Preliminary results of the computation of the new Italian Permanent Network RDN of GPS Stations

摘要

We present preliminary results of the adjustment of Rete Dinamica Nazionale (RDN), a new reference frame for Italy defined by the coordinates of 100 permanent GPS stations. The network includes 21 Italian stations included in the EUREF Permanent Network (EPN) and 6 EPN stations in neighbouring countries. Fourteen stations are included in the ITRF2005 (International Terrestrial Reference Frame 2005) solution. The time span of the data processing covers the GPS weeks 1459 to 1462, and the reference epoch is 2008.0. The processing of the 28 daily sessions was done with the Bernese 5.0 software (Dach et al., 2007) using state of the art models, including absolute antenna Phase Center Variations (PCV's). The daily Normal Equations were stacked and minimum constrains (MC) were imposed on the coordinates of nine ITRF2005 reference stations. The ITRF2005 coordinates of the 100 stations have been referred to the ETRF2000 frame using the Helmert parameters adopted at the 2008 EUREF Symposium in Brussels (Boucher and Altamimi, 2008).rnThe procedure of Normal Equations stacking has been repeated by imposing minimum constraints to coordinates of the EPN stations extracted from the weekly SINEX (Software Independent Exchange format) files which are generated as part of the activities of the EPN. We refer to this frame as the IGS05 frame. Two approaches to compute RDN in IGS05 are tested: approach A consists of imposing MC on the IGS05 coordinates of 27 EPN stations which are included in the RDN; approach B consists in stacking on top of the 28 daily Normal Equations the four additional EPN Normal Equations EUR14597.SNX to EUR14627.SNX, and imposing the MC on the same 26 stations used EUREF to tie the weekly EPN solution to the IGS05. We show that the two corresponding coordinate sets (approach A and B) are coincident, within a formal uncertainty smaller than 1 mm. The equivalence between the IGS05 and ITRF2005 base solution is demonstrated by a Helmert comparison between the two coordinate sets.rnWe analyze those ten ITRF2005 stations used in the RDN that are in common with the PDR05 (Potsdam Dresden Reprocessing 2005) solution. We compare the ITRF2005 and IGS05 coordinates on the one hand with their correspondents in the PDR05 at epoch 2008.0 on the other hand, allowing only 3 translations in a Helmert comparison. We find that the PDR05 origin is offset to the IGS05/ITRF2005 by 4.7/3.6, -12.6/-11.2 and 1.3/1.3 mm in the x, y and z direction respectively, with a formal uncertainty of 0.7 mm. This is equivalent to a bias in the east direction of -13.3 mm for IGS05 and -12.6 mm for ITRF2005. This systematic offset is certainly non negligible.rnWe conclude by estimating the lifetime of the RDN coordinates, based on the knowledge of the velocity field not accounted for by the ETRF2000 rigid rotation of Eurasia relative to ITRF2005, and which can reach several mm/yr in Southern Italy. We expect that a 3 cm coordinate discrepancy to a frame realized in 2008 can be reached in less than 5 years in the most tectonically active areas, and expect a lifetime of 15-20 years in the more stable areas in North West Italy.