| 1. |
- Kwak, Younghee, et al.
(författare)
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Assessing the Impact of Global GNSS-VLBI Hybrid Observations
- 2015
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Ingår i: European Geosciences Union General Assembly 2015.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 2. |
- Kwak, Younghee, et al.
(författare)
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Combination of Two Radio Space-Geodetic Techniques with VieVS during CONT14
- 2016
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Ingår i: IVS 2016 General Meeting Proceedings "New Horizons with VGOS". ; :NASA/CP-2016-219016, s. 265-269
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 3. |
- Kwak, Younghee, et al.
(författare)
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Observation Level Combination of GNSS and VLBI with VieVS: a simulation based on CONT11
- 2015
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Ingår i: AGU FALL MEETING.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 4. |
- Kwak, Younghee, et al.
(författare)
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On the Analysis of VLBI Observations to GNSS Satellites
- 2014
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Ingår i: IAG Commission 1 Symposium 2014: Reference Frames for Applications in Geosciences (REFAG2014), 13-17 October, 2014 Kirchberg, Luxemburg.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- 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 of utmost importance to combine the observations from the different techniques to fully exploit the strengths and unique characteristics of the techniques, however, inaccurate local ties are problematic for a rigorous combination. 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 between the ranges from two stations to a satellite. However, it is still difficult to acquire those observations and thus we apply post-processed range measurements from a precise point positioning (PPP) solution with the C5++ software to build those single differences which are then used in the Vienna VLBI Software (VieVS). We use the CONT11 data set with identical clocks at seven sites to validate the models in VieVS and to assess the impact of the combined solution on the geodetic products.
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