Local effects of redundant terrestrial and GPS-based tie vectors in ITRF-like combinations |
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Authors: | Claudio Abbondanza Zuheir Altamimi Pierguido Sarti Monia Negusini Luca Vittuari |
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Institution: | 1.Istituto di Radioastronomia (IRA), Istituto Nazionale di Astrofisica (INAF),Bologna,Italy;2.Institut Géographique National (IGN), Ecole Nationale des Sciences Géographiques (ENSG),Marne-la-Vallée Cedex 2, Paris,France;3.DISTART, Area Geodesia e Topografia,Universitá di Bologna,Bologna,Italy |
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Abstract: | Tie vectors (TVs) between co-located space geodetic instruments are essential for combining terrestrial reference frames (TRFs)
realised using different techniques. They provide relative positioning between instrumental reference points (RPs) which are
part of a global geodetic network such as the international terrestrial reference frame (ITRF). This paper gathers the set
of very long baseline interferometry (VLBI)–global positioning system (GPS) local ties performed at the observatory of Medicina
(Northern Italy) during the years 2001–2006 and discusses some important aspects related to the usage of co-location ties
in the combinations of TRFs. Two measurement approaches of local survey are considered here: a GPS-based approach and a classical
approach based on terrestrial observations (i.e. angles, distances and height differences). The behaviour of terrestrial local
ties, which routinely join combinations of space geodetic solutions, is compared to that of GPS-based local ties. In particular,
we have performed and analysed different combinations of satellite laser ranging (SLR), VLBI and GPS long term solutions in
order to (i) evaluate the local effects of the insertion of the series of TVs computed at Medicina, (ii) investigate the consistency
of GPS-based TVs with respect to space geodetic solutions, (iii) discuss the effects of an imprecise alignment of TVs from
a local to a global reference frame. Results of ITRF-like combinations show that terrestrial TVs originate the smallest residuals
in all the three components. In most cases, GPS-based TVs fit space geodetic solutions very well, especially in the horizontal
components (N, E). On the contrary, the estimation of the VLBI RP Up component through GPS technique appears to be awkward,
since the corresponding post fit residuals are considerably larger. Besides, combination tests including multi-temporal TVs
display local effects of residual redistribution, when compared to those solutions where Medicina TVs are added one at a time.
Finally, the combination of TRFs turns out to be sensitive to the orientation of the local tie into the global frame. |
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