A deep understanding of mass distribution and mass transport in System Earth is needed to answer central questions in hydrology, oceanography, glaciology, geophysics and climate research. The necessary information is primarily derived from satellite mission data as provided by GRACE (Gravity Recovery and Climate Experiment) and GRACE-FO (Follow-on) describing the gravity field of the Earth and its temporal variations.

The research group (RG) „New Refined Observations of Climate Change from Spaceborne Gravity Missions (NEROGRAV)”, funded by the German Research Foundation (DFG), develops new analysis methods and modeling approaches to improve GRACE and GRACE-FO mission data analysis and focuses on geophysical applications that benefit from significantly reduced error levels in the time series of monthly gravity fields. Phase 1 lasted from May 2019 till April 2022. After successful evaluation in January 2022 the second phase (again three years) started in January 2023.  

Spokesman of the RG is Section Leader Prof. Dr. Frank Flechtner in his function as Chair of Physical Geodesy at the TU Berlin.

The central hypothesis of the research group, slightly updated for phase 2, is: Only by concurrently improving and better understanding of sensor data, background models, and processing strategies of satellite gravimetry, the resolution, accuracy, and long-term consistency of mass transport series can be significantly increased; the science return in various fields of application improved and the potential of future technological sensor developments fully exploited.

In order to reach this overarching goal, the RG in particular concentrates on four different objectives:

1. Improvement and error quantification of geophysical background models,
2. Improvement of spatial-temporal parameterizations,
3. Validation of improved background models and gravity field models against independent data, and
4. Synthesis of results and recommendations for Next Generation Gravity Missions (phase 1) and novel geophysical applications and provision of recommendations for NGGMs (phase 2), respectively,

which were elaborated in six Individual Projects (IP) in phase 1:

• IP 1: Improved Tidal Dynamics and Uncertainty Estimation for Satellite Gravimetry (TIDUS; PIs: Maik Thomas (FU Berlin), Denise Dettmering (DGFI - TU Munich))
• IP 2: Next Generation Non-tidal Atmospheric and Oceanic De-aliasing Models (NAODEMO; PI: Henryk Dobslaw (GFZ))
• IP 3: High-Resolution Atmospheric-hydrological Background Modelling for GRACE/GRACE-FO – regional refinement and validation (HIRABAM; PIs: Petra Friederichs, Jürgen Kusche, Andreas Hense, Michael Schindelegger (University Bonn))
• IP 4: Optimized Space-Time Parameterization for GRACE and GRACE-FO data Analysis (OSTPAGA; PIs: Roland Pail (TU Munich), Frank Flechtner (TU Berlin (Spokesman of RG))
• IP 5: Improved Stochastic Modeling in GRACE/GRACE-FO Real data processing (ISTORE; PI: Rolf König (GFZ))
• IP 6: Post-process Techniques, Impact on NGGM And Recommendations (POTINAR; PI: Roland Pail (TU Munich))

and were continued since January 2023 in phase 2:

• IP 1: Improved Tidal Dynamics and Uncertainty Estimation for Satellite Gravimetry (TIDUS-2; PIs: Maik Thomas (FU Berlin), Denise Dettmering (DGFI – TU Munich))
• IP 2: Atlantic Meridional Overturning Circulation: Inferences from Satellite Gravimetry and Numerical Ocean Models (AMOCING; PIs: Henryk Dobslaw (GFZ), Michael Schindelegger (University Bonn))
• IP 3: High-Resolution Atmospheric-hydrological Background Modelling for GRACE/GRACE-FO – regional refinement and validation (HIRABAM-2; PIs: Petra Friederichs and Jürgen Kusche (University Bonn))
• IP 4: Near-real time, Long-term, LRI and SLR combination aspects (NELOS; PIs: Natalia Panafidina (GFZ), Thomas Gruber (TU Munich))
• IP 5: Optimized Space-Time Parameterization for GRACE and GRACE-FO data Analysis (OSTPAGA-2; PIs: Roland Pail (TU Munich), Frank Flechtner (TU Berlin (Spokesman of RG))
• IP 6: Climate Signals from GRACE/GRACE-FO and Next Generation Gravity Missions (CLISGY; PIs: Annette Eicker (HCU Hamburg), Roland Pail (TU Munich))

Section 1.2 was funded in phase 1 for project ISTORE (Improved Stochastic Modeling in GRACE/GRACE-FO Real Data Processing) was dealing with

• taking into account extensive stochastic error characteristics of K-Band Ranging, Laser Ranging Interferometer and accelerometer data during gravity field determination and related testing in real data applications,
• utilizing full background model error variance-covariance matrices (VCM) of ocean tides and atmosphere/ocean de-aliasing products, supported by Monte-Carlo simulations, and
• analyzing the impact of utilization full error VCMs in real data processing.

In phase 2 Section 1.2 (with partner TU Munich) works in project NELOS on Near-real time, Long-term, LRI and SLR combination aspects. The main research objectives are

• Derive daily/NRT gravity field models,
• Find optimal parametrization for “bad months” and develop co-parametrization methods for trend signals,
• Derive a consistent 20+ years GRACE/GRACE-FO time series, and
• Investigate the impact of LRI data for medium to high frequencies of the static gravity field.

Already existing data products of the phase 1 IPs can be found at the GFZ Data Services. Final results of phase 2 are planned for spring 2026. Further details can be found at the Research Group main page.

Project Partners:

• See phase 1 and 2 individual projects above

Project Duration:

• May 2019 – December 2025

Funding:

• German Research Foundation (Deutsche Forschungsgemeinschaft, DFG), FOR2736