Seit November 2012 existiert die neugegründete VLBI (Very Long Baseline Interferometry) Arbeitsgr... more Seit November 2012 existiert die neugegründete VLBI (Very Long Baseline Interferometry) Arbeitsgruppe am Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum (GFZ), die sich speziell der Thematik „Anwendungen der VLBI im Weltraum“ und ihren verschiedenen Problemstellungen widmet. Mit der VLBI können alle fünf Erdorientierungsparameter (EOP) gemessen werden, die für die Transformation zwischen dem erdfesten (TRF) und dem himmelfesten Referenzrahmen (CRF) benötigt werden, wobei VLBI das einzige geodätische Weltraumverfahren ist, das die Bestimmung von Präzession/Nutation und Weltzeit (UT1) über längere Zeiträume erlaubt. Der Forschungsschwerpunkt der VLBI-Gruppe am GFZ liegt auf der Beobachtung von künstlichen Radioquellen wie Satelliten oder Raumsonden mit VLBI-Radioteleskopen. Dies erfordert technische sowie modellseitige Anpassungen und Erweiterungen. Die abwechselnde Beobachtung von GNSS Satelliten und extragalaktischen Radioquellen ermöglicht die Verknüpfung von GNSS und VLBI...
International Association of Geodesy Symposia, 2015
Earth Orientation Parameters (EOP) provide the rotation of the International Terrestrial Referenc... more Earth Orientation Parameters (EOP) provide the rotation of the International Terrestrial Reference System (ITRS) to the Geocentric Celestial Reference System (GCRS) as a function of time. When estimating a Celestial Reference Frame (CRF) usually a number of radio sources with a long history of observations and stable positions are included in the datum used to define the orientation of the frame. How many and which radio sources are taken into account for the datum definition has a significant effect on the estimated EOP. In this study we analyze the effects of different options for the celestial datum definition on the precision of the EOP and on the agreement w.r.t the last realization of the International Celestial Reference Frame (ICRF2; Fey et al., The second realization of the international celestial reference frame by very long baseline interferometry, Presented on behalf of the IERS/IVS working group (IERS Technical Note No. 35), Frankfurt am Main: Verlag des Bundesamts fur Kartographie und Geodasie, p 204, ISBN 3-89888-918-6, 2009). The resulting EOP of the special VLBI session IYA09 are compared to the C04 08 EOP series (Bizouard and Gambis, The combined solution C04 for Earth orientation parameters consistent with international terrestrial reference frame 2008, IERS Notice 2011, ftp://hpiers.obspm.fr/iers/eop/eopc04/C04.guide.pdf, 2011). The analysis shows that the smallest uncertainties for EOP are achieved when the maximum number of defining sources is chosen for the datum. Comparing with a typical VLBI session, the precision of the EOP and the agreement of the axes w.r.t. ICRF2 could be improved if more defining sources, especially in the southern hemisphere, were considered.
High resolution Earth Rotation Parameter time series are derived from VLBI and GNSS observation d... more High resolution Earth Rotation Parameter time series are derived from VLBI and GNSS observation data for a period of four months (Jul. 3^rd - Oct. 29^th, 2005). Earth Rotation Parameters (ERP), i.e. polar motion and lod are computed from GPS observation data with hourly resolution using the Bernese GPS Software. For this purpose a subset of 79 fairly stable stations out of the IGb00 reference frame sites were selected. To gather a comparable time series from VLBI data routine VLBI campaigns as well as the continuous observation campaign CONT05 are processed by means of the OCCAM software. All computations are performed with respect to the IAU2000 nutation model. Both software packages allow to choose between two different a priori models for the effect of oceanic tides on polar motion and lod/dUT1 - the Ray model and the Eanes model (according to IERS Conventions 1996 and 2003, respectively). In order to analyze the resulting residuals to the specific model we generate two separate ...
ABSTRACT Love and Shida numbers are proportionality factors characterizing the deformation of the... more ABSTRACT Love and Shida numbers are proportionality factors characterizing the deformation of the anelastic Earth which arises as a response to external forces from the Moon and Sun. The increasing precision and quality of the Very Long Baseline Interferometry (VLBI) measurements allow determining those parameters. In particular, the long history of the VLBI data enables the estimation of Love and Shida numbers at the low frequencies of the tidal waves including the periods from 14 days to 18.6 years. In this study we analyse 27 years of VLBI measurements (1984.0 - 2011.0) following the recent IERS Conventions 2010. In several global solutions, we estimate the complex Love and Shida numbers of the solid Earth tides for the main long-period tidal waves. Furthermore, we determine the Love and Shida numbers of the rotational deformation due to polar motion, the so-called pole tide. We also focus on station displacement where still some deficiencies in the long-period signal modelling can be seen.
ABSTRACT VLBI provides a consistent set of group delay and meteorological observations for more t... more ABSTRACT VLBI provides a consistent set of group delay and meteorological observations for more then twenty years at some stations. Hence VLBI tropospheric estimates could play an important role for climate studies. To detect changes in the water vapor content of the troposphere the long-term characteristics of wet zenith delays (WZD) are investigated, which depend on various parameters. A re-analysis of all VLBI sessions with systematically varying analysis options was performed at the IGG, to understand the sources of influence on the trends of tropospheric parameters. The choice of the terrestrial reference frame (TRF), its treatment in the estimation process, different mapping functions, and cutoff elevation angles are considered in this study.
ABSTRACT Since January 2002 tropospheric parameters have been combined on a weekly basis at the I... more ABSTRACT Since January 2002 tropospheric parameters have been combined on a weekly basis at the Institute of Geodesy and Geophysics (IGG), Vienna. The results from individual solutions agree within a few mm, but differ in bias and standard deviation. Recently the IVS tropospheric combination was extended by two more contributions, the new axis offsets were considered in the analysis, and a new tropospheric product webpage was set up at the IGG.
ABSTRACT Monte Carlo simulations are carried out at the Institute of Geodesy and Geophysics (IGG)... more ABSTRACT Monte Carlo simulations are carried out at the Institute of Geodesy and Geophysics (IGG), Vienna, and at Goddard Space Flight Center (GSFC), Greenbelt (USA), with the goal to design a new geodetic Very Long Baseline Interferometry (VLBI) system. Influences of the schedule, the network geometry and the main stochastic processes on the geodetic results are investigated. Therefore schedules are prepared with the software package SKED (Vandenberg 1999), and different strategies are applied to produce temporally very dense schedules which are compared in terms of baseline length repeatabilities. For the simulation of VLBI observations a Monte Carlo Simulator was set up which creates artificial observations by randomly simulating wet zenith delay and clock values as well as additive white noise representing the antenna errors. For the simulation at IGG the VLBI analysis software OCCAM (Titov et al. 2004) was adapted. Random walk processes with power spectrum densities of 0.7 and 0.1 psec 2 /sec are used for the simulation of wet zenith delays. The clocks are simulated with Allan Standard Deviations RI Â -14 #PLQ DQG Â -15 @15min and three levels of white noise, 4 psec, 8 psec and, 16 psec, are added to the artificial observations. The variations of the power spectrum densities of the clocks and wet zenith delays, and the application of different white noise levels show clearly that the wet delay is the critical factor for the improvement of the geodetic VLBI system. At GSFC the software CalcSolve is used for the VLBI analysis, therefore a comparison between the software packages OCCAM and CalcSolve was done with simulated data. For further simulations the wet zenith delay was modeled by a turbulence model. This data was provided by Nilsson T. and was added to the simulation work. Different schedules have been run.
In our poster we concentrate on the estimation of nutation offset series from VLBI (Very Long Bas... more In our poster we concentrate on the estimation of nutation offset series from VLBI (Very Long Baseline Interferometry) and nutation rate series from GPS (Global Position System) data for the year 2005. The nutation series are estimated w.r.t. both IAU80 and IAU2000 nutation models. Our work was performed in several steps. Using the OCCAM 6.1 software for VLBI data analysis
Abstract This paper investigates whether in very long base-line interferometry (VLBI) analysis at... more Abstract This paper investigates whether in very long base-line interferometry (VLBI) analysis atmospheric loading cor-rections should be applied a priori at the observation level or whether it is sufficient to correct for atmospheric loading effects a posteriori by adding constant ...
Seit November 2012 existiert die neugegründete VLBI (Very Long Baseline Interferometry) Arbeitsgr... more Seit November 2012 existiert die neugegründete VLBI (Very Long Baseline Interferometry) Arbeitsgruppe am Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum (GFZ), die sich speziell der Thematik „Anwendungen der VLBI im Weltraum“ und ihren verschiedenen Problemstellungen widmet. Mit der VLBI können alle fünf Erdorientierungsparameter (EOP) gemessen werden, die für die Transformation zwischen dem erdfesten (TRF) und dem himmelfesten Referenzrahmen (CRF) benötigt werden, wobei VLBI das einzige geodätische Weltraumverfahren ist, das die Bestimmung von Präzession/Nutation und Weltzeit (UT1) über längere Zeiträume erlaubt. Der Forschungsschwerpunkt der VLBI-Gruppe am GFZ liegt auf der Beobachtung von künstlichen Radioquellen wie Satelliten oder Raumsonden mit VLBI-Radioteleskopen. Dies erfordert technische sowie modellseitige Anpassungen und Erweiterungen. Die abwechselnde Beobachtung von GNSS Satelliten und extragalaktischen Radioquellen ermöglicht die Verknüpfung von GNSS und VLBI...
International Association of Geodesy Symposia, 2015
Earth Orientation Parameters (EOP) provide the rotation of the International Terrestrial Referenc... more Earth Orientation Parameters (EOP) provide the rotation of the International Terrestrial Reference System (ITRS) to the Geocentric Celestial Reference System (GCRS) as a function of time. When estimating a Celestial Reference Frame (CRF) usually a number of radio sources with a long history of observations and stable positions are included in the datum used to define the orientation of the frame. How many and which radio sources are taken into account for the datum definition has a significant effect on the estimated EOP. In this study we analyze the effects of different options for the celestial datum definition on the precision of the EOP and on the agreement w.r.t the last realization of the International Celestial Reference Frame (ICRF2; Fey et al., The second realization of the international celestial reference frame by very long baseline interferometry, Presented on behalf of the IERS/IVS working group (IERS Technical Note No. 35), Frankfurt am Main: Verlag des Bundesamts fur Kartographie und Geodasie, p 204, ISBN 3-89888-918-6, 2009). The resulting EOP of the special VLBI session IYA09 are compared to the C04 08 EOP series (Bizouard and Gambis, The combined solution C04 for Earth orientation parameters consistent with international terrestrial reference frame 2008, IERS Notice 2011, ftp://hpiers.obspm.fr/iers/eop/eopc04/C04.guide.pdf, 2011). The analysis shows that the smallest uncertainties for EOP are achieved when the maximum number of defining sources is chosen for the datum. Comparing with a typical VLBI session, the precision of the EOP and the agreement of the axes w.r.t. ICRF2 could be improved if more defining sources, especially in the southern hemisphere, were considered.
High resolution Earth Rotation Parameter time series are derived from VLBI and GNSS observation d... more High resolution Earth Rotation Parameter time series are derived from VLBI and GNSS observation data for a period of four months (Jul. 3^rd - Oct. 29^th, 2005). Earth Rotation Parameters (ERP), i.e. polar motion and lod are computed from GPS observation data with hourly resolution using the Bernese GPS Software. For this purpose a subset of 79 fairly stable stations out of the IGb00 reference frame sites were selected. To gather a comparable time series from VLBI data routine VLBI campaigns as well as the continuous observation campaign CONT05 are processed by means of the OCCAM software. All computations are performed with respect to the IAU2000 nutation model. Both software packages allow to choose between two different a priori models for the effect of oceanic tides on polar motion and lod/dUT1 - the Ray model and the Eanes model (according to IERS Conventions 1996 and 2003, respectively). In order to analyze the resulting residuals to the specific model we generate two separate ...
ABSTRACT Love and Shida numbers are proportionality factors characterizing the deformation of the... more ABSTRACT Love and Shida numbers are proportionality factors characterizing the deformation of the anelastic Earth which arises as a response to external forces from the Moon and Sun. The increasing precision and quality of the Very Long Baseline Interferometry (VLBI) measurements allow determining those parameters. In particular, the long history of the VLBI data enables the estimation of Love and Shida numbers at the low frequencies of the tidal waves including the periods from 14 days to 18.6 years. In this study we analyse 27 years of VLBI measurements (1984.0 - 2011.0) following the recent IERS Conventions 2010. In several global solutions, we estimate the complex Love and Shida numbers of the solid Earth tides for the main long-period tidal waves. Furthermore, we determine the Love and Shida numbers of the rotational deformation due to polar motion, the so-called pole tide. We also focus on station displacement where still some deficiencies in the long-period signal modelling can be seen.
ABSTRACT VLBI provides a consistent set of group delay and meteorological observations for more t... more ABSTRACT VLBI provides a consistent set of group delay and meteorological observations for more then twenty years at some stations. Hence VLBI tropospheric estimates could play an important role for climate studies. To detect changes in the water vapor content of the troposphere the long-term characteristics of wet zenith delays (WZD) are investigated, which depend on various parameters. A re-analysis of all VLBI sessions with systematically varying analysis options was performed at the IGG, to understand the sources of influence on the trends of tropospheric parameters. The choice of the terrestrial reference frame (TRF), its treatment in the estimation process, different mapping functions, and cutoff elevation angles are considered in this study.
ABSTRACT Since January 2002 tropospheric parameters have been combined on a weekly basis at the I... more ABSTRACT Since January 2002 tropospheric parameters have been combined on a weekly basis at the Institute of Geodesy and Geophysics (IGG), Vienna. The results from individual solutions agree within a few mm, but differ in bias and standard deviation. Recently the IVS tropospheric combination was extended by two more contributions, the new axis offsets were considered in the analysis, and a new tropospheric product webpage was set up at the IGG.
ABSTRACT Monte Carlo simulations are carried out at the Institute of Geodesy and Geophysics (IGG)... more ABSTRACT Monte Carlo simulations are carried out at the Institute of Geodesy and Geophysics (IGG), Vienna, and at Goddard Space Flight Center (GSFC), Greenbelt (USA), with the goal to design a new geodetic Very Long Baseline Interferometry (VLBI) system. Influences of the schedule, the network geometry and the main stochastic processes on the geodetic results are investigated. Therefore schedules are prepared with the software package SKED (Vandenberg 1999), and different strategies are applied to produce temporally very dense schedules which are compared in terms of baseline length repeatabilities. For the simulation of VLBI observations a Monte Carlo Simulator was set up which creates artificial observations by randomly simulating wet zenith delay and clock values as well as additive white noise representing the antenna errors. For the simulation at IGG the VLBI analysis software OCCAM (Titov et al. 2004) was adapted. Random walk processes with power spectrum densities of 0.7 and 0.1 psec 2 /sec are used for the simulation of wet zenith delays. The clocks are simulated with Allan Standard Deviations RI Â -14 #PLQ DQG Â -15 @15min and three levels of white noise, 4 psec, 8 psec and, 16 psec, are added to the artificial observations. The variations of the power spectrum densities of the clocks and wet zenith delays, and the application of different white noise levels show clearly that the wet delay is the critical factor for the improvement of the geodetic VLBI system. At GSFC the software CalcSolve is used for the VLBI analysis, therefore a comparison between the software packages OCCAM and CalcSolve was done with simulated data. For further simulations the wet zenith delay was modeled by a turbulence model. This data was provided by Nilsson T. and was added to the simulation work. Different schedules have been run.
In our poster we concentrate on the estimation of nutation offset series from VLBI (Very Long Bas... more In our poster we concentrate on the estimation of nutation offset series from VLBI (Very Long Baseline Interferometry) and nutation rate series from GPS (Global Position System) data for the year 2005. The nutation series are estimated w.r.t. both IAU80 and IAU2000 nutation models. Our work was performed in several steps. Using the OCCAM 6.1 software for VLBI data analysis
Abstract This paper investigates whether in very long base-line interferometry (VLBI) analysis at... more Abstract This paper investigates whether in very long base-line interferometry (VLBI) analysis atmospheric loading cor-rections should be applied a priori at the observation level or whether it is sufficient to correct for atmospheric loading effects a posteriori by adding constant ...
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Papers by H. Schuh