| 1. |
- Elgered, Gunnar, 1955, et al.
(författare)
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The Onsala Tide Gauge Station: Experiences from the first four years of operation
- 2019
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Ingår i: Proceedings of the 24th European VLBI Group for Geodesy and Astrometry Working Meeting. ; , s. 75-79
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Konferensbidrag (refereegranskat)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.
(författare)
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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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Ingår i: Proceedings of the 20th Meeting of the European VLBI Group for Geodesy and Astrometry. - 1864-1113. ; , s. 133-137
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)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.
(författare)
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Simulations of Different Antenna Velocities in VLBI Networks
- 2009
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Ingår i: Proceedings of the 19th European VLBI for Geodesy and Astrometry Working Meeting, 24-25 March 2009, Bordeaux. ; , s. 169-172
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)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.
(författare)
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Space Geodesy at Yebes: Station Motion from VLBI and GPS
- 2008
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Ingår i: in Proceedings of the 5th IVS General Meeting "Measuring the future", eds A. Finkelstein, D. Behrend. - 9785020253322 ; , s. 93-97
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 8. |
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| 9. |
- Haas, Rüdiger, 1966, et al.
(författare)
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Status of the Onsala Twin Telescopes – Two Years After the Inauguration
- 2019
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Ingår i: Proceedings of the 24th European VLBI Group for Geodesy and Astrometry Working Meeting. - 9788441656345 ; , s. 5-9
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Konferensbidrag (refereegranskat)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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