Volcanic aerosol optical characteristics of Mt. Etna tropospheric plume retrieved by means of airborne multispectral images

Tropospheric volcanic plume features have been derived from airborne multispectral images collected during field measurement campaigns at the Mt. Etna volcano in June 1997, during a quiescent period, and in July 2001 during an eruptive period. Results have been obtained in terms of mapping the volcanic aerosol optical thickness (AOT), the Ångström parameters and the water vapor content using different bands from visible to infrared. The AOT values show average values of 0.1 and 1, for quiescent and eruptive plumes, respectively, demonstrating that this geophysical parameter well indicates a major contribution of particulates in the explosive plume with respect to the quiescent one. The mapping of Ångström parameters, in the explosive case, indicates the presence of larger particles and their distribution along the plume, while in the quiescent case indicates the particle size is dominated by small particles with an effective radius about 1 μm. Further in the quiescent case, the map of water vapor shows low values indicating that water vapor emitted condenses mainly in aerosols.