Atomic Clocks in Satellite Gravimetry, Investigation of Precision Requirements by Closed Loop Simulations

More precise determination of mass-redistribution processes in the Earth system demands novel measurement concepts and sensors for future satellite gravimetry missions. On the sensor side, atomic clocks are interesting candidates due to the gravitational red-shift effecting the clock’s frequency. However, clocks also experience a red-shift due to their state of motion. Hence their velocity needs to be known very precisely. This problem can be solved by utilizing a classical time-wise variational equation approach for gravity field recovery. In this approach the satellite's orbit in terms of position and velocity is adjusted together with the gravitational field coefficients and hence no prior high accuracy knowledge of the satellite's (clock's) velocity is needed.

This contribution gives detailed insights into satellite-based clock measurements used in gravity-field recovery. We present the mathematical foundations for an idealised measurement and a realistic one-way frequency comparison via laser. Results are evaluated in a closed-loop approach for multiple scenarios, like GRACE, Bender, Helix, and High-Low.

We investigated the performance of clock measurements between satellites in different mission scenarios, noise levels and clock integration times under consideration of increasingly realistic simulation and processing conditions. Comparison of these analyses to KBR measurements gives insights into the limits and required technological improvements concerning atomic clocks that are needed to benefit from clocks in gravimetric missions.

 

This work has been part of the Collaborative Research Center 1464 TerraQ and funded by DFG.