## 3 Discussion
### Monitoring and Displacements
In addition, the time series of the displacements by GNSS monitoring were compared with remote sensing assessments to discuss a relationship between the orthogonal component of the displacements by GNSS and the estimated water levels by remote sensing and in situ. During the periods of variations in water level, the time series of the displacements of the central section on the dam crest was able to resolve a small range of variability (\(\pm\)2 mm). Also, it was possible to highlight the different behaviour of the dam deformation versus the reservoir water level during the periods of reservoir emptying and filling (Figure 5). Figure 4: The shift with time of \(\Delta E\), \(\Delta N\), and \(\Delta UP\) solutions is estimated via Bernese 5.0 and NDA (blue and black dots, respectively) at the receivers’ positions BIV01, BIV02, and BIV03. Adapted from [111]. The behaviour of the displacements with water levels and temperature has led a few years later to further research; in [113] quasi-PS (Persistent Scatter) Interferometric SAR, diachronic thermal analysis and optical-based classification techniques were employed to assess both forcing factors and resulting displacements at the top of the dam over one year. Again, beyond Earth Observation images, including Sentinel-1A interferometric images and Landsat 8 thermal images, the GNSS data were essential to proving the concept. Indeed, the results revealed that it is possible to monitor both temperature-periodic forcing factors and the water levels of the dam and the resulting displacements through the combined use of different remotely sensed data (Figure 6). Over the years, UNIPA CORS has also been used for geological and geodynamic monitoring and displacement. In [114], an interesting study was presented in which a team of researchers from several international research organisations analysed a stalactite from a karst cave in north-western Sicily (Italy) that provided the first evidence for numerous marine inundations associated with relative sea-level high-stand during the past Middle Pleistocene Transition. The speleothem is approximately a hundred metres above mean sea level because of quaternary uplift. Three marine hiatuses and a coral overgrowth indicate the age of the final marine ingression, making the speleothem the oldest stalactite with marine hiatuses investigated. By integrating the coral-constrained depth with the geologically constrained uplift rate and making a probabilistic assessment, it was found that the age of the last marine ingression likely corresponds with a marine isotope stage. Figure 5: On the top panel: in situ water levels (light blue, primary axis), with superimposed levels estimated from remote sensing during the emptying and filling periods (green and blue circles, respectively), and GNSS-measured displacements (dark blue, secondary axis). On the lower panels: GNSS displacements (\(d_{s}\), black curve) versus in situ water levels (\(H\), blue curve in the left panel) and versus air temperature (\(\theta\), red curve in the right panel). In this analysis, the orthometric height of the slatactite is determined because of two integrated geodetic survey techniques: GNSS positioning and tacheometric levelling. The static GNSS survey was conducted at several control points near the NRTK over an observation time of 4 h for each point and a 10 km baseline distance. The data were referred to the permanent station of Trapani (TRAP) of the UNIPA NRTK GNSS network. The backward intersection method was used to link the survey inside the cave with the GNSS survey. Another geological and geodynamics study, presented in a recent paper [115], employed a multidisciplinary approach to detect active geological structures with GNSS static analyses, both onshore and offshore, tectonostrigraphic and morphotectonic. The test area was selected between the two cities of Termini Imerese and Palermo (in the Apennine-Maghrebian fold and accommodating the Africa-Europe plate convergence).