| 21. |
- Haas, Rüdiger, 1966, et al.
(författare)
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Onsala Space Observatory – IVS Network Station Activities during 2014
- 2015
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- We participated in 39 IVS sessions, includ-ing CONT14. Eleven out of the initially planned ses-sions could not be observed due to the installation ofa new radome for the 20-m radio telescope. As in theprevious six years, we used several of the sessions thatinvolved both Onsala and Tsukuba to perform ultra-rapid UT1-UTC sessions together with our colleaguesin Tsukuba. This included the complete CONT14 cam-paign where near real-time UT1-UTC on the baselineOnsala—Tsukuba could be determined. The procure-ment of the telescopes for the Onsala Twin Telescopeswas started in the summer of 2014. The contract to buytwo VGOS radio telescopes was signed at the end of the year.
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| 22. |
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| 23. |
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| 24. |
- Haas, Rüdiger, 1966, et al.
(författare)
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Status of the Onsala Twin Telescopes – One Year After the Inauguration
- 2019
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Ingår i: IVS 2018 General Meeting Proceedings "Global Geodesy and the Role of VGOS – Fundamental to Sustainable Development". ; NASA/CP-2019-219039, s. 17-19
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Konferensbidrag (refereegranskat)abstract
- We briefly describe the status of the Onsala twin telescopes and the experience gained since the official inauguration in May 2017.
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| 25. |
- Haas, Rüdiger, 1966, et al.
(författare)
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Ultra-Rapid DUT1-Observations with E-VLBI
- 2010
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Ingår i: Artificial Satellites. - : Walter de Gruyter GmbH. - 0208-841X .- 2083-6104. ; 45:2 / 2010, s. 75-79
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Konferensbidrag (refereegranskat)abstract
- We give a short overview about the achievements of the Fennoscandian- Japanese ultra-rapid dUT1-project that was initiated in early 2007. The combination of real-time data transfer, near real-time data conversion and correlation, together with near-real time data analysis allows to determine dUT1 with a very low latency of less than 5 minutes after the end of a VLBI-session. The accuracy of these ultra-rapid dUT1-results is on the same order than the results of the standard rapid-service of the International Earth Rotation and Reference Frame Service (IERS). The ultra-rapid approach is currently extended to 24 hour sessions and is expected to become an important contribution for the future next generation VLBI system called VLBI2010.
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| 26. |
- Haas, Rüdiger, 1966, et al.
(författare)
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Ultra-rapid earth rotation determination with VLBI during CONT11 and CONT14
- 2017
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Ingår i: Journal of Geodesy. - : Springer Science and Business Media LLC. - 0949-7714 .- 1432-1394. ; 91:7, s. 831-837
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Tidskriftsartikel (refereegranskat)abstract
- We present earth rotation results from the ultra-rapid operations during the continuous VLBI campaigns CONT11 and CONT14. The baseline Onsala--Tsukuba, i.e., using two out of the 13 and 17 stations contributing to CONT11 and CONT14, respectively, was used to derive UT1-UTC in ultra-rapid mode during the ongoing campaigns. The latency between a new observation and a new UT1-UTC result was less than 10 min for more than 95{\%} of the observations. The accuracy of the derived ultra-rapid UT1-UTC results is approximately a factor of three worse than results from optimized one-baseline sessions and/or complete analysis of large VLBI networks. This is, however, due to that the one-baseline picked from the CONT campaigns is not optimized for earth rotation determination. Our results prove that the 24/7 operation mode planned for VGOS, the next-generation VLBI system, is possible already today. However, further improvements in data connectivity of stations and correlators as well in the automated analysis are necessary to realize the ambitious VGOS plans.
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| 27. |
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| 28. |
- Haas, Rüdiger, 1966, et al.
(författare)
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VLBI with GNSS signals on intercontinental baselines
- 2018
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Ingår i: - 9789188041142
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Konferensbidrag (refereegranskat)abstract
- The International Terrestrial Reference Frame (ITRF) is constructed based on analysis results of several space geodetic techniques, among them geodetic Very Long Baseline Interferometry (VLBI) and Global Navigation Satellite Systems (GNSS). The meaningful combination of the different techniques requires possibilities to link the various instruments and their reference points. So-called co-location stations that are equipped with instrumentation for several techniques play an important role for the ITRF combination since so-called local-tie vectors on the ground enable the connection between the various instruments. Since several years, ideas have been discussed to include additional possibilities to link the different techniques, with the main goal to improve the ITRF. One of these ideas is to use GNSS signals for VLBI observations and by this improve the link between VLBI and GNSS. In our presentations we describe so-called GNSS-VLBI experiments performed in 2017 with VLBI stations at intercontinental distances. The observations, data correlation and data analysis is described and initial results are presented.
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| 29. |
- Hobiger, Thomas, 1978, et al.
(författare)
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Combining GPS and VLBI for inter-continental frequency transfer
- 2015
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Ingår i: Metrologia. - : IOP Publishing. - 0026-1394 .- 1681-7575. ; 52:2, s. 251-261
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Tidskriftsartikel (refereegranskat)abstract
- For decades the global positioning system (GPS) has been the only space geodetic technique routinely used for inter-continental frequency transfer applications. In the past very long baseline interferometry (VLBI) has also been considered for this purpose and the method's capabilities were studied several times. However, compared to GPS current VLBI technology only provides few observations per hour, thus limiting its potential to improve frequency comparisons. We therefore investigate the effect of combining GPS and VLBI on the observation level in order to draw the maximum benefit from the strength of each individual technique. As a test-bed for our study we use the CONT11 campaign observed in 2011. First we review the frequency transfer performance that can be achieved with independent technique-specific analyses, both with individual software packages and with the multi-technique software c5++. With this analysis approach both techniques, GPS and VLBI, show similar frequency link instabilities at the level of 10−14 to 10−15 (MDEV) on inter-continental baselines for averaging times of one day. Then we use the c5++ software for a combined analysis of GPS and VLBI data on the observation level. We demonstrate that our combination approach leads to small but consistent improvements for frequency transfer of up to 10%, in particular for averaging periods longer than 3000 s.
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| 30. |
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