# Potential and Limitations of the New European Ground Motion Service in Landslides at a Local Scale
## 4 Discussion
### Potential and Limitations of the EGMS  
The potential advantages and limitations of the EGMS for detecting and monitoring landslides at a local scale are also evaluated in this research. We can state that the new EGMS proves to be a very useful and fast tool to apply in big and complex slope movements at a local scale. Thus, the main potential advantage of this platform is that the algorithms implemented in the EGMS [50, 63, 64, 65] make it possible to detect and process MP (PS+DS) in both urban and non-urban areas. Also, another potential advantage is the high-resolution  
Figure 7: Conceptual geological cross-section of the La Miera landslide from W to E (see Figure 4), showing the MP detected and the location of Pola de Lena town and Los Campos and La Miera neighborhood. pixel products of levels 2a and 2b [32], which is the Sentinel-1 full resolution; this resolution allows detailed analysis of mass movements at a local scale. In addition, this service is a fast and easy-to-use tool for expert and non-expert users to apply and export in a GIS, where the EGMS products [32] can be cross-referenced with different geospatial layers. We also have proved that the deformation time series from the EGMS can be compared with daily rainfall data, providing accurate information on the role of meteorological conditions as triggering factors of mass movements. Based on the relationship between precipitation and mass movements, rainfall records can be used to validate the deformation records revealed by the EGMS. The combined studies of these data series with the building damage inventory represent the basis for future research into landslide hazards and mass movement risk reduction [66; 67]. The main limitation of the EGMS is the null degree of selection, control, and manipulation of the input parameters for Sentinel-1 A-DInSAR processing. This condition prevents the reprocessing of SAR data in the areas of interest and, therefore, the improvement of the Sentinel-1 A-DInSAR measurements. Moreover, in the case of level 2a, the products refer to a local reference point established during Sentinel-1 processing on a frame-by-frame basis [33; 51]. As a consequence, ground motion measurements are only meaningful within a small subset of the entire product, so it is not possible to compare the deformation of adjacent zones belonging to different processing units of the same level [33; 51]. Regarding the limitations of the EGMS observed in this study, large areas of the landslide could not be monitored because there was no MP. These areas corresponded to the northern and southern sectors and at the foot of the landslide (Figures 2 and 4). Furthermore, in the mapped flow deposits (Figure 4) ground motion could not be quantified (Figure 4), although they showed signs of recent activity (creep phenomena, Figure 4). This is due to the total lack of suitable reflectors and the orientation of these deposits with respect to the satellite orbit. Future research in the La Miera landslide (and therefore in other reactivated landslides), can be addressed to the application of other remote sensing techniques and other A-DInSAR techniques. The first includes the application of remote sensing techniques, such as unmanned aerial vehicle (UAV) photogrammetry [68]; this technique, based on the construction of high-resolution digital elevation models, can identify depletion or accumulation of material, being useful to evaluate geomorphological features and to interpret the failure mechanism and the evolutionary behavior of instability process [69; 70]. The second (other A-DInSAR techniques) could be also applied to corroborate and validate the MP and the velocity rates detected using robust software such as StaMPS version 4.1b1 [71], SPINUA [72], or Ground-Based SAR (GB-SAR) [73]. Also, the application of advanced SAR processing techniques could improve the accuracy of the Sentinel-1 A-DInSAR results by mitigating range ambiguity [74]. An alternative method to overcome the lack of suitable reflectors is to install passive or active corner reflectors.