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ASAR Interferometry at Piton de la Fournaise, Preliminary Results

Jean-Luc Froger(1) and Yo Fukushima(2)

(1) Lab. Magmas & Volcans, IRD-UR31, 5 rue Kessler, 63038 Clermont-Ferrand, France
(2) Université Blaise Pascal, 5 rue Kessler, 63038, France


Since the detection of surface deformation at Mount Etna, several geodesic studies have been done on volcanoes with radar interferometric data acquired by the European ERS-1 and ERS-2 satellites, the Japanese JERS-1 satellite and the Canadian RADARSAT-1 satellite. Here we present the preliminary results of an interferometric study of Piton de la Fournaise volcano, Réunion Island, with Synthetic Aperture Radar images acquired by the ASAR-ENVISAT satellite. Launched in March 2002 by the European Space Agency, ENVISAT is an Earth observation dedicated satellite which the payload consists of a set of instruments for measuring the atmosphere and the surface through the atmosphere. One of these instruments is the ASAR radar designed to provide for continuity of the observations started with the SAR on board of the ERS satellites.

By combining two ASAR images, we formed an interferogram spanning 35 days from 27 of July 2003 to 31 of August 2003, and covering the eruption that began at Piton de la Fournaise on 22 August and stopped on 27 August. On 23 August, at about 21h20, a first fissure opened at the summit of the volcano, in Bory crater. A second fissure opened at 22h10 on the north flank at about 2450 m altitude. At 23h30 a final fissure opened at 2200 m altitude on the north flank, about 50 m east of 1998 Piton Kapor. The interferogram exhibits a clear fringes pattern centred on the Soufriere pit crater, on the external northern flank of the summit Dolomieu caldeira. As previously observed on Radarsat interferograms of the March 1998 eruption, the range change pattern is asymmetric with respect to the eruptive fissures. Up to eleven fringes occur in the area east of the fissures indicating a displacement of the ground toward the satellite of about 30 cm, while less than three fringes are visible west of the fissures indicating a displacement of the ground away from the satellite of about 7 cm. Modelling of these displacements using a set of rectangular dislocation in an uniform elastic half-space shows that they most likely result from the opening of a shallow dike with varying inclination.

This preliminary study provide new geodesic data that confirm the well known seaward displacement of the eastern flank of Piton de la Fournaise. It also demonstrate the total efficiency and high potentials of ASAR as a successor of ERS for interferometric applications.

Acknowledgments. We thank the European Space Agency for providing ASAR data to us through the EO-746 project. This work was supported by the Groupe De Recherche 515 STRAINSAR (CNRS, France).


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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