Subsidence phenomena, as well as landslides and floods, are one of the main geohazards affecting the Tuscany region (central Italy). The monitoring of related ground deformations plays a key role in their management to avoid problems for buildings and infrastructure. In this scenario, Earth observation offers a better solution in terms of costs and benefits than traditional techniques (e.g., GNSS (Global Navigation Satellite System) or levelling networks), especially for wide area applications. In this work, the subsidence-related ground motions in the Firenze–Prato–Pistoia plain were back-investigated to track the evolution of displacement from 2003 to 2017 by means of multi-interferometric analysis of ENVISAT and Sentinel-1 imagery combined with GNSS data. The resulting vertical deformation velocities are aligned to the European Terrestrial Reference System 89 (ETRS89) datum and can be considered real velocity of displacement. The vertical ground deformation maps derived by ENVISAT and Sentinel-1 data, corrected with the GNSS, show how the area affected by subsidence for the period 2003–2010 and the period 2014–2017 evolved. The differences between the two datasets in terms of the extension and velocity values were analysed and then associated with the geological setting of the basin and external factors, e.g., new greenhouses and nurseries. This analysis allowed for reconstructing the evolution of the subsidence for the area of interest showing an increment of ground deformation in the historic centre of Pistoia Town, a decrement of subsidence in the nursery area between Pistoia and Prato cities, and changes in the industrial sector close to Prato.
Global Navigation Satellite System (GNSS) and satellite synthetic aperture radar (SAR) interferometry represent the most important space geodetic techniques usually exploited to measure millimetric ground deformation on earth surface at both local and wide-area scale. SAR images processed with persistent scatterers interferometry (PSI) multitemporal approach lack of an absolute reference datum. In this paper, SAR images are calibrated with data derived from permanent GNSS stations, in order to obtain absolute and more accurate displacement values. The method used to correct PSI with GNSS is based on existing methodologies commonly applied in the geodetic practice of combining crustal and local deformation studies with geospatial statistical analysis. The spatial distribution of vertical terrain deformations and their temporal changes are coherently measured, leading to a fine-scale surface velocity map in the centraleastern Po Plain, Northern Apennines, and Southern Alps in Italy. The results reveal significant subsidence rates on the northwestern Adriatic coast including the Po Delta and the lagoon of Venice, as well as on Bologna and Ferrara cities in agreement with long-term displacement motion values provided by geological data and other previous works performed at local scale. This paper demonstrates the importance and effectiveness in creating a single, unique surface motion map by merging different data sets in which geodesy plays a relevant role in the datum alignment of PSI products before the stacking of the SAR maps.
We present a detailed map of ground movement in Italy derived from the combination of the Global Navigation Satellite System (GNSS) and Satellite Synthetic Aperture Radar (SAR) interferometry. These techniques are two of the most used space geodetic techniques to study Earth surface deformation. The above techniques provide displacements with respect to different components of the ground point position; GNSSs use the geocentric International Terrestrial Reference System 1989 (ITRS89), whereas the satellite SAR interferometry components are identified by the Lines of Sight (LOSs) between a satellite and ground points. Moreover, SAR interferometry is a differential technique, and for that reason, displacements have no absolute reference datum. We performed datum alignment of InSAR products using precise velocity fields derived from GNSS permanent stations. The result is a coherent ground velocity field with detailed boundaries of velocity patterns that provide new information about the complex geodynamics involved on the Italian peninsula and about local movements.
Multi-temporal interferometric Persistent Scatterers Interferometry (PSI) techniques derive from the elaboration of satellite Synthetic Aperture Radar (SAR) images and represent a useful tool to detect ground millimetric movements over wide areas; thanks to noninvasiveness and high accuracy. However, PSI data are relative measurements estimated along the sensor Line Of Sight and referred to a chosen stable motionless reference point, so they lack absolute reference both in time and space. In this work, we propose a methodological procedure that exploits Global Navigation Satellite System (GNSS) data acquired from permanent stations to calibrate and fix relative InSAR results into conventional geodetic reference systems. Mean yearly velocities of PSI radar targets are corrected with GNSS values throughout operative procedures used in geodesy for crustal and local deformation data. The methodology is tested in Ravenna and Ferrara cities on the north-western Adriatic coast within the eastern alluvial plain of Po river (Italy), extensively affected by subsidence with strong spatial and temporal variations. The results reveal high rates of longterm subsidence of the study area and the effectiveness of the presented methodology for producing unique ground deformation maps over wide areas. . ARTICLE HISTORY
A new crustal velocity field for the Alpine Mediterranean area was determined by using a time series spanning 6.5 years of 113 global navigation satellite system (GNSS) permanent stations. This area is characterized by a complex tectonic setting driven by the interaction of Eurasian and African plates. The processing was performed by using a state-of-the-art absolute antenna phase center correction model and by using recomputed precise International GNSS Service orbits, available since April 2014. Thus, a new and more accurate tropospheric mapping function for geodetic applications was adopted. Results provide a new detailed map of the kinematics throughout the entire study area. In some area of the Italian peninsula, such as in the central Apennines, the velocity vector orientation appears rotated with respect to previous results. These discrepancies suggest that the geodynamic setting of this sector of Mediterranean area should be revised in accordance with these new results.
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