Monitoring volcanic activity from space: Retrieval of sulphur dioxide plumes from ERS-2/GOME backscatter data
Werner Thomas(5), Thilo Erbertseder(1), Thomas Ruppert(1), Michel van Roozendael(2), Dimitris Balis(3), Chariklea Meleti(3) and Christos Zerefos(4)
(1) Deutsches Zentrum fuer Luft- und Raumfahrt (DLR), Muenchener Str. 20, 82234 Wessling, Germany
(2) Belgian Institute of Space Aeronomy (BIRA-IASB), Avenue Circulaire 3, 1180 Brussels, Belgium
(3) Aristotle University of Thessaloniki, , 54006 Thessaloniki, Greece
(4) University of Athens, , 15784 Athens , Greece
(5) Deutscher Wetterdienst (DWD), Kaiserleistr. 29/35, 63067 Offenbach, Germany
We focus on the retrieval of volcanic sulphur dioxide (SO2) emissions from an analysis of atmospheric UV backscatter spectra obtained by the Global Ozone Monitoring Experiment (GOME) spectrometer on board the ESA European Remote Sensing Satellite (ERS-2). Here, the last major eruptions of Mt. Etna on Sicily (Italy) in July/August 2001 and October/November 2002 provided an excellent opportunity to study the retrieval of sulphur dioxide columnar amounts from ground-based, LIDAR and satellite measurements.
In general, the retrieval of volcanic sulphur dioxide emissions from space suffers from the sparse temporal and spatial coverage of actual satellite sensors but also from clouds in the troposphere. The short tropospheric lifetime of SO2 and the separation of the background SO2 content from volcanic emissions also hampers the estimation of the volcanic source strength. Other typically unknown but important parameters are the aerosol loading in and around the volcanic plume and the height above ground level of emissions (particles and gases).
A sensitivity analysis was performed to identify the main physical parameters that influence the retrieval results. We could show that the combination of trajectory analysis, ground-based measurements and GOME observations can be used to confirm the presence of large amounts of sulphur dioxide of volcanic origin away from the volcano. Although the latest eruptions of Mt. Etna were more powerful as others observed in recent years we believe that the bulk of emitted sulphur dioxide was confined in the troposphere, mainly between 700 hPa and 400 hPa which is confirmed by trajectory analysis, by LIDAR observations and AVHRR observations. For the first time, GOME-derived SO2 total columns were successfully validated against ground-based measurements from a Brewer spectrophotometer.
Our analysis further revealed that information about the plume height of volcanic eruptions and aerosol parameters is necessary for a reliable quantitative retrieval of sulphur dioxide from space-borne sensor data at periods perturbed by volcanic eruptions.
Thomas W., T. Erbertseder, T. Ruppert, M. van Roozendael, J. Verdebout, D. Balis, C. Meleti, and C. Zerefos, On the retrieval of volcanic sulphur dioxide emissions from GOME backscatter measurements, J. Atm. Chem., 50, 295—320, 2005.
Zerefos C, P. Nastos, D. Balis, A. Papayannis, A. Kelepertsis, E. Kannelopoulou, D. Nikolakis, C. Eleftheratos, W. Thomas, and C. Varotsos, A Complex Study of Etna’s Volcanic Plume from Ground-based, In-situ and Space-borne Observations, accepted for publication in Int. J. Rem. Sens., 2005.
Keywords: ESA European
Space Agency - Agence spatiale europeenne,
observation de la terre, earth observation,
satellite remote sensing,
teledetection, geophysique, altimetrie, radar,
chimique atmospherique, geophysics, altimetry, radar,