Every fire on Earth broadcasts its existence in a language satellites are built to read: infrared. A burning pixel of forest is hundreds of degrees hotter than the land around it, and at the mid-infrared wavelength of about 4 microns that difference is enormous — a fire can outshine its surroundings by a factor of thousands. Detection is, at heart, that simple: scan the planet, flag the pixels that glow.
The satellites doing the work
Two instrument families dominate. MODIS, flying on NASA’s Terra and Aqua satellites since the early 2000s, sees the entire planet roughly four times a day at about 1 km resolution. Its successor, VIIRS, on the Suomi-NPP and NOAA polar orbiters, sharpens that to 375 m — good enough to catch a fire covering a couple of football pitches. These are polar orbiters: they sweep pole to pole while the Earth rotates beneath them, stitching global coverage from overlapping passes. That design trades immediacy for coverage — a fire may burn for a few hours before the next pass sees it.
Geostationary satellites — GOES over the Americas, Himawari over Asia-Pacific, Meteosat over Europe and Africa — solve the timing problem from the other direction. Parked 36,000 km up, they photograph the same hemisphere every ten minutes, but at kilometres-per-pixel resolution. Modern systems (including Google’s wildfire boundary alerts) fuse both: geostationary for the “when”, polar orbiters for the “where exactly”.
What fire radiative power tells you
Beyond “something is burning here”, the instruments measure fire radiative power (FRP) — the rate of energy the fire radiates, in megawatts. FRP tracks how much fuel is combusting per second, which makes it an honest intensity measure: a smouldering peat fire might read a few megawatts, while a crown fire tearing through eucalyptus can radiate tens of thousands. When EarthPulse labels a fire cluster “2,400 MW”, that’s the combined radiative output of every detection in the cluster — physics, not vibes.
Why raw detections aren’t fires
Look at a raw detection map and Britain appears to be burning. It isn’t — you’re seeing stubble burns, landfill flares, steelworks, and the occasional sun-glint false positive. A single hot pixel is a detection; a fire worth your attention is a pattern of detections, clustered in space and persistent in time. That’s why EarthPulse clusters NASA FIRMS detections on a ~55 km grid and requires several confident detections before a cluster becomes an event on the globe: the Kent bonfire is filtered, the Zamora wildfire is not.
The pipeline’s honesty matters in the other direction too. Satellites miss fires under cloud, can’t see through heavy smoke plumes at some wavelengths, and a fast fire can ignite and die between polar passes. Space-based detection is the best planetary view humanity has ever had — and it is still a sample, not a census.