## 3 Methods  
### Satellite Radar Interferometric Dataset  
Monitoring of ground deformation at Campi Flegrei volcanic caldera (Figure 2) has been carried out through ground-based topographic leveling networks since 1905 [71]. Since the 2000s, this classic geodetic system has been integrated with a permanent Global Positioning System (GPS) monitoring network on land [83, 84].  
In the last decade, MT-InSAR has become a powerful technique for measuring slow ground deformation movements occurring in a range of dynamic processes, including volcanism and volcano-tectonics processes [85, 86, 87]. The MT-InSAR technique provides very accurate, unidimensional, millimetric measurements of ground movements along the line of sight (LOS), which is the straight line between the radar sensor and the target [88, 89]. Due to its capability to accurately monitor slow deformation processes, the use of MT-InSAR in monitoring ground deformation has been widely applied in areas of volcanic risk [90, 91], as for example at Ischia and La Palma volcanic islands [92, 93].  
Several differential inteferometric SAR techniques have already been used for analyzing the spatial distribution of recent ground deformation in Campi Flegrei volcanic area, exploiting the C-band sensors onboard ERS (from 1992 to 2001), ENVISAT (from 2002 to 2010), and RADARSAT (from 2003 to 2007) satellites in several papers [78, 87, 94, 95].  
In this paper, vertical ground deformation movements (VGDMs) were assessed during the Jan. 2016-Dec. 2021 interval by analyzing European Ground Motion Service (EGMS) data in vertical and horizontal polarizations available for the Campi Flegrei area. The EGMS is implemented by the European Space Agency processing Synthetic Aperture Radar (SAR) images of Sentinel-1 satellites' constellation [96, 97] to provide Advanced Differential Interferometric SAR (A-DInSAR) data over the main part of the European territory since 2015 ([[https://land.copernicus.eu/en/products/european-ground-motion-service](https://land.copernicus.eu/en/products/european-ground-motion-service)]([https://land.copernicus.eu/en/products/european-ground-motion-service](https://land.copernicus.eu/en/products/european-ground-motion-service)), accessed on 28 November 2024). This service processes average velocities and deformation time series, derived by both persistent scatterer [98] and distributed scatterer [99, 100] techniques. The EGMS provides data at full resolution (20 by 5 m) in the locally referenced satellite LOS (the basic product) or the globally referenced GNNS (the calibrated product) and, finally, two Orho datasets by combining DInSAR displacement calibrated data of ascending and descending orbits resampled to a 100 m grid. One of the layers is a purely vertical displacement (EGMS Ortho Vertical), while the other is a purely east-west horizontal displacement (EGMS Ortho East/West) in a final resolution of 100 by 100 m. These datasets (Table 1) were downloaded and imported into a Geographic Information System (GIS) by using ArcGIS Pro software, version 2.3.1, produced by ESRI ([[https://www.esri.com/en-us/arcgis/products/arcgis-pro/overview](https://www.esri.com/en-us/arcgis/products/arcgis-pro/overview)]([https://www.esri.com/en-us/arcgis/products/arcgis-pro/overview](https://www.esri.com/en-us/arcgis/products/arcgis-pro/overview)), accessed on 28 November 2024) to identify the places with active ground deformation process in the Campi Flegrei area.