共查询到20条相似文献,搜索用时 31 毫秒
1.
Johannes Böhm T. Hobiger R. Ichikawa T. Kondo Y. Koyama A. Pany H. Schuh K. Teke 《Journal of Geodesy》2010,84(5):319-325
One-baseline 1-h Very Long Baseline Interferometry (VLBI) Intensive sessions are carried out every day to determine Universal
Time (UT1). Azimuthal asymmetry of tropospheric delays around the stations is usually ignored and not estimated because of
the small number of observations. In this study we use external information about the asymmetry for the Intensive sessions
between Tsukuba (Japan) and Wettzell (Germany), which are carried out on Saturdays and Sundays (1) from direct ray-tracing
for each observation at Tsukuba and (2) in the form of linear horizontal north and east gradients every 6 h at both stations.
The change of the UT1 estimates is at the 10 μs level with maximum differences of up to 50 μs, which is clearly above the
formal uncertainties of the UT1 estimates (between 5 and 20 μs). Spectral analysis reveals that delays from direct ray-tracing
for the station Tsukuba add significant power at short periods (1–2 weeks) w.r.t. the state-of-the-art approach, and comparisons
with length-of-day (LOD) estimates from Global Positioning System (GPS) indicate that these ray-traced delays slightly improve
the UT1 estimates from Intensive sessions. 相似文献
2.
Methodology for the combination of sub-daily Earth rotation from GPS and VLBI observations 总被引:3,自引:3,他引:0
A combination procedure of Earth orientation parameters from Global Positioning System (GPS) and Very Long Baseline Interferometry
(VLBI) observations was developed on the basis of homogeneous normal equation systems. The emphasis and purpose of the combination
was the determination of sub-daily polar motion (PM) and universal time (UT1) for a long time-span of 13 years. Time series
with an hourly resolution and a model for tidal variations of PM and UT1-TAI (dUT1) were estimated. In both cases, 14-day
nutation corrections were estimated simultaneously with the ERPs. Due to the combination procedure, it was warranted that
the strengths of both techniques were preserved. At the same time, only a minimum of de-correlating or stabilizing constraints
were necessary. Hereby, a PM time series was determined, whose precision is mainly dominated by GPS observations. However,
this setup benefits from the fact that VLBI delivered nutation and dUT1 estimates at the same time. An even bigger enhancement
can be seen for the dUT1 estimation, where the high-frequency variations are provided by GPS, while the long term trend is
defined by VLBI. The estimated combined tidal PM and dUT1 model was predominantly determined from the GPS observations. Overall,
the combined tidal model for the first time completely comprises the geometrical benefits of VLBI and GPS observations. In
terms of root mean squared (RMS) differences, the tidal amplitudes agree with other empirical single-technique tidal models
below 4 μas in PM and 0.25 μs in dUT1. The noise floor of the tidal ERP model was investigated in three ways resulting in about 1 μas for diurnal PM and 0.07 μs for diurnal dUT1 while the semi-diurnal components have a slightly better accuracy. 相似文献
3.
Assessment of periodic sub-diurnal Earth rotation variations at tidal frequencies through transformation of VLBI normal equation systems 总被引:3,自引:2,他引:1
We present an empirical model for periodic variations of diurnal and sub-diurnal Earth rotation parameters (ERPs) that was
derived based on the transformation of normal equation (NEQ) systems of Very Long Baseline Interferometry (VLBI) observing
sessions. NEQ systems that contain highly resolved polar motion and UT1-TAI with a temporal resolution of 15 min were generated
and then transformed to the coefficients of the tidal ERP model to be solved for. To investigate the quality of this model,
comparisons with empirical models from the Global Positioning System (GPS), another VLBI model and the model adopted by the
conventions of the International Earth Rotation and Reference Systems Service (IERS) were performed. The absolute coefficients
of these models agree almost completely within 7.5 μ as in polar motion and 0.5 μs in UT1-TAI. Several bigger differences exist, which are discussed in this paper. To be able to compare the model estimates
with results of the continuous VLBI campaigns, where signals with periods of 8 and 6 h were detected, terms in the ter- and
quarter-diurnal band were included in the tidal ERP model. Unfortunately, almost no common features with the results of continuous
VLBI campaigns or ERP predictions in these tidal bands can be seen. 相似文献
4.
The impact of errors in polar motion and nutation on UT1 determinations from VLBI Intensive observations 总被引:2,自引:2,他引:0
The earth’s phase of rotation, expressed as Universal Time UT1, is the most variable component of the earth’s rotation. Continuous
monitoring of this quantity is realised through daily single-baseline VLBI observations which are interleaved with VLBI network
observations. The accuracy of these single-baseline observations is established mainly through statistically determined standard
deviations of the adjustment process although the results of these measurements are prone to systematic errors. The two major
effects are caused by inaccuracies in the polar motion and nutation angles introduced as a priori values which propagate into
the UT1 results. In this paper, we analyse the transfer of these components into UT1 depending on the two VLBI baselines being
used for short duration UT1 monitoring. We develop transfer functions of the errors in polar motion and nutation into the
UT1 estimates. Maximum values reach 30 [μs per milliarcsecond] which is quite large considering that observations of nutation
offsets w.r.t. the state-of-the-art nutation model show deviations of as much as one milliarcsecond. 相似文献
5.
Summary In May 1989 and April 1990 the radio telescopes of the Wettzell Geodetic Fundamental Station in Germany and of the Shanghai Observatory near Seshan in China observed two series of daily VLBI experiments of short duration for precise determination of UT1. In 1990 a few experiments were complemented by the Hartebeesthoek Radio Astronomy Observatory in South Africa and the Medicina telescope of the Bologna Istituto di Radioastronomia in Italy. Employing the South African station together with the east-west baseline formed by the observatories of Seshan and Medicina permitted simultaneous determinations of UT1 and polar motion. Here we report on the results of these observations. Comparing the UT1 results with those of the IRIS Intensive series gives a clear indication of the absolute accuracy of such short duration VLBI measurements which is estimated to be of the order of ±60µs. 相似文献
6.
Z. Malkin 《Journal of Geodesy》2008,82(6):325-329
The scatter of the celestial pole offset (CPO) time-series obtained from very long baseline interferometry (VLBI) observations
is used as a measure of the accuracy of celestial reference frame (CRF) realizations. Several scatter indices (SI), including
some proposed for the first time, are investigated. The first SI is based on residual analysis of CPO series with respect
to a free core nutation (FCN) model. The second group of SIs includes Allan deviation and its extensions, which allow the
treatment of unequally weighted and multidimensional observations. Application of these criteria to several radio source catalogues
(RSCs) showed their ability to perform a preliminary assessment of the quality of each RSC. The 2D Allan deviation estimate
seems to be the most sensitive measure. The proposed extensions of Allan deviation, weighted and multidimensional, can also
be used for the statistical analysis of other time-series. 相似文献
7.
Zinovy Malkin 《Journal of Geodesy》2017,91(7):839-848
Three combined celestial pole offset (CPO) series computed at the Paris Observatory (C04), the United States Naval Observatory (USNO), and the International VLBI Service for Geodesy and Astrometry (IVS), as well as six free core nutation (FCN) models, were compared from different perspectives, such as stochastic and systematic differences, and FCN amplitude and phase variations. The differences between the C04 and IVS CPO series were mostly stochastic, whereas a low-frequency bias at the level of several tens of \(\upmu \)as was found between the C04 and USNO CPO series. The stochastic differences between the C04 and USNO series became considerably smaller when computed at the IVS epochs, which can indicate possible problems with the interpolation of the IVS data at the midnight epochs during the computation of the C04 and USNO series. The comparison of the FCN series showed that the series computed with similar window widths of 1.1–1.2 years were close to one another at a level of 10–20 \(\upmu \)as, whereas the differences between these series and the series computed with a larger window width of 4 and 7 years reached 100 \(\upmu \)as. The dependence of the FCN model on the underlying CPO series was investigated. The RMS differences between the FCN models derived from the C04, USNO, and IVS CPO series were at a level of approximately 15 \(\upmu \)as, which was considerably smaller than the differences among the CPO series. The analysis of the differences between the IVS, C04, and USNO CPO series suggested that the IVS series would be preferable for both precession-nutation and FCN-related studies. 相似文献
8.
Real-time orbit determination and interplanetary navigation require accurate predictions of the orientation of the Earth in
the celestial reference frame and in particular that for Universal Time UT1. Much of the UT1 variations over periods ranging
from hours to a couple of years are due to the global atmospheric circulation. Therefore, the axial atmospheric angular momentum
(AAM) forecast series may be used as a proxy index to predict UT1. Our approach taking advantage of this fact is based on
an adaptive procedure. It involves incorporating integrations of AAM estimates into UT1 series. The procedure runs on a routine
basis using AAM forecasts that are based on the two meteorological series, from the US National Centers for Environmental
Prediction and the Japan Meteorological Agency. It is pertinent to test the prediction method for the period that includes
the special CONT08 campaign over which we expect a significant improvement in UT1 accuracy. The studies we carried out were
aimed both to compare atmospheric forecasts and analyses, as well as to compare the skills of the UT1 forecasts based on the
method with atmospheric forecasts and that using current statistical processes, as applied to the C04 Earth orientation parameters
series derived by the International Earth rotation and Reference Systems service (IERS). Here we neglect the oceanic sub-diurnal
and diurnal variations, as these signals are expected to be smaller than the UT1-equivalent of 100 μs, when averaged over a few days. The prediction performances for a 2-day forecast are similar, but at a forecast horizon of
a week, the AAM-based forecast is roughly twice as skillful as the statistically based one. 相似文献
9.
Combinations of station coordinates and velocities from independent space-geodetic techniques have long been the standard
method to realize robust global terrestrial reference frames (TRFs). In principle, the particular strengths of one observing
method can compensate for weaknesses in others if the combination is properly constructed, suitable weights are found, and
accurate co-location ties are available. More recently, the methodology has been extended to combine time-series of results
at the normal equation level. This allows Earth orientation parameters (EOPs) to be included and aligned in a fully consistent
way with the TRF. While the utility of such multi-technique combinations is generally recognized for the reference frame,
the benefits for the EOPs are yet to be quantitatively assessed. In this contribution, which is a sequel to a recent paper
on co-location ties (Ray and Altamimi in J Geod 79(4–5): 189–195, 2005), we have studied test combinations of very long baseline
interferometry (VLBI) and Global Positioning System (GPS) time-series solutions to evaluate the effects on combined EOP measurements
compared with geophysical excitations. One expects any effect to be small, considering that GPS dominates the polar motion
estimates due to its relatively dense and uniform global network coverage, high precision, continuous daily sampling, and
homogeneity, while VLBI alone observes UT1-UTC. Presently, although clearly desirable, we see no practical method to rigorously
include the GPS estimates of length-of-day variations due to significant time-varying biases. Nevertheless, our results, which
are the first of this type, indicate that more accurate polar motion from GPS contributes to improved UT1-UTC results from
VLBI. The situation with combined polar motion is more complex. The VLBI data contribute directly only very slightly, if at
all, with an impact that is probably affected by the weakness of the current VLBI networks (small size and sparseness) and
the quality of local ties relating the VLBI and GPS frames. Instead, the VLBI polar motion information is used primarily in
rotationally aligning the VLBI and GPS frames, thereby reducing the dependence on co-location tie information. Further research
is needed to determine an optimal VLBI-GPS combination strategy that yields the highest quality EOP estimates. Improved local
ties (including internal systematic effects within the techniques) will be critically important in such an effort. 相似文献
10.
在国际甚长基线干涉测量(very long baseline interferometry, VLBI)大地测量与天体测量服务组织协调下,首次利用隶属于VLBI全球观测系统(VLBI global observing system, VGOS)的美国Kokee和德国Wettzell观测站及并置的传统VLBI观测站开展了世界时(universal time, UT1)联合测量试验,观测数据在上海VLBI中心进行了干涉处理。结果表明,VGOS超宽带观测系统的UT1测量精度约为7 μs,并置基线的传统S/X双频系统测量精度约为14 μs,VGOS系统的UT1解算结果优于S/X系统。通过试验建立了从相关处理、相关后处理到UT1参数解算的完整数据处理流程,验证了上海VLBI相关处理机的VGOS数据处理能力,为承担国内和国际VGOS观测数据的相关处理任务奠定了基础。 相似文献
11.
Susanne Glaser Rolf König Dimitrios Ampatzidis Tobias Nilsson Robert Heinkelmann Frank Flechtner Harald Schuh 《Journal of Geodesy》2017,91(7):723-733
In this study, we assess the impact of two combination strategies, namely local ties (LT) and global ties (GT), on the datum realization of Global Terrestrial Reference Frames in view of the Global Geodetic Observing System requiring 1 mm-accuracy. Simulated Very Long Baseline Interferometry (VLBI) and Satellite Laser Ranging (SLR) data over a 7 year time span was used. The LT results show that the geodetic datum can be best transferred if the precision of the LT is at least 1 mm. Investigating different numbers of LT, the lack of co-located sites on the southern hemisphere is evidenced by differences of 9 mm in translation and rotation compared to the solution using all available LT. For the GT, the combination applying all Earth rotation parameters (ERP), such as pole coordinates and UT1-UTC, indicates that the rotation around the Z axis cannot be adequately transferred from VLBI to SLR within the combination. Applying exclusively the pole coordinates as GT, we show that the datum can be transferred with mm-accuracy within the combination. Furthermore, adding artificial stations in Tahiti and Nigeria to the current VLBI network results in an improvement in station positions by 13 and 12%, respectively, and in ERP by 17 and 11%, respectively. Extending to every day VLBI observations leads to 65% better ERP estimates compared to usual twice-weekly VLBI observations. 相似文献
12.
Possible improvement of Earth orientation forecast using autocovariance prediction procedures 总被引:3,自引:2,他引:1
Autocovariance prediction has been applied to attempt to improve polar motion and UT1-UTC predictions. The predicted polar
motion is the sum of the least-squares extrapolation model based on the Chandler circle, annual and semiannual ellipses, and
a bias fit to the past 3 years of observations and the autocovariance prediction of these extrapolation residuals computed
after subtraction of this model from pole coordinate data. This prediction method has been applied also to the UT1-UTC data,
from which all known predictable effects were removed, but the prediction error has not been reduced with respect to the error
of the current prediction model. However, the results show the possibility of decreasing polar motion prediction errors by
about 50 for different prediction lengths from 50 to 200 days with respect to the errors of the current prediction model.
Because of irregular variations in polar motion and UT1-UTC, the accuracy of the autocovariance prediction does depend on
the epoch of the prediction. To explain irregular variations in x, y pole coordinate data, time-variable spectra of the equatorial components of the effective atmospheric angular momentum, determined
by the National Center for Environmental Prediction, were computed. These time-variable spectra maxima for oscillations with
periods of 100–140 days, which occurred in 1985, 1988, and 1990 could be responsible for excitation of the irregular short-period
variations in pole coordinate data. Additionally, time-variable coherence between geodetic and atmospheric excitation function
was computed, and the coherence maxima coincide also with the greatest irregular variations in polar motion extrapolation
residuals.
Received: 22 October 1996 / Accepted: 16 September 1997 相似文献
13.
VLBI terrestrial reference frame contributions to ITRF2008 总被引:6,自引:5,他引:1
In late 2008, the Product Center for the International Terrestrial Reference Frame (ITRF) of the International Earth Rotation
and Reference Systems Service (IERS) issued a call for contributions to the next realization of the International Terrestrial
Reference System, ITRF2008. The official contribution of the International VLBI Service for Geodesy and Astrometry (IVS) to
ITRF2008 consists of session-wise datum-free normal equations of altogether 4,539 daily Very Long Baseline Interferometry
(VLBI) sessions from 1979.7 to 2009.0 including data of 115 different VLBI sites. It is the result of a combination of individual
series of session-wise datum-free normal equations provided by seven analysis centers (ACs) of the IVS. All series are completely
reprocessed following homogeneous analysis options according to the IERS Conventions 2003 and IVS Analysis Conventions. Altogether,
nine IVS ACs analyzed the full history of VLBI observations with four different software packages. Unfortunately, the contributions
of two ACs, Institute of Applied Astronomy (IAA) and Geoscience Australia (AUS), had to be excluded from the combination process.
This was mostly done because the IAA series exhibits a clear scale offset while the solution computed from normal equations
contained in the AUS SINEX files yielded unreliable results. Based on the experience gathered since the combination efforts
for ITRF2005, some discrepancies between the individual series were discovered and overcome. Thus, the consistency of the
individual VLBI solutions has improved considerably. The agreement in terms of WRMS of the Terrestrial Reference Frame (TRF)
horizontal components is 1 mm, of the height component 2 mm. Comparisons between ITRF2005 and the combined TRF solution for
ITRF2008 yielded systematic height differences of up to 5 mm with a zonal signature. These differences can be related to a
pole tide correction referenced to a zero mean pole used by four of five IVS ACs in the ITRF2005 contribution instead of a
linear mean pole path as recommended in the IERS Conventions. Furthermore, these systematics are the reason for an offset
in the scale of 0.4 ppb between the IVS’ contribution to ITRF2008 and ITRF2005. The Earth orientation parameters of seven
series used as input for the IVS combined series are consistent to a huge amount with about 50 μas WRMS in polar motion and
3 μs in dUT1. 相似文献
14.
At the present time, the daily VLBI observations on the Westford-Wettzell baseline is the only continually running VLBI project
for studies of high-frequency Earth rotation variations. An analysis of this experiment with regard to the potential errors
in the atmospheric delay model and in adopted celestial and terrestrial reference frames is presented in the paper. A new
VLBI geometric delay model is applied and an algorithm for global adjustment for this specific single-baseline VLBI developed.
The results over three years show discrepancies at the milliarcsecond level between the daily observations and the adopted
atmospheric model as well as the combined celestial reference frame. A significant number of these discrepancies are removed
by the global adjustment.
Received: 19 August 1996; Accepted: 13 September 1996 相似文献
15.
European geodetic very long baseline interferometry (VLBI) sessions (also known as EUROPE sessions) have been carried out
on a regular basis for the past 15 years to study relative crustal motions within Europe. These sessions are based on observations
of extragalactic radio sources, which serve as distant fiducial marks to establish an accurate and stable celestial reference
frame for long-term geodetic measurements. The radio sources, however, are not always point-like on milliarcsecond scales,
as VLBI imaging has revealed. In this work, we quantify the magnitude of the expected effect of intrinsic source structure
on geodetic bandwidth synthesis delay VLBI measurements for a subset of 14 sources regularly observed during the EUROPE sessions.
These sources have been imaged at both X-band (8.4 GHz) and S-band (2.3 GHz) based on dedicated observations acquired with
the European VLBI Network (EVN) in November 1996. The results of this calculation indicate that the reference source 0457+024
causes significant structural effects in measurements obtained on European VLBI baselines (about 10 picoseconds on average),
whereas most of the other sources produce effects that are only occasionally larger than a few picoseconds. Applying the derived
source structure models to the data of the EUROPE5-96 session carried out at the same epoch as the EVN experiment shows no
noticeable changes in the estimated VLBI station locations. 相似文献
16.
Tobias Nilsson Benedikt Soja Kyriakos Balidakis Maria Karbon Robert Heinkelmann Zhiguo Deng Harald Schuh 《Journal of Geodesy》2017,91(7):857-866
The very long baseline interferometry (VLBI) Intensive sessions are typically 1-h and single-baseline VLBI sessions, specifically designed to yield low-latency estimates of UT1-UTC. In this work, we investigate what accuracy is obtained from these sessions and how it can be improved. In particular, we study the modeling of the troposphere in the data analysis. The impact of including external information on the zenith wet delays (ZWD) and tropospheric gradients from GPS or numerical weather prediction models is studied. Additionally, we test estimating tropospheric gradients in the data analysis, which is normally not done. To evaluate the results, we compared the UT1-UTC values from the Intensives to those from simultaneous 24-h VLBI session. Furthermore, we calculated length of day (LOD) estimates using the UT1-UTC values from consecutive Intensives and compared these to the LOD estimated by GPS. We find that there is not much benefit in using external ZWD; however, including external information on the gradients improves the agreement with the reference data. If gradients are estimated in the data analysis, and appropriate constraints are applied, the WRMS difference w.r.t. UT1-UTC from 24-h sessions is reduced by 5% and the WRMS difference w.r.t. the LOD from GPS by up to 12%. The best agreement between Intensives and the reference time series is obtained when using both external gradients from GPS and additionally estimating gradients in the data analysis. 相似文献
17.
The contribution of the International VLBI Service for Geodesy and Astrometry (IVS) to the ITRF2005 (International Terrestrial
Reference Frame 2005) has been computed by the IVS Analysis Coordinator’s office at the Geodetic Institute of the University
of Bonn, Germany. For this purpose the IVS Analysis Centres (ACs) provided datum-free normal equation matrices in Solution
INdependent EXchange (SINEX) format for each 24 h observing session to be combined on a session-by-session basis by a stacking
procedure. In this process, common sets of parameters, transformed to identical reference epochs and a prioris, and especially representative relative weights have been taken into account for each session. In order to assess the quality
of the combined IVS files, Earth orientation parameters (EOPs) and scaling factors have been derived from the combined normal
equation matrices. The agreement of the EOPs of the combined normal equation matrices with those of the individual ACs in
terms of weighted root mean square (WRMS) is in the range of 50–60 μas for the two polar motion components and about 3 μs
for UT1−UTC. External comparisons with International GNSS Serive (IGS) polar motion components is at the level of 130–170 μas
and 21 μs/day for length of day (LOD). The scale of the terrestrial reference frame realized through the IVS SINEX files agrees
with ITRF2000 at the level of 0.2 ppb. 相似文献
18.
Zinovy Malkin 《Journal of Geodesy》2013,87(6):505-514
UT1 estimates obtained from the very long baseline interferometry (VLBI) Intensives data depend on the station displacement model used during processing. In particular, because of seasonal variations, the instantaneous station position during the specific intensive session differs from the position predicted by the linear model generally used. This can cause systematic errors in UT1 Intensives results. In this paper, we first investigated the seasonal signal in the station displacements for the 5 VLBI antennas participating in UT1 Intensives observing programs, along with the 8 collocated GPS stations. It was found that a significant annual term is present in the time series for most stations, and its amplitude can reach 8 mm in the height component, and 2 mm in horizontal components. However, the annual signals found in the displacements of the collocated VLBI and GPS stations at some sites differ substantially in amplitude and phase. The semiannual harmonics are relatively small and unstable, and for most stations no prevailing signal was found in the corresponding frequency band. Then two UT1 Intensives series were computed with and without including the seasonal term found in the previous step in the station movement model. Comparison of these series has shown that neglecting the seasonal station position variations can cause a systematic error in UT1 estimates, which can exceed 1 $\upmu $ s, depending on the observing program. 相似文献
19.
In recent years, ocean tide loading displacements (OTLD) have been measured using the Global Positioning System (GPS) and
Very Long Baseline Interferometry (VLBI). This study assesses the accuracy of GPS measurements of OTLD by comparison with
VLBI measurements and estimates derived from numerical ocean tide models. A daily precise point positioning (PPP) analysis
was carried out on ∼11 years of GPS data for each of 25 sites that have previous OTLD estimates based on data from co-located
VLBI sites. Ambiguities were fixed to integer values where possible. The resulting daily estimates of OTLD, at eight principal
diurnal and semi-diurnal tidal frequencies, were combined to give GPS measurements of OTLD at each site. The 3D GPS and VLBI
measurements of OTLD were compared with estimates computed (by convolution with Green’s functions) from five modern ocean
tide models (CSR4.0, FES2004, GOT00.2, NAO99b and TPXO6.2). The GPS/model agreement is shown to be similar to the VLBI/model
agreement. In the important radial direction, the GPS/model misfit is shown to be smaller than the VLBI/model misfit for seven
of the eight tidal constituents; the exception being the K2 constituent. Fixing of GPS carrier-phase ambiguities to integer
values resulted in a marginal improvement to the GPS/model agreement. Statistically, it is shown there is no significance
to the difference between the fit of the GPS and VLBI measurements of OTLD to modelled values. Equally, differences in fit
of either the complete set of GPS or VLBI estimates to the five sets of model-derived values cannot be identified with statistical
significance. It is thus concluded that, overall, we cannot distinguish between GPS and VLBI measurements of OTLD, and that
at the global scale, present ocean tide models are accurate to within the current measurement noise of these techniques. 相似文献
20.
Combined Earth orientation parameters based on homogeneous and continuous VLBI and GPS data 总被引:1,自引:3,他引:1
Daniela Thaller Manuela Krügel Markus Rothacher Volker Tesmer Ralf Schmid Detlef Angermann 《Journal of Geodesy》2007,81(6-8):529-541
The CONT02 campaign is of great interest for studies combining very long baseline interferometry (VLBI) with other space-geodetic
techniques, because of the continuously available VLBI observations over 2 weeks in October 2002 from a homogeneous network.
Especially, the combination with the Global Positioning System (GPS) offers a broad spectrum of common parameters. We combined
station coordinates, Earth orientation parameters (EOPs) and troposphere parameters consistently in one solution using technique-
specific datum-free normal equation systems. In this paper, we focus on the analyses concerning the EOPs, whereas the comparison
and combination of the troposphere parameters and station coordinates are covered in a companion paper in Journal of Geodesy. In order to demonstrate the potential of the VLBI and GPS space-geodetic techniques, we chose a sub-daily resolution for
polar motion (PM) and universal time (UT). A consequence of this solution set-up is the presence of a one-to-one correlation
between the nutation angles and a retrograde diurnal signal in PM. The Bernese GPS Software used for the combination provides
a constraining approach to handle this singularity. Simulation studies involving both nutation offsets and rates helped to
get a deeper understanding of this singularity. With a rigorous combination of UT1–UTC and length of day (LOD) from VLBI and
GPS, we showed that such a combination works very well and does not suffer from the systematic effects present in the GPS-derived
LOD values. By means of wavelet analyses and the formal errors of the estimates, we explain this important result. The same
holds for the combination of nutation offsets and rates. The local geodetic ties between GPS and VLBI antennas play an essential
role within the inter-technique combination. Several studies already revealed non-negligible discrepancies between the terrestrial
measurements and the space-geodetic solutions. We demonstrate to what extent these discrepancies propagate into the combined
EOP solution. 相似文献