Integrated Processing of GNSS, VLBI, and SLR on the Observation Level

The terrestrial and celestial reference frames (TRF and CRF) linked by the Earth Orientation Parameters (EOP) serve as the foundation in geodesy. The reference frames and EOP are determined by combining four space geodetic techniques, including Very Long Baseline Interferometry (VLBI), Satellite Laser Ranging (SLR), Global Navigation Satellite Systems (GNSS), and DORIS (Doppler Orbitography and Radiopositioning Integrated by Satellite). Currently the combination is performed either on the parameter or on the normal equation level. In contrast, a combination on the observation level allows fully consistent modeling and parameterization, and thus provides the TRF, CRF, and EOP with the highest consistency, precision, and reliability. In this study, we present preliminary results of the multi-technique integrated processing, including GNSS, VLBI, and SLR, using the upgraded Positioning And Navigation Data Analyst (PANDA) software which can process the three techniques in combination on the observation level. We investigate the impact of global ties, that is, EOP, local ties, and tropospheric ties, with the focus on handling the systematic tie biases automatically. We demonstrate the contributions of the different techniques on the reference frames and EOP. The integrated solution is dominated by the huge number of globally distributed GNSS observations. The VLBI observations contribute to the determination of the full set of EOP and the TRF network scale parameter, whereas the SLR observations contribute to the determination of the network scale and the geocenter. By combining the three techniques, the results outperform any single-technique solution in terms of precision and reliability.