On simulation studies for novel combination strategies of space geodetic techniques

This effort as part of the research unit "Clock Metrology" funded by the German Research Foundation (DFG) focuses on innovative strategies for combining all four space geodetic techniques—DORIS, GNSS, SLR, and VLBI—to significantly enhance the global Terrestrial Reference Frames (TRF) with the goal to achieve the GGOS (Global Geodetic Observing System) requirements of 1 mm accuracy and long-term stability of 1 mm/decade. To achieve this goal, a novel approach of combining the space geodetic techniques is being developed. A common target (CT) will be introduced at the Geodetic Observatory Wettzell (GOW) to combine all the techniques at a common reference point. Additionally, a common clock (CC) will be established at GOW to reference the observations of all techniques to a single time frame. The impact of the CT and CC on the TRF combination is evaluated through simulations involving all four space geodetic techniques. In this study, we exhibit the results of the SLR, GNSS, and VLBI simulations of global station networks as reference solutions for the following implementation of CT and CC. As basis for these simulations, we used current state-of-the-art models and standards based on real observation data to determine realistic accuracy measures for today’s technique-specific observations. We assume a white noise of the observations with an amplitude corresponding to the noise derived from actual data analysis of the real observations for each technique. Subsequently, weekly normal equation systems from the simulated data were accumulated into a combined global TRF solution over a 7-year period to assess the impact on the derived station coordinates and velocities, as well as the Earth Rotation Parameters. The estimated corrections to the station positions remain within a few millimeters, indicating a consistent solution w.r.t a priori. Additionally, in order to perform the combination via a CC, extended software modifications are carried out as in the space geodetic data analysis the clock parameters are usually pre-eliminated and no longer available for further processing. Based on these modifications, first results of the novel combination of intra- and inter-techniques at GOW will be presented.