Localized evaluation of time-variable satellite gravimetry observations

• Applicant: Dr.-Ing. Philipp Zingerle
• Subject Area: Geodesy, Photogrammetry, Remote Sensing, Geoinformatics, Cartography
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 568370707

Time-variable gravity observations from dedicated satellite gravity missions are becoming increasingly popular in many geosciences since they pose an independent and global information source for all mass-related study areas (such as climatology, hydrology, seismology, oceanography, glaciology, etc.). To accommodate the need for high-quality satellite gravity observations, several future dedicated (LL-SST) earth observation missions are currently being planned (e.g., NASA/DLR GRACE-C, ESA NGGM). These missions strive to further improve the accuracy and availability of time-variable gravity observation. As it is expected that observation quality will further improve, it is foreseeable that the current standard methods for processing satellite gravity data will soon become the main bottleneck: in the current standard processing, gravity observations are accumulated over a longer period (e.g., a month), and a static global gravity field solution is then obtained for this period. Longer accumulation periods are needed to obtain global observation coverage, which is required to derive a global gravity field. The main downside of this approach is that the Earth's gravity signal exhibits significant short-term fluctuations (e.g., on daily and sub-daily scales), which cannot be captured by a long-term parameterization. Eventually, this introduces the unavoidable so-called temporal aliasing, which limits the accuracy of the final time-variable gravity field solution. For the near future, the only feasible way to mitigate temporal aliasing is to avoid deriving a global solution in the first place and, with that, also the required accumulation times. Without the global approach, gravity observations must be evaluated in a local environment based on the in-situ observations of the satellites. For LL-SST missions, these in-situ observations are the so-called line-of-sight gravity differences (LGDs), which are not easily interpretable by non-experts (e.g., other geoscientists). This circumstance currently limits the applicability of the LGD for the broader audience. This is our motivation for proposing this project, which will aim to fundamentally improve the usability of the LGD by (1) finding a transfer function to translate the LGD into an intuitively understandable quantity and by (2) establishing the LGD as a suitable tool for near real-time applications (such as event detection). Hence, this project will focus on method development and validation. For an objective and meaningful validation, it is required to work in a simulated environment where the ground truth is well defined. Hence, setting up this environment and selected scenarios will be another main task (3) of this project. Finally (4), it shall also be shown, based on real (GRACE-FO) data examples, that the developed methods also work outside the simulation world.

• DFG Programme: Research Grants
• Co-Investigators: Dr.-Ing. Thomas Gruber; Professor Dr. Roland Pail