Simulation of relativistic and environmental influences on laser signals used for gravity field recovery with spaceborne optical clocks

One major objective of Geodesy is the observation of the Earth, its gravity field and climate. To study subtle but impactful changes in the gravitational field, novel paradigms and high-precision measurement schemes are emerging.

According to Einstein’s Theory of General Relativity, the proper time of a clock is the four-dimensional length of its worldline through curved spacetime. Thus, the comparison of clocks always is a comparison of local spacetime geometries. Thereupon, clock comparison could be used as a new method, termed chronometry, for gravity field recovery (GFR) via high-precision timing and redshift measurements. With the fast development of new, better, and smaller time measurement devices, optical clocks are a promising tool for GFR. Such clocks can be compared using, e.g., a light signal propagating in free space. For the determination of all gravitational degrees of freedom, it is necessary to relocate at least one clock around the planet. This can be done via moving clocks on satellites. To interpret these precise measurements correctly, it is essential to consider all influences on the laser signal used.

For this purpose, DLR and ZARM developed a simulation platform called XHPS in the scope of the DFG Collaborative Research Center 1464 TerraQ to model the environmental effects on satellites. It is used to study the influences on the laser signal between a ground station and satellites (or between two satellites). In particular, we want to simulate the signal loss caused by the Earth’s atmosphere, as well as other influences such as the relativistic redshift. It might also be interesting to compare the magnitude of redshift and atmospheric perturbations. This work will present the current state of our research.