Volcanic eruptions can inject large amounts (Tg) of gas and particles into the troposphere and, sometimes, intothe stratosphere. Besides the main gases (H2O, CO2 , SO2 and HCl), volcanic clouds contain a mix of silicateash particles in the size range 0.1μm to mm or larger. Interest in the ash presence detection is high in particularbecause it represents a serious hazard for air traffic. Particles with dimension of several millimeters can damagethe aircraft structure (windows, wings, ailerons), while particles less than 10μm may be extremely dangerous forthe jet engines and are undetectable by the pilots during night or in low visibility conditions.Satellite data are useful for measuring volcanic clouds because of the large vertical range of these emissions andtheir likely large horizontal spread. Moreover, since volcanoes are globally distributed and inherently dangerous,satellite measurements offer a practical and safe platform from which to make observations. Two differenttechniques used to detect volcanic clouds from satellite data are considered here for a preliminary comparison,with possible implications on quantitative retrievals of plume parameters. In particular, the Robust SatelliteTechniques (RST) approach and a water vapour corrected version of the Brightness Temperature Difference(BTD) procedure, will be compared.The RST approach is based on the multi-temporal analysis of historical, long-term satellite records, devoted to aformer characterization of the measured signal, in terms of expected value and natural variability and a furtherrecognition of signal anomalies by an automatic, unsupervised change detection step. The BTD method is basedon the difference between the brightness temperature measured in two channels centered around 11 and 12 mm.To take into account the atmospheric water vapour differential absorption in the 11–12 μm spectral range thattends to reduce (and in some cases completely mask) the BTD signal, a water vapor correction procedure, basedon measured or synthetic atmospheric profiles, has been applied. Results independently achieved by both methodsduring recent Mt. Etna eruptions are presented, compared and discussed also in terms of further implications forquantitative retrievals of plume parameters.
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