Landslide mapping and monitoring using Persistent Scatterer InSAR in the framework of Terrafirma project

Persistent Scatterer InSAR (Synthetic Aperture Radar Interferometry) is demonstrating its suitability for detection and monitoring of extremely to very slow moving landslides, ranging from regional to local scale. Integrating conventional instrumentation for the analysis of landslide-induced deformation, this advanced technique allows both spatial and temporal characterization of landslide phenomena, improving the quality of landslide maps, resolving the temporal variability of slope movements, and also assessing their state of activity and intensity. The exploitation of Persistent Scatterer (PS) techniques within landslide analysis has been recently promoted by several European initiatives, such as the Terrafirma project, a pan-European ground motion hazard information service supported by the European Space Agency's GMES (Global Monitoring for Environment and Security) programme. Terrafirma Stage 3 was launched in December 2009 and has as its aim the sustainability of the terrain motion service. This stage features a new focus on several thematic lines for terrain motion analysis: Tectonics, Flooding, Hydrogeology (ground water, landslides and inactive mines) and the innovative Wide Area service, aimed at measuring land deformation at pan-European scale. Terrafirma Stage 3 consortium is lead by Altamira Information, with the Dutch Geological Survey leading the Flood Theme, the Italian National Institute of Geophysics and Volcanology leading the Tectonics Theme, the University of Firenze leading the Hydrogeology Theme, and the German Space Agency leading the Wide Area Mapping task. As in previous stages, the services are based on advanced interferometry products, mainly PS methodologies; however they exploit additional data sources, including non-EO, coupled with site-specific expert interpretation. Terrafirma services are delivered to civil protection agencies, disaster management organisms, and coastal, rail and motorway authorities to support risk assessment and mitigation. Part of the Hydrogeology theme, Landslide services cover mountainous areas affected by slope instability, providing Landslide Inventory (LSI) and Landslide Monitoring (LSM) products. LSI generally operates at regional scale and integrates pre-existing landslide inventories with PS measures and multi-temporal aerial and/or satellite optical imagery. This integration aims at assessing similarities and differences in landslide spatial distribution and activity with respect to PS data, improving qualitative and quantitative information of each mapped phenomenon, and also mapping those phenomena not previously identified through conventional in situ investigations. LSM operates at local scale and relies on long term monitoring of movements induced by specific slope movements, using both PS data and conventional in situ networks, e.g. inclinometers, extensometers, topographic leveling, GPS. Within LSM analyses, PS data are well suited for assessing the temporal evolution of landslides affecting built-up areas, by providing precise measures of ground motions without necessity of positioning any targets on the ground or any physical contact with the slope. Besides the use of PS data, single-interferograms (conventional InSAR) are also exploited to analyze the temporal variability of landslide-induced motions with a step-wise approach; use of single-interferograms allows analyzing not only motion velocities exceeding the limitation of the PS approaches (i.e. few tens of cm/yr), but also deformation trends significantly differing from the deformation model (e.g. linear) used during the multi-temporal PS processing (e.g. non-linear and/or accelerated motion). Validated LSI and LSM case studies are presented, showing the essential contribution of PS and InSAR data for the detection and analysis of landslide-induced movements at both regional and local scale, and demonstrating their fundamental role for the improvement of hazard and risk management strategies.