On Sept. 19, 2012, NASA’s Terra satellite collected views of the Three Sisters and Broken Top volcanoes in the Cascade Mountains near Bend, Ore. The accompanying image comprises an eclectic mix of cirrus clouds, glaciers and the Pole Creek Fire, which blazed nearby in the Deschutes National Forest.
Vegetated areas appear bright red; snow and ice looks white; and clouds are a wispier off-white. Exposed rock and barren land near the summits of the mountains are shades of brown. Smoke billowing from the fire appears gray.
The smoke is transparent to the Terra ASTER sensor’s thermal band because smoke plumes consist of ash particles and other combustion products so fine they’re easily penetrated by the relatively long wavelengths of thermal infrared radiation. In contrast, ASTER can’t see through clouds because they tend to have larger particles that thermal infrared radiation can’t easily pass through.
Image courtesy of NASA.