## 4 Discussions  
The ACD/CCD results clearly reveal the different capabilities of sensors with different resolutions and acquisition geometries to perform single-building damage mapping after earthquakes. As we can see from Figures 4 and 6, COSMO-SkyMed Spotlight images allowed very detailed single-building damage mapping. In Figure 5C, the yellow pixels represent the line-of-sight (LOS) visible front of the building that is now collapsed, while the blue pixels represent the shadowed-in-LOS portion of the church that is now covered by backscattering debris. In Figure 5D, the CCD method achieved a perimeter of the shape of the collapsed structure with a high precision. Additionally, the COSMO-SkyMed StripMap  
Figure 7: Extracts of two portions of the ancient walls of Norcia [source: Google maps in (**A**,**B**)]. (**A**,**C**,**E**) show the locations and ACD results of the northwestern sector of the walls. (**B**,**D**,**F**) show the locations and ACD results of the eastern sector of the walls. ACD results (Figure 5E) showed an adequate capability of mapping the collapsed building, though with less detail than that obtained with Spotlight (Figure 6). On the other hand, the Sentinel-1 ACD results (Figure 5F) did not allow single-building damage mapping to be achieved because of the relatively poor geometric resolution of the sensors. In this study, the pros and the cons of the three analyzed datasets are deepened as follows; COSMO-SkyMed was designed for both civil and military purposes. In its nominal configuration, the constellation can guarantee a 12-h revisit time (in emergency conditions) for 100% of the Earth's surface. With the aim of creating a regularly updated interferometric archive according to the specific needs of the Italian Civil Protection Department, the ASI activated the \"MapItaly project\" in 2009. Thanks to this project, historical image series were acquired over the whole Italian territory based on 16-day, 40 \(\times\) 40-km-swath StripMap acquisitions obtained in double-orbital geometry. On the other hand, Spotlight COSMO-SkyMed was not planned as a \"background mission\" acquisition in Italy. This implies that there is no already-acquired pre-event radar map of the territory, but image collection is instead planned on demand or for specific purposes. The ascending and the descending acquisition geometries that are available for StripMap data have proven to be fundamental for obtaining the information of villages, structures, and infrastructures in complex topographic environments, as demonstrated by the results obtained for Castelluccio village. In contrast with the Norcia village results, we can see how the radar images in Castelluccio were affected by typical foreshortening and layover geometric distortions [13], affecting the visibility of the village. Specifically, the east-facing portion of the village was visible under descending geometry, while the west-facing portion was affected by foreshortening under this condition (Figure 4B). In contrast, under ascending geometry, we could map and detect damage to the west-facing portion of the village (Figure 4A). In such a scenario, if a single orbital geometry had been used to map damaged areas, incomplete information would have been provided to emergency units. By comparing the ACD and the CCD results obtained for the same satellite mission, we can see how both processing methodologies can be effectively applied for damage-mapping purposes with comparable results (Figures 4 and 5). Since CCD is related to phase variations, it is worth mentioning that the satellite revisit time plays a key role in the results. The greater the time span between the image pair, the lower the effectiveness of the approach because of the temporal decorrelation of the InSAR coherence [30]. In contrast, the ACD method is less affected by the temporal decorrelation effect than the CCD method. The Spotlight images were also proven to be effective in mapping EQtLs, which--in several cases--are the main causes of routes interruptions.