Abstract
Abstract. The VLBI (Very Long Baseline Interferometry) technique can provide the full set of parameters needed for the transformation between celestial and terrestrial reference frames with high accuracy. Yet it has some limitations regarding temporal resolution and continuity, and the accuracy of the resulting Earth Orientation Parameters (EOP) varies depending on the network geometry. In this work we explore the benefit of combining VLBI observations with the measurements of the large ring laser gyroscope “G” in Wettzell for deriving highly resolved ERP (Earth Rotation Parameters, i.e. polar motion and universal time variations, δUT1). We examine the observations collected by two simultaneously operating VLBI networks during the 15 d of the CONT17 campaign. These two networks, of 14 globally distributed telescopes each, were designed for the estimation of Earth rotation variations, for which reason the resulting hourly ERP are appointed as benchmark in this investigation. To evaluate the advantage of a VLBI and ring laser combined solution, we create degraded versions of the original networks, containing only six stations. The ERP derived from those sparse networks and from the VLBI sparse plus ring laser solutions are then compared in terms of differences to the reference values. It should certainly be considered that these are relative numbers, since they are also determined by the number and selection of the stations remaining in the sparse networks. The root mean square of the difference to the benchmark is reduced by 24 % in case of δUT1 from one network. The polar motion yp component from the same network moves 14 % closer to the reference value due to the inclusion of the ring laser data. The impact on xp and on all ERP from the other network ranges between 2 % and 9 %. The research again confirms the feasibility and also the potential gain of a combined evaluation of VLBI and ring laser observations, but the full capacity of such a sensor fusion will emerge once the ring laser gyroscopes reach a level of accuracy similar to VLBI.
Highlights
The Earth’s variable rotation can be monitored accurately by space geodetic techniques
Very Long Baseline Interferometry (VLBI) uses Earth-tied station networks to observe signals emitted by extragalactic radio sources and establishes a direct link between the terrestrial and the celestial reference frames
We investigate the current potential of combined VLBI and ring laser solutions to compensate for an adverse VLBI network geometry
Summary
The Earth’s variable rotation can be monitored accurately by space geodetic techniques. Nilsson et al (2012) already demonstrated the feasibility of combining VLBI and ring laser data for the estimation of high-resolution polar motion and δUT1. They investigated routine 24 h VLBI sessions and ring laser data for five and a half months in 2010 and evaluated the combination effect by comparing the resulting Earth rotation parameters (ERP) to the sum of the C04 05 EOP series and the conventional model for high-frequency ocean tidal Earth rotation variations (IERS Conventions, 2010), both provided by the International Earth Rotation and Reference Systems Service (IERS). Ring lasers are referenced to the local inertial frame and have a high temporal resolution of say one minute between data points This desirable property is a suitable supplement to the very good long term stability of the VLBI technology. We construct artificially diminished versions of the original networks with six stations each and compare the ERP obtained from VLBI only and the VLBI – ring laser combination to the reference solutions
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