## 3 InSAR Adopted Tecnique
During the processing the precise orbital files (Envisat case) were used to estimate and remove orbital errors and Ground Control Points (GCPs) were selected, especially along the frame borders (in slant range geometry) and possibly over stable areas, to remove residual ramps. A stable point (under the geological point of view) was chosen as reference point (red star) for the retrieved mean ground velocity maps (Figure 3). Initially, we validated our results comparing the ascending and descending velocity map after shifting the former with respect to the reference point of the latter preventing the subsidence areas. We also validated the Envisat results comparing with the available GPS in the whole SAR frames (Figure 3). Firstly, we projected the GPS velocities onto the ascending and descending SAR LOS respectively then we averaged the InSAR velocities in correspondence of the GPS benchmarks considering a buffer area of 200 meters. The comparison between GPS and InSAR velocities is shown in Figure 3a,b for the ascending and descending tracks. Except for very few GPS benchmarks, the velocities differences are within 1.5 mm/yr, which is the associated error to the multi-temporal SAR outputs. Unfortunately, it has not been possible to perform the same validation method for the CSK results because not enough CGPS are available. However, considering the common similar patterns and trends for both Envisat and CSK ascending and descending retrieved maps, we convinced the good quality of the obtained CSK results. Note that for the CSK processing we focused our study on the Sibari Plain. To this aim, we calculated the East (\(E\)) and Vertical (\(V\)) component solving the following system of equation:  
\[E = \left((u2d/\text{det})\times(Asc-(n2a)\times N))\right)-\left((u2a /\text{det})\times(Dsc-(n2d\times N))\right) \tag{1}\] \[V = \left((-e2a/det)\times(Asc-(n2a)\times N)\right)+\left((e2a/ \text{det})\times(Dsc-(n2d\times N))\right)\] \[\text{where }det=\left((e2d\times u2d)-(u2a\times e2d)\right.\]  
where \(u2d\), \(e2d\), \(n2d\), \(u2a\), \(e2a\) and \(n2a\) are the descending and ascending cosine directors respectively, and Asc and Dsc are the ascending and descending mean velocity maps. Concerning the third condition, we imposed the North equal to the interpolated CGPS one. The final Vertical and East component (Figure 4) result quite sparse, this mainly depends on the difficulty to obtain a large coverage for the ascending and descending velocity maps due to the land cover  
Figure 3: (**a**) Ascending and (**b**) descending line of sight (LOS) ground velocity maps. Red star represents the stable point (stable means that the mean velocity is 0 mm/yr) used as reference point. In the maps are also plotted the GPS benchmarks used during the validation of the Envisat results. The diagrams show the comparison between the LOS Synthetic Aperture Radar (SAR) velocities and GPS. The correlation coefficient is respectively 0.51 and 0.65 for the ascending and descending cases, while the mean squared error is 1.1 mm and 1.2 mm. and agricultural use of the investigated area leading to a fast coherence loss. Moreover, about the East component some overestimated values are present in the North Eastern part probably due to unwrapping errors due to the presence of the mountains. We performed the previous post-processing steps for the full SAR frames and only at a later stage; we focused our analysis and interpretations referring to the East and Vertical component about the Sibari Plain area. Figure 4: Mean deformation velocity components computed from (**a,b**) Envisat and (**b,c**) COSMO-SkyMed dataset. (**a,c**) Vertical velocity component; positive values indicate uplift and negative values subsidence. (**b,d**) East component; positive values indicate eastward displacement and negative values indicate westward displacement. The area covered by COSMO-SkyMed data is represented by inset (1) in the panel a.