Fire near Saint Bonnet-Laval

What the satellites measured

This fire was tracked from 5 July at 22:19 to 7 July at 15:53, that is 2 days, through 50 satellite detections. The detected extent reaches 2,121 ha.

Detected extent

2,121 ha

Cumulative power

936 MW

Peak power, one pixel

269 MW

VIIRS and MODIS detections

50

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.

The detected extent

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 4 days; beyond that, clustering would merge two successive fires in the same place.

Satellite passes in detail

2 other fires near Saint Bonnet-Laval

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.

• on 7 August123 ha
• 13 to 14 July1,911 ha

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