FireWatch — glossary
Plain-language definitions of the terms used across FireWatch (NASA EONET + FIRMS).
Detection
- Active-fire detection (hot spot)
- A satellite pixel flagged as anomalously hot, indicating fire at that overpass. Plotted as a point event; a cluster, not a single pixel, indicates a fire’s extent.
- Fire Radiative Power (FRP)
- The radiant energy a fire emits in a pixel, in megawatts — a proxy for fire intensity. FireWatch’s intensity scale is based on FRP.
- MODIS / VIIRS
- The satellite instruments behind most active-fire data. VIIRS (375 m) resolves smaller and cooler fires than the older MODIS (1 km).
- Brightness temperature
- The infrared temperature a sensor measures for a pixel; used with surroundings to decide whether it is a fire.
Fire behavior
- Fire triangle
- The three ingredients a fire needs: fuel, oxygen and heat. Remove any one and the fire goes out.
- Crown fire
- A fire that spreads through the canopy from treetop to treetop — fast, intense and hard to stop, versus a slower surface fire.
- Spotting
- Wind-carried embers that ignite new fires ahead of the main front, letting a fire jump roads, rivers and control lines.
- Red Flag Warning
- An alert that warm, dry and windy conditions make rapid fire growth likely, so any ignition is especially dangerous.
Incidents
- Containment
- The percentage of a fire’s perimeter secured by a control line expected to hold — not the share of fire extinguished.
- Control line
- A natural or constructed barrier (cleared ground, road, river) used to stop a fire’s spread.
- Evacuation order vs. warning
- A warning means be ready to leave; an order means leave now. Orders are issued when life-safety is at immediate risk.
Intensity scale (MW (FRP))
- Low
- 0 MW (FRP)
- Moderate
- 25 MW (FRP)
- Elevated
- 50 MW (FRP)
- High
- 100 MW (FRP)
- Very High
- 200 MW (FRP)
- Extreme
- 350 MW (FRP)
- Catastrophic
- 500 MW (FRP)