Combination of long time-series of troposphere zenith delays observed by VLBI |
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Authors: | R Heinkelmann J Boehm H Schuh S Bolotin G Engelhardt D S MacMillan M Negusini E Skurikhina V Tesmer O Titov |
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Institution: | 1. Institute of Geodesy and Geophysics, Vienna University of Technology, Gusshausstr. 27–29, 1040, Vienna, Austria 2. Main Astronomical Observatory, National Academy of Sciences of Ukraine, Akademika Zabolotnoho Str. 27, 03680, Kiev, Ukraine 3. Bundesamt für Kartographie und Geod?sie (BKG), Karl-Rothe-Str. 10–14, 04105, Leipzig, Germany 4. NVI Incorporated and NASA Goddard Space Flight Center (GSFC), Greenbelt, MD, 20771, USA 5. Istituto di Radioastronomia (IRA), Istituto Nazionale di Astrofisica (INAF), Via P. Gobetti 101, 40129, Bologna, Italy 6. Institute of Applied Astronomy (IAA), nab. Kutuzova, 10, St., Petersburg, 191187, Russia 7. Deutsches Geod?tisches Forschungsinstitut (DGFI), Alfons-Goppel-Str. 11, 80539, München, Germany 8. Geoscience Australia, PO Box 378, Canberra, 2601, Australia
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Abstract: | Within the International Very Long Baseline Interferometry (VLBI) Service for Geodesy and Astrometry (IVS), long time-series
of zenith wet and total troposphere delays have been combined at the level of parameter estimates. The data sets were submitted
by eight IVS Analysis Centers (ACs) and cover January 1984 to December 2004. In this paper, the combination method is presented
and the time-series submitted by the eight IVS ACs are compared with each other. The combined zenith delays are compared with
time-series provided by the International Global Navigation Satellite System (GNSS) Service (IGS), and with zenith delays
derived from the European Centre for Medium-Range Weather Forecasts (ECMWF). Before the combination, outliers are eliminated
from the individual time-series using the robust BIBER (bounded influence by standardized residuals) estimator. For each station
and AC, relative weight factors are obtained by variance component estimation. The mean bias of the IVS ACs’ time-series with
respect to the IVS combined time-series is 0.89 mm and the mean root mean square is 7.67 mm. Small differences between stations
and ACs can be found, which are due to the inhomogeneous analysis options, different parameterizations, and different treatment
of missing in-situ pressure records. Compared to the IGS zenith total delays, the combined IVS series show small positive
mean biases and different long-term trends. Zenith wet delays from the ECMWF are used to validate the IVS combined series.
Inconsistencies, e.g., long-term inhomogeneity of the in-situ pressure data used for the determination of VLBI zenith delays,
are identified. |
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Keywords: | Troposphere delays Intra-technique combination VLBI |
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