Current Status of the EU-VGOS Project

The EU-VGOS project began in 2018 with\ua0the aim of using the VGOS infrastructure in Europe\ua0to investigate methods for VGOS data processing. The\ua0project is now structured into Working Groups dealing\ua0with operations (stations), e-transfer, correlation and\ua0post-processing, and analysis. This is a report on the\ua0status of the project

Assessing the Impact of Global GNSS-VLBI Hybrid Observations

GNSS-VLBI hybrid observations refer to an approach where GNSS signals are received by GNSS antennas and correlated with VLBI correlators. The VLBI-like GNSS single differences (two stations to one satellite) are then analyzed together with standard VLBI observations. In this work, we use GNSS observations during CONT11, a continuous VLBI campaign over 15 days in September 2011. During CONT11, GNSS and VLBI are connected to the identical clocks at seven sites, which mean clock parameters can be regarded as site common parameters. We construct GNSS single differences between the ranges from two stations to a satellite, using post-processed range measurements from a precise point positioning (PPP) GPS solution with the C5++ software. Combining VLBI and VLBI-like GNSS delays during CONT11, we estimate station coordinates, Earth orientation parameters, and site common parameters, i.e. zenith wet delays and clock parameters with the Vienna VLBI Software (VieVS). We compare combined solutions with single technique solutions and assess the impact of GNSS-VLBI hybrid observations with respect to those parameters

Assessing the Impact of Global GNSS-VLBI Hybrid Observations

GNSS-VLBI hybrid observations refer to an approach where GNSS signals are received by GNSS antennas and correlated with VLBI correlators. The VLBI-like GNSS single differences (two stations to one satellite) are then analyzed together with standard VLBI observations. In this work, we use GNSS observations during CONT11, a continuous VLBI campaign over 15 days in September 2011. During CONT11, GNSS and VLBI are connected to the identical clocks at seven sites, which mean clock parameters can be regarded as site common parameters. We construct GNSS single differences between the ranges from two stations to a satellite, using post-processed range measurements from a precise point positioning (PPP) GPS solution with the C5++ software. Combining VLBI and VLBI-like GNSS delays during CONT11, we estimate station coordinates, Earth orientation parameters, and site common parameters, i.e. zenith wet delays and clock parameters with the Vienna VLBI Software (VieVS). We compare combined solutions with single technique solutions and assess the impact of GNSS-VLBI hybrid observations with respect to those parameters

The processing of single differenced GNSS data with VLBI software

\ua9 Springer International Publishing Switzerland 2015.Space geodetic techniques such as Very Long Baseline Interferometry (VLBI) and Global Navigation Satellite Systems (GNSS) are used for the determination of celestial and terrestrial reference frames and Earth orientation parameters. It is potentially valuable to combine the observations from the different techniques to fully exploit the strengths and unique characteristics of the techniques. Today, discrepancies of locally measured ties between reference points of two techniques and the space geodesy results are a potential issue in the determination of reference frames. To improve the link between the techniques, tests are under way to observe GNSS signals with VLBI radio telescopes directly, and to observe GNSS signals in GNSS antennas with subsequent processing in the VLBI system (“GNSS-VLBI Hybrid System”) including VLBI correlation. In both cases, the GNSS data type is the difference in travel time from the satellite to two ground stations. However, it is still difficult to acquire those observations and thus we apply post-processed phase measurements from a precise point positioning (PPP) solution with the c5++ software to build those difference values which are then used in the Vienna VLBI Software (VieVS). We take seven GNSS sites, exclusively Global Positioning System (GPS) in this study, colocated with CONT11 VLBI sites to validate the models in VieVS for single differenced GNSS data, and estimate geodetic parameters. We find root mean square values of postfit residuals for the VLBI-like observations of about 3.3 cm, compared to less than 2.0 cm fromthe GNSS PPP solution. At this stage, we do also find degradation in station coordinate repeatabilities (by a factor of 2 to 8), which is related to the systematic residuals

Zonal Love and Shida numbers estimated by VLBI

The deformation of the anelastic Earth as aresponse to external forces from the Moon and Sun ischaracterized with proportionality parameters, the so-called Love and Shida numbers. The increasing pre-cision and quality of the VLBI (Very Long BaselineInterferometry) measurements allow determining thoseparameters. In particular, the long history of the VLBIdata enables the estimation of Love and Shida numbersat the low frequencies with the longest period of a tidalwave at 18.6 years. In this study we analyze 27 yearsof VLBI measurements (1984.0 - 2011.0) following therecent IERS Conventions 2010. In several global solu-tions, we estimate the complex Love and Shida num-bers of the solid Earth tides for the main long-periodtidal waves. Furthermore, we determine the Love andShida numbers of the rotational deformation due to po-lar motion, the so-called pole tide

Zonal Love and Shida numbers estimated by VLBI

The deformation of the anelastic Earth as aresponse to external forces from the Moon and Sun ischaracterized with proportionality parameters, the so-called Love and Shida numbers. The increasing pre-cision and quality of the VLBI (Very Long BaselineInterferometry) measurements allow determining thoseparameters. In particular, the long history of the VLBIdata enables the estimation of Love and Shida numbersat the low frequencies with the longest period of a tidalwave at 18.6 years. In this study we analyze 27 yearsof VLBI measurements (1984.0 - 2011.0) following therecent IERS Conventions 2010. In several global solu-tions, we estimate the complex Love and Shida num-bers of the solid Earth tides for the main long-periodtidal waves. Furthermore, we determine the Love andShida numbers of the rotational deformation due to po-lar motion, the so-called pole tide

Observation Level Combination of GNSS and VLBI with VieVS: a simulation based on CONT11

GNSS and VLBI antennas were connected to the identical hydrogen maser clocks at seven sites during CONT11, which means that clock parameters can be regarded as common parameters at those sites as well as troposphere parameters. We construct GNSS single differences between the ranges from two stations to a satellite, using corrected phase measurements with the c5++ software. Combining GNSS single difference and VLBI data during CONT11, we estimate station coordinates and site common parameters, i.e. zenith wet delays, troposphere gradients and clock parameters, with the Vienna VLBI Software (VieVS). Local tie vectors, which contribute to the combination of terrestrial frames between GNSS and VLBI, are introduced as fictitious observations. We compare combination solutions with single technique solutions, assess the impact of the combination at the observation level with respect to geodetic results and discuss the current limitation and potentials to be developed

Combination of Two Radio Space-Geodetic Techniques with VieVS during CONT14

Unlike CONT11, CONT14 does not have official information on common frequency standards for co-located sites. Nevertheless, according to Kwak et al. (2015) [1], we have a possibility to find the co-located sites, which used the same clocks, through comparing clock rates from single technique solutions. Moreover, CONT14 includes co-located VLBI radio telescopes, i.e. HOBART26 and HOBART12. Therefore, it is also a good test bed to develop the analysis strategy for future twin/sibling telescopes. In this study, we compute VLBI-like GNSS delays (GNSS single differences) between the ranges from two stations to a satellite, using phase measurements with most of the errors correctedby the c5++ software. We estimate station coordinates and site common parameters, i.e. zenith wet delays, troposphere gradients and clock parameters, with the Vienna VLBI Software. Common clock parameters are limited to the sites sharing the same frequency standard and having good performance of it during CONT14. Local tie vectors are introduced as fictitious observations for co-located instruments, GNSS-VLBI and even VLBI-VLBI, i.e. at Hobart. In this paper, we show the comparison results between the combination solutions and the single technique solutions in terms of station position repeatability during 15 days