | €1,800 to €3,000 |
| Annual framework agreement with a town or an exposed forest tract | on quotation |
These amounts are modest compared with what is at stake: an undetected reignition can undo, in a few hours, several days of firefighting work and put hamlets or already weakened forest tracts back at risk. Many local authorities in high-risk areas now set up framework agreements with their fire brigade, allowing a callout within hours as soon as a fire is declared under control on their territory, without having to negotiate a quote under pressure.
Frequently asked questions on drone hot-spot detection
Can a drone operate while the fire is still active? No, never without being formally integrated into the rescue operation by the fire commander. Any private mission takes place after the incident has been declared under control, in coordination with the services involved.
How long after apparent extinction does monitoring need to continue? Authorities generally require reinforced monitoring for 24 to 72 hours depending on the area and the type of ground (a peat bog or soil rich in organic matter smoulders longer than mineral soil). One or two extra flights within that window are usually enough to confirm there is no reignition.
Does the drone replace firefighters' or forestry-office patrols? No: it directs them. The drone maps the whole area in minutes and prioritises the points to check on the ground; ground teams are the ones who confirm and deal with each residual hot spot identified.
Is this service available to private individuals too? Rarely direct: missions are commissioned by local authorities, the forestry office, forest operators or insurers. A private forest owner affected by a fire usually goes through their forest expert or town hall to trigger the intervention.
Put it into practice
- Drone aerial thermal imaging: rates and cities covered from €500
- Aerial thermal imaging in Versailles Île-de-France
- Aerial thermal imaging in Saint-Maur-des-Fossés Île-de-France
- Aerial thermal imaging in Calais Hauts-de-France