Mitigating Temporal Aliasing Effects by the Space-Wise Approach for Quantum Gravimetry Missions

The aliasing problem in gravity field recovery arises from the under-sampling of geophysical signals which have a period less than twice the sampling period of the mission. This temporal aliasing problem matters even more for future gravity missions when assessing the actual improvement provided by using new technologies such as cold atom gradiometers or flying drag-free with a laser interferometer. The level of errors caused by temporal aliasing is significantly higher than these instrument errors. This indicates that to see any sort of improvement in time-variable gravity field recovery from quantum technologies, the aliasing problem must be overcome first.

In this study, we propose a way of mitigating temporal aliasing effects by the space-wise approach. This approach consists of first estimating the very long wavelengths by some global technique (e.g., a least-squares adjustment) and then using this estimation to reduce filtered gravity gradients. A modification considering the short-term variations in the time-variable signal is here introduced into the filtering procedure. Later, the computed residuals are processed by a local collocation gridding procedure with the aim of improving the solution, especially for the shorter wavelengths. The signal covariance function estimation required for the gridding is here modified to account for the time variable signal.

The data analysis based on the newly modified mathematical model is applied for the monthly time-variable gravity field retrieval by performing simulations over half a year time span. This is done along with the static gravity field estimation with the aim of evaluating the possible overall improvement coming from the use of quantum gradiometers.