Consistent celestial and terrestrial reference frames by improved modelling and combination

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The goal of this project is to deliver a celestial reference frame (CRF), a terrestrial reference frame (TRF), and the corresponding Earth orientation parameters (EOPs) with highest possible consistency based on improved modelling of the space geodetic observations and on the development and application of advanced combination methods. The combination of the homogeneously processed VLBI, SLR and GNSS observation time series to derive those reference frames will be performed by applying two different approaches: a) on the level of observation equations (at BKG), and b) on the level of constraint-free normal equations (at DGFI). Both institutions will compute epoch reference frames by combining the different space geodetic techniques on a weekly basis, in addition to the computation of long-term multi-year reference frames. Thereby, BKG generates solutions with suitable geophysical fluid models consistently applied, and the impact of the latter on the reference frame results will be studied. BKG will also develop improved combination methods for a consistent TRF and EOP estimation by including satellite co-locations, i.e., by additionally using SLR observations to GNSS satellites. DGFI will apply the extended parameterization of non-linear station motions for long-term reference frame computations and will generate consistent results for CRF, TRF and EOPs. The different strategies and reference frame results will be compared with each other and with external solutions provided by the IERS. Finally, the results of this project shall allow to assess the gain of the improved combination methods for TRF, CRF and EOP compared to standard IERS approaches.