Abstract
Past temporal gravity field solutions from the Gravity Recovery and Climate Experiment (GRACE), as well as current solutions from GRACE Follow-On, suffer from temporal aliasing errors due to undersampling of the signal to be recovered (e.g., hydrology), which arise in terms of stripes caused by the north–south observation direction. In this paper, we investigate the potential of the proposed mass variation observing system by high–low inter-satellite links (MOBILE) mission. We quantify the impact of instrument errors of the main sensors (inter-satellite link and accelerometer) and high-frequency tidal and non-tidal gravity signals on achievable performance of the temporal gravity field retrieval. The multi-directional observation geometry of the MOBILE concept with a strong dominance of the radial component result in a close-to-isotropic error behavior, and the retrieved gravity field solutions show reduced temporal aliasing errors of at least 30% for non-tidal, as well as tidal, mass variation signals compared to a low–low satellite pair configuration. The quality of the MOBILE range observations enables the application of extended alternative processing methods leading to further reduction of temporal aliasing errors. The results demonstrate that such a mission can help to get an improved understanding of different components of the Earth system.
Highlights
In times of a changing climate the need for innovative observation techniques for capturing geophysical processes in the Earth system becomes increasingly urgent
When considering all instrument error sources together, the retrieval errors of the low–low satellite pair are dominated by the accelerometer plus star camera sensor performance, while for the MOBILE constellation, the laser link error was the dominating error source for SH degrees higher than 20, and the accelerometer plus star camera noise only dominated the spectrum in the lower degrees
These results led to the conclusion that the gravity field retrieval based on instrument error sources showed smaller errors below SH degree 40 for the MOBILE concept compared to the low–low pair, but increased errors in the higher frequency spectrum due to the lower accuracy of the laser interferometer
Summary
In times of a changing climate the need for innovative observation techniques for capturing geophysical processes in the Earth system becomes increasingly urgent. The GRACE mission reached spatial scales of the temporal gravity field of ≈300 km and below due to a combination of K-band microwave low–low inter-satellite ranging between two identical satellites following each other in the same orbit at a distance of about 220 km with micrometer precision, and high–low GPS satellite-to-satellite tracking plus accelerometer observations These missions improved our knowledge of water mass variations on the continents, in the oceans, and the atmosphere to a great extent. A further concept is the pendulum formation where two satellites are on slightly shifted orbit planes in such a way that the line of sight between the satellites does contain along-track components, and cross-track components [22] Such innovative satellite constellations offer the application of improved gravity field processing methodologies in order to exploit the full potential of gravity field solutions with enhanced spatial and temporal resolution.
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