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  • 1
    Publication Date: 2018-06-06
    Description: The main activities of the VLBI group at the Department of Geodesy and Geoinformation of the Vienna University of Technology were related to the development of the Vienna VLBI Software VieVS (http://vievs.hg.tuwien.ac.at/) and its application for various studies. For example, we dealt with scheduling, satellite tracking, and the estimation of geodynamical and astronomical parameters from VLBI observations. One highlight was the release of VieVS 2.0 just before the third VieVS User Workshop in September 2012.
    Keywords: Geosciences (General)
    Type: International VLBI Service for Geodesy and Astrometry 2012 Annual Report; 325-328; NASA/TP-2013-217511
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  • 2
    Publication Date: 2018-06-06
    Description: Since 2008 the VLBI group at the Institute of Geodesy and Geophysics at TU Vienna has focused on the development of a new VLBI data analysis software called VieVS (Vienna VLBI Software). One part of the program, currently under development, is a unit for parameter estimation in so-called global solutions, where the connection of the single sessions is done by stacking at the normal equation level. We can determine time independent geodynamical parameters such as Love and Shida numbers of the solid Earth tides. Apart from the estimation of the constant nominal values of Love and Shida numbers for the second degree of the tidal potential, it is possible to determine frequency dependent values in the diurnal band together with the resonance frequency of Free Core Nutation. In this paper we show first results obtained from the 24-hour IVS R1 and R4 sessions.
    Keywords: Geophysics
    Type: Proceedings of the Sixth General Meeting of the International VLBI Service for Geodesy and Astrometry; 202-206; NASA/CP-2010-215864
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  • 3
    Publication Date: 2016-11-25
    Description: Abstract
    Description: Very Long Baseline Interferometry (VLBI) is a primary space-geodetic technique for determining precise coordinates on the Earth, for monitoring the variable Earth rotation and orientation with highest precision, and for deriving many other parameters of the Earth system. The International VLBI Service for Geodesy and Astrometry (IVS, http://ivscc.gsfc.nasa.gov/) is a service of the International Association of Geodesy (IAG) and the International Astronomical Union (IAU). The datasets published here are the results of individual Very Long Baseline Interferometry (VLBI) sessions in the form of normal equations in SINEX 2.0 format (http://www.iers.org/IERS/EN/Organization/AnalysisCoordinator/SinexFormat/sinex.html, the SINEX 2.0 description is attached as pdf) provided by IVS as the input for the next release of the International Terrestrial Reference System (ITRF): ITRF2014. This is a new version of the ITRF2008 release (Böckmann et al., 2009). For each session/ file, the normal equation systems contain elements for the coordinate components of all stations having participated in the respective session as well as for the Earth orientation parameters (x-pole, y-pole, UT1 and its time derivatives plus offset to the IAU2006 precession-nutation components dX, dY (https://www.iau.org/static/resolutions/IAU2006_Resol1.pdf). The terrestrial part is free of datum. The data sets are the result of a weighted combination of the input of several IVS Analysis Centers. The IVS contribution for ITRF2014 is described in Bachmann et al (2015), Schuh and Behrend (2012) provide a general overview on the VLBI method, details on the internal data handling can be found at Behrend (2013).
    Keywords: Very Long Baseline Interferometry ; VLBI ; International VLBI Service for Geodesy and Astrometry ; IVS ; International Terrestrial Reference Frame ; ITRF2014 ; Earth Orientation Parameters ; EOP ; precession ; nutations ; Earth rotation ; dUT1 ; length of day ; LOD ; polar motion ; IVS-SINEX-ITRF2014
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  • 4
    Publication Date: 2019-07-12
    Description: This report summarizes the progress made in developing the next generation VLBI system, dubbed the VLBI2010 system. The VLBI2010 Committee of the International VLBI Service for Geodesy and Astrometry (IVS) worked on the design aspects of the new system. The report covers Monte Carlo simulations showing the impact of the new operating modes on the final products. A section on system considerations describes the implications for the VLBI2010 system parameters by considering the new modes and system-related issues such as sensitivity, antenna slew rate, delay measurement error. RF1, frequency requirements, antenna deformation, and source structure corrections_ This is followed by a description of all major subsystems and recommendations for the network, station. and antenna. Then aspects of the feed, polarization processing. calibration, digital back end, and correlator subsystems are covered. A section is dedicated to the NASA. proof-of-concept demonstration. Finally, sections tm operational considerations, on risks and fallback options, and on the next steps complete the report.
    Keywords: Geophysics
    Type: NASA/TM-2009-214180 , 200901964
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  • 5
    Publication Date: 2019-07-12
    Description: This report briefly provides general information and a component description of the recently established IVS Analysis Center at GFZ and outlines the planned activities.
    Keywords: Geophysics
    Type: International VLBI Service for Geodesy and Astrometry 2012 Annual Report; 255-256; NASA/TP-2013-217511
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  • 6
    Publication Date: 2019-07-12
    Description: Very Long Baseline Interferometry (VLBI) Intensives are one-hour single baseline sessions to provide Universal Time (UT1) in near real-time up to a delay of three days if a site is not e-transferring the observational data. Due to the importance of UT1 estimates for the prediction of Earth orientation parameters, as well as any kind of navigation on Earth or in space, there is not only the need to improve the timeliness of the results but also their accuracy. We identify the asymmetry of the tropospheric delays as the major error source, and we provide two strategies to improve the results, in particular of those Intensives which include the station Tsukuba in Japan with its large tropospheric variation. We find an improvement when (1) using ray-traced delays from a numerical weather model, and (2) when estimating tropospheric gradients within the analysis of Intensive sessions. The improvement is shown in terms of reduction of rms of length-of-day estimates w.r.t. those derived from Global Positioning System observations
    Keywords: Geophysics
    Type: Proceedings of the Sixth General Meeting of the International VLBI Service for Geodesy and Astrometry; 251-255; NASA/CP-2010-215864
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  • 7
    Publication Date: 2017-06-08
    Type: http://purl.org/escidoc/metadata/ves/publication-types/paper
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  • 8
    Publication Date: 2014-03-12
    Description: Continuous, very long baseline interferometry (VLBI) campaigns over 2 weeks have been carried out repeatedly, i.e., CONT02 in October 2002, CONT05 in September 2005, CONT08 in August 2008, and CONT11 in September 2011, to demonstrate the highest accuracy the current VLBI was capable at that time. In this study, we have compared zenith total delays (ZTD) and troposphere gradients as consistently estimated from the observations of VLBI, Global Navigation Satellite Systems (GNSS), and Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) at VLBI sites participating in the CONT campaigns. We analyzed the CONT campaigns using the state-of-the-art software following common processing strategies as closely as possible. In parallel, ZTD and gradients were derived from numerical weather models, i.e., from the global European Centre for Medium-Range Weather Forecasts (ECMWF) analysis fields, the High Resolution Limited Area Model (European sites), the Japan Meteorological Agency-Operational Meso-Analysis Field (MANAL, over Japan), and the Cloud Resolving Storm Simulator (Tsukuba, Japan). Finally, zenith wet delays were estimated from the observations of water vapor radiometers (WVR) at sites where the WVR observables are available during the CONT sessions. The best ZTD agreement, interpreted as the smallest standard deviation, was found between GNSS and VLBI techniques to be about 5–6 mm at most of the co-located sites and CONT campaigns. We did not detect any significant improvement in the ZTD agreement between various techniques over time, except for DORIS and MANAL. On the other hand, the agreement and thus the accuracy of the troposphere parameters mainly depend on the amount of humidity in the atmosphere.
    Type: http://purl.org/escidoc/metadata/ves/publication-types/article
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  • 9
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    In:  Acta Geodaetica et Geophysica ; Year: 2013 ; Volume: 48 ; Issue: 4 ; Pages: 389-404
    Publication Date: 2014-01-28
    Description: Since 1990 the International VLBI Service for Geodesy and Astrometry (IVS) has been performing geodetic Very Long Baseline Interferometry (VLBI) observations within the European geodetic VLBI network. In this work, 114 European VLBI sessions from January 1990 to September 2011 are analysed using the Vienna VLBI Software (VieVS). A total of 58 baselines with lengths ranging from 59 m to 4581 km are investigated and the lengths of most of them indicate repeatabilities at the sub-centimetre level. The horizontal station motions which describe the motion of the Eurasian plate are compared to the NUVEL-1A and MORVEL tectonic plate models. Intraplate crustal motions are investigated by estimating the station velocities with respect to Wettzell (Germany), a station on the geodynamically stable part of Eurasia. The northern part of Europe is dominated by the postglacial isostatic rebound, confirmed by four VLBI sites in this region with an uplift from 2.89±0.71 mm/yr (Svetloe, Russia) to 7.23±1.00 mm/yr (Ny-Ålesund, Norway) with respect to the central part of the European plate. Besides the vertical uplift, these radio telescopes evidence a horizontal motion from the centre of the former ice sheet towards its border. In the southern part of Europe the motion of the VLBI sites is caused by the collision of the African plate with the Eurasian plate, while the stations on the stable part of Europe do not present any significant relative motions. Our results are compared against those by Haas et al. (J. Geodyn. 35:391–414, 2003) and with velocities of the current reference frame of the International Global Navigation Satellite Systems Service.
    Type: http://purl.org/escidoc/metadata/ves/publication-types/article
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  • 10
    Publication Date: 2014-01-19
    Description: [1]  Boreal peatlands are a major long-term reservoir of atmospheric carbon (C) and play an important role in the global C cycle. It is unclear how C accumulation in peatlands responds to changing temperatures and nutrients (specifically, nitrogen and sulfur). In this study, we assessed how the C input rate and C accumulation rate in decadal old peat layers respond to increased air temperatures (+3.6 ºC) during the growing season and the annual additions of nitrogen (N) and sulfur (S) (30 and 20 kg ha -1  yr -1 , respectively) over 12 years of field treatments in a boreal mire. An empirical mass-balance model was applied to 210 Pb dated peat cores to evaluate changes in C inputs, C mass-loss and net C accumulation rates in response to the treatments. We found that: i) none of the treatments generated a significant effect on peat mass-loss decay rates, ii) C input rates were positively affected by N additions and negatively affected by S additions, iii) the C accumulation rate in the uppermost (10 to 12 cm) peat was increased by N additions and decreased by S additions, and iv) only air temperature significantly affected the main effects induced by N and S additions. Based on our findings, we argue that C accumulation rates in surface peat layers of nutrient-poor boreal mires can increase despite the predicted rise in air temperatures as long as N loads increase and acid atmospheric S remains low.
    Print ISSN: 0148-0227
    Topics: Biology , Geosciences
    Published by Wiley on behalf of American Geophysical Union (AGU).
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