15 Years of the Italian GNSS Geodetic Reference Frame (RDN): Preliminary Analysis and Considerations

In 2011, the IGMI (Istituto Geografico Militare Italiano) defined the new Italian geodetic reference, materialized by the Rete Dinamica Nazionale (RDN), a cluster of 99 GNSS permanent stations located in Italy and, few of them, in neighbouring areas. RDN also includes some IGS and EPN sites, so that it constitutes a densification of those two networks. The official coordinates of the 99 GNSS stations were initially obtained by computing a limited period of 28 days starting from the end of 2007 and aligned to the datum ETRS89-ETRF2000 at epoch 2008.0. After years of continuously acquired data, other studies published the stations’ coordinates together with the associated velocities. This paper presents the updated results of the velocity trends considering the whole dataset now available, consisting of 15 years of data. The analysis considered only the 77 stations that worked consistently for at least five years. The workflow starts with the archive organization and pre-analysis, followed by the geodetic computation using the Precise Point Positioning approach implemented in the GIPSYX software. After the post-processing of the solutions, which included the alignment to the ETRF2000 frame and the analysis of discontinuities, the mean velocities have been computed. The latter were compared to those estimated in a previous work basing on 8 years long dataset. The comparison shows the overall agreement between the linear trends, but also highlights the importance of considering the whole dataset nowadays available to assess the behaviour of those few sites who underwent velocity changes over time.