A Combined Procedure Using Satellite-Based Differential SAR Interferometry And Field Measurements For Landslide Characterization In Small Urban Settings

Landslides represent globally one of the most noticeable and widespread “natural hazards”, responsible for significant economic damage as well as large quantities of fatalities. To this regard, non-structural actions, such as monitoring, assume a key role, in order to prevent and acquire knowledge about these critical phenomena. Differential SAR Interferometry (DInSAR) represents nowadays one of the main and most advanced techniques for satellite data-based landslide monitoring. In this paper, a solid procedure structured in two phases is proposed: the first, based on the exploitation of DInSAR data at municipal scale, and the latter, focused on a slope-scale analysis, integrating SAR and traditional in-situ data. The municipal scale analysis allows the detection and identification of critical landslide-affected areas, through a statistical Persistent Scattererer (PS) clustering process. Such methodology takes into account 4 requirements, used as input to generate cells that can represent evidence of instability : i) threshold of minimum velocity, to select PSs that can be considered as moving targets; ii) maximum inter-point distance between two close targets; iii) density of moving targets; iv) homogeneity index, consisting in the ratio between the total number of PSs within the cell and the number of “moving” PSs. According to the identification of the cells, higher priority sectors (i.e. characterized by higher hazard) can be selected in order to perform the slope-scale analysis. The latter is carried out by means of geomorphological and geological field survey, as to define landslide’s boundaries, geometries, and the potential damage of the area involved. Moreover, field activity is integrated with in-situ measurements, such as inclinometers and piezometers, with geotechnical data, deriving from boreholes and with DInSAR data, in order to comprehend landslide’s dynamic and triggering factors. The above-described procedure has been implemented on the test site of Cirò, a small town of ca. 3000 inhabitants, located in the Crotone province (Southern Italy). For the Cirò case, the municipal scale analysis has been applied using a dataset of 35 TerraSAR-X images, acquired in descending orbit in the time span 2008-2010 and processed through the Coherence Pixels Technique (CPT). Among all the landslides detected in Cirò, an event occurred in February 1, 2011, involving one of the main access roads to the town center and causing severe damage, forcing people to abandon five houses, has been classified of priority importance. Hence, for the slope-scale analysis, PSs deriving from the third edition of the Extraordinary Environmental Remote Sensing Plan (PST-A in Italian) have been exploited. Such data have been obtained through the processing of COSMO-SkyMed data acquired between 2011 and 2014 by means of the Persistent Scatterer Pairs (PSP) technique. To integrate the DInSAR information, field surveys have been carried out among 2013 and 2015 and in-situ data have been collected between 2011 and 2014. The results so far obtained through the proposed procedure showed promising outcomes, which can in future be applied and tested on further landslide affected areas, in order to provide a valuable tool for local administrations and to prevent damage and economic losses