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- Kareinen, Niko Petteri, 1986, et al.
(författare)
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Identifying optimal tag-along station locations for improving VLBI Intensive sessions
- 2017
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Ingår i: Earth, Planets and Space. - : Springer Science and Business Media LLC. - 1880-5981 .- 1343-8832. ; 69:1, s. 16-
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Tidskriftsartikel (refereegranskat)abstract
- Very Long Baseline Interferometry (VLBI) is a unique space-geodetic technique capable of direct observation of the Earth’s phase of rotation, namely Universal Time (UT1). The International VLBI Service for Geodesy and Astrometry (IVS) conducts daily 1-h Intensive VLBI sessions to determine rapid variations in the difference between UT1 and Coordinated Universal Time (UTC). The main objective of the Intensive sessions is to provide timely UT1–UTC estimates. These estimates are especially crucial for Global Navigation Satellite Systems (GNSS). The monitoring of rapid variations in Earth rotation also provides insight into various geophysical phenomena. There is an ongoing effort to improve the quality of the UT1–UTC estimates from single-baseline Intensive sessions to realise the expected accuracy and to bring them to a better agreement with the 24-h VLBI sessions. In this paper, we investigate the possibility to improve the Intensives by including a third station in tag-along mode to these regularly observed sessions. The impact of the additional station is studied via extensive simulations using the c5++ analysis software. The location of the station is varied within a predetermined grid. Based on actual Intensive session schedules, a set of simulated observations are generated for the two original stations and each grid point. These simulated data are used to estimate UT1–UTC for every Intensive session scheduled during the year 2014 on the Kokee–Wettzell and Tsukuba–Wettzell baselines, with the addition of a third station. We find that in tag-along mode when a third station is added to the schedule we can identify areas where the UT1–UTC estimates are improved up to 67% w.r.t. the original single-baseline network. There are multiple operational VLBI stations in these areas, which could with little effort be included in a tag-along mode to the currently scheduled Intensive sessions, thus providing the possibility to improve the UT1–UTC estimates by extending the observation network.
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- Klopotek, Grzegorz, 1990, et al.
(författare)
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Implementation of VLBI Near-Field Delay Models in the c5++ Analysis Software
- 2017
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Ingår i: Proceedings of the First International Workshop on VLBI Observations of Near-field Targets, October 5 - 6, 2016, A. Nothnagel and F. Jaron (eds.). - 1864-1113. ; 54, s. 29-33
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We describe the implementation of two near-field delay models in the c5++ analysis software. The motivation for this work is to allow the calculation of a priori delay information for the correlation of VLBI raw observations of near-field targets and to prepare for the analysis of VLBI data of near-field objects. The software is tested by correlating VLBI observations of the Chinese Chang’E lunar lander on the Onsala– Wettzell baseline.
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- Klopotek, Grzegorz, 1990, et al.
(författare)
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Lunar Observations and Geodetic VLBI – A Simulation Study
- 2017
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Ingår i: Proceedings of the 23rd European VLBI Group for Geodesy and Astrometry Working Meeting. ; , s. 122-126
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The recent OCEL (Observing the Chang’E Lander with VLBI) sessions allow the geodetic VLBI community to gain new experience concerning observations of an artificial lunar radio source. Although the analysis of obtained data is still ongoing, the performance of the OCEL sessions, in terms of lunar-based parameters, is still rather unclear. In order to address this and related questions, we carried out Monte Carlo simulations using the c5++ analysis software and OCEL schedules with the purpose to evaluate the accuracy with which the position of an artificial radio source on the surface of the Moon can be determined with geodetic VLBI. We present the results of our study and discuss the limiting factors of this concept. Our simulation results can provide valuable insights concerning global observations of lunar radio transmitters and stimulate new observing ideas for space geodesy.
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- Klopotek, Grzegorz, 1990
(författare)
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Simulation studies of new observing concepts for geodetic Very Long Baseline Interferometry
- 2017
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Very Long Baseline Interferometry (VLBI) is a space-geodetic technique in which observations are carried out simultaneously by radio telescopes separated by hundreds or thousands of kilometers. The time difference of signal reception between the telescopes is the basic observable used in geodetic VLBI. This technique is capable of determining all five Earth Orientation Parameters (EOP), which provide the connection between the Earth-fixed and space-fixed reference frames. Currently, there is an ongoing effort concerning the establishment of the VLBI Global Observing System (VGOS), which will significantly improve the present measurement precision and increase the total number of observations per session. This requires the key components of the infrastructure, data handling as well as observation approaches to be upgraded and refined. Thus, the focus of this thesis is set on new observing concepts for VGOS. This includes extensive simulations regarding an improved determination of the rotation of the Earth (UT1-UTC) from one-hour VLBI sessions and investigations on the potential of lunar observations in regular geodetic VLBI sessions. The studies summarized in this work address the main topic from two different aspects, providing valuable insights concerning observations in the VGOS era and stimulating new concepts for space geodesy.
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