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Techniques), in June 1997 an airborne campaign was organised on Mt. Etna to study different characteristics of
the volcanic plume emitted by the summit craters in quiescent conditions. Digital images were collected with
the Airborne Multispectral Imaging Spectrometer (MIVIS), together with ground-based measurements. MIVIS
images were used to calculate the aerosol optical thickness of the volcanic plume. For this purpose, an inversion
algorithm was developed based on radiative transfer equations and applied to the upwelling radiance data measured
by the sensor. This article presents the preliminary results from this inversion method. One image was selected
following the criteria of concomitant atmospheric ground-based measurements necessary to model the atmosphere,
plume centrality in the scene to analyse the largest plume area and cloudless conditions. The selected image was
calibrated in radiance and geometrically corrected. The 6S (Second Simulation of the Satellite Signal in the Solar
Spectrum) radiative transfer model was used to invert the radiative transfer equation and derive the aerosol optical
thickness. The inversion procedure takes into account both the spectral albedo of the surface under the plume and
the topographic effects on the refl ected radiance, due to the surface orientation and elevation. The result of the
inversion procedure is the spatial distribution of the plume optical depth. An average value of 0.1 in the wavelength
range 454-474 nm was found for the selected measurement day.
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