Monitoring of the Italian GNSS Geodetic Reference Frame

In 2011, Italy established a new geodetic reference system, the European Terrestrial Reference System 1989 (ETRS89), which was based upon the ETRF2000 reference frame at epoch 2008.0. In order to maintain this reference, the IGMI defined a permanent GNSS network within the EPN densification project, known as the “Rete Dinamica Nazionale” (RDN) and composed of 99 tracking stations located in and around Italy. Eight years of data are now available and the aim of this work is to estimate the velocities of the official RDN sites. It was necessary to pre-analyze the data accurately because of the incomplete maintenance of the associated repository. The network was calculated using a PPP approach and applying the GIPSY-OASIS II software package, and the solutions were aligned to ITRS using a customized procedure. After they were transformed into ETRF2000, the time series of the solutions were properly analyzed to find discontinuities and solve jumps caused by earthquakes and instrumental changes. Results highlighted the residual velocities with respect to ETRS89, which can reach 5 mm/year in some areas. The velocity field is shown to be very inhomogeneous, with clusters of sites presenting very different behaviours.