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 ...
An overview of the abilities of Very Long Baseline Interferometry (VLBI) to measure the variable ... more An overview of the abilities of Very Long Baseline Interferometry (VLBI) to measure the variable Earth rotation and of the international VLBI collaboration is given. The paper concentrates on the short-period, i.e. subseasonal variations of Earth rotation which can be seen in VLBI measurements of length of day (lod) and polar motion between 1981 and 1999. The wavelet transform allows the time localisation of an irregular quasi-harmonic signal within a given data set. The wavelet analysis of lod series yields in the high-frequency range periods of ∼28 days, ∼14 days down to 6.86 days caused by the lunisolar tides and irregular quasi-periodic variations between 40 and 130 days. These are mainly associated with global zonal wind changes which can be seen when looking on the wavelet cross-scalogram between the lod series and the atmospheric angular momentum (AAM) time series. In polar motion variable periods between two and five months and even down to 7-10 days can be made visible by the wavelet scalograms.Today it is possible by VLBI to determine polar motion and UT1-UTC with a temporal resolution of as short as 3-7 minutes. The results of parallel VLBI sessions which took place since 1998 using two independent VLBI networks were analyzed in the subdiurnal period range and compared by computing the wavelet cross-scalograms, the covariance spectrum and the normed coherency. Periods between 5 and 7 hours can be seen in many of the UT1-UTC data sets besides the well-known diurnal and semi-diurnal periods. The wavelet analyses reveal interesting patterns in the subdiurnal range in polar motion, too.
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.
Love and Shida numbers describe the Earth's response to external forces exerted by celestial bodi... more Love and Shida numbers describe the Earth's response to external forces exerted by celestial bodies due to the elasticity of the Earth. Modern space geodetic techniques, such as VLBI (Very Long Baseline Interferometry), allow the empirical validation of theoretical Love and Shida numbers. In the VLBI analysis software package OCCAM tidal displacements on the Earth's surface are modelled according to the International Earth rotation and Reference systems Service (IERS) Conventions 2003. Snapshots of corrections to the nominal displacements for the complete Earth's surface with a spatial resolution of 1°x1° are shown. Nominal degree-2 Love and Shida numbers, h 2 and l 2 , were determined from the continuous 15 days VLBI campaign CONT05. Frequency dependence was considered in the diurnal band due to the retrograde Free Core Nutation (FCN) resonance: we determined h 2 and l 2 at those diurnal tidal waves with the largest amplitudes, two of them lying very close to the resonance frequency.
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
International Association of Geodesy Symposia, 2007
Over the two weeks of the CONT02 campaign in October 2002 the Earth rotation parameters, ERP (xpo... more Over the two weeks of the CONT02 campaign in October 2002 the Earth rotation parameters, ERP (xpol, ypol, UT1-UTC) were determined with a resolution of one hour by VLBI and also by GPS. Analyses of these two very precise polar motion and UT1-UTC series reveal oscillations with periods of 8, and weak 6 hours. Rapid oscillations of polar motion with periods of 8 and 5-6 hours had already been found in the two-hourly polar motion series determined by GPS (CODE) in the period 1997.5 through 2001.0. In that time it was not possible to explain the origin of the oscillations and to decide whether the oscillation of 8 hours comes from the GPS technique (e.g. caused by the orbit computation) or is a real oscillation of polar motion. The detection of the 8 and weak 6 hours oscillations in ERP independently determined by two accurate space geodetic techniques is a first evidence for a real sub-semidiurnal variation of the ERP. On the other hand the oscillations might still be an artifact stemming from similar methods of data sampling or from un-recovered diurnal drifts in the time series. Additionally, time variable spectra of polar motion were computed by the Fourier Transform Band Pass Filter, showing variations of amplitudes of these oscillations. Analyses and results Analyses and results
International Association of Geodesy Symposia, 2009
This paper gives an overview about the progress of the simulation work, carried out at the Instit... more This paper gives an overview about the progress of the simulation work, carried out at the Institute of Geodesy and Geophysics (IGG), 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. For this purpose temporally very dense schedules are prepared with the software package SKED (Vandenberg 1999), which are then 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 zenith wet delay and clock values as well as additive white noise representing the antenna errors. For this purpose the VLBI analysis software OCCAM (Titov et al. 2004) was adapted to run the simulator and analyze the simulated observations. Random walk processes with power spectral densities of 0.7 and 0.1 psec 2 /sec are used for the simulation of zenith wet delays. The clocks are simulated with Allan Standard Deviations of 1•10-14 @50min and 2•10-15 @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 zenith wet 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.
Since 1990 the International VLBI Service for Geodesy and Astrometry (IVS) has been performing ge... more 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.
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 ...
An overview of the abilities of Very Long Baseline Interferometry (VLBI) to measure the variable ... more An overview of the abilities of Very Long Baseline Interferometry (VLBI) to measure the variable Earth rotation and of the international VLBI collaboration is given. The paper concentrates on the short-period, i.e. subseasonal variations of Earth rotation which can be seen in VLBI measurements of length of day (lod) and polar motion between 1981 and 1999. The wavelet transform allows the time localisation of an irregular quasi-harmonic signal within a given data set. The wavelet analysis of lod series yields in the high-frequency range periods of ∼28 days, ∼14 days down to 6.86 days caused by the lunisolar tides and irregular quasi-periodic variations between 40 and 130 days. These are mainly associated with global zonal wind changes which can be seen when looking on the wavelet cross-scalogram between the lod series and the atmospheric angular momentum (AAM) time series. In polar motion variable periods between two and five months and even down to 7-10 days can be made visible by the wavelet scalograms.Today it is possible by VLBI to determine polar motion and UT1-UTC with a temporal resolution of as short as 3-7 minutes. The results of parallel VLBI sessions which took place since 1998 using two independent VLBI networks were analyzed in the subdiurnal period range and compared by computing the wavelet cross-scalograms, the covariance spectrum and the normed coherency. Periods between 5 and 7 hours can be seen in many of the UT1-UTC data sets besides the well-known diurnal and semi-diurnal periods. The wavelet analyses reveal interesting patterns in the subdiurnal range in polar motion, too.
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.
Love and Shida numbers describe the Earth's response to external forces exerted by celestial bodi... more Love and Shida numbers describe the Earth's response to external forces exerted by celestial bodies due to the elasticity of the Earth. Modern space geodetic techniques, such as VLBI (Very Long Baseline Interferometry), allow the empirical validation of theoretical Love and Shida numbers. In the VLBI analysis software package OCCAM tidal displacements on the Earth's surface are modelled according to the International Earth rotation and Reference systems Service (IERS) Conventions 2003. Snapshots of corrections to the nominal displacements for the complete Earth's surface with a spatial resolution of 1°x1° are shown. Nominal degree-2 Love and Shida numbers, h 2 and l 2 , were determined from the continuous 15 days VLBI campaign CONT05. Frequency dependence was considered in the diurnal band due to the retrograde Free Core Nutation (FCN) resonance: we determined h 2 and l 2 at those diurnal tidal waves with the largest amplitudes, two of them lying very close to the resonance frequency.
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
International Association of Geodesy Symposia, 2007
Over the two weeks of the CONT02 campaign in October 2002 the Earth rotation parameters, ERP (xpo... more Over the two weeks of the CONT02 campaign in October 2002 the Earth rotation parameters, ERP (xpol, ypol, UT1-UTC) were determined with a resolution of one hour by VLBI and also by GPS. Analyses of these two very precise polar motion and UT1-UTC series reveal oscillations with periods of 8, and weak 6 hours. Rapid oscillations of polar motion with periods of 8 and 5-6 hours had already been found in the two-hourly polar motion series determined by GPS (CODE) in the period 1997.5 through 2001.0. In that time it was not possible to explain the origin of the oscillations and to decide whether the oscillation of 8 hours comes from the GPS technique (e.g. caused by the orbit computation) or is a real oscillation of polar motion. The detection of the 8 and weak 6 hours oscillations in ERP independently determined by two accurate space geodetic techniques is a first evidence for a real sub-semidiurnal variation of the ERP. On the other hand the oscillations might still be an artifact stemming from similar methods of data sampling or from un-recovered diurnal drifts in the time series. Additionally, time variable spectra of polar motion were computed by the Fourier Transform Band Pass Filter, showing variations of amplitudes of these oscillations. Analyses and results Analyses and results
International Association of Geodesy Symposia, 2009
This paper gives an overview about the progress of the simulation work, carried out at the Instit... more This paper gives an overview about the progress of the simulation work, carried out at the Institute of Geodesy and Geophysics (IGG), 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. For this purpose temporally very dense schedules are prepared with the software package SKED (Vandenberg 1999), which are then 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 zenith wet delay and clock values as well as additive white noise representing the antenna errors. For this purpose the VLBI analysis software OCCAM (Titov et al. 2004) was adapted to run the simulator and analyze the simulated observations. Random walk processes with power spectral densities of 0.7 and 0.1 psec 2 /sec are used for the simulation of zenith wet delays. The clocks are simulated with Allan Standard Deviations of 1•10-14 @50min and 2•10-15 @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 zenith wet 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.
Since 1990 the International VLBI Service for Geodesy and Astrometry (IVS) has been performing ge... more 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.
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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