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

Abstract

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.

Automated ambiguity estimation for VLBI Intensive sessions using L1-norm

“…The differences in all categories are below 0.2 µs. These values reflect the general level of UT1-UTC accuracy obtainable from INT sessions (Kareinen et al, 2015).…”

“…Automated near-real time analysis of INT sessions has been investigated in e.g. Hobiger et al (2010) and Kareinen et al (2015). Geodetic VLBI sessions are typically observed on two frequency bands centred around 8.4 GHz (X-band) and 2.3 GHz (S-band).…”

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

“…In contrast to increasing the observing time of the Intensive sessions from the 1-h duration, the three-station approach addresses 19,4) in addition to the increased number of observations also the weaknesses in the observing geometry. Approaches to improve the performance of the INT sessions with an emphasis on near-real time applications have been studied in, e.g., Hobiger et al (2010) and Kareinen et al (2015). Similarly, the TAF and UT1-UTC WRMS maps are suitable for near-real time applications by providing a spatially dependent selection criteria for scheduling.…”

Ultra-rapid earth rotation determination with VLBI during CONT11 and CONT14

“…However, the latter has so far only been demonstrated for a restricted number of participating stations and not yet for longer than 24 h. Furthermore, so far all real-time operations have been done with rather moderate data rates of less than 1 Gb/s, which is much lower than the planned data rates for VGOS. It is anticipated that the currently existing strategies for automated analysis Kareinen et al 2015) will be extended in the near future from single baseline observations to network observations. In this context, it is highly desirable to also include robust analysis strategies, as described by Kareinen et al (2016).…”