# Review of Satellite Interferometry for Landslide Detection in Italy
## 6 How InSAR Products Have Been Used for Landslide Studies in Italy  
With the aim of providing a comprehensive overview of InSAR applications in Italy, we defined six macro-classes of data usage:  
* _Back-analysis_: Satellite radar images are analyzed in response to the occurrence of a highly impactful and damaging landslide. InSAR is used to reconstruct the recent history and evolution of the landslide, as well as to investigate possible motion precursors before its catastrophic failure.
* _Characterization_: The activity focuses on a single landslide, where the classical geomorphological analysis, supported by ground survey evidence and in situ measurements, is integrated with interferometric results. Commonly, multi-band and multi-sensor data are used to cover the largest temporal span possible, reconstructing the evolution of the landslide. Such activity is mainly focused on the evaluation of the potential risk posed by the landslide, assessing its behavior and the possibility of a future failure.
* _Input for models_: Satellite evidence can become the input for different kind of models, depending on the working scale and on the landslide typology. For example, interferometric data can be used as inputs for landslide susceptibility refinement or for landslide model calibration and validation. This activity emphasizes the high interoperability of InSAR data with models and ancillary data in general.
* _Landslide inventory update_: One of the most useful features of InSAR products is the wide-area coverage coupled with millimeter accuracy. This potential is exploited for landslide inventory refinement, where landslide databases are available. This activity comprises the definition of the state of activity of known landslides, information to be used for urban planning, and risk management purposes, including the identification of stable areas for relocation [128];
* _Mapping_: This activity aimed to show what is moving in an area. Interferometric data are a valuable support to detect the motion of new and unknown landslides within the technical boundaries of the technique, in terms of maximum measurable displacement and considering the land coverage.
* _Monitoring_: The most advanced application of interferometric products, relying on a frequently updated processing plan. This activity is possible thanks to the low revisiting time of the most recent satellite constellations, such as Sentinel-1 (6 days) or COSMO-SkyMed (4-16 days). Satellite monitoring cannot be considered as a real-time product for obvious reasons, but, for some landslide types, a bi-weekly update frequency is enough to follow their evolution. Indeed, some authors refer to this activity as \"near-real-time monitoring.\"  
This classification is subjective and reflects the points of view of the authors of this review paper. Many articles were connected to multiple classes since different data exploitation methodologies have been applied. The percentages of papers for each category are shown in Figure 3. Some considerations, supported by study cases for each usage category, are proposed in the following sections.