ALBERT

Description: The GRACE and GRACE-FO missions have been fundamental in establishing a near-continuous time series of global mass transport since 2002. However, gravity field recovery using these mission data includes errors limiting the spatial and temporal resolution of gravity field solutions. The primary error contributions arise from instrument noise, temporal aliasing errors, uncertainties in the de-aliasing models, and imperfect ocean tide models. Particularly the latter will remain a limiting factor in determining high-resolution gravity fields from Next-Generation Gravity Missions.The topic has been investigated within the DFG research unit NEROGRAV and ESA´s Third Party Mission Program. One of the projects concerns stochastic modeling of ocean tide background models utilizing covariance information for eight major tidal constituents. The repeatable pattern of the tidal signal enables the extraction of uncertainty information by an ensemble of different ocean tide models. This information is introduced into the gravity field recovery process as a covariance matrix while expanding the parameter space by additional tidal parameters.An overview is provided of the recovered monthly gravity fields from GRACE/GRACE-FO when applying this covariance information. Additionally, realistic simulations have been performed for GRACE-like and MAGIC constellations to assess the impact that covariance information has on tidal errors and tidal constituents which have been co-estimated over one year and used to generate an improved ocean tide model for gravity field recovery. It is shown that the application of ocean tide covariance information contributes to the reduction of temporal aliasing caused by the mismodeling of ocean tide background models.

Description: Based on the large success of GRACE and GRACE-FO and their contributions to climate change research, there is a large interest in Germany to continue mass change measurements. Since 2020 GFZ and the German Space Agency at DLR have investigated a mission concept together with NASA based on a GRACE-like concept with a fully redundant Laser Ranging Interferometer (LRI). A Phase A study was successfully performed in 2022 with significant support of JPL. In October 2022 the German Parliament secured funds for the German mission elements Launcher, LRI optical components, Mission Operations and Science Data System (SDS). MPG and GFZ will additionally provide significant funding for LRI development and testing, SDS and Mission Operations after launch. To realize the GRACE-FO successor with launch not later than 2028 DLR is currently in close contact with NASA for the implementation of the next joint US/German Gravity mission. The GRACE-FO successor could be the first pair (P1) of a hybrid “Bender” constellation if combined with a second inclined pair (P2). The realization of this Mass-change And Geoscience International Constellation is currently discussed between ESA and NASA. P2 will fly lower than P1 and will be based on advanced instrumentation. Therefore, Phase A also investigated the option to add adapted MicroStar accelerometers to the baseline GRACE-FO like accelerometer on each P1 satellite as technology demonstrator for P2. We will present the current P1 mission status from a German view and discuss further steps towards realization.

Description: Being part of the GRACE/GRACE-FO Science Data System, the GFZ German Research Centre for Geosciences 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’s surface. Currently, the operationally processed monthly gravity fields are still based on release 6 (RL06) standards, but developments in view of a reprocessed and improved GFZ RL07 time series are already ongoing. Most of these improvements have been developed within the Research Unit “New Refined Observations of Climate Change from Spaceborne Gravity Missions” (NEROGRAV) funded by the German Research Foundation DFG. After a successful first phase, the second three years phase of NEROGRAV has started at the beginning of this year. Regarding an advanced gravity field processing strategy for RL07, the main focus is on an optimized stochastic modelling of: (1) instrument errors for the main observations (K-band/LRI ranging, GPS, and accelerometer), and (2) background model errors for ocean tides and non-tidal atmosphere and ocean de-aliasing (AOD), making use of respective variance-covariance matrices. This presentation provides an overview of the main outcomes of the advanced processing strategies. Details on the applied stochastic modelling approaches will be discussed. Preliminary monthly gravity field results will be presented and compared to current GFZ RL06 solutions.