Time as observable in integrated ground and space-based GNSS analysis

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In the future, ultra-stable clocks will be available on the ground and in space, as well as high-precision time and frequency transmission systems. The goal of this project is to integrate data from these new tools into GNSS geodetic data analysis and to analyse their potential for computing global geodetic precision products derived from GNSS. The project is part of the FOR5456 research group, whose overarching goal is to fully exploit ultra-stable clocks and high-precision frequency and time transmission in geodesy. Within the research group the technology for a lossless link between clocks and GNSS signals will be developed, a high-precision laser space link between the Wettzell (GOW) and Potsdam geodetic observatories will be provided, an ultra-stable optical clock at the GOW will installed and operated, and a link between the Potsdam observatory and the PTB optical clocks in Braunschweig via a compensated optical fiber or, alternatively, an optical clock operated in Potsdam is planned. The resulting opportunities will be investigated in detail in this project with a focus on GNSS. The benefits of lossless linking of GNSS receivers to a common clock on short baselines on the GOW campus and on the long baseline between GOW and Potsdam will be evaluated using closure experiments. In parallel, the full potential of modelling the available ground and space clocks for satellite orbit improvement, decorrelation of estimated parameters, and determination of geodetic parameters in a global network will be explored. The obtained findings are extrapolated to global GNSS networks using simulations and real data to evaluate, by means of the developed methods, the potential of time coherence realized by ground and space links in a global network and of modelling highly stable ground and space clocks for the estimation of global geodetic parameters.