# Review of Satellite Interferometry for Landslide Detection in Italy
## 7 Final Remarks
* _The kinematic of the landslide._ In a noise-free situation, the radar signal should not change by more than a quarter-wavelength (e.g., 14 mm for C-band sensors) between two consecutive samples. Due to noise, this threshold is in reality lower. Because of this, landslides characterized by non-linear deformation rates higher than 2 mm/day are challenging targets for InSAR. InSAR processing based on linear phase unwrapping would not be able to capture such motions. Higher order deformation models may be applied to solve the phase ambiguity for single applications [189]. For a more comprehensive review of InSAR limitations for landslide studies, we refer to [PERSON] & [PERSON] [19] and to [PERSON] et al. [190]. Although these well-known (and sometimes predictable) limitations exist, the interferometric technique is a reliable choice for many landslide-related applications, such as the following:  
* _Landslide mapping over wide areas._ As seen in Section 6.5, it is possible to retrieve reliable information about the presence of landslides over entire basins or regions. The analysis is limited to certain landslide types, i.e., extremely slow and very slow landslides, according to the Cruden & Varnes classification [191]. Moreover, the quality of the results depends on the land cover, the presence of snow or geometric effects. Nevertheless, InSAR is useful when no other ground or remotely sensed information is available or where it is impossible to gather them. In Italy, InSAR gave positive responses for landslide mapping in both Alpine and Apennine contexts. * _Landslide state of activity estimation._ InSAR is becoming a reliable and recognized tool to assess the multi-temporal behavior of landslides, including the evaluation of their state of activity. This line of research is relevant for land planners since the presence of an active landslide forbids the construction of new structures. Landslide databases sometimes lack information about the current activity of landslides, limiting the correct management of a territory. InSAR is the right tool to provide such information and to be included in regional/national landslide-related policies. The Tuscany region is an example of this [152,164]. * _Landslide characterization._ One of the more powerful characteristics of InSAR is its multi-scale capability. With proper processing configurations and according to the satellite band, it can be profitably employed from the continental to the local scale. In the second case, it is the perfect complement for in situ motion instruments and for use as input for landslide models. * _Back-analysis._ Nowadays, an InSAR database can cover a 28-year time span with different satellite images acquired by multi-band sensors. This is a relevant feature for the post-collapse reconstruction of the landslide behavior. Considering that InSAR is used not only for research purposes, but also to produce outputs for national or regional entities, data validation is a common request and requirement. Validation is the process to evaluate the applicability and detection capability of the InSAR products through an independent assessment, i.e., by using external data not connected to the data production. In the context of InSAR, validation is aimed to demonstrate the completeness and reliability of satellite measurements. Almost 70% of the revised paper highlighted the need for validation data of various types, ranging from classical in situ instruments to other remote sensing monitoring tools, such as GNSS, GBInSAR, or TLS (cfr. Section 6.3 and Figure 3). Validation was performed at a single landslide scale and when managing a large InSAR dataset. For example, [PERSON] et al. [192] validated the results of the national interferometric coverage produced in the frame of the PST-A project. These authors proposed a validation approach known as the Landslide Detection Integrated System (LaDIS, [188]). Two hundred forty-nine sites were chosen as field validation targets affected by landslides.