Earth Imaging Journal: Remote Sensing, Satellite Images, Satellite Imagery
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February 26, 2013
Mount Etna Boils Over


In this ALI image of Etna, fresh lava is bright red, as the hot surface emits enough energy to saturate the instrument’s shortwave infrared detectors but is dark in near-infrared and green light. Snow is blue-green because it absorbs shortwave infrared light but reflects near-infrared and green light. Clouds made of water droplets (not ice crystals) reflect all three wavelengths of light similarly and appear white. Forests and other vegetation reflect near-infrared more strongly than shortwave infrared and green, so they appear green. Dark gray areas are lightly vegetated lava flows, 30 to 350 years old.

After maintaining a low simmer for 10 months, NASA’s EO-1 satellite finally caught Italy’s Etna volcano erupting on Feb. 19 and 20, 2013, with three outbursts in 36 hours.

According to the Italian Istituto Nazionale di Geofisica e Vulcanologia, each outburst (paroxysm) featured “emission of lava flows, pyroclastic flows, lahars and an ash cloud.” The Advanced Land Imager (ALI) on the Earth Observing-1 (EO-1) satellite captured Mount Etna on Feb. 19, 2013, about three hours after the end of the first paroxysm. The false-color image combines shortwave infrared, near-infrared, and green light in the red, green, and blue channels of an RGB picture. This combination makes it easier to differentiate between fresh lava, snow, clouds and forest.

Image courtesy of NASA.

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