Wildfire data field guide
Wildfire Hotspot vs Fire Perimeter: why they are not the same thing.
A satellite hotspot is evidence of thermal activity inside a sensor footprint. A fire perimeter is a mapped boundary. Plotting detections as if they were the exact fire edge creates false precision.
Core distinction
Point or pixel detection vs mapped boundary.
NASA FIRMS distributes satellite-derived active fire / thermal anomaly detections. NWCG defines a fire perimeter as the entire outer edge or boundary of a fire.
A sensor has detected unusual heat within a pixel or footprint. The plotted location is not necessarily the exact location or size of the flame front.
A line or polygon representing the mapped outer boundary of the incident at a particular time.
Pixel size
A red square does not mean the whole square is burning.
FIRMS notes that MODIS detections are associated with roughly kilometre-scale pixels while VIIRS commonly uses 375 m active-fire products. The detected activity can be a small intense source or a larger fire within that footprint.
Why detections move
Satellite geometry and overpass time matter.
- Satellites observe at discrete overpass times rather than continuously.
- Cloud and thick smoke can obscure detections.
- Sensor resolution and viewing geometry affect the footprint.
- Hot smoke, agriculture or other thermal sources can sometimes trigger anomalies.
- A fire can burn between satellite observations without producing a point at every location.
Black Box use
Keep detections and perimeters as separate evidence layers.
For reproducible incident analysis, Tecnobosque treats thermal detections, mapped perimeters, official acreage and narrative updates as different data products with different timestamps and uncertainty.
Sources
NASA FIRMS and NWCG.
NASA FIRMS — Active Fires / Thermal Anomalies ↗
NASA Earthdata — FIRMS overview ↗
Published 21 September 2026.