The activities of extraction/storage of hydrocarbons and re-injection of fluids underground can induce surface deformation. Through geodetic satellite monitoring (DInSAR), it is possible to measure the trends over time of ground displacements with an accuracy of one centimetre, and in some cases even a few millimetres, on spatially extensive areas (from tens to tens of thousands of square kilometres). The ability to measure the deformations of the ground over large areas compared with the size of the deposit and above all to follow their temporal evolution allows highlighting any variations associated with the storage activities with respect to the pre-existing deformation scenario.
The Global Navigation Satellite System (English acronym GNSS) is a system for geo-radiolocation and navigation on land, sea or air, using a network of artificial satellites in orbit and pseudolites.
The geolocation systems provide a geo-spatial positioning service with global coverage that allows small, purpose-built, electronic receivers to determine their geographical coordinates (longitude, latitude and elevation or altitude) at any point on the Earth's surface or in the atmosphere with an error of a few metres (and up to millimetres in precise realizations such as permanent stations for geodetic use), by processing radiofrequency signals transmitted in the line of sight by such satellites.
DInSAR data are measurements of the deformation of the Earth's surface (expressed in centimetres or millimetres) obtained using radar data acquired by satellite. In particular, we use image sequences obtained using systems called SAR (synthetic aperture radar) acquired in a certain time interval by one or more satellites in an area of interest; through processing techniques called DInSAR (differential interferometry SAR), we obtain maps of the ground deformation in the area of interest, and for each point on these maps, we determine the evolution of the deformation in the time interval considered (i.e., how the deformation varies over time).
The DInSAR analysis natively generates measurements of the ground deformation projected along the line of sight (LOS) of the sensor, which, in fact, "looks" at the globe not perpendicularly but at a certain angle. Taking advantage, however, of the fact that the sensors acquire data by covering both ascending orbits (i.e., moving from south to north) and descending orbits (moving from north to south), it is possible to combine the DInSAR results of the analysis performed for the different orbits and obtain the measurements of the vertical and east-west components of the ground movements.
In particular, the maps of average terrain deformation velocity generated by the DInSAR analysis of the Cornegliano Laudense area are geocoded maps; therefore, they can be superimposed on existing maps of the area and are represented in false colours, which correspond to the displacements of the ground. Usually, green represents stable zones (which do not deform over time), yellow and red indicate subsidence zones, and light blue and blue mark uplifted zones.