After maintaining a low simmer for ten months, Italy’s Etna volcano boiled
over on February 19–20, 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 February 19 at 9:59 a.m. Central European
Time, about 3 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.
In the image, 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, and so appear
green. Dark gray areas are lightly vegetated lava flows, 30 to 350 years old.
1. References
2.
Abrams, M, Bianchi, R,
and Pieri, D. (1996 December) Revised Mapping of Lava Flows on Mount Etna, Sicily.Photogrammetric Engineering & Remote Sensing. 62(12), 1353–1359.
3.
Cooperative Institute for
Research in the Atmosphere. (n.d.) Snow/Cloud Discriminator (3-color technique)—Basic Information. Accessed February 20, 2013.
4.
Istituto Nazionale di
Geofisica e Vulcanologia, Sezione di Catania. (2013, February 19) Etna and Stromboli update, 19 February 2013. Accessed February 20, 2013.
5.
Istituto Nazionale di
Geofisica e Vulcanologia, Sezione di Catania. (2013, February 20) Etna update, 20 February 2013.Accessed February 20,
2013.
·
Further Reading
NASA Earth Observatory image by Jesse Allen and Robert Simmon,
using EO-1 ALI data from the NASA EO-1 team.Caption
by Robert Simmon.
Instrument:
EO-1 -
ALI
هیچ نظری موجود نیست:
ارسال یک نظر