Fire near Wyoming (US)

What the satellites measured

This fire was tracked from 8 September at 10:58 to 13 September at 21:45, that is 5 days, through 1,361 satellite detections. The detected extent reaches 3,797 ha.

Detected extent

3,797 ha

Cumulative power

38,577 MW

Peak power, one pixel

825 MW

VIIRS and MODIS detections

1,361

These four figures cover the polar orbits alone, the ones that measure an area. The pass table below also counts geostationary detections, more frequent but too coarse for geometry, and its power column sums a whole pass where the peak above is that of a single pixel.

“Detected extent” is not “burned area”: it is the union of the ground footprints of the satellite pixels, and a pixel counts in full (375 m for VIIRS, 1 km for MODIS) even when only a forest edge is burning. Compared with press figures it is in practice one and a half to three times the area reported. Detections taken at the edge of the scan swath, too coarse to measure anything at all, are excluded. These figures come from thermal detection and are not an official assessment: only the emergency services and the competent authorities are authoritative.

Replay how the fire spread

The map is framed on this fire's footprint and loads only its detections. The timeline below covers the period in which satellites saw it, from the first to the last detection, with twelve hours before and twenty-four after; the ticks on the bar mark the emergency services' announcements that fall within it. The cursor opens on the most powerful pass, and playback replays the whole fire in about thirty seconds. “1 h” shows what is burning within an hour of the chosen moment : the map then follows the power curve below and empties when it falls. “24 h” stacks twenty-four hours : a fire stays visible between two satellite passes, which come two to four times a day. Both are true, but they say different things.

How the radiative power evolved

One point per satellite pass: the sum of the fire radiative power measured over the fire. This is the curve that says whether the fire eased off or picked up again, which no cumulative figure shows. The window covers 8 days; beyond that, clustering would merge two successive fires in the same place.

Satellite passes in detail

One other fire near Wyoming (US)

Separate fires, apart in time or in space, not pieces of this one. A single municipality can have several over one summer, and a forest massif often covers more than a hundred square kilometres.

• 6 to 9 October1,870 ha

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