Advanced space-borne Persistant Scatterers Interferometry (PSI) can provide wide-area coverage (thousands km2) and precise (mm-cm resolution), spatially dense information (from hundreds to over thousand measurement points/km2) on ground surface deformations. Furthermore, new application opportunities are emerging thanks to i) the greater data availability offered by recent launches of radar satellites, ii) the improved capabilities of the new space radar sensors (Cosmo-SkyMed, TerraSAR-X) in terms of resolution (from 3 to 1 m) and revisit time (from 11 to 4 days). Although, the applicability of radar interferometry to regional and local-scale investigations of slope instability have been demonstrated in several studies, more progress is needed in the integration of PSI results with ground data and in their validation in order to foster a more profitable use of this technique. It is also expected that numerical modeling slope deformations detected by radar satellites should help to constrain the data interpretation.
The satellite-based Synthetic Aperture Radar (SAR) Differential Interferometry (DInSAR) can be used to measure ground surface deformations with millimetercentimeter precision. However, the applicability of DInSAR is limited to areas with scarce vegetation cover. The advanced multi-temporal InSAR techniques such as Persistent Scatterer Interferometry (PSI) (e.g. Ferretti et al. 2001) mitigate this limitation by focusing on selected radar targets (PS) exhibiting coherent radar backscattering properties (mainly man-made structures and rock outcrops). This allows detecting and monitoring with millimeter precision displacements occurring between successive satellite overpasses of the same area. With their capability to provide wide-area coverage (thousands km2) and precise spatially dense measurements (from hundreds to over thousand measurement points/km2), the PSI techniques can assist in both regional and local scale investigations of landslides (e.g. Hilley et al. 2004, Bovenga et al. 2006, Colesanti & Wasowski 2006, Farina et al. 2006, Cascini et al. 2010).
Furthermore, new application opportunities have emerged thanks to i) the greater data availability offered by recent launches of radar satellites, and ii) the improved capabilities of the new space radar sensors (X-band Cosmo-SkyMed, C-band RADARSAT-2, TerraSAR-X; see Table 1) in terms of resolution (from 3 to 1 m) and revisit time (from 11 to 4 days for X-band acquisitions). The availability of higher spatial and temporal resolution information about ground surface displacements implies improved slope instability investigation and monitoring capabilities (e.g. Bovenga et al. 2012).
It appears that the geotechnical community is not fully aware of the actual potential and limitations of PSI as applied to landslide investigations. Some skepticism, especially among practitioners and end users, may have resulted from the initial enthusiastic promotion of the technique, which has not paid enough attention to its limitations.
This work aims to contribute to a better informed use of PSI in slope instability detection and monitoring by presenting application examples from areas characterized by different geological settings. We will illustrate i) the potential of the technique to provide, under suitable conditions (favorable slope aspect/inclination, limited vegetation), reconnaissance and site-specific information on slope instability, ii) the difficulties in inferring the exact cause(s) of slow displacements (mm-cm/year) commonly registered on radar targets.
