## 5 Discussion  
We have shown that the GPOD-SBAS service may allow for the revelation of information about the ground displacements occurring in difficult environments such as high mountain regions. The GPOD-SBAS service, which is a completely free web-tool, operating on a grid infrastructure, supplies the resources to process an enormous amount of data through the distribution of computing environments via the Parallel-SBAS (P-SBAS) technique [52]. The web-tool operates in an unsupervised manner, processing the P-SBAS chain step-by-step: (i) raw data focusing; (ii) SAR image co-registration: (iii) interferogram generation; (iv) the unwrapping of the computed phases; (v) the generation of the final results. However, in most cases all over the world, the unsupervised manner is not sufficient. For this reason, in order to maximize the number of coherent targets and their distribution over those areas, a number of best practices have to be performed. First, geomorphological and meteo-climatic settings of the study area have to be carefully considered. High topography gradients and complex orography, the predominance of abundant vegetation (e.g., forested areas), and unsuitable valley flank orientation are recognized as challenging environments for DInSAR techniques. The computation of the R-Index [43], considering the satellite's acquisition geometries to analyze the potential distribution of the targets, is important preliminary information. In our example, the prevalent distribution has been observed not only on the south-facing slope in the ERS and Envisat ascending orbits and on the north-facing slope for the descending orbits, for the east-west oriented valleys, but also on the east-facing slope in the ascending orbits and on the west-facing slope in the descending orbits, for the north-south oriented valleys. Moreover, our results have shown the importance of a day-by-day analysis of the meteo-climatic parameters in correspondence to the satellite acquisition epoch, removing the SAR acquisitions affected by snow, causing temporal decorrelation effects. It is worth noting that the crosscheck of the local information obtained by the weather stations parameters available, with the large-scale information provided by the interferograms elaborated by the GPOD-SBAS service, has been crucial. In addition, by fine-tuning the advanced parameters of the GPOD-SBAS service, we have additionally improved the number of coherent targets and their distribution over the study area (Table 2). In particular, we have proved that of the parameter \"coherent threshold,\" which influences the spatial network of the pixels to be unwrapped, mountainous environments have to be increased with respect to the default values, and only very high-quality targets guarantee a significant improvement in the PhU operation. Our study allowed for the obtainment of ground deformation  
Figure 11: Mean deformation velocity map of La Clapey Gerbioz relict rock glacier for (**a**) Envisat ascending orbit and (**b**) descending orbit. maps and the associated time series of ERS-1/2 and ASAR-Envisat data, over the entire VDA territory, for the time period respectively from June 1995 to May 2000 and from June 2004 to October 2010. The comparison of the results obtained for the VDA region to the regional inventory including glaciers, rock glaciers, and DsGSDs shows good general agreement describing the deformation processes of already known phenomena. On glaciers, no displacement has been retrieved due to decorrelation effects caused by their fast evolution. On rock glaciers, a general lack of targets has been observed, limiting the deformation degree establishment (e.g., active, inactive, and relict). In general, an increment in LOS deformation during summer and mid-autumn could be revealed for the intact rock glaciers, while for the relict rock glaciers a slight LOS displacement has been detected, despite the absence of ice within.