## 4 Results  
By exploiting the GPOD-SBAS, we obtained mean deformation velocity maps and displacement time series for the VDA regional territory, covering a time interval of more than 4 years (ERS-1/2) and of more than 6 years (ASAR-Envisat), respectively (see also Figure S1). Table 2 summarizes the testing activity done to perform the iterative procedure implemented for the high mountain region, operating on the Envisat dataset, and later directly applied to the ERS-1/2 dataset. All of the processed tasks were successfully completed by the unsupervised GPOD-SBAS service in less than 24 h. Depending on the SAR images considered, and on the processing parameters applied, we obtained a different amount of coherent targets (see Table 2). In Figure 5, we show the distribution of coherent targets subdivided according to slope class, obtained by the slope calculation from a DTM with 10 m square grid spacing for each processed task of the Envisat datasets. We note that, for all the datasets, we have a general increase in the number of coherent targets for all slope classes. In the first task T1, the prevalent distribution corresponds to the lowest degree slope (0\({}^{\circ}\)-20\({}^{\circ}\)), coincident to the most urbanized areas, corresponding to the most coherent sectors. On the contrary, on the high to very high classes (40\({}^{\circ}\)-60\({}^{\circ}\) and >60\({}^{\circ}\)), we note a general lack of target distribution. However, the number of targets obtained in T4 is as large as one order of magnitude with respect to T1.  
In Figures 6 and 7, we present the best results obtained for both Envisat (ascending and descending orbits) and ERS (ascending orbit) datasets (see also Figure S1). Coherent targets are mainly located at the main valley bottom, where urbanized areas (e.g., streets, railway, main towns, hamlets, and isolated building) are located. Within the observed period, LOS velocities in these areas are rather small, ranging from about \(\pm\)0.2 cm/year and comparable between Envisat and ERS processes, confirming an overall ground stability. Relative to the ERS-1/2 dataset, directly processed on the basis of the results achieved with the Envisat analysis, a significantly lower data coverage respect to the Envisat resulted, presenting a total amount of targets of 8574. As expected from the SAR visibility analysis performed (see Figure 2), coherent target distribution is mainly on east-facing slopes, in ascending orbit, and on west-facing slopes, in descending orbit. Moreover, in the valleys, targets are mainly localized in hamlets and villages, as well as in areas of little or no vegetation (e.g., tal From the comparison between the GPOD-SBAS process results and the known distribution of the VDA gravitational process considered in this work, we notice that, in correspondence to glaciated sectors, a decorrelation effect due to their large displacement, and a consequently total absence of targets, was revealed.  
Figure 5: Graph of the number of targets of each dataset available for the Envisat satellite for each task processed. The targets are subdivided and classified with respect four slope classes, based on the slope calculation of the VDA region.  
Figure 6: Surface velocities measured along the satellite LOS for the Envisat dataset: (**a**) in ascending orbit for the time period from June 2004 to October 2010 and (**b**) in descending orbit for the time period from September 2004 to October 2010. The **light blue** polygons correspond to the present glaciers.