Available technologiess

The spatial scale for landslide hazard analysis ranges from regional to local, i.e. varies from studies of landslides mapping over very wide areas (up to a few thousands of square kilometres) to the analysis of single phenomenon. Hence, technologies supporting landslide studies should guarantee on the one hand to cover territories of huge extension, but on the other hand to be able to provide access to detailed information for the understanding of phenomena occurring over very small areas (e.g. a few square meters) and for the characterization of ground motion with high accuracy.

Beyond traditional in situ surveys, remote sensed data currently used both in near-real time and deferred time can give support for the creation and updating of landslide inventory maps over large areas, as well as for the local long-term monitoring of single unstable slopes. In many cases, EO (Earth Observation) aerial and satellite remote sensing data can provide precise estimates of ground motion and indicators of landslide geometry and activity, without requiring the installation of any targets or instrument on the ground. 

EO satellite technologies are well-suited to support both operational and scientific tasks in landslide identification, mapping, characterisation, and monitoring. The ability to rapidly image large areas at relatively low cost and at high resolution enables the monitoring of landslide-induced surface features and land motion. For many areas, long historical records of acquisitions are available. High resolution multi-spectral and other optical sensors are used to assess fault rupture and damage assessment and to identify secondary hazards such as triggered landslides.

EO geohazard optical imagery is often used to map and monitor regions at greatest risk and is most heavily used as a post response tool. Satellite radar is used on a case-by-case basis to further characterize the risks associated with a given landslide. More recently, satellite radar interferometry has been used to monitor areas on an on-going basis to identify areas at high risk and support mitigation activities. Access to EO data and the capacity to generate relevant information for decision makers is critical in order to implement better land use practices and to be prepared for crisis management. EO resources available or soon to be available can address most of the spatial and temporal observational requirements of the landslide community.

Conventional methods for the production of landslide maps rely chiefly on the visual interpretation of stereoscopic aerial photography, aided by field surveys, or in some cases by field surveys complemented by stereoscopic aerial photography. These methods are time consuming and resource intensive (e.g., Brabb, 1991; Galli et al., 2008). New and emerging techniques based on satellite, airborne, and terrestrial remote sensing technologies, facilitate the production of landslide maps, reducing the time and resources required for their compilation and systematic update (Guzzetti et al. 2012). Several techniques and methods can be grouped in three main categories:

• • analysis of surface morphology, exploiting very-high resolution digital elevation models (DEMs); 

Jaboyedoff et al. (2010) and Guzzetti et al. (2012) reviewed the literature on applications of very-high resolution DEMs obtained by airborne LiDAR surveys for landslide investigations, and have shown that DEMs and derivative products (e.g., contour maps, shaded relief images, maps of slope, curvature, measures of surface roughness) are used primarily for the visual analysis of the topographic surface, and the semi-automatic recognition of morphometric landslide features (Booth et al., 2009).

• • monoscopic and/or stereoscopic analysis of panchromatic multispectral and hyperspectral satellite imagery, with visual and semi-automated classification and interpretation methods; 

Techniques based on the interpretation of panchromatic, multispectral and hyperspectral images include: (i) visual (heuristic) interpretation of panchromatic, composite, false-colour, and pan sharpened (“fused”) images; and (ii) analysis of multispectral and hyperspectral images, including image classification methods and semi-automatic detection and mapping of landslides (e.g., Metternicht et al., 2005). Multispectral data of variable spatial and spectral resolution (e.g., Quickbird, IKONOS, SPOT-5, Geoeye, Resourcesat-1, Landsat, Sentinel-2) are extensively exploited for mapping, monitoring and forecasting landslides. Stereoscopic interpretation of pan-sharpened images (e.g., Nichol et al., 2006, Kouli et al., 2010) and automatic pixel- and object-oriented classification methods (e.g, Martha et al., 2010; Mondini et al., 2011; Hölbling et al., 2012) showed potential for landslide mapping. Change detection based on temporal variations of landscape spectral properties (pre- and post- landslide event) are particularly effective for updating landslide-affected areas (e.g., Fiorucci et al., 2011). Correlation of high-quality optical images showed good performances to quantify ground motions and monitoring landslide activity, and can ease the understanding of slope failure mechanisms (Delacourt et al., 2007). Furthermore, imaging spectroscopy is essential for retrieving hydrological and geomorphological diagnostic features, such as soil properties, land use, rainfall fields, that are used as inputs in many landslide predictive models (e.g., van Westen et al., 2008).

• • interpretation of SAR (Synthetic Aperture Radar) images processed through Differential InSAR and multi-temporal interferometric techniques 

Differential InSAR techniques and multi-temporal interferometric techniques such as  PSI (Persistent Scatterers Interferometry) techniques (Ferretti et al., 2001, 2011) demonstrated their suitability for the detection, monitoring and characterization of extremely to very slow moving landslides, and their complementarity with on-site measurements, at both regional and local scales (e.g., Strozzi et al, 2005; Farina et al. 2006; Colesanti & Wasowski, 2006; Cigna et al., 2012; Bianchini et al., 2013; Tofani et al., 2013 etc ). Recent review of PSI approaches for landslide studies can be found in Crosetto et al. (2016).  

The main use of the above mentioned approaches for landslide hazard evaluation with the aim of creation or updating of landslide maps at regional scale, and long-term monitoring of unstable slopes at local scale, are 

• • Landslide Mapping and inventory,  
• • Landslide Monitoring and characterization
• • Landslide hazard Modelling
• • Early Warning Systems & Forecasting