On Removing Discrepancies Between Local Ties and GPS-Based Coordinates
Local ties are vectors that link reference points of different space geodetic instruments at co-located stations. Discrepancies between local ties and solutions from space geodetic techniques weaken the determination of reference frames. Terrestrially determined local ties and GPS-derived coordinates differences can disagree at the cm-level due to suboptimal GPS processing.
In this paper, we propose a post-processing correction strategy to reduce apparent height differences which occur when, unnecessarily, tropospheric delay are estimated between co-located stations or tropospheric constraints between co-located stations are not taken into account. A site-dependent correction factor is determined which stays constant over time and thus can be calibrated. The correction strategy is successfully applied to co-located stations in the pillar network of our institute where the local tie is well-controlled. We find that height discrepancies between levelling survey and post-processed GPS results can be reduced from the centimeter-level to some millimeters. This holds also true for co-located GPS stations of the EUREF Permanent Network.
KeywordsGPS Local ties Tropospheric delay
We gratefully acknowledge funding from the European Metrology Research Program (EMRP). The EMRP is jointly funded by the EMRP participating countries within EURAMET and the European Union. We further thank the IGS and CODE for its products and the station operators for providing the GPS data used in the analyses and their support on the local tie information. The comments of the three anonymous reviewers helped to improve the text.
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