Improved modeling for hybrid accelerometers onboard future gravity missions

Cold Atom Interferometry (CAI) has proven to be a very efficient technique to achieve high sensitivity for absolute inertial sensing. It is proposed to use CAI accelerometers onboard future generations of satellite gravimetry missions to provide long-term stability and precise measurements of the non-gravitational forces acting on the satellites. This would reduce the overall instrumental errors and improve our knowledge of the Earth gravity field and its change over time. This would allow a better understanding of climate change processes and various geophysical phenomena (e.g. post-glacial rebound). Even though the accuracy and long-term stability of CAI-based accelerometers seem promising, they suffer from long dead times and a comparatively small dynamic range of the sensor. One promising way to handle those drawbacks is to use them in hybrid combination together with a conventional electrostatic accelerometer. We have previously discussed a specific possible solution to employ the measurements of a CAI accelerometer together with a classical accelerometer by applying a Kalman filter Framework which had already shown an improved navigation solution with respect to a reference trajectory (Tennstedt and Schön, 2021). Here, we implement an improved CAI modeling in the simulation to consider the in-flight conditions of a GRACE-like gravimetry mission (e. g. the impact of satellite rotation and gravity gradients) on the CAI measurements. The noise model is also improved to generate more realistic simulated measurements, by considering the impact of different noise sources (e.g. shot noise, detection noise, laser frequency noise and the vibration of the reference mirror). We then perform a closed-loop simulation in which we employ measurements of a CAI accelerometer together with a conventional Inertial Measurement Unit (IMU) using the improved Kalman filter framework and we compare the combined accuracy in the determination of the non-gravitational forces. In addition, we perform simulations using two or three CAI axes. We also study the possibility of having a CAI with a very long interrogation time (>10 seconds) and discuss the challenges and potential improvements. Finally, we compare the recovered gravity field for the various test cases with GRACE solutions. We acknowledge the support by the Deutsche Forschungsgemeinschaft (DFG) under Germany's Excellence Strategy - EXC 2123 "QuantumFrontiers, Project-ID 390837967", the Collaborative Research Center SFB 1464 "TerraQ" -, Project ID 434617780, and the Federal Ministry for Economic Affairs and Energy (BMWi), Project-ID 50RK1957. Reference 1 Tennstedt B, Schön S (2021) Integration of atom interferometers and inertial measurement units to improve navigation performance. In: 28th Saint Petersburg International Conference on Integrated Navigation Systems (ICINS), 31.05.-02.06.2021, St. Petersburg, Russia, IEEE, Piscataway, NJ, https://doi.org/10.23919/ICINS43216.2021.947080