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News  Satellite survey enhances knowledge of Tuscan landslides
The 240-km-long River Arno winds its way seaward through the tranquil countryside of Umbria and Tuscany, but this tranquillity masks potential danger. There are more than 300 areas within Italy's Arno Basin at high risk of landslides, and over 20 000 individual landslides have been recorded. Italy's combination of geography, geology and climate makes it one of Europe's most landslide-prone territories, with an average of 54 lives lost for each year of the last half century. However a new service based on satellite imagery can provide early warning of areas susceptible to landslides, by highlighting tiny millimetre-scale slope motion that occurs ahead of larger-scale movement.
The ESA-funded Service for Landslide Monitoring (SLAM) is being applied to the densely populated Arno Basin. More than 350 satellite images of the region, taken by ESA’s ERS satellites, have been combined with ground-gathered data to generate detailed products, in order to identify and assess slope instability and risk across 8 830 square kilometres of territory.
"The experience of being a SLAM end-user has been very positive," stated Dr Lorenzo Sulli of the Arno National Basin Authority. "Most of all because it has been possible to combine the technical and scientific information with the way we normally work, in support of decision making. This is not always possible with such highly innovative projects."
Funded by ESA's Data User Programme (DUP) and begun back in May 2003, the objective of the SLAM project has been to implement landslide mapping and monitoring services combining Earth Observation and in-situ data sources, tailored for the use of institutions involved in hydro-geological risk management.
Local end users are the environmental and soil conservation division of the Campania region around Naples (Regione Campania Assessoroato all'Ambiente e alla Difesa del Suolo) and the Arno Basin National Authority.
"The final results are now undergoing a process of implementation within land planning and risk prevention policies of the Arno Basin National Authority for its PAI. The proposed methodology represents one of the first examples in Europe of full integration of remote sensing data into land regulations concerning landslide hazard."
The second is the Displacement Monitoring Service. Updated more regularly than the Landslide Motion Survey, it has a maximum spatial resolution of five metres and measures ground movement on a scale of millimetres in order to evaluate slight slope movement over time. Finally comes the Landslide Susceptibility Mapping product, which integrates space data with all available thematic maps showing slope, land use, geomorphology and other parameters to create geological hazard maps, for updating every few years.
"The SLAM products are currently used to verify issues related to slope instability," Sulli added. "As an end user we have always decided to compare the interpreted information – derived from geological analysis – with the initial data – displacement information from satellite radar interferometry – in order to validate the results independently and on a case-by-case basis.”
Casagli explained that GNDCI played a role in assessing the SLAM products "in terms of completeness of the methodology and conformity with the international scientific state-of-the-art. This has been particularly relevant with Landslide Susceptibility Mapping, where an innovative method based on artificial neural network technology has been applied to hazard mapping at the basin scale."
Preliminary SLAM results were presented in January to the World Conference on Disaster Reduction in Kobe, Japan– the country with the highest rate of landslides in the world.
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