| 1. |
- Albentosa, Ezequiel, et al.
(författare)
-
Current Status of the EU-VGOS Project
- 2023
-
Ingår i: International VLBI Service for Geodesy and Astrometry 2022 General Meeting Proceedings. ; NASA/ CP–20220018789, s. 85-89
-
Konferensbidrag (refereegranskat)abstract
- The EU-VGOS project began in 2018 with the aim of using the VGOS infrastructure in Europe to investigate methods for VGOS data processing. The project is now structured into Working Groups dealing with operations (stations), e-transfer, correlation and post-processing, and analysis. This is a report on the status of the project.
|
|
| 2. |
- Alef, Walter, et al.
(författare)
-
Geodetic data analysis of VGOS experiments
- 2021
-
Ingår i: 2021 34th General Assembly and Scientific Symposium of the International Union of Radio Science, URSI GASS 2021.
-
Konferensbidrag (refereegranskat)abstract
- Very Long Baseline Interferometry (VLBI) serves as one of the common geodetic methods to define the global reference frames and monitor Earth's orientation variations. The technical upgrade of the VLBI method known as the VLBI Global Observing System (VGOS) includes a critical re-design of the observed frequencies from the dual band mode (S and X band, i.e. 2 GHz and 8 GHz) to observations in a broadband (2-14 GHz). Since 2019 the first VGOS experiments are available for the geodetic analysis in free access at the International VLBI service for Geodesy and Astrometry (IVS). Also regional-only subnetworks such as European VLBI stations have succeeded already in VGOS mode. Based on these brand-new observations we review the current geodetic data analysis workflow to build a bridge between geodetic observed delays derived from different bands.
|
|
| 3. |
- Delva, Pacôme, et al.
(författare)
-
GENESIS: co-location of geodetic techniques in space
- 2023
-
Ingår i: Earth, Planets and Space. - : Springer Science and Business Media LLC. - 1880-5981 .- 1343-8832. ; 75:1
-
Tidskriftsartikel (refereegranskat)abstract
- Improving and homogenizing time and space reference systems on Earth and, more specifically, realizing the Terrestrial Reference Frame (TRF) with an accuracy of 1 mm and a long-term stability of 0.1 mm/year are relevant for many scientific and societal endeavors. The knowledge of the TRF is fundamental for Earth and navigation sciences. For instance, quantifying sea level change strongly depends on an accurate determination of the geocenter motion but also of the positions of continental and island reference stations, such as those located at tide gauges, as well as the ground stations of tracking networks. Also, numerous applications in geophysics require absolute millimeter precision from the reference frame, as for example monitoring tectonic motion or crustal deformation, contributing to a better understanding of natural hazards. The TRF accuracy to be achieved represents the consensus of various authorities, including the International Association of Geodesy (IAG), which has enunciated geodesy requirements for Earth sciences. Moreover, the United Nations Resolution 69/266 states that the full societal benefits in developing satellite missions for positioning and Remote Sensing of the Earth are realized only if they are referenced to a common global geodetic reference frame at the national, regional and global levels. Today we are still far from these ambitious accuracy and stability goals for the realization of the TRF. However, a combination and co-location of all four space geodetic techniques on one satellite platform can significantly contribute to achieving these goals. This is the purpose of the GENESIS mission, a component of the FutureNAV program of the European Space Agency. The GENESIS platform will be a dynamic space geodetic observatory carrying all the geodetic instruments referenced to one another through carefully calibrated space ties. The co-location of the techniques in space will solve the inconsistencies and biases between the different geodetic techniques in order to reach the TRF accuracy and stability goals endorsed by the various international authorities and the scientific community. The purpose of this paper is to review the state-of-the-art and explain the benefits of the GENESIS mission in Earth sciences, navigation sciences and metrology. This paper has been written and supported by a large community of scientists from many countries and working in several different fields of science, ranging from geophysics and geodesy to time and frequency metrology, navigation and positioning. As it is explained throughout this paper, there is a very high scientific consensus that the GENESIS mission would deliver exemplary science and societal benefits across a multidisciplinary range of Navigation and Earth sciences applications, constituting a global infrastructure that is internationally agreed to be strongly desirable. Graphical Abstract: [Figure not available: see fulltext.]
|
|
| 4. |
- Krasna, Hana, et al.
(författare)
-
Zonal Love and Shida numbers estimated by VLBI
- 2013
-
Ingår i: Reports of the Finnish Geodetic Institute - Proceedings of the 21st Meeting of the European VLBI Group for Geodesy and Astronomy, Ed. by N. Zubko and M. Poutanen. - 0355-1962. ; 2013:1, s. 121-125
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- 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.
|
|
| 5. |
- Liu, Li, et al.
(författare)
-
New Progress in VLBI tracking of GNSS satellites at GFZ
- 2014
-
Ingår i: IVS 2014 General Meeting Proceedings "VGOS: The New VLBI Network", Edited by Dirk Behrend, Karen D. Baver, and Kyla L. Armstrong, Science Press (Beijing). - 9787030429742 ; , s. 456-460
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)
|
|
| 6. |
|
|
| 7. |
- Wresnik, Jörg, et al.
(författare)
-
Modeling thermal deformation of VLBI antennas with a new temperature model
- 2007
-
Ingår i: Journal of Geodesy. - : Springer Science and Business Media LLC. - 0949-7714 .- 1432-1394. ; 81:6-8, s. 433-441
-
Tidskriftsartikel (refereegranskat)abstract
- Temperature variations at very long baseline interferometry (VLBI) sites cause thermal deformations of the VLBI antennas and corresponding displacements of the VLBI reference points. The thermal deformation effects typically contain seasonal and daily signatures. The amplitudes of the annual vertical motion of the antenna reference point can reach several millimeters, depending on the design of the antenna structure, on the material, and on the environmental effects such as global station position, station height and climatology effects. Simple methods to correct this effect use the difference of the environmental temperature with respect to a defined reference temperature, the antenna dimensions, the elevation of the antenna, the material of antenna structure. Applying these simple models for thermal deformation in the VLBI data analysis improves the baseline length repeatability by 3.5%. A comparison of these simple models with local thermal deformation measurements at the antennas in Onsala and Wettzell show that the local measurements and the modeled corrections agree well when the temperature of the antenna structure is used, but agree less good when the surrounding air temperatures are used. To overcome this problem we present a method to model temperature penetration into the antenna structures, that allows to model thermal deformation effects that agree with the observed vertical deformation of the Onsala and Wettzell radio telescopes with a root mean square deviation of 0.07 and 0.13 mm, respectively. Possible implementations in the VLBI analysis are presented, and the definition of an adequate reference temperature is discussed. © Springer-Verlag 2006.
|
|
| 8. |
- Xu, Minghui, et al.
(författare)
-
Baseline Vector Repeatability at the Sub-Millimeter Level Enabled by Radio Interferometer Phase Delays of Intra-Site Baselines
- 2023
-
Ingår i: Journal of Geophysical Research: Solid Earth. - 2169-9356 .- 2169-9313. ; 128:3
-
Tidskriftsartikel (refereegranskat)abstract
- We report the results of position ties for short baselines at eight geodetic sites based on phase delays that are extracted from global geodetic very-long-baseline interferometry (VLBI) observations rather than dedicated short-baseline experiments. An analysis of phase delay observables at X band from two antennas at the Geodetic Observatory Wettzell, Germany, extracted from 107 global 24-hr VLBI sessions since 2019 yields weighted root-mean-square scatters about the mean baseline vector of 0.3, 0.3, and 0.8 mm in the east, north, and up directions, respectively. Position ties are also obtained for other short baselines between legacy antennas and nearby, newly built antennas. They are critical for maintaining a consistent continuation of the realization of the terrestrial reference frame, especially when including the new VGOS network. The phase delays of the baseline WETTZ13N–WETTZELL enable an investigation of sources of error at the sub-millimeter level. We found that a systematic variation of larger than 1 mm can be introduced to the Up estimates of this baseline vector when atmospheric delays were estimated. Although the sub-millimeter repeatability has been achieved for the baseline vector WETTZ13N–WETTZELL, we conclude that long term monitoring should be conducted for more short baselines to assess the instrumental effects, in particular the systematic differences between phase delays and group delays, and to find common solutions for reducing them. This will be an important step toward the goal of global geodesy at the 1 mm level.
|
|
