Abstract. Accurately quantifying global mass changes at the Earth's surface is essential for understanding climate system dynamics and their evolution. Satellite gravimetry, as realized with the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GRACE-FO) missions, is the only currently operative remote sensing technique that can track large-scale mass variations, making it a unique monitoring opportunity for various geoscientific disciplines. To facilitate easy accessibility of GRACE and GRACE-FO (GRACE/-FO in the following) results (also beyond the geodetic community), the Helmholtz Centre for Geosciences (GFZ) developed the Gravity Information Service (GravIS) portal (https://gravis.gfz.de, last access: 21 January 2025). This work aims to introduce the user-friendly mass anomaly products provided at GravIS that are specifically processed for hydrology, glaciology, and oceanography applications. These mass change data, available in both a gridded representation and as time series for predefined regions, are routinely updated when new monthly GRACE/-FO gravity field models become available. The associated GravIS web portal visualizes and describes the products, demonstrating their usefulness for various studies and applications in the geosciences. Together with GFZ's complementary information portal https://www.globalwaterstorage.info/ (last access: 21 January 2025), GravIS supports widening the dissemination of knowledge about satellite gravimetry in science and society and highlights the significance and contributions of the GRACE/-FO missions for understanding changes in the climate system. The GravIS products, divided into several data sets corresponding to their specific application, are available at https://doi.org/10.5880/GFZ.GRAVIS_06_L2B (Dahle and Murböck, 2019), https://doi.org/10.5880/COST-G.GRAVIS_01_L2B (Dahle and Murböck, 2020), https://doi.org/10.5880/GFZ.GRAVIS_06_L3_ICE (Sasgen et al., 2019), https://doi.org/10.5880/COST-G.GRAVIS.5880/GFZ.GRAVIS_01_L3_ICE (Sasgen et al., 2020), https://doi.org/10.5880/GFZ.GRAVIS_06_L3_TWS (Boergens et al., 2019), https://doi.org/10.5880/COST-G.GRAVIS_01_L3_TWS (Boergens et al., 2020a), https://doi.org/10.5880/GFZ.GRAVIS_06_L3_OBP (Dobslaw et al., 2019), and https://doi.org/10.5880/COST-G.GRAVIS_01_L3_OBP (Dobslaw et al., 2020a).
<p>The GRACE Follow-On (GRACE-FO) mission was successfully launched on May 22<sup>nd</sup>, 2018 and continues the 15-year data record of monthly global mass changes from the GRACE mission (2002-2017). The German Research Centre for Geosciences (GFZ) as part of the GRACE/GRACE-FO Science Data System (SDS) has recently reprocessed the complete GRACE mission data (RL06 in the SDS nomenclature). These RL06 processing standards serve as common baseline for the continuation with GRACE-FO data.</p><p>This presentation provides an overview of the current processing status and the validation of the GFZ GRACE/GRACE-FO RL06 gravity field products. Besides its Level-2 products (monthly sets of spherical harmonic coefficients representing the Earth's gravity potential), GFZ additionally generates user-friendly Level-3 products in collaboration with the Alfred-Wegener-Institut (AWI) and TU Dresden. These Level-3 data products comprise dedicated mass anomaly products of terrestrial water storage over non-glaciated regions, bottom pressure variations in the oceans and ice mass changes in Antarctica and Greenland, available via GFZ's Gravity Information Service (GravIS) portal (http://gravis.gfz-potsdam.de/).</p>
The gravity field plays a crucial role in Earth System Sciences. Access to the entire field on global scale is only possible via mathematical modelling. The heterogeneous gravity field shapes the mean sea level surface and can be used e.g., to determine ocean surface currents, to unify height systems globally, and to map mass distributions that mirror the processes in Earth’s interior, such as plate tectonics, mantle convection, seafloor spreading and volcanic eruption. Currently available static global gravity field models are limited in resolution due to the band-limited spectral content of the input data from satellite observations and gravity measurements on the Earth’s surface. We can complement such models beyond their current limits using high-resolution digital elevation models (DEMs) and laterally varying density estimates. Here we present a study, where we aim to compute a new very high-resolution topographic gravity field model in terms of harmonic coefficients via direct numerical integration of Newton’s law of gravitation using state-of-the-art DEM and density models. This work is a continuation of our previous activities in this field (Ince et al. 2020) and first results of a DFG project GRAV4GEO (GRAVitational field modelling of Earth’s topography For GEOdetic and GEOphysical applications). The outcomes of this project will be reduction of the omission error and enhancement of the spectral and spatial resolution of global gravity field models and delivery of topography/density-based gravity information particularly in hard-to reach areas. A third result will be the improved reduction of the gravity measurements for the topographic effect to investigate the residual signal of deeper Earth layers. This should help in the 3D crustal and lithospheric modelling especially in geologically complex areas, Finally, improvement in the accuracy of gravity modelling is expected from using laterally varying density instead of the commonly used averaged density values. With the high-resolution topographic gravity field model delivered at the end of the project, the spatial resolution of recent global gravity field models shall be increased up to ~2 km Uncertainty estimates, which have not been presented in current topographic gravity field models, will be provided. Our project will lead to an improved global gravity field up to degree/order 10800 which will also deliver a more accurate reference surface for global vertical datum and basis for better geophysical modelling especially in the regions of density discontinuities. In this presentation, we will be conveying the first results of the project which uses a laterally varying density model in the development of topographic gravity field model and its contribution to the state-of-the-art model EIGEN-6C4. Reference:Ince ES, Abrykosov O, Förste C, and Flechtner F (2020) Forward Gravity Modelling to Augment High-Resolution Combined Gravity Field Models. Surv. Geop., 1-38. doi:10.1007/s10712-020-09590-9
<p>GFZ, as part of the GRACE/GRACE-FO Science Data System, is one of the official Level-2 processing centers routinely providing monthly gravity models. These models are used by a wide variety of geoscientists to infer mass changes mainly at the Earth&#8217;s surface. While the current release 6 (RL06) is still operationally processed, plans and internal tests for a reprocessed GFZ RL07 time series are already in progress.</p> <p>In this context, advanced processing strategies are developed within the Research Unit (RU) NEROGRAV (New Refined Observations of Climate Change from Spaceborne Gravity Missions) funded by the German Research Foundation DFG. The main focus is on an improved stochastic modeling regarding both instrument data (accelerometer and inter-satellite ranging observations) as well as background models (e.g. by the utilization of covariance information for these models). At the same time, the solved-for parameter space, in particular regarding empirical accelerations, has been revised. Finally, also the potential benefit by adding observations of the laser-ranging interferometer (LRI) onboard GRACE-FO has been investigated.</p> <p>This poster provides an overview of the developed advanced processing strategies, and their individual and combined impact on GFZ&#8217;s Level-2 products compared to current GFZ RL06 solutions.</p>
