Landslide detection integrated system (LaDIS) based on in-situ and satellite SAR interferometry measurements

An integrated system to analyze slope instabilities over vast areas through the intercomparison of measurements obtained by in-situ and persistent scatterer (PS) interferometry processing of satellite synthetic aperture radar (SAR) data, is here introduced and tentatively named landslide detection integrated system (LaDIS).The persistent scatterer pair (PSP) SAR interferometry technique has been used to process high-resolution SAR images acquired in the 2008-2011 time span by the COSMO-SkyMed satellite constellation, available in a 40 km × 40 km study area in the Palermo Province (Sicily region-Italy). Derived displacement rate estimates from COSMO-SkyMedPS measurements have been analyzed in approximately 10% of the study area for landslide research. Within this area, according to the official landslide inventory map, extremely slow to very slow landslides are dominant, being favored by the presence of heterogeneous clay formations characterized by poor mechanical properties. To prove COSMO-SkyMedPS displacement rates an engineering-geological approach was adopted, tailored to allow a continuous and rapid updating of landslide-inventory maps; to this aim a detailed geological field work has been performed. To guarantee an independent assessment, field surveys have been carried out without sharing information derived from PS data.

Almost half (49%) of the active unstable areas identified through COSMO-SkyMedPS measurements were confirmed by the field work. In an additional 26% of cases the greater sensitivity of the satellite has allowed to identify movements, even if very slow, that did not show superficial evidence.

A confirmation of the great potentialities of the latest generation of satellite systems also comes from the comparison with the current official landslide-inventory map, updated in 2006. Among the 58% of the total PS measurements that have been used to contour the landslides "in remote", 84.3% falls outside the polygons of the failures detected in the existing maps, which implies a significant percentage of data to be associated to new landslides or extension of pre-existing landslides.

Advantages and drawbacks of exploiting COSMO-SkyMed X-band SAR data to study landslides over wide areas through the proposed approach are finally discussed.