## 5 Discussion
In all cases, PS-MTI underestimates the magnitude of cumulative displacements. However, despite the theoretical limitations regarding the ability to monitor displacements higher than a quarter of wavelength between two acquisitions (which for CSK corresponds to an ambiguous velocity of 0.015 m/month if SAR scenes are acquired at 16 days intervals) PS-MTI processing enable us to measure displacements up to 0.08 cm/month. Nevertheless, displacements occurring parallel to the satellite track were largely underestimated. In this latter case, the PS-MTI technique might also have problems in the precise detection of points moving with velocities below 3.5 cm/year in the LOS, as found by [PERSON] et al. (2017). The limitations of PS-MTI regarding the ability to monitor high velocities of ground displacements strongly affected this study. For the most active part of the Corvara landslide, no PS-MTI results could be obtained. Additional problems arose for points that experienced large and sudden displacements (i.e., in relation to the used wavelength and the revisit time of the satellite) in short periods. Some improvements with respect to these issues can be expected in the near future as the monitoring system is currently being overhauled to be able to be used with the Sentine-1 constellation characterized by longer C-band wavelength and a short revisiting time of six days ([PERSON], 2016). A possible complementary strategy to correctly detect these displacements could certainly be the so-called Imaging Geodesy (IG), exploiting the amplitude instead of (or jointly with) phase of the SAR data, as more powerful and accurate as higher resolution imagery is used ([PERSON], 2016; [PERSON], 2017; [PERSON], 2018; [PERSON], 2019). The limitation regarding the orientation of movements excludes some areas from PS-MTI monitoring in Corvara, and information on geomorphological process activity could only be derived by using other monitoring techniques, e.g., UAV-based photogrammetric study ([PERSON], 2016) may be complemented by the already mentioned low-cost GNSS receivers on the ground. The limitation regarding the direction of movement could at least partly be overcome by using both ascending and descending SAR imagery. However, this would also require the presence of scatterers (i.e., additional CRs in the case of the Corvara landslide) that reflect into opposite directions. Another method is Offset Tracking (OT) based on SAR amplitude data. This represents a good complementary approach to MTI for a more complete utilization of SAR data as OT is not only able to measure displacements in north-south direction but can also be applied to faster ground displacement; however, only with a comparably low spatial accuracy and only in X and Y direction. This technique was already effectively applied for glaciers surface velocity field monitoring, and it could be useful at least to monitor the fastest zone of the landslide ([PERSON] et al., 2016; [PERSON], 2016; [PERSON], 2016; [PERSON], 2016). A preliminary application of OT to the Corvara landslide presenting its spatial accuracy limits is given in [PERSON] et al. (2016). Overall, the present study was able to give landslide practitioners and stakeholders involved in landslide risk management a better insight into the opportunities and limitations of PS-MTI. PS-MTI processing of SAR data is a time-consuming and complex procedure and requires substantial expertiseand experience. For most public administration offices, carrying out the analyses in-house will not be an option but they need service-providers for processing and providing the results. To be able to adequately assess the hazard conditions, end-users of landslide monitoring, e.g., planning departments, geological offices or civil protection agencies, have specific demands towards landslide monitoring data. These are in particular related to the quality and reliability of the data, as well as the frequency and timeliness of their delivery.