Evaluation of SO2 emission from Mount Etna using diurnal and nocturnal multispectral IR and visible imaging spectrometer thermal IR remote sensing images and radiative transfer models

We describe a model to evaluate the volcanic SO2 emission using images acqu ired by the airborne multispectral infrared and visible imaging spectromete r (MIVIS) in the thermal infrared spectral region. The estimating procedure consists of mapping of the SO2 columnar content and evaluation of the tota l SO2 flux emitted by the volcano. All the atmospheric radiative effects, i ncluding the SO2 plume emission/absorption, are computed by the MODTRAN 3.5 radiative transfer code. We apply the model to two MIVIS images acquired o ver Mount Etna, located on the east coast of Sicily, Italy, during the "Sic ilia-94" remote sensing campaign on July 24 and 25, 1994. The June 25 image was acquired during the night; this is the first attempt to estimate the S O2 content in volcanic plume using nocturnal thermal infrared images. The t otal flux estimates range from 20.9 kg (s-1) (1810 t d(-1)) to 82.2 kg s(-1 ) (7100 t d(-1)) depending on the plume geometry used in the procedure. The se results, except one case (82.2 kg s(-1)), are in agreement with the esti mates derived from correlation spectrometer (COSPEC) measurements collected during the same period. We also evaluate the dependencies of the results o n several parameters such as plume geometry, surface emissivity, water vapo r content, and wind speed.