Analysis of InSAR datasets from the EGMS and Veneto region using ground-based GNSS velocities for the monitoring of land subsidence in the Po river delta (Italy)

Global navigation satellite system (GNSS) and interferometric synthetic aperture radar (InSAR) are used in the monitoring of structures, infrastructures and ground deformations. In many cases satellite data are calibrated and validated using ground-based information. In this context, the increasing number of sensors, fixed on structures or mounted on satellites, that permanently and automatically acquire information, are generating large open datasets used by many researchers in many different fields and for many different applications. Calibration, validation, and evaluation of the performance and quality of these large datasets will pose a real challenge in the coming years. An example is given by the open InSAR data available from the European ground motion service (EGMS) of the Copernicus program and Veneto Region databases. Few information about the quality of these datasets are often available: not always the data are checked, calibrated, and validated; they may contain outliers, biases, unquantified uncertainties, etc . In this work, interferometric information available from the EGMS dataset (ascending tracks 44 and 117, and descending track 95), and Veneto Region dataset (ascending track 117 and descending track 95), were calibrated and validated using ground-based GNSS data from 3 continuous stations and 46 non-permanent sites (NPS) of the Po delta network (PODELNET); subsequently, the data were integrated to monitor land subsidence in the Po river delta (PRD), located in northern Italy. In this way, this study gave an opportunity to analyse open InSAR datasets by means of reference ground-based information during the period 2018–2022. This is the first study to systematically validate EGMS and Veneto Region InSAR data against a dense GNSS network in the PRD. The results allowed to verify that in the study area the EGMS data do not require a calibration, while for the Veneto Region InSAR velocities the calibration is recommended. The integration of GNSS and InSAR data allowed to extract maps of land subsidence in an integrated monitoring system. The velocities obtained showed increasing values from west to east in the PRD; the maximum values, up to −15 mm/year, were detected along the coastal area, where sea embankments are exposed to increasing risks of instability exacerbated by the rise of sea level caused by climate change.