Optimized scheduling of VLBI UT1 intensive sessions for twin telescopes employing impact factor analysis

Leek, Judith; Artz, Thomas; Nothnagel, A.

doi:10.1007/s00190-015-0823-3

Cited by 15 publications

(13 citation statements)

References 22 publications

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“…In doing so, the expectation is that not only the precision of the UT1-UTC will increase, but also its accuracy. Another potential for improvement might be found in sophisticated scheduling algorithms, as presented by Leek et al (2015). In general, the next-generation VLBI system, VGOS (Petrachenko et al 2012), promises improvements due to for example broadband observations with fast-slewing telescopes.…”

Section: Discussionmentioning

confidence: 99%

Automated analysis of Kokee–Wettzell Intensive VLBI sessions—algorithms, results, and recommendations

2015

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The time-dependent variations in the rotation and orientation of the Earth are represented by a set of Earth Orientation Parameters (EOP). Currently, Very Long Baseline Interferometry (VLBI) is the only technique able to measure all EOP simultaneously and to provide direct observation of universal time, usually expressed as UT1-UTC. To produce estimates for UT1-UTC on a daily basis, 1-h VLBI experiments involving two or three stations are organised by the International VLBI Service for Geodesy and Astrometry (IVS), the IVS Intensive (INT) series. There is an ongoing effort to minimise the turn-around time for the INT sessions in order to achieve near real-time and high quality UT1-UTC estimates. As a step further towards true fully automated real-time analysis of UT1-UTC, we carry out an extensive investigation with INT sessions on the Kokee-Wettzell baseline. Our analysis starts with the first versions of the observational files in S-and X-band and includes an automatic group delay ambiguity resolution and ionospheric calibration. Several different analysis strategies are investigated. In particular, we focus on the impact of external information, such as meteorological and cable delay data provided in the station log-files, and a priori EOP information. The latter is studied by extensive Monte Carlo simulations. Our main findings are that it is easily possible to analyse the INT sessions in a fully automated mode to provide UT1-UTC with very low latency. The information found in the station log-files is important for the accuracy of the UT1-UTC results, provided that the data in the station log-files are reliable. Furthermore, to guarantee UT1-UTC with an accuracy of less than 20 μs, it is necessary to use predicted a priori polar motion data in the analysis that are not older than 12 h.

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Section: Discussionmentioning

confidence: 99%

Automated analysis of Kokee–Wettzell Intensive VLBI sessions—algorithms, results, and recommendations

2015

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“…Uunila et al (2012) looked at classifying sessions based on the distributions of the observed sources. Leek et al (2015) studied the use of impact factors to optimise the observing geometry. This approach was also applied to scheduling Intensive sessions for a twin-telescope system at Wettzell.…”

Section: Introductionmentioning

confidence: 99%

Identifying optimal tag-along station locations for improving VLBI Intensive sessions

Kareinen

Kłopotek

Hobiger

et al. 2017

Earth Planets Space

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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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“…From the point of view of keeping good temperature stability of the time transfer, it is important to know the sensitivity of the time transfer results on changes of the internal delays. The sensitivity of the time difference and link delay estimations to the change of the temperature in the unit A are: (13) and the sensitivity to the change of the temperature in the unit B are:…”

Section: Two-way Time Transfer Analysismentioning

confidence: 99%

“…Some of these projects are dealing with a high performance optical frequency transfer [8][9][10], which is typically used for comparing optical frequency standards. However, in many applications high accurate time transfer is required as well [11][12][13]. In cases where slightly subnanosecond accuracy is sufficient, the time transfer can be solved using the popular White Rabbit technique [14], but in other cases like the fundamental geodesy the accuracy requirements are much more severe.…”

Section: Introductionmentioning

confidence: 99%

Two-way time transfer via optical fiber providing subpicosecond precision and high temperature stability

2015

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We are reporting on analysis, design, construction, and key parameters of the device for a two-way time transfer via an optical fiber. The dominant source of errors in the two-way optical time transfer (TWOTT) via relatively short optical fibers is the temperature dependence of internal delays within the terminal units. We have performed an analysis of the influence of the internal delays and their temperature dependence on the TWOTT process considering two different configurations of the terminals with the feedback coupling in optical and electrical domains. The achieved results have been used for the optimal design of a TWOTT system implementing standard small form-factor pluggable optical transceivers. The operational tests of this new TWOTT system confirmed the precision of the time transfer on the subpicosecond level, the time transfer stability characterized by TDEV better than 60 fs for averaging intervals from 100 s to 10 000 s, and the temperature stability better than 100 fs K −1 .

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Optimized scheduling of VLBI UT1 intensive sessions for twin telescopes employing impact factor analysis

Cited by 15 publications

References 22 publications

Automated analysis of Kokee–Wettzell Intensive VLBI sessions—algorithms, results, and recommendations

Automated analysis of Kokee–Wettzell Intensive VLBI sessions—algorithms, results, and recommendations

Identifying optimal tag-along station locations for improving VLBI Intensive sessions

Two-way time transfer via optical fiber providing subpicosecond precision and high temperature stability

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