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Valeria Pancioli, University of Florence (Italy)
Teresa Campolmi, University of Florence (Italy)
Hugo Raetzo, Swiss Federal Office for the Environment (Switzerland)
Nicola Casagli, University of Florence (Italy)
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In the framework of ESA-GMES Terrafirma project a landslide inventory (LSI) product, in a prone landslide area affected by extensive unstable areas occurring mainly on Flysch formations, was activated. Terrafirma is an initiative funded by ESA (European Space Agency) aims at providing pan-European services based on the latest technology to measure terrain motion from satellite InSAR data relating to subsidence, landslides, crustal and volcanic deformation. LSI product consists of a landslide inventory map, updated on a pre-existing inventory map, when available, through the integration of InSAR Persistent Scatterers ground displacements information with conventional geomorphologic tools.
The most involved users of this kind of product are represented by Public Authorities in charge of landslide risk management at national or local level. The present work focuses on the results obtained for a landslide inventory in the Canton Graubuenden located in the Swiss Alps between the Gotthard Cristalline Massive and Austrian-Italian Border. The densely populated region is a landslide prone area. There are also many installations for tourist purposes in the unstable slopes, sometimes they are located in the Permafrost areas, many other landslides are still active and there are high annually costs for the mitigation and the countermeasures; the stakeholder involved is the Swiss Federal Office for the Environment (FOEN).
For the Canton, that cover an area of about 3800 km2, a landslide inventory is not available, but several of the large landslides are well known and geological documents and field surveys allowed an integration of InSAR technique for hazard assessment. Radar datasets used were SAR images acquired by ERS1 and ERS2 satellite from 1992 to 2002, and SAR images from ENVISAT satellite from 2002 to 2006); both datasets were acquired in ascending and descending geometry processed through the Interferometyric Point Target Analysis (IPTA) technique developed by Gamma Remote sensing. The analysis was carried out in the following steps: acquisition of geological documents, acquisition of thematic layers, homogenization of IPTA datasets, IPTA and optical data interpretation integrated with field surveys. For this purpose thematic layers, including aerial photos, digital elevation model and topographic maps, were managed within a GIS environment. IPTA analysis allowed to map a landslide inventory for the Canton, that consists of about 100 phenomena with a landslide density of around 6% of the whole area; according with the FOEN recommendations quite almost of the large known landslides were confirmed and several new landslides were identified, chiefly IPTA analysis has permitted to detect almost of the large landslide active parts, compared with the data instrumentations available.
The results confirm the capabilities of multi-interferometric InSAR data, integrated and coupled with conventional techniques, to support landslides investigation at regional scale.
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