Indirect approach to invariant point determination for SLR and VLBI systems: an assessment |
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Authors: | John Dawson Pierguido Sarti Gary M Johnston Luca Vittuari |
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Institution: | (1) Geoscience Australia, Cnr Jerrabomberra Ave and Hindmarsh Drive, GPO Box 378, Canberra, ACT, 2601, Australia;(2) Present address: Research School of Earth Sciences, The Australian National University, Canberra, ACT, Australia;(3) Istituto di Radioastronomia (IRA), Istituto Nazionale di Astrofisica (INAF), Via P. Gobetti N.101, Bologna, 40129, Italy;(4) Geoscience Australia, Cnr Jerrabomberra Ave and Hindmarsh Drive, GPO Box 378, Canberra, ACT, 2601, Australia;(5) Dipartimento di Ingegneria delle Strutture, dei Trasporti, delle Acque, del Rilevamento, del Territorio, Università Bologna, V.le Risorgimento 2, Bologna, 40136, Italy |
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Abstract: | We assess the accuracy of some indirect approaches to invariant point (IVP), or system reference point, determination of satellite
laser ranging (SLR) and very long baseline interferometry (VLBI) systems using both observed and simulated survey data sets.
Indirect IVP determination involves the observation of targets located on these systems during specific rotational sequences
and by application of geometrical models that describe the target motion during these sequences. Of concern is that most SLR
and VLBI systems have limited rotational freedom thereby placing constraint on the reliability of parameter estimation, including
the IVP position. We assess two current approaches to IVP analysis using survey data observed at the Yarragadee (Australia)
SLR and the Medicina (Italy) VLBI sites and also simulated data of a large rotationally constrained (azimuth-elevation) VLBI
system. To improve reliability we introduce and assess some new geometric conditions, including inter-axis, inter-circle and
inter-target conditions, to existing IVP analysis strategies. The error component of a local tie specifically associated with
the indirect determination of SLR and VLBI IVP is less than 0.5 mm. For systems with significant rotational limits we find
that the inter-axis and inter-circle conditions are critical to the computation of unbiased IVP coordinates at the sub-millimetre
level. When the inter-axis and inter-circle geometric conditions are not imposed, we retrieve biased vertical coordinates
of the IVP (in our simulated VLBI system) in the range of 1.2–3.4 mm. Using the new geometric conditions we also find that
the axis-offset estimates can be recovered at the sub- millimetre accuracy (0.5 mm). |
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Keywords: | Local tie Indirect method Invariant point (IVP) SLR VLBI |
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