| 1. |
- Elgered, Gunnar, 1955, et al.
(author)
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The Onsala Tide Gauge Station: Experiences from the first four years of operation
- 2019
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In: Proceedings of the 24th European VLBI Group for Geodesy and Astrometry Working Meeting. ; , s. 75-79
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Conference paper (peer-reviewed)abstract
- A tide gauge station was installed at the Onsala Space Observatory in 2015. The official tide gauge station includes several independent senors: one radar and three pneumatic sensors (also referred to as bubblers). The radar and two bubblers are mounted in a well and one bubbler outside the well. Additional sensors such as one laser sensor and three radar sensors have been used during dierent time periods in order to further assess the quality of the acquired sea level data. Here we compare the four ocial sensors and the laser sensor which was installed in April 2016. The expected accuracy (one standard deviation) for all of these sensors is approximately 3 mm, according to the datasheet specifications. Results from the first four years of operations are used to assess and estimate the actual accuracies by means of comparisons between the sensors. We observe typical biases over time scales of months of up to 10 mm. Biases are caused by uncertainties of the reference level of the sensor, the density of the water for the bubblers, multipath eects for the radar, and nonlinearities with temperature for the laser. The observed monthly standard deviation between the sensors in the well vary between 2 mm and 6 mm, which is roughly consistent with the data sheet specifications.
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| 2. |
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| 3. |
- García Espada, Susana, 1979, et al.
(author)
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Application of ray-tracing through the high resolution numerical weather model HIRLAM applying the Conformal Theory of Refraction
- 2011
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In: Proceedings of the 20th Meeting of the European VLBI Group for Geodesy and Astrometry. - 1864-1113. ; , s. 133-137
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Conference paper (other academic/artistic)abstract
- In space geodetic techniques like VLBI and GPS, accuracyis limited by atmospheric propagation effects by neutralatmosphere in the troposphere. In recent years numerical weather models (NWM) have been applied to improve mapping functions which are used for tropospheric delay modeling in VLBI and GPS data analyses. A troposphere correction model applying ray-tracing through the Limited Area numerical weather prediction (NWP) HIRLAM 3D-VAR model and applying the Conformal Theory of Refraction is developed. The advantages of HIRLAM model are the high spatial resolution (0.2◦x0.2◦) and the high temporal resolution in prediction mode (every 3 hours). The advantages of the Conformal Theory of Refraction (Moritz, 1967) is that the atmospheric propagation effects are evaluated along the line of sight and the known vacuum elevation angle is used so no iterative calculations are needed. When ray-tracing through HIRLAM profiles and calculating the slant delays using the Conformal Theory of Refraction, we include the effect of an inhomogeneous atmosphere in the slant delays values.
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| 4. |
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| 5. |
- García Espada, Susana, 1979, et al.
(author)
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Simulations of Different Antenna Velocities in VLBI Networks
- 2009
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In: Proceedings of the 19th European VLBI for Geodesy and Astrometry Working Meeting, 24-25 March 2009, Bordeaux. ; , s. 169-172
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Conference paper (other academic/artistic)abstract
- The new 40-m radiotelescope of the National Geographical Institute (IGN) in Yebes (code Ys) started to participate in IVS geodetic VLBI sessions in 2008. The azimuth and elevation slew velocities cause stress on the structure,and therefore has an impact on the expected life of the instrument; this calls for slow velocities and accelerations. However, high velocities are needed for better network geodetic results because, in principle, they allow more observations to be performed. In order to evaluate the optimum slew velocities for the new antenna,we used the scheduling software SKED and created schedules with different antenna velocities for Ys. We focussed on the two sessions EURO94 and R1331 and analyzed the scheduleswith SKED itself, and with the VLBI analysis software SOLVE, both with and without introducing simulated atmosphere and clock contributions. We found that the schedules with a fast Ys antenna (3◦/s in az. and el.) give slightly better results than the ones with a slow Ys antenna(1◦/s in az. and el.). For the studied EURO session the standard deviation of the estimated topocentric U-component for Yebes is similar for a fast and slow antenna. For the R1-experiment the standard deviations of all three topocentric station components improve for a fast antenna. The SKED-only results appear to be too optimistic, while the SOLVE results show more realistic estimates for the UEN components and sigmas. We found no significant difference in the UEN sigmas with or without introducing simulatedatmospheric and clock contributions, although the wrms fit becomes slightly worse.
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| 6. |
- García Espada, Susana, 1979, et al.
(author)
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Space Geodesy at Yebes: Station Motion from VLBI and GPS
- 2008
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In: in Proceedings of the 5th IVS General Meeting "Measuring the future", eds A. Finkelstein, D. Behrend. - 9785020253322 ; , s. 93-97
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Conference paper (other academic/artistic)
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| 7. |
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| 8. |
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| 9. |
- Haas, Rüdiger, 1966, et al.
(author)
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Status of the Onsala Twin Telescopes – Two Years After the Inauguration
- 2019
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In: Proceedings of the 24th European VLBI Group for Geodesy and Astrometry Working Meeting. - 9788441656345 ; , s. 5-9
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Conference paper (peer-reviewed)abstract
- We give a brief overview on the status of the Onsala twin telescopes (OTT), two years after their inauguration. The dierent components of the VGOS systems are briefly described, and the development towards routine operations.
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| 10. |
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| 11. |
- Pantaleev, Miroslav, 1970, et al.
(author)
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Onsala Space Observatory – IVS Technology Development Center
- 2011
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In: International VLBI Service for Geodesy and Astrometry 2010 Annual Report, edited by D. Behrend and K.Baver. ; :NASA/TP-2011-215880, s. 280-283
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Book chapter (other academic/artistic)abstract
- This report briefly describes the technical development relevant for geodetic/astrometric VLBI done during 2010 at the Onsala Space Observatory.
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| 12. |
- Albentosa, Ezequiel, et al.
(author)
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Current Status of the EU-VGOS Project
- 2023
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In: International VLBI Service for Geodesy and Astrometry 2022 General Meeting Proceedings. ; NASA/ CP–20220018789, s. 85-89
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Conference paper (peer-reviewed)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.
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| 13. |
- Alef, Walter, et al.
(author)
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Geodetic data analysis of VGOS experiments
- 2021
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In: 2021 34th General Assembly and Scientific Symposium of the International Union of Radio Science, URSI GASS 2021.
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Conference paper (peer-reviewed)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.
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| 14. |
- Alef, Walter, et al.
(author)
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The EUropean-VGOS Project
- 2019
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In: Proceedings of the 24th European VLBI Group for Geodesy and Astrometry Working Meeting. - 9788441656345 ; , s. 107-111
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Conference paper (peer-reviewed)abstract
- In Spring 2018 the Bonn correlation centre started a collaboration with the three European stations of Wettzell, Onsala and Yebes, equipped with both S/X- and broadband systems, to perform VGOS-like test sessions. The aim is to verify and develop further the processing chain for VGOS experiments end-to-end, from the scheduling to the analysis of the derived observables. We will present the current status of the project.
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| 15. |
- Asgarimehr, Milad, et al.
(author)
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Remote Sensing of Precipitation Using Reflected GNSS Signals: Response Analysis of Polarimetric Observations
- 2022
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In: IEEE Transactions on Geoscience and Remote Sensing. - 0196-2892 .- 1558-0644. ; 60
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Journal article (peer-reviewed)abstract
- For the first time, rain effects on the polarimetric observations of the global navigation satellite system reflectometry (GNSS-R) are investigated. The physical feasibility of tracking the modifications in the surface roughness by rain splash and the surface salinity by the accumulation of freshwater is theoretically discussed. An empirical analysis is carried out using measurements of a coastal GNSS-R station with two side-looking antennas in right- and left-handed circular polarizations (RHCP and LHCP). Discernible drops in RHCP and LHCP powers are observed during rain over a calm sea. The power drop becomes larger at higher elevation angles. The average LHCP power drops by ≈ 5 dB at an elevation angle of 45°. The amplitude of the correlation sum shows a dampening, responding to rain rate systematically. The LHCP observations show higher sensitivity to rainfall compared to RHCP observations. The retrieved standard deviation of surface heights shows a steady increase with the rain rate. The derived surface salinity shows a decrease at rains higher than 10 mm/h. This study confirms the potential under environmental conditions of the GNSS-R ground-based station, e.g., with salinity mostly lower than 30 psu, over a calm sea, being a starting point for future investigations.
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| 16. |
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| 17. |
- Behrend, Dirk, et al.
(author)
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Recent Progress in the VLBI2010 Development
- 2008
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In: in Proceedings of the 2007 IAG General Assembly, Perugia, Italy, July 2-13, 2007, ed. M. Sideris, Springer. - Berlin, Heidelberg : Springer Berlin Heidelberg. - 0939-9585. - 9783540854258 ; 133:Part 5, s. 833-840
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Conference paper (peer-reviewed)abstract
- From October 2003 to September 2005, the International VLBI Service for Geodesy and Astrometry (IVS) examined current and future requirements for geodetic VLBI, including all components from antennas to analysis. IVS Working Group 3 "VLBI 2010", which was tasked with this effort, concluded with recommendations for a new generation of VLBI systems. These recommendations were based on the goals of achieving 1mm measurement accuracy on global baselines, performing continuous measurements for time series of station positions and Earth orientation parameters, and reaching a turnaround time from measurement to initial geodetic results of less than 24 h. To realize these recommendations and goals, along with the need for low cost of construction and operation, requires a complete examination of all aspects of geodetic VLBI including equipment, processes, and observational strategies. Hence, in October 2005, the IVS VLBI2010 Committee (V2C) commenced work on defining the VLBI2010 system specifications. In this paper we give a summary of the recent progress of the VLBI2010 project. © Springer-Verlag Berlin Heidelberg 2009.
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| 18. |
- Behrend, Dirk, et al.
(author)
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Reports of IERS Components: International VLBI Service (IVS)
- 2011
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In: IERS Annual Report 2008-09. Edited by Wolfgang R. Dick and Bernd Richter. International Earth Rotation and Reference Systems Service, Central Bureau. Frankfurt am Main: Verlag des Bundesamts für Kartographie und Geodäsie, 2011. 237 p.. - 1029-0060. ; , s. 72-82
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Journal article (other academic/artistic)
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| 19. |
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| 20. |
- Bergstrand, Sten, et al.
(author)
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A gravitational telescope deformation model for geodetic VLBI
- 2019
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In: Journal of Geodesy. - : Springer Science and Business Media LLC. - 0949-7714 .- 1432-1394. ; 93:5, s. 669-680
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Journal article (peer-reviewed)abstract
- We have measured the geometric deformations of the Onsala 20 m VLBI telescope utilizing a combination of laser scanner, laser tracker, and electronic distance meters. The data put geometric constraints on the electromagnetic raypath variations inside the telescope. The results show that the propagated distance of the electromagnetic signal inside the telescope differs from the telescope’s focal length variation, and that the deformations alias as a vertical or tropospheric component. We find that for geodetic purposes, structural deformations of the telescope are more important than optic properties, and that for geodetic modelling the variations in raypath centroid rather than focal length should be used. All variations that have been identified as significant in previous studies can be quantified. We derived coefficients to model the gravitational deformation effect on the path length and provide uncertainty intervals for this model. The path length variation due to gravitational deformation of the Onsala 20 m telescope is in the range of 7–11 mm, comparing elevation 0$$^{\circ }$$∘and 90$$^{\circ }$$∘, and can be modelled with an uncertainty of 0.3 mm.
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| 21. |
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| 22. |
- Bergstrand, Sten, 1971, et al.
(author)
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Geometric Variations of a Geodetic Radio Telescope
- 2017
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In: Proceedings of the 23rd European VLBI Group for Geodesy and Astrometry Working Meeting. - 9789188041104 ; , s. 61-64
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Conference paper (other academic/artistic)
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| 23. |
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| 24. |
- Calves, G. M., et al.
(author)
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Observations and analysis of phase scintillation of spacecraft signal on the interplanetary plasma
- 2014
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 564
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Journal article (peer-reviewed)abstract
- Aims. The phase scintillation of the European Space Agency's Venus Express (VEX) spacecraft telemetry signal was observed at X-band (lambda = 3.6 cm) with a number of radio telescopes of the European Very Long Baseline Interferometry (VLBI) Network in the period 2009-2013. Methods. We found a phase fluctuation spectrum along the Venus orbit with a nearly constant spectral index of -2.42 +/- 0.25 over the full range of solar elongation angles from 0 degrees to 45 degrees, which is consistent with Kolmogorov turbulence. Radio astronomical observations of spacecraft signals within the solar system give a unique opportunity to study the temporal behaviour of the signal's phase fluctuations caused by its propagation through the interplanetary plasma and the Earth's ionosphere. This gives complementary data to the classical interplanetary scintillation (IPS) study based on observations of the flux variability of distant natural radio sources. Results. We present here our technique and the results on IPS. We compare these with the total electron content for the line of sight through the solar wind. Finally, we evaluate the applicability of the presented technique to phase-referencing VLBI and Doppler observations of currently operational and prospective space missions.
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| 25. |
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