Description: An important source of noise in the current global monthly time-varying gravity field obtained on the basis of GRACE-like missions (GRACE, GRACE-FO) is the error due to the aliasing of the high frequency non-tidal atmospheric and oceanic mass changes (AOD error). And due to the orbital configuration, the inter-satellite ranging system (K-band ranging system, KBR; laser interferometer, LRI) of gravity satellites is under-sampled in the east-west direction, leading to striping errors in the north-south direction. In our study, we introduced a new independent observational quantity called the angular velocity of the line-of-sight (LOS), i.e. the orientation change of the LOS caused by the gravity field, which has complementary information perpendicular to the LOS obtained from KBR/LRI. We call the combination of angular velocity sensing (AVS) and ranging observations GRACE-3D because it contains three-dimensional gravity observations, not just along the line-of-sight as in GRACE. We developed observation equations for AVS based on the dynamic approach and on the acceleration approach and solved them jointly with the observation equations generated by GPS and KBR/LRI using two independent software suites for cross-validation. The simulation results show that the AVS-based gravity field can reduce the effect of AOD error and significantly improve the north-south strip error when compared to the results obtained using only a combination of KBR/LRI and GPS. And the optimum results are achieved when GPS, LRI and AVS are combined. Finally, We will also briefly discuss how AVS measurements could be obtained in future missions.

Description: The continuing retreat of sea ice affects the Arctic mesoscale eddies, and its future evolution will strongly influence air-sea-ice interactions. However, knowledge of eddy activity is limited to sparse observations and coarse resolution models. How future eddies and their effects will evolve remains uncertain. Here, we apply the global unstructured model FESOM2 for 143 years of 4.5 km-Arctic simulations up to 2100 and 1 km-Arctic simulations for 5 years from 2010; 2090 to reveal the interactions between eddies, winds, sea ice and the energy budget of eddy kinetic energy (EKE) in a high resolution view. We demonstrate a significant increase in future Arctic EKE from 0-200 m, which is stronger in summer when sea ice melts. The future abundance of EKE can be explained by an increase in winter eddy generation and a decrease in summer eddy dissipation. This also leads to an enhancement of the horizontal velocity field, thus filling the Arctic Ocean with eddies in the future.

Description: The Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission is observing the time variable gravity field by measuring distance variations between two satellites. The first Laser Ranging Interferometer (LRI) between distant spacecraft uses a so-called Fast Steering Mirror (FSM) to satisfy the narrow LRI pointing requirements despite the larger spacecraft pointing variations. The position readout of these mirrors allow to compute the inter-satellite pointing angles yaw and pitch w.r.t. the line-of-sight connecting both satellites. The nominal pointing variations have a magnitude of a few 100 µrad. Typically, the attitude information of roll, pitch and yaw angles is derived from three star cameras and fibre optic gyroscopes. Since we are particularly interested in the characterization of the FSM at low-frequencies, we compare the FSM readout with star camera measurements for the time-span of December 2018 until December 2022. The residuals show temperature induced changes which are related to the varying orientation of the orbital plane and the sun, expressed through the angle β’. We will present our analysis that attempts to attribute and model the residuals. This analysis is of interest for future gravity missions, where the FSM could be implemented as an additional attitude sensor to control the satellite orientation.

Description: The GRACE Follow-On satellite mission measures distance variations between its two satellites in order to derive monthly gravity field maps, indicating mass variability on Earth on a scale of a few 100 km originating from hydrology, seismology, climatology and other sources. This mission hosts two ranging instruments, a conventional microwave system based on K(a)-band ranging (KBR) and a novel laser ranging instrument (LRI), both relying on interferometric phase readout. In this paper, we show how the phase measurements can be converted into range data using a time-dependent carrier frequency (or wavelength) that takes into account potential intraday variability in the microwave or laser frequency. Moreover, we analyze the KBR-LRI residuals and discuss which error and noise contributors limit the residuals at high and low Fourier frequencies. It turns out that the agreement between KBR and LRI biased range observations can be slightly improved by considering intraday carrier frequency variations in the processing. Although the effect is probably small enough to have little relevance for gravity field determination at the current precision level, this analysis is of relevance for detailed instrument characterization and potentially for future more precise missions.

Description: Mesoscale eddies are significant drivers of the dynamics in the Arctic Ocean and are crucial to understanding ongoing changes in the region. However, adequately resolving these small-scale features in ocean models is challenging, and high-resolution simulations are required to accurately represent mesoscale processes.In this study, we utilized a simulation from the unstructured-mesh Finite volumE Sea ice-Ocean Model (FESOM2) with a 1-km horizontal resolution in the Arctic Ocean, which can be considered eddy-resolving. This model has been previously used to study the distribution of eddy kinetic energy (EKE) in the Arctic, and we now evaluate the changes of EKE in the Eurasian Basin from seasonal to interannual time scales and their connection to other properties, such as sea-ice cover, baroclinic conversion rate, and stratification.We found that EKE seasonality is predominantly influenced by changes in sea-ice cover, while monthly anomalies have different drivers at different depths. The mixed layer, which is strongly linked to the surface, is primarily affected by sea-ice variability. In contrast, deeper levels are shielded from the surface by stratification and are more strongly influenced by baroclinic conversion.Overall, our high-resolution simulation sheds light on the complex relationship between mesoscale eddies, sea-ice cover, baroclinic conversion and stratification in the Arctic Ocean.

Description: The Arctic Ocean is a challenge to model accurately. Its exchanges with the rest of the global ocean occur through narrow gateways. Ventilation within the Arctic requires a realistic continental shelf hydrography and slope, interaction with the sea ice and atmosphere, and preservation of dense overflows. At all depth levels, an accurate bathymetry is needed to properly represent the circulation. The uppermost layers depend on both surface heat fluxes and freshwater fluxes from rivers, glaciers, sea ice, and the atmosphere, while the deepest layers are impacted by geothermal heating. Despite this, many parameterisations and tuning processes applied in the Arctic are not representative of the polar regions. In addition, observations used to constrain Arctic models are often limited to the summer season, ice-free regions, or upper ocean. Therefore, unsurprisingly, the coarse-resolution CMIP-type models are highly inaccurate in the Arctic Ocean. In this presentation, we review a non-exhaustive list of biases in Arctic Ocean water mass representation and circulation in CMIP6 models, with a specific focus on how these biases impact our ability to accurately project future Arctic Ocean and global changes. Key directions for improving the Arctic Ocean in climate models will be discussed. We will finish with promising examples of ongoing Arctic model development: regional high-resolution modelling to improve simulations of sea ice and the exchanges with the global ocean, including overflow representation; pan-Arctic modelling with an adaptative mesh to improve the representation of mesoscale eddies and mixing; and the nudging of an ultra-high-resolution model (250 m) against observations.

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: More than 20 years of satellite gravimetry missions have provided unique data about mass redistribution processes in the Earth system. Ongoing climate change underlines the urgent need to continue this kind of measurements with enhanced concepts and sensors. Here, we focus on accelerometers (ACC). Drifts of the electrostatic accelerometers (EA) are one of the limiting factors in the current space gravimetry missions dominating the error contribution at low frequencies. The focus of this study is on the modelling of enhanced EAs with laser-interferometric readout, so called ‘optical accelerometers’ and evaluating their performance at Low Earth Orbit (LEO). Contrary to present-day EAs, which measure capacitively the TM displacement and actuate it electrostatically, optical ACC, beside a similar actuation scheme, track the TM with laser interferometry. Our research is based on promising results of the mission LISA-Pathfinder which demonstrated the benefit of using a drag-free system in combination with optical accelerometry and UV TM discharge which allowed sensing of non-gravitational accelerations several orders of magnitude more accurate than it is realized in current gravity missions. In this presentation, we now introduce a framework for modeling novel EA with laser-interferometric readout mainly developed by IGP including major noise sources, like actuation noise, capacitive sensing, etc. Also, parametrization of the developed ACC model will be discussed including different TM weights and TM-electrode housing gaps. Finally, improved results of the recovered gravity field will be shown for various mission scenarios applying optical accelerometry and gradiometry. This project is funded by: Deutsche Forschungsgemeinschaft (DFG) – Project-ID 434617780-SFB 1464.

Description: With GRACE Follow-On in orbit for almost five years, developments for the next generation of gravity missions have begun. Firstly, there is the continuation mission of the US-German collaboration that already realized GRACE and GRACE Follow-On. Secondly, ESA is pursuing the so-called Next-Generation Gravity Mission (NGGM) for a launch around 2031. Both pairs are expected to form a constellation with optimized orbit geometry, i.e., a so-called Bender configuration. All of these activities include an improved version of the laser ranging or tracking instrument (LRI/LTI) as the primary ranging instrument, which will be the subject of this presentation. We will present the operating principle of the LRI/LTI and address the key requirements and challenges of the instruments needed to achieve a ranging noise below the requirement of 40...80 nanometer/sqrt(Hz) for the 200 km satellite separation. We will highlight some of the adaptions needed to evolve the technology demonstrator from GRACE-FO to a primary instrument and discuss the lessons learned so far. Since microwave ranging is not available in future missions, the LRI/LTI scale factor given by the absolute laser frequency needs to be determined by other means, which will also be covered.

Description: The currently on-going NGGM preparatory activities encompass two parallel Phase A system studies, which are complemented by a science support study with the goal to identify of optimum set-up for a MAGIC constellation regarding science return, technical feasibility, and costs. As an extension of the Phase A science study and preparation for the upcoming Phase B, several aspects are treated in detail, such as to advance processing methods and algorithms towards an integrated L0-L3 processing, to demonstrate the scientific readiness of end-to-end simulations, to quantify the relative contributions of the two involved pairs to the total mission performance, to analyze specific aspects such the optimum set-up regarding short-term products for operational service applications, and to demonstrate the science impact of MAGIC in numerous application fields. Additionally, the study involves technical aspects such as the refinement of L0-L1b inter-satellite distance algorithm, or the in-flight calibration of the accelerometers. In this contribution will we will summarize the main finding of the first phase of the project and report on recent results of the extension phase. The underlying numerical E2E simulations are performed based on realistic error assumptions for the instruments and the involved background models. The simulation results are evaluated against the science requirements defined in the MRD and MRTD, with special focus on new application fields and short-term service applications.