Accurate long distance optical time transfer | Clock Metrology
Within project 2 of the Research Unit “Accurate long distance optical time transfer from ground-to-ground via a satellite link”, we explore a novel concept of geodetic ties, derived from a highly precise clock. These clock ties allow us to measure and remove the detrimental effect of variable system delays, which are not accessible otherwise. Therefore, this project has two main goals:
- It connects two remote clocks via optical time transfer over a satellite link, utilizing the Atomic Clock Ensemble in Space (ACES) implemented on the International Space Station (ISS) in spring 2025 in order to transport a stable phase relationship (phase coherence) of a clock frequency from one Satellite Laser Ranging observatory (Wettzell) to the next (Potsdam) over several hundred kilometers. This demonstrates the general feasibility of spreading time coherence adequately over larger networks, a prerequisite for the application of clocks as a viable novel tie in space geodesy.
- It explores highly accurate delay-compensated clock comparisons via an optical free space link in common-view, so that the physical properties of the respective clock transitions can be exploited for the determination of the physical height difference between the two clocks. It literally ties two distant geometrical geodetic markers to the same timescale to demonstrate that time coherence can be used as a valuable strong tie in space geodesy. Furthermore, it allows us to accurately link time to space, a prerequisite for the path towards a relativistic geodesy. Physically, we realize an Einstein Synchronization process between ground and space. The validity of this approach is demonstrated by a direct comparison of the optical clocks over the ACES microwave link. In addition, we can closely study the properties of the ACES composite clock to extract relativistic corrections with high accuracy.
Project Partners:
- Bundesamt für Kartographie und Geodäsie (BKG)
- Technische Universität München (TUM)
Project Duration:
- 2023 until 2027
Project Funding:
- German Research Foundation (Deutsche Forschungsgemeinschaft, DFG), Project number 490990195
Project Website:
