The application of time in closure as a novel strategy towards error-free space geodeticobservations

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This project is the closest to the outlined concept of the clock tweezers as given in the cover application of this research unit. The project closely cooperates with several other projects of the research unit, namely P1, P5, P6, P8, P9 and P10. This highlights the central role of the project for the whole research unit. It aims at different foci for the improvement of space-geodetic techniques by exploiting the common space-time reference point, realized at GOW. The overall goal of the project is the identification and minimization of measurement errors and the development of calibration procedures applicable in routine operations. In addition, the separation of observation errors and atmospheric delays is envisaged. The accuracy provided by the techniques today still suffers from a combination of unknown systematic instrumental and model errors. In a first step, the already existing closure measurements for SLR and VLBI are revisited to identify, extract and resolve the hidden biases. Afterwards, together with the team at GOW we will design, conduct and analyse further measurements in order to come up with the best strategy for the mitigation of systematic errors, based on clock ties. DORIS does not directly depend on the ground clock and GNSS will eventually have an independent calibration via a pseudolite. This requires a different analysis strategy compared to SLR and VLBI. The reliable identification and extraction of the variable systematic errors based on clock ties are central. Finally, corrected (calibrated) observations are provided to other projects of the research unit (P9 and P10) for the inter-technique combination. This project strongly contributes to the technical redesign of the station fiducial marker as a role model for a possible future GGOS core station requirement and validates its performance.