Geodetic measurements to control a large research infrastructure: The Virgo detector at the European Gravitational Observatory

The Advanced Virgo (AdV) detector is a 3 km long arms Michelson interferometer for gravitational waves detection. The management of a complex and large research infrastructure requires high-precision geodetic surveying for positioning and rearrangement of instruments. This paper describes the establishment of Virgo Reference System (VRS) consisting in a wide-scale high precision geodetic network based on GPS and Total Station measurements, that support the positioning and the alignment of the different elements forming the interferometer. Ground settlement monitoring is strictly required to verify and adapt the interferometer vertical alignment in presence of a steady subsidence process due to infrastructures overloads. The paper describes also the monitoring activity conducted over the years by means of periodic high precision levelling, that was compared with the results with those obtained using differential interferometry based on satellite Synthetic Aperture Radar (SAR) data.