Abstract
We study the effects of combination on the observation level (COL) of different space-geodetic techniques and of networks of the same technique and present the corresponding improvement for the determination of station positions and earth orientation parameters. Data from the continuous geodetic very long baseline interferometry (VLBI) campaign CONT17 are used in a batch least-squares (LSQ) estimator. This campaign includes 15 days of observations with two legacy S/X networks, namely Legacy-1 (L1) and Legacy-2 (L2). For this study the VLBI L1 network is used as the base and reference solution. Data from the L1 network are combined first with data from co-located Global Positioning System (GPS) stations by estimating common tropospheric parameters. The derived station positions repeatabilities of the VLBI and GPS networks are evaluated with respect to single-technique solutions. In terms of precision, we find a 25% improvement for the vertical repeatability of the L1 network, and a 10% improvement for the horizontal one. The GPS network also benefits by 20% and 10% in the horizontal and vertical components, respectively. Furthermore, a combined solution using data of the L1 and L2 network is performed by estimating common earth orientation parameters. The combined L1&GPS and L1&L2 solutions are compared to the reference solution by investigating UT1 and polar motion estimates. UT1 is evaluated in terms of mean bias and formal errors with respect to the International Earth Rotation Service (IERS) C04 products which were used as a priori values. The L1&GPS solution has the lowest formal error and mean bias for UT1 with a 30% improvement. The weighted root mean square (WRMS) and weighted mean offset (WMO) differences between the obtained polar motion estimates and the ones derived by the International GNSS Service (IGS) are also compared. We find that the L1&GPS solution gives the lowest WRMS and WMO, exhibiting an average 40% improvement with respect to the reference solution. The presented results highlight the potential of COL for ongoing transition to multi-space geodetic analysis, e.g., Global Navigation Satellite Systems (GNSS) with the next-generation VLBI system.Graphic
Highlights
Two-week continuous geodetic very long baseline interferometry (VLBI) campaigns have been organized by the International VLBI Service for Geodesy and Astrometry (IVS, Nothnagel et al 2017) every third year since 2002
The effect of combination on the L1 network by employing combination on the observation level (COL) of VLBI with co-located Global Posi‐ tioning System (GPS) stations is examined in the following context
The GPS network on the other hand experiences the biggest improvement in the north component by 40%, followed by the up component by 10%, while the east shows a slight degradation of 5%
Summary
Two-week continuous geodetic VLBI campaigns have been organized by the International VLBI Service for Geodesy and Astrometry (IVS, Nothnagel et al 2017) every third year since 2002. Space-geodetic techniques have different strengths and weaknesses for recovering global geodetic parameters Their combination is beneficial to fully exploit the strengths of each of them and overcome the technique-specific weaknesses (Artz et al 2012), assuming that the combination is properly constructed, suitable weights are applied and good quality ties at co-location sites are available. One such example could be the geocenter coordinates that can be transferred from SLR to the GNSS network, in the case of a combined SLR-GNSS solution (Sośnica et al 2019). Utilization of many space-geodetic techniques improves the global geometrical coverage, the quantity of observations and their density, and helps in the reduction of correlations between the estimated parameters
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