## 5 Discussion  
The cross-comparison of interferometric products, in situ damage survey results, and available HSP landslide inventory map showed a good correspondence between cause (landslide-induced movement) and effect (damage along road surface), leading at identifying sections along linear infrastructure characterized by different damage susceptibility. Furthermore, a significant advantage of the proposed approach is that it enabled to identify new ground instability phenomena, thus obtaining a new landslide inventory map updated to January 2015. High density of COSMO-SkyMed data allowed to investigate deformations along the whole linear infrastructure development. Therefore, all 24 historical landslides interacting with \"P.R. 264\", mapped by Hydro-geomorphological Setting Plan (HSP) of South Campania River Basin Authority in 2012, are covered by interferometric measurements; in addition, starting from topographic and stable/unstable pixels maps, results of geomorphological field campaigns detected 30 new events (Figure 10a). To this purpose, the distribution of unstable pixels along linear infrastructure, as an indicator of ground movement occurrence, facilitates the identification of anomalous zones where on- site checks and  
Figure 9: Vulnerability map of “P.R. 264” (**a**) and examples of some road sections that showed different vulnerability level (**b**). surveys have been carried out in order to validate all the information performed through satellite radar interpretation. Damage on road pavement, on surrounding buildings and infrastructures, and other geomorphological indicators and features induced by ground instability, allowed to define the boundary of new mapped phenomena. No landslide detected through interferometric measurements, but not identified in the field, has been mapped; instead, one landslide movement not identified by satellite data, but surveyed in the field, has been mapped. Such event, undetected by the satellite, mostly occurred in the surrounding vegetated area of P.R. 264, where no scatterers have been identified. The updated map contains not only the new instability phenomena investigated through both satellite data and field surveys, but also the updated information concerning the state of activity of both the new and historical landslides (Figure 10b). Indeed, the satellite in situ data engineering-geological inter-comparison allowed to classify as active the new 30 mapped phenomena (areas affected by new landslides in January 2015): moreover, over out of 24 historical landslides (HSP, 2012), 14 reactivations (areas classified as dormant in 2012 affected by likely local reactivations) and 10 phenomena characterized by a continuous landslide activity (eight dormant and two active in 2012) have been assessed. The study of the \"P.R. 264\" vulnerability through the proposed procedure has led to interesting results, also considering the fact that this is one of the first applications using \"I-Pro MONALISA\"  
Figure 10: Updated HSP landslide inventory (**a**) and state of activity (**b**) maps along “P.R. 264” at January 2015.  
tool. It is worth to recall that such approach represents an engineering inter-comparison of both the satellite analysis and the field survey results combined with available geological information, thanks to the total absence of shared and mutual influences in drafting the maps shown in Figures 7 and 8. Ground instability kinematics and damage survey data should be carried out separately, and after merged to update available landslide inventory map and to investigate road vulnerability, as output. The results of our study confirm that differential radar interferometry technique can be conveniently used to control the behavior of linear infrastructures affected by ground instability phenomena over large areas.