FOR 5456:  Clock Metrology: A Novel Approach to TIME in Geodesy

• Subject Area: Geosciences ; Physics
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 490990195

The goal of this research unit is a highly accurate long-term stable realization of the geodetic reference systems by linking the geometric systems to time, thus demonstrating a clear path towards a consistent realization of space-time. Global reference frames are the metrological basis for a multitude of applications, reaching from the quantification of change processes in system Earth over all positioning tasks to terrestrial and space navigation. In view of the high societal relevance of these tasks, the United Nations adopted the UN resolution Global Geodetic Reference Frame for Sustainable Development (GGRF) on February 26, 2015. The GGRF includes the geometry, the gravity field of the Earth (including physical heights) and the orientation of the Earth with respect to the celestial reference frame. This research unit will provide fundamental contributions to the implementation of such an integrated GGRF. Highest accuracy and long-term stability of the reference frame are of paramount importance for the quantification of long-lasting trends, such as sea level changes. These global reference systems are realized by the combination of measurements from a diversity of space geodetic techniques, tied together employing geodetic local surveys at a number of globally distributed core stations, such as the Geodetic Observatory Wettzell (GOW) and the integrated fundamental stations of the National Aeronautics and Space Administration (NASA). Since the local surveys only refer to the geometric but not to the actual reference, systematic errors are inevitable. We propose to establish time coherence as a novel true tie in order to also remove persisting systematic errors from the measurements in space geodesy. Closure measurements utilizing a common clock and ground reference proof and quantify this novel approach. In summary, with this research unit we want to exploit the great opportunity that is presented by the introduction of optical clocks and long distance optical fiber lines for time and frequency transfer to space geodesy, the utilization of the Atomic Clock Ensemble in Space (ACES) and last but not least a novel time and frequency distribution system, enclosing an entire geodetic observatory.

• DFG Programme: Research Units

Projects

• Accurate long distance optical time transfer from ground to ground via a satellite link (Applicants Flechtner, Frank ;  Klügel, Thomas ;  Schlicht, Anja ;  Schreiber, Ulrich )
• ATMO-DEL: Determination of the atmospheric delay via line-of-sight modelling and measurements of the tropospheric composition and the ionospheric electron distribution. (Applicant Palm, Mathias )
• Combination of Space Geodetic Techniques with Clock Ties and Atmospheric Ties (COCAT) (Applicants Balidakis, Kyriakos ;  Schuh, Harald )
• Coordination Funds (Applicant Schreiber, Ulrich )
• Determination of Physical Heights via Time Transfer (Applicants Lisdat, Christian ;  Müller, Jürgen )
• Galileo pseudolite calibration target used to consolidate time between space geodetic techniques (Applicants Kodet, Ph.D., Jan ;  Pany, Thomas )
• General Relativity and coherent time (Applicant Hackmann, Eva )
• Novel clock technologies for combination on ground and in space: real data and simulation (Applicants Glaser, Susanne ;  Seitz, Manuela )
• Performance optimization of the optical clock “SOC2”, installation and operation at Wettzell for geodesy and fundamental physics studies (Applicant Schiller, Ph.D., Stephan )
• The application of time in closure as a novel strategy towards error-free space geodetic observations (Applicant Bloßfeld, Mathis )
• Time as observable in integrated ground and space-based GNSS analysis (Applicants Hugentobler, Urs ;  Männel, Benjamin )

• Spokesperson: Professor Dr.-Ing. Ulrich Schreiber