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ESA satellites capture Etna aftermath

31 Oct 2002

Three ESA satellites take striking images of the plumes of ash and gases emitted by the Mount Etna volcano in Italy.

The European Space Agency (ESA) has released a gallery of multispectral images charting the huge amounts of ash and trace gases that Mount Etna has thrown into the atmosphere after erupting on Sunday. The images, taken by three separate satellites, track the path of the ash plume and show that it contains at least 20 times more sulphur dioxide than normally present in the atmosphere.

On Monday, MERIS [Medium Resolution Imaging Spectrometer] onboard the Envisat satellite acquired detailed images of the plume stretching south-west from Sicily towards Africa. MERIS measures the solar radiation reflected by the Earth in 15 spectral bands throughout the visible and near infrared.

MERIS is monitoring the sulphur dioxide levels around Etna. This will let scientists examine the impact on cloud cover, cloud properties and precipitation as sulphur dioxide is known to be responsible for the so-called "acid-rain" phenomena.

CHRIS [Compact High Resolution Imaging Spectrometer] onboard the PROBA satellite has also tracked the path of the ash. PROBA is ESA's first small autonomous satellite and contains a range of instruments for environmental monitoring. CHRIS, the largest piece of kit on PROBA, provides multispectral data of the Earth's surface reflectance in 19 bands within the range 415 to 1050 nm.

The final instrument to send back data is GOME [Global Ozone Monitoring Experiment], which is housed on the european remote sensing satellite ERS-2. The spectrometer, which measures the solar radiation scattered by the atmosphere in ultraviolet and visible from 240 to 790 nm, can detect a range of atmospheric trace constituents, including sulphur dioxide.

Since the eruption, scientists have used GOME to look at the increasing concentration of sulphur dioxide. Results show that the plume contains at least 20 times more than the standard amount of the gas compared with normal atmospheric levels.

The first results were collected on Tuesday. Researchers will continue to use GOME to monitor the amount of sulphur dioxide in the troposphere. This is the lowest part of the atmosphere where most weather changes occur.

Jacqueline Hewett is news reporter on Optics.org and Opto & Laser Europe magazine.

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