Virgo GPS network: Survey and data processing

Virgo is an interferometric antenna devoted to the detection of gravitational waves developed by a cooperation between Istituto Nazionale di Fisica Nucleare (INFN - Pisa, Italy) and Centre Nationale de la Recherche Scientifique (CNRS - Orsay, France). This antenna, at present under construction in the Cascina area (Pisa), mainly consists of two rectilinear orthogonal paths about 3 km long in which two laser beams propagate. The interference analysis of these two beams can evidence the presence of gravitational waves. In this framework, it should be highlighted the importance of the definition of a precise (1σ < 1 cm) and reliable fundamental 3-D network for the construction of Virgo. To achieve this goal it is very useful to work independently from the local anomalous gravity field, so that the GPS technique was used. This paper shows how this network was designed and surveyed and the data processing developed. The precision and reliability achieved meet the stated requirements, although high electromagnetic noise damaged the L2 carrier phase.