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Figure 1: Vis/NIR Image Closeup | Figure 2: Difference Image |
October 2002
Mt. Etna, a volcano on the island of Sicily, erupted on
October 26, 2002. Preliminary analysis of data taken by the Atmospheric
Infrared Sounder (AIRS) on NASA's Aqua satellite on October 28 shows the
instrument can provide an excellent means to study the evolution and
structure of the sulfur dioxide (SO2) plume emitted from volcanoes. These
data also demonstrate that AIRS can be used to obtain the total mass of
SO2 injected into the atmosphere during a volcanic event, information that
may help us to better understand these dangerous natural occurrences in
the future.
This image was made from a sensor on the AIRS instrument that is sensitive
to the visible and near-infrared portions of the spectrum. The
visible/near infrared data show the smoke plume from Mt. Etna. The view
is of Europe and the central Mediterranean with Italy in the center.
Since the visible/near infrared sensor on AIRS is sensitive to wavelengths
that are different than the human eye, vegetated regions appear red
(compare the red color of Europe with the tan desert of North Africa in
the lower left). Figure 1 is a closer view of Sicily and shows a long,
brownish smoke plume extending across the Mediterranean to Africa. This
is consistent with the enhanced feature in the difference image in Figure
2 and helps validate the information inferred from that image.
Figure 2 clearly shows the SO2 plume. This image was created by comparing
data taken at two different frequencies, or channels, and creating one
image that highlights the differences between these two channels. Both
channels are sensitive to water vapor, but one of the channels is also
sensitive to SO2. By subtracting out the common water vapor signal in
both channels, the SO2 feature remains and shows up as an enhancement in
the difference image.
The Atmospheric Infrared Sounder Experiment, with its visible, infrared,
and microwave detectors, provides a three-dimensional look at Earth's
weather. Working in tandem, the three instruments can make simultaneous
observations all the way down to the Earth's surface, even in the presence
of heavy clouds. With more than 2,000 channels sensing different regions
of the atmosphere, the system creates a global, 3-D map of atmospheric
temperature and humidity and provides information on clouds, greenhouse
gases, and many other atmospheric phenomena. The AIRS Infrared Sounder
Experiment flies onboard NASA's Aqua spacecraft and is managed by NASA's
Jet Propulsion Laboratory, Pasadena, Calif., under contract to NASA. JPL
is a division of the California Institute of Technology in Pasadena