The most interesting Satellite Observations of Forest Fires

Fires in Idaho

Fire in southwest Idaho 1996 Aug 21 01:25 UT
The images are labeled in UT so are dated Aug 21 but the view is for the evening of Aug 20 local time. A very obvious fire shows the relation between the bright areas on a channel 3 image and a smoke plume. Two color composite images are available: small (321 Kb), or large (666 Kb). Two channel 3 images are also available: small (357 Kb), or large (662 Kb).

These images show a lot of detail. The pass map helps set the context, showing that the sun was low, only about 12 degrees above the western horizon. This explains the long shadows cast by the clouds, seen well in the southwest part of the color composite image. A shaded relief map shows that this part of Idaho is dominated by the relatively flat Snake River Plain. The map is to the same scale as the small images above and, because of the late afternoon sunlight, has nearly the same lighting as the color composite image.

The color composite image shows some scattered clouds (deep yellow and white), plus a lot of detail in the smoke plume. The white color in the plume at it's beginning is most likely due to the brightness of the fire on the channel 3, the one colored blue in the color composite. Elsewhere the smoke plume does not show on this channel at all (see the channel 3 image, no smoke is visible), so the only colors in the plume in the color composite are red and green which make yellow (for light). The plume blows toward the northeast and spreads out, then bends a bit more toward the east at the edge of the mountains. As the plume passes over the mountains it appears that subplumes blow from the west side toward the southeast (it looks like it folds over itself). The channel 3 image shows a large bright area at the narrow end of the smoke plume. This set of images makes it very clear that what appears to be smoke and fire really are smoke and fire.

What appears to be another, more diffuse, smoke plume enters the state of Idaho at the southwest corner. The origin of this smoke may be determined from a color composite showing a larger area. In this larger area view the SW corner of Idaho touches the center of the northern edge of Nevada. The diffuse smoke plume may be traced back to the large area of smoke in northern California at about latitude 39 degrees. This smoke is from the Fork fire, its position may be seen more clearly from the channel 3 image, which cuts through the smoke.

The scar from yesterday's fire
The location of fire shown in the last section is well seen on a view taken less than 24 hours later. A color composite ( large version) from a daytime view from the NOAA-14 satellite shows little if any smoke (maybe a trace on the southwest side of the scar). The position of the fire now has a dark blue patch. This is the fire scar. This spot was not present on yesterday's view ( large version). The deep blue color is typical of fire scars as seen on the color composite images on this site. The color composite images here are usually made by coloring AVHRR channel 2 red, channel 1 green, and channel 3 blue. Channel 1 is the visible band, a burned area would appear dark in visible light so this channel would contribute less to the composite image. Channel 2 is in the near infrared where vegetation has a high reflectance. A burned area would have reduced vegetation so this channel would contribute less to the composite image. Channel 3 is in the mid-infrared and shows both reflected infrared from sunlight and also the glow of the warm earth, both still occur in the burned area so the blue is not reduced. Thus the result is a deep blue color.

Cutting through the smoke
It is well known that infrared can see through smoke and haze better than visible light. The pair of images here show this well. A color composite shows central Idaho covered by smoke (this is another late afternoon view as shown by the pass map). The smoke plumes are very diffuse and ill defined, perhaps due to light winds. It is not easy to determine where the plumes originate. The channel 3 image clearly shows a number of small fires scattered over central Idaho. This area is quite mountainous as shown by a shaded relief map.

List of images
This section gives a convenient list of the images discussed above, plus a few extras.

1996 Aug 21 01:25 UT     NOAA-12 evening     Fire and Smoke

1996 Aug 21 20:29 UT     NOAA-14 daytime     Fire scar

1996 Aug 26 01:16 UT     NOAA-12 evening     Fires and smoke