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  • 1.
    Bergstrand, Sten
    et al.
    RISE - Research Institutes of Sweden, Safety and Transport, Measurement Science and Technology.
    Herbertsson, Magnus
    RISE - Research Institutes of Sweden, Safety and Transport, Measurement Science and Technology.
    Rieck, Carsten
    RISE - Research Institutes of Sweden, Safety and Transport, Measurement Science and Technology.
    Spetz, Jörgen
    RISE - Research Institutes of Sweden, Safety and Transport, Measurement Science and Technology.
    Svantesson, Claes-Göran
    RISE - Research Institutes of Sweden, Safety and Transport, Measurement Science and Technology.
    Haas, Rüdiger
    Chalmers University of Technology, Sweden.
    A gravitational telescope deformation model for geodetic VLBI2019In: Journal of Geodesy, ISSN 0949-7714, E-ISSN 1432-1394, Vol. 93, no 5, p. 669-680Article in journal (Refereed)
    Abstract [en]

    We have measured the geometric deformations of the Onsala 20 m VLBI telescope utilizing a combination of laser scanner, laser tracker, and electronic distance meters. The data put geometric constraints on the electromagnetic raypath variations inside the telescope. The results show that the propagated distance of the electromagnetic signal inside the telescope differs from the telescope’s focal length variation, and that the deformations alias as a vertical or tropospheric component. We find that for geodetic purposes, structural deformations of the telescope are more important than optic properties, and that for geodetic modelling the variations in raypath centroid rather than focal length should be used. All variations that have been identified as significant in previous studies can be quantified. We derived coefficients to model the gravitational deformation effect on the path length and provide uncertainty intervals for this model. The path length variation due to gravitational deformation of the Onsala 20 m telescope is in the range of 7–11 mm, comparing elevation 0$$^{\circ }$$∘and 90$$^{\circ }$$∘, and can be modelled with an uncertainty of 0.3 mm.

  • 2.
    Bergstrand, Sten
    et al.
    RISE Research Institutes of Sweden, Safety and Transport, Measurement Technology.
    Jarlemark, Per
    RISE Research Institutes of Sweden, Safety and Transport, Measurement Technology.
    Herbertsson, Magnus
    RISE Research Institutes of Sweden, Safety and Transport, Measurement Technology.
    Quantifying errors in GNSS antenna calibrations: Towards in situ phase center corrections2020In: Journal of Geodesy, ISSN 0949-7714, E-ISSN 1432-1394, Vol. 94, no 10, article id 105Article in journal (Refereed)
    Abstract [en]

    We evaluated the performance of GNSS absolute antenna calibrations and its impact on accurate positioning with a new assessment method that combines inter-antenna differentials and laser tracker measurements. We thus separated the calibration method contributions from those attainable by various geometric constraints and produced corrections for the calibrations. We investigated antennas calibrated by two IGS-approved institutions and in the worst case found the calibration’s contribution to the vertical component being in excess of 1 cm on the ionosphere-free frequency combination L3. In relation to nearby objects, we gauge the 1 σ accuracies of our method to determine the antenna phase centers within ±0.38 mm on L1 and within ±0.62 mm on L3, the latter applicable to global frame determinations where atmospheric influence cannot be neglected. In addition to antenna calibration corrections, the results can be used with an equivalent tracker combination to determine the phase centers of as-installed individual receiver antennas at system critical sites to the same level without compromising the permanent installations. © 2020, The Author(s).

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