# Review of Satellite Interferometry for Landslide Detection in Italy
## 6 How InSAR Products Have Been Used for Landslide Studies in Italy
### InSAR Data as Inputs for Models  
Satellite-derived displacement information has been used by some authors as input or calibration for models. InSAR is a precious resource where in situ measurements are unavailable or where the working scale does not allow for the acquisition of thousands of point-like data. Models usually require high-quality inputs, a requirement fulfilled by InSAR products, which can reach millimetric accuracy in the estimation of annual velocity.  
Our bibliographic review revealed that there are two main areas where InSAR is used as input for models: single landslide modelling or basin-scale susceptibility modeling.  
The first activity is aimed to the quantification of the landslide kinematic, for assessing the current landslide behavior and forecasting its future evolution [156]. A good coverage of InSAR measurement points allows for the detection of landslide sectors with different velocities. This information is fundamental for the proper definition of the model boundaries, and for the identification of different kinematic areas (e.g., [121]). InSAR can provide a temporal overview of landslide behavior several years before the time of the analysis. Multi-temporal InSAR results are used to optimize time-dependent landslide models, and as a starting point to forecast the future evolution of the phenomenon on the basis of viscosity/creep models (e.g., [58]).  
The goal of landslide susceptibility is to produce maps indicating the propensity of an area to generate landslides [157]. Hundreds of types of numerical susceptibility models exist, more or less complex and based on different input data, parameters, and validation methodologies. For a review of susceptibility models, we refer to [158]. Some authors proposed landslide susceptibility models refined by means of InSAR data. For example, [PERSON] et al. [51] presented a methodology for susceptibility map refinement in the Nebrodi Range (Northern Sicily), based on X-band SqueezeSAR ascending and descending datasets. First, line of sight velocity was projected along the slope. An empirical contingency matrix that considers the susceptibility degree, and the projected velocities are then used to integrate the two datasets. As a result, the prediction capability of the Random Forest algorithm used the generate the landslide susceptibility map was improved. A similar approach was recently followed in the case of the Sorrentina Peninsula (Campania region [159]).  
In recent years, InSAR results have been used for a further model purpose: as input for the calculation of fragility curves for concrete and masonry buildings. The fragility curves represent the probability of exceeding a given damage as a function of ground displacements. Satellite-derived deformation is used to tune the fragility curves and to provide velocity measures for each damagedbuilding whose state of conservation is assessed through ground surveys. This engineering methodology has been applied to landslide studies supported by interferometric results by, e.g., [PERSON] et al. [160], [PERSON] et al. [161], and [PERSON] et al. [162].