SO2 and ash plume retrievals using MSG-SEVIRI measurements. Test case: 24 November 2006 Mt. Etna eruption

In this work the Thermal InfraRed (TIR) measurements of the Spin Enhanced Visible and Infrared Imager (SEVIRI)on board the Meteosat Second Generation (MSG) geosyncronous satellite, have been used to estimate the daily evolution of the SO₂ columnar abundance and ash plume optical thickness, particle effective radius and total mass of Mt. Etna volcanic plume. As test case the 24 November 2006 eruption has been considered. SEVIRI is an optical imaging radiometer characterized by 12 spectral channels, a high temporal resolution (one image every 15 minutes) and a 9 km² footprint. The instrument¿s spectral range includes the 8.7 ¿m band (channel 7) and the 10.8 and 12.0 ¿m split window bands (channels 9 and 10) used respectively for SO₂ retrieval and volcanic ash detection and retrievals. The SO₂ columnar abundance is estimated by means of a Look-Up Table (LUT) least squares fit procedure applied to channel 7, while the ash detection and retrievals are carried out by using the Brightness Temperature Difference algorithm applied to channels 9 and 10. All the simulations needed for the retrievals have been realized using MODTRAN 4 radiative transfer model. The SEVIRI volcanic plume SO₂ and ash retrievals have been compared with the results obtained by processing the data collected at 12:20 GMT by the MODIS sensor on board of Aqua satellite. Results show the ability of SEVIRI to recognize and estimate the daily trend of SO₂ and ash in an eruptive plume; for the 24 November 2006 eruption, the SO₂ and ash emissions started at about 4 and 8 GMT respectively and terminated simultaneously at about 14 GMT. The comparison between SEVIRI and MODIS retrievals indicate a general good agreement.