A04 - Optical Clocks for Chronometric Levelling

We will realise the potential of chronometric levelling by demonstrating off-campus height measurements with the same or better resolution than geometric levelling and the Global Navigation Satellite System (GNSS)/geoid approach can presently achieve, in joint campaigns with project A05. This demonstration will be strengthened by the application of our measurement capabilities to geodetic problems of high relevance through cooperation with the TerraQ projects employing gravimetric and GNSS techniques to e.g. monitor water storage and other mass changes (projects Terrestrial Clock Networks: Fundamental Physics and Applications (C02), Modelling of Mass Variations Down to Small Scales by Quantum Sensor Fusion (C05), and Atmosphere-Ocean Background Modelling for Terrestrial Gravimetry (C06)). We will begin with quasi-static observations for the detection and verification of height offsets or tilts in networks and the connection of a small island to the mainland. In the following funding periods of TerraQ, we will expand towards time-resolved observations, initially focusing on seasonal changes, but aiming at the observations of daily variations. To achieve these goals, we need transportable optical clocks that reach fractional uncertainties of 10^-18 and lower. In view of the very small number of laboratory clocks that have been evaluated at this level, this is a very ambitious task. Though we will not put our main focus on the instrument development in this project, constant improvement and repeated validation of the clocks are paramount to reach the confidence that is required to make the transition from a proof-of-concept demonstration to routine operation.