## 2 Overview of InSAR Methodology
### Multi-Pass InSAR Techniques for the Retrieval of Surface Displacement Time-Series
A cross-comparison analysis between different SB approaches is provided in [121]. To illustrate the capability of the SBAS methodology, we present the results  
Figure 12: An example describing how SBAS works with two subsets identified by blue and orange dots. Dotted line refers to the actual deformation time-series, red and orange lines refer to the estimated minimum-norm-velocity and minimum-norm phase deformation time-series, respectively. of experiments conducted for three different applications (Figures 13-15). The first investigation concerns the study of urban deformations within the metropolitan area of Istanbul, Turkey. The second experiment is relevant to the Mt. Etna volcano area, Sicily Island, Italy, while the third one pertains to the analysis of landslide deformations in the city of Assisi, Italy. Figure 13 shows the SBAS-DInSAR results achieved over Istanbul by processing 43 TerraSAR-X data (3 m \(\times\) 3 m spatial resolution) collected during the 2010-2012 period. In particular, the produced spatially-dense deformation velocity map and time-series associated to points affected by land subsidence, have been reported, pointing out the relevance of DInSAR techniques as tools for supporting sustainable urban planning and management [122]. Figure 13: SBAS-DInSAR products for Istanbul megacity, Turkey (Adapted with permission from [122], MDPI, 2017). (**a**) Deformation velocity map generated by processing TerraSAR-X data acquired from 2010 to 2012. (**b**) Zoomed view of the deformation velocity map over the Golden Horn heritage district. (**c,d**) Displacement time-series for two SAR points located in Miniaturk and Yenikap areas. Figure 14a-c show the LOS mean deformation velocity maps obtained by processing COSMO-SkyMed, ALOS and ERS/ENVISAT data, respectively, for the north-eastern flank of Mt. Etna volcano, Sicily, which corresponds to the area of the well-known Pernicana Fault [123]. An increased spatial coverage of the COSMO-SkyMed measurements, with respect to the C-band case, is clearly observed. On the other hand, a denser spatial coverage achieved by ALOS data shown in Figure 14b is visible, especially for areas closer to the fault. In this case, the coherence improvement due to the longer L-band wavelength is predominant over the effect of the different spatial resolution. On 3 April 2010, a Mw = 4.3 earthquake occurred in the Pernicana area, thus making this region particularly interesting for a time series analysis. When discontinuous seismic signals are expected, the choice of the SBAS approach is particularly appropriate since no temporal model is required. A comparison of the three datasets regarding their temporal features is shown in Figure 14d-f wherein the time series of the relative displacement across the Pernicana Fault are reported. Figure 14: SBAS-DInSAR products for the Mt. Etna volcano (Italy), during the 2009–2010 period. (**a**) Mean deformation velocity map of the area obtained by using X-band COSMO-SkyMed data. (**b**) Mean deformation velocity map of the same area obtained by using L-band ALOS-1 data. (**c**) Mean deformation velocity map of the same area obtained by using C-band ERS/ENVISAT data. (**d**) COSMO-SkyMed time series of deformations across the Pernicana Fault trace: the plot shows the displacement of the point labelled as a red star in (**a**) with respect to the one marked with a red circle in (**a**). (**e**) Same as (**d**) for ALOS. (**f**) Same as (**d**) for ERS/ENVISAT. The vertical red line identifies the occurrence of the 3 April 2010 M = 4.3 seismic event. (Adapted with permission from [123], Elsevier, 2014). The SBAS-DInSAR technique has been successfully applied also to investigate mass movements, as the Ivancich landslide affecting the city of Assisi, Central Italy. In particular, a dataset of 39 COSMO-SkyMed images collected in the 2009-2012 time interval, along descending orbits with a 3 m \(\times\) 3 m spatial resolution has been used.