# Review of Satellite Interferometry for Landslide Detection in Italy
## 6 How InSAR Products Have Been Used for Landslide Studies in Italy
### Back-Analysis  
When a landslide occurs, one of the first questions asked to experts and scientists is: Did the landslide show any precursory sign that could have been used to forecast its occurrence? The answer is not immediate if in-situ deformation monitoring systems are not available. Thanks to the possibility to back-track the target deformation over the past 28 years, satellite interferometry is a very good answer to this question. Post-failure reconstruction of landslide behavior using InSAR data is a rather new application in Italy. This is due to (i) landslide type, as many landslides in Italy are connected to intense rainfall events that trigger newly or reactivated fast to very fast landslides, whose pre-failure can be considered instantaneous by the point of view of satellite interferometry; (ii) unfavorable morphology and land use of the slope; and (iii) the fact that InSAR is sometimes not a priority for some geohazard risk management entities, and it is not well integrated in risk management practices. It is worth recalling thatthe Italian Civil Protection usually requests interferometric analysis in the case of damaging landslide events (when technically feasible). [PERSON] et al. [128] showed that satellite interferometry has been used in every phase of the Civil Protection cycle, starting from prevention to recovery. [PERSON] et al. [137] used InSAR to monitor strategic buildings in the framework of civil protection activities. [PERSON] et al. [138] analyzed a set of COSMO-SkyMed images with the SPINUA algorithm [28] in order to reconstruct the recent history of a slope affected by landslide whose runout interrupted the underlying railway line along the Ligurian coast, causing the derailment of a train. The PSI analysis confirmed the motion of the upper portion of the slope, in the proximity of the crown of the landslide, some years before its failure. In February 2010, a large complex rotational landslide affected the eastward part of the town of San Fratello in the Nebrodi Mountains (Northern Sicily), and caused severe damage to tens of buildings. [PERSON] et al. [42] investigated the pre- and post-event behavior of the landslide combining satellite- and ground-based interferometric data. On the one hand, Envisat and RADARSAT-1 InSAR products confirmed the motion of the central portion of the landslide five years before its failure. On the other hand, COSMO-SkyMed InSAR data and Ground-Based Interferometry (GBInSAR) deformation maps allowed for the detection of residual motions in the whole crown area of the February 2010 failure. This approach was followed by [PERSON] et al. [92] in the case of the San Leo rockfall event of 27 February 2014. In this case, GBInSAR and InSAR measurements were integrated with terrestrial laser scanning data. [PERSON] et al. [130] characterized the pre- and post-failure evolution of the Papanice landslide (Crotene Province, Calabria), which occurred on 23 February 2012. Two different stacks of TerraSAR-X images were analyzed using the Coherent Pixel Technique-Temporal Sublook Coherence (CPT-TSC) and SBAS techniques. The interferometric analysis was supported by rainfall data, geomorphological evidence collected during ground surveys and slope stability analysis. This compound study allowed the authors to visualize the pre-failure evolution of the landslide and to highlight the activation of a landslide sector which was incorrectly considered stable. InSAR is a powerful technique for ground motion assessment when the velocity of the phenomenon of interest does not exceed the phase unwrapping limits imposed by the nature of the radar signal. Some authors overcame this limitation by applying amplitude-based techniques, which allowed for the reconstruction of the sin-event deformation field. [PERSON] et al. [139] and [PERSON] et al. [118] applied, for the first time in Italy, the pixel-offset amplitude tracking to reconstruct the deformation field of the large complex landslide of Montescaglioso (Basilicata region). This approach was followed by [PERSON] et al.