Combination of space-geodetic techniques in the era of VGOS and multi-GNSS

Doctoral thesis, 2023

The definition and maintenance of accurate and stable Earth-fixed and inertial reference frames is crucial in studying, among else, geophysical and geodynamical phenomena, precise positioning, and space navigation. The tools used to this end are space-geodetic techniques, like e.g., Very Long Baseline Interferometry (VLBI) and Global Navigation Satellite Systems (GNSS) which utilize signals from extraterrestrial radio sources to determine parameters of interest. An important concept in this regard is that of co-location. Stations of different space-geodetic techniques that are in close vicinity can be linked to the same frequency standards, are subject to similar loading effects, and share common atmosphere. In practice, they are also linked with observations that determine the vector between their respective reference points. These common features and inter-technique observations allow for the stacking of the heterogeneous space-geodetic observables in an estimation process that has been shown to suppress technique-specific biases and improve the accuracy and precision of the inferred parameters. The combination of space-geodetic techniques at co-location sites is delivering high-quality geodetic products. Recent developments in GNSS and VLBI include the incorporation of state-of-the-art instrumentation, in the form of satellite constellations in so-called multi-GNSS, or next-generation radio telescopes in VLBI that comprise the VLBI Global Observing System (VGOS). This thesis presents the principles of VLBI and GNSS, and then studies the untapped potential of novel concepts for the combination of space-geodetic techniques in the era of VGOS and multi-GNSS.