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Mt. Etna volcanic aerosol and ash using MERIS and AATSR data

Claudia Spinetti(1), Stefano Corradini(1), Elisa Carboni(2), Gareth Thomas(2), Roy Gordon Grainger(2) and Maria Fabrizia Buongiorno(1)

(1) INGV, Via di Vigna Murata 605, 00143, Italy
(2) University of Oxford, Parks Road, OX1 3PU, United Kingdom


Envisat MERIS and AATSR data have been acquired in the framework of the Eurorisk-Preview project. The project addresses European civil protections and proposes to develop, at the European scale, new information services to support the risk management. In Italy one of the most important natural risks is due to the presence of volcanoes. Mt. Etna in Sicily, displays persistent activity, periodically interrupted by eruptions, which emit volcanic aerosol and ash to different altitudes in troposphere affecting the central Mediterranean area. In order to test the use of MERIS and AATSR data to monitor the emitted particles in troposphere the already developed remote sensing techniques have been adapted and applied to MERIS and AATSR data acquired during the Mt. Etna 2002-2003 volcanic eruption. The data have been requested via Category 1 n. 3560. In the remote sensing approach a radiative transfer inversion algorithm (Spinetti et al., 2003) has been applied to MERIS data recorded on October 2002 during Mt. Etna eruption. The algorithm use the visible channels, since scattering effects are in the short wavelength range of the solar radiation. Explosive plume particles component optical characteristics has been retrieved as a spatial distribution of optical thickness. Using multispectral TIR bands, around 11 and 12 micron, the possibility to detect the ash component during eruptive episodes has been demonstrated using the BTD method (Prata, 1989; Wen and Rose, 1994). This method has been applied to AATSR data choosing the same eruption episodes recorded by MERIS. After calculating the optical properties of the volcanic ash a radiative transfer model has been used to simulated the signal measured by AATSR. Fitting the model simulations to the data provides estimates of the optical thickness of the eruptive plume, mean radius of the ash particles and the ash loading. Using the AATSR visible and near infrared channels we have estimated the optical depth (at 550nm) and the effective radius using the ORAC aerosol retrieval algorithm, developed at Oxford University and Rutherford Appleton Laboratory. The ORAC scheme has been used and validated in several projects including NERC GRAPE and ESA Globaerosol. The radiative transfer model used for the vis/nir channels takes into account atmospheric scattering and absorption as obtained by DISORT (DIScrete Ordinate Radiative Transfer) radiative transfer code. Here the algorithm is extended to include the optical properties of a volcanic aerosol model. The use of VIS and TIR bands of the two sensor demonstrates the potential to monitor the volcanic plume during eruption if frequent and high resolution data is available in near real time.


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, atmospheric chemistry