B07 – CRC 1128: Relativistic Geodesy and Gravimetry with Quantum Sensors (geo-Q)

In the wake of the far-reaching benefits of the gravity missions GRACE and GOCE, there is a strong demand for sustaining a global and continuous mapping of the Earth‘s gravitational field.

In project B07, we study to what extent gravitational gradiometry could be a good candidate for future missions in the light of current developments in sensor physics. This has led us to study new concepts of inertial sensors based on laser interferometry and to a lower extent cold atom interferometry. The work carried out includes analytical studies and simulations to

Figure 01: Scheme of one axis of the optical gradiometer concept

Figure 02: Noise level requirement for the optical gradiometer and comparison to GOCE

quantify the requirements of the end-users in terms of precision and resolution of the recovered gravity field model
derive the corresponding requirements at the level of the different sensors, e.g., gradiometer (figure 02), accelerometers, attitude determination system, etc.
design, model and characterize gradiometer concepts that can meet these requirements and
test and evaluate such concepts based on end-to-end simulations.

So far, we modeled the full gradiometry measurement chain, partly with simplified assumptions on calibration and drag-free control. A sensitivity level of 10^-4E/√Hz for the gradiometer seems to be feasible.The gradiometer concept consisting of pairs of electrostatic accelerometers with a laser interferometry read-out (figure 01) seems particularly promising. The resolution and noise level can indeed be significantly improved compared to the GOCE gradiometer and the recovery of tiny temporal variations of the gravity field becomes possible. While a parallel project, A07, aims to develop the optical read-out system for such a gradiometer, we focus on the system-level implications, e.g., the optimization of the physical parameters of the accelerometers, the trade-off between the gradiometer dynamic range and the spacecraft dynamics, the processing of raw data and their calibration and eventually the evaluation of the performance of the sensor concept in the framework of realistic simulations.

Publications in B07