The GRACE Follow-On satellite mission, a partnership between NASA (US) and GFZ (Germany), successfully completed its nominal five-year prime mission phase in May 2023, and has already entered its extended mission phase. GRACE-FO continues the unique essential climate data record of mass change in the Earth system initiated in 2002 by the GRACE mission (2002-2017). The combined GRACE & GRACE-FO data records now span over 22 years and provide foundational observations of monthly to decadal global mass changes and transports in the Earth system derived from temporal variations in the Earth’s gravity field. These observations have become indispensable for climate-related studies that enable process understanding of the evolving global water cycle, including ocean dynamics, polar ice mass changes, and near-surface and global ground water changes.

In this presentation, we will present recent GRACE/GRACE-FO science and applications highlights, review key data processing and calibration approaches for GRACE-FO and lessons learned during the recent years, and discuss the GRACE-FO mission plan to operate and collect high-quality science data through the intensifying solar cycle 25, aiming for continuity with the upcoming NASA/DLR Continuation mission GRACE-C, targeted to launch in 2028.

How to cite: Flechtner, F., Landerer, F., Save, H., Mccullough, C., Dahle, C., Bettadpur, S., Gaston, R., and Snopek, K.: GRACE-FO: science results, project status and further plans , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7426, https://doi.org/10.5194/egusphere-egu24-7426, 2024.

We have developed a GRACE-D accelerometer product that relies more heavily on modeled acceleration data instead of a transplant. Here we present our approach and a performance evaluation of our data products with different models, processing options and compared to transplant products from other institutes.

Comparisons of the artificial acceleration data to the real ACT1B data for GRACE-C show that models related to the atmospheric drag (especially density and drag coefficient) are the limiting factors in the high precision environment modeling approach. Even though it is still possible to generate monthly gravity field solutions with a combination of ACT1B data for GRACE-C and artificial data for GRACE-D that show all prominent hydrological signals, we also implemented a minimalistic transplant where we estimate the atmospheric density from GRACE-C and transplanted it to GRACE-D.

We compare our transplant data by incorporation of the GROOPS software to generate monthly gravity field solutions. This enables us to compare the results with other monthly solutions and the ITSG solutions, without getting differences due to the GFR processing tool.

We publish the ZARM GRACE-D data product, all modeled non-gravitational accelerations and additional data on a publicly accessible server.

How to cite: Huckfeldt, M., Wöske, F., Rievers, B., and List, M.: GRACE Follow-On gravity-field results incorporating the ZARM ACC transplant based on high-precision environment modeling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8595, https://doi.org/10.5194/egusphere-egu24-8595, 2024.

The performance degradation of one onboard accelerometer of the GRACE-FO mission presents a significant challenge to the scientific community. This issue has been largely mitigated by transplanting data from the other fully functional accelerometer. Various accelerometer data transplant (ACT) products have been developed using distinct methodologies, each showing different performances in gravity field recovery. In this study, we conduct a systematic evaluation of three available ACT products—JPL-ACT and JPL-ACH from NASA's Jet Propulsion Laboratory, and TUG-ACT from Graz University of Technology—utilizing a uniform Level-1B data processing approach. Our analysis reveals that these ACT products exhibit inconsistent quality across different time periods. Consequently, we introduce a novel approach combining these ACT products at the normal equation level to enhance gravity field solution accuracy. Compared to solutions using the JPL-ACT, the combined solution gives a notable noise reduction of 5% to 12% depending on the choice of post-processing filters and the replacement of C₂₀/C₃₀ coefficients, which doubles the noise reduction achieved by the next best individual ACT product, JPL-ACH. Furthermore, the C₂₀ coefficient derived from the combined solution agrees better with the Satellite Laser Ranging (SLR) benchmark, compared to those derived from individual ACT products. This advancement largely reduces the spurious 161-day signal observed in polar regions. Regarding the C₃₀ coefficient, while JPL-ACT solutions exhibit suboptimal estimates, the JPL-ACH, TUG-ACT, and combined solutions all contribute to substantial improvements.

How to cite: Nie, Y., Chen, J., Shen, Y., and Chen, Q.: Enhancing GRACE-FO Gravity Field Solutions: A Comparative Assessment and Novel Combination of ACT Products, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3692, https://doi.org/10.5194/egusphere-egu24-3692, 2024.

The LRI on GRACE Follow-On (GRACE-FO) provided range and range rate measurements for more than 4 years. At our institute we produce monthly gravity field coefficients from these observation data. We apply different techniques to analyse the post-fit range rate residuals and the post-fit range acceleration residuals to identify unknown characteristics and systematic effects within the LRI measurement system. We identified several effect: the range rate effect, the panel effect, the CNR effect and the polar effect. All these effects have not been detected in the KBR residuals. Beside the current status of GRACE/GRACE-FO processing standards at our institute, the focus lies on the characterisation of the range rate effect as well as the panel effect. The range rate effect occurs when the range rate observation is around 0 m/s and shows a very specific butterfly pattern. The panel effect is induced by the interaction of the spacecraft body panels and the sun. There is also an interaction of the LRI steering mirrors observable when the LRI laser beam is aligned with the sun.

How to cite: Duwe, M., Koch, I., and Flury, J.: Patterns in GRACE-FO LRI Post-Fit Range Rate Residuals, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11987, https://doi.org/10.5194/egusphere-egu24-11987, 2024.

The Gravity Recovery and Climate Experiment (GRACE) and its subsequent GRACE Follow-On (GRACE-FO) missions have been instrumental in monitoring Earth’s mass changes through time-variable gravity field models. However, these models suffer from high-frequency noise and significant north-south striping (NSS) noise. The most widely used spectral filter for addressing these issues is the decorrelation and denoising kernel (DDK) filter, utilized by official processing agencies. The key operation of DDK filtering is to regularize the normal equation built by the Level-1b data. However, the regularization parameter used in original DDK filters is empirically determined by the signal-to-noise ratios and remains unchanged across all months. This is improper due to the heterogeneity of the monthly covariance matrix. Additionally, a single regularization parameter may not effectively address the ill-posedness of the inversion equation. For this reason, we propose a multiple-parameter regularization approach for filtering GRACE gravity field models, with regularization parameters determined by minimizing the mean squared error (MSE) for each month. The proposed method is used to process the ITSG-Grace2018 and ITSG-Grace_operational Level-2 spherical harmonic coefficients with degree/order 96 from April 2002 to December 2022. The results show that our method produces the filtered mass anomalies, global trend, and annual signal amplitudes that align better with three mascon solutions (CSR, JPL, and GSFC) compared to DDK filters and ordinary Tikhonov regularization with a single regularization parameter. In some typical areas with significant signals, our approach retains more detailed characteristics in filtered signals compared to DDK filters and ordinary Tikhonov regularization. Repeated simulations demonstrate that the filtered signals by our approach are closer to the simulated true signals than those by other methods.

How to cite: Ji, K., Shen, Y., Zhang, L., Chen, Q., Lou, L., and Yao, L.: A multiple-parameter regularization approach for filtering monthly GRACE/GRACE-FO gravity models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6953, https://doi.org/10.5194/egusphere-egu24-6953, 2024.

It is common to convert GRACE-based level-2 data product (spherical harmonic coefficients) into mass anomalies at the Earth’s surface using spherical harmonic synthesis. We claim that it is more appropriate to use for that purpose a least-squares adjustment (which can be understood in this context as a variant of mascon approach). Among other, this allows one to take into account the stochastic model of errors in the spherical harmonic coefficients, as well as a various physical constraints, such as geometry of coastal lines, geometry of deserts, etc. The latter constraints can be implemented, e.g., by introducing a spatially-varying first-order Tikhonov regularization. We apply such an approach to make a state-of-the-art estimate of Greenland Ice Sheet (GrIS) mass losses.

First, a numerical study is carried out to optimize the spatially-varying regularization and demonstrate the performance of the developed approach. We show, among other, that the optimal regularization parameters strongly depend on the region and the spatial scale of interest. For instance, a substantially different regularization is recommended for the best global estimates of mass anomalies, for the best estimates of mass anomalies with Greenland only (pointwise), and for the best estimates of total mass anomalies per GrIS drainage system. This suggests that an optimal estimate of mass anomalies produced by a regularized least-squares adjustment tailored for a particular application is, in general, superior to an off-the-shelf mascon-type data product.

Second, the mass trends in 2002–2023 per drainage system and over entire Greenland are estimated from actual GRACE/GRACE-FO level-2 data products. We show, among other, that the average rate of total mass loss in Greenland in the considered time interval is of the order of 270 Gt/yr. Furthermore, we analyze the factors that affect the estimated trends and quantify the uncertainties of the obtained estimates.

How to cite: Ditmar, P.: Optimization of GRACE-based mass anomaly estimates using the first-order Tikhonov regularization, with application to the Greenland Ice Sheet, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18889, https://doi.org/10.5194/egusphere-egu24-18889, 2024.

The spatial resolution of the total water storage changes from GRACE data is a conundrum, but also the most sought after quantity. The availability of various solutions exacerbates the situation -- unconstrained spherical harmonics, constrained spherical harmonics, mascons and different data processing centers. Some attempts have been made previously to arrive at an answer, and some numbers have been proposed. Notably, in the context of hydrologic applications, the spatial resolution morphs into a question of the catchment sizes and shapes, thereby rendering some of these numbers deficient. This study uses ideas from leakage analysis to arrive at answers for the spatial resolution issue. Care is taken to incorporate the morphometric characteristics of catchments in the answers being arrived at.

How to cite: Bharath Narayana Reddy, K. and Devaraju, B.: Role of catchment morphometrics in addressing the spatial resolution of GRACE-derived total water storage changes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-680, https://doi.org/10.5194/egusphere-egu24-680, 2024.

Gravity field solutions from the Gravity Recovery and Climate Experiment (GRACE) and its follow-on (GRACE-FO) satellite mission provide an essential way to monitor mass changes in the climate system, comprising terrestrial water storage (TWS) anomalies and ocean bottom pressure (OBP) fluctuations. However, the coarse spatial resolution of the GRACE fields blurs important spatial detail, such as OBP gradients or mass fluxes in individual catchments. By contrast, classical hydrological or ocean models provide small-scale mass change information but of doubtful accuracy, especially for trends. To combine the strengths of both data sources, we develop a self-supervised data assimilation algorithm based on deep learning concepts and apply it successfully to global TWS and OBP anomalies. The specific design of the loss function allows the model to be optimised without requiring a high-resolution ground truth. Instead, the model parameters are optimised by weighing monthly GRACE(-FO) and numerical model inputs according to their respective advantages (i.e., spatial scales where their fidelity is highest). We obtain downscaled TWS and OBP anomaly maps with grid spacings of 0.5° and 0.25°, respectively, preserving reasonable large-scale agreement with monthly GRACE(-FO) fields. We validate our downscaled products on various time scales against satellite altimetry-measured water levels, tide gauge data, and in-situ bottom pressure measurements. The downscaled products facilitate analyses beyond the nominal GRACE(-FO) resolution, including closing the water balance equation in small basins or monitoring coastal ocean mass changes. Over the terrestrial water, our downscaled product provides an average improvement of 0.79 in terms of Nash–Sutcliffe efficiency (w.r.t. ERA5-Land water budget components) for the basins smaller than the effective resolution of GRACE(-FO) missions. Over the ocean, our downscaled product agrees better with coastal tide gauge measurements at more than 78% of studied stations. We anticipate our approach to be generally applicable to other GRACE(-FO) level-3 products and other gridded Earth observation data.

How to cite: Gou, J., Börger, L., Schindelegger, M., and Soja, B.: Improving the spatial resolution of global mass changes observed by GRACE(-FO) using deep learning — from terrestrial water to the ocean, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5322, https://doi.org/10.5194/egusphere-egu24-5322, 2024.

The Next Generation Gravity Mission (NGGM) is European Space Agency’s (ESA) next Mission of Opportunity.  It aims to extend and improve time series of satellite gravity missions by providing enhanced spatial and temporal resolution time-varying gravity field measurements with reduced uncertainty and latency to address the international user needs as expressed by the International Union of Geodesy and Geophysics (IUGG[1]) and the Global Climate Observing System (GCOS[2]) and demonstrate the critical capabilities for a potential future operational gravity mission.

The NGGM principal observable is the variation of the range (distance) and range rates between two satellites measured by a laser interferometer; ultra-precise accelerometers measure the non-gravitational accelerations to correct the gravity signal retrieval in the on-ground data processing. The current baseline NGGM mission concept comprises a pair of satellites on a 397km-altitude circular orbit, at 220 km separation with an inclination of 70°. The satellite-to-satellite tracking technique for detecting the temporal variations of gravity was established by GRACE (300-400 km spatial resolution at monthly intervals) using tracking in the microwave band. Today, GRACE is being continued by GRACE-Follow-On, with similar objectives, where the laser interferometry has improved the measurement resolution by a factor of 100 (upper Measurement Bandwidth.

MAss Change and Geosciences International Constellation (MAGIC) is the European Space Agency (ESA) and National Aeronautics and Space Administration (NASA) jointly developed concept for collaboration on future satellite gravity constellation that addresses the needs of the international user community. MAGIC will consist of the GRACE-C (NASA and German Aerospace Center (DLR)) and NGGM (ESA) staggered deployment of 2 satellite pairs, with progressively improving measurement performance, to form a Bender-type constellation. It builds on the success of previous missions such as GOCE, GRACE and GRACE-FO therefore is considered a mature system architecture, that maximises the scientific benefit and enables new applications.

This presentation provides a status overview of the NGGM system and technology development activities resulting from NGGM Phase A, entering NGGM Phase B1 as currently implemented by the European Space Agency and the scientific outlook of NGGM and MAGIC. In preparation for the MAGIC constellation, ESA and NASA have established a joint science and application plan on MAGIC, with the priority to identify and resolve the challenges in the development of the new MAGIC constellation products. We will present ESA’s plans on the development of the MAGIC higher-level products which involves the optimal combination of GRACE-C and NGGM data. We will also highlight the expected impact of NGGM and MAGIC on dedicated scientific research fields and applications.

How to cite: Daras, I., Massotti, L., Willemsen, P., March, G., Francois, M., and Carnicero Dominguez, B.: Next Generation Gravity Mission (NGGM) status overview and scientific outlook, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11271, https://doi.org/10.5194/egusphere-egu24-11271, 2024.

The upcoming gravity missions anticipated in the next decade are expected to significantly reduce noise levels compared to current data acquisitions from GRACE and GRACE Follow On. Our objective is to proactively prepare for these future datasets and develop scientific processing tools that can yield innovative applications in solid earth research. These applications have the potential to evolve into community-relevant ser-vices for earth monitoring and exploration.

We specifically focus on key categories such as earthquakes, crustal uplift and subsidence, seamounts, and lithospheric structure. Accurately estimating the gravity field necessitates the formulation of realistic 3D models of density and their temporal changes.

Uplift and subsidence is considered for the Alpine mountain arc, where a lithosphere density model has been formulated (Tadiello & Braitenberg, 2021) imposing vertical movements from measured GNSS rates. The exploration of the lithosphere is tested on a recent 3D density model of Iran (Maurizio et al., 2023) which was inverted from the presently available gravity field integrated with a seismic tomography model. We distinguish crustal and mantle signals and evaluate prospective improvements to detect structures in crust and mantle.

In the context of earthquakes, our focus lies in improving the minimum detectable magnitude, depending on fault plane mechanisms, and detecting post-seismic relaxation. Seamounts pose a unique challenge with limited alternatives for detection, placing gravity detection in a primary role, provided the associated mass changes are sufficiently significant. Therefore, we conduct a review of documented seamount eruptions, estimating the associated mass changes. Particularly intriguing are 'silent' seamounts that grow several hundred meters high without breaking the ocean surface, remaining invisible.

We compare the signals against noise levels of the future gravity missions, including the polar and inclined satellite couples with inter satellite distance measurement, the MAGIC proposal (Daras et al., 2024) and proposals with the payload of quantum technology gradiometers presently under discussion at ESA and NASA.

References

Daras, I., March, G., Pail, R., Hughes, C. W., Braitenberg, C., Güntner, A., Eicker, A., Wouters, B., Heller-Kaikov, B., Pivetta, T., & Pastorutti, A. (2024). Mass-change And Geosciences International Constellation (MAGIC) expected impact on science and applications. Geophysical Journal International, 236(3), 1288–1308. https://doi.org/10.1093/gji/ggad472

Maurizio, G., Braitenberg, C., Sampietro, D., & Capponi, M. (2023). A New Lithospheric Density and Magnetic Susceptibility Model of Iran, Starting From High‐Resolution Seismic Tomography. Journal of Geophysical Research: Solid Earth, 128(12), e2023JB027383. https://doi.org/10.1029/2023JB027383

Tadiello, D., & Braitenberg, C. (2021). Gravity modeling of the Alpine lithosphere affected by magmatism based on seismic tomography. Solid Earth, 12(2), 539–561. https://doi.org/10.5194/se-12-539-2021

How to cite: Braitenberg, C., Fantoni, A., Maurizio, G., and Pastorutti, A.: Innovative solid Earth applications of future gravity field missions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19340, https://doi.org/10.5194/egusphere-egu24-19340, 2024.

The limited achievable temporal resolution poses one of the main limitations of current satellite gravity field missions such as GRACE and GRACE-FO and is, eventually, responsible for temporal aliasing. Increasing the temporal resolution is thus one of the most important tasks for future satellite gravity field missions. This, however, can only be achieved by means of larger satellite constellations since the temporal resolution can basically be defined as the time needed to achieve a global observation coverage. This needed (retrieval) time scales linearly with the number of satellites: e.g., a two-pair mission such as the upcoming joint ESA/NASA MAGIC mission can easily achieve global coverage with sufficient spatial resolution within less than a week. For a hypothetical 6-pair mission, even an independent daily retrieval is feasible. Future missions will hence allow to sample the gravity field in much shorter intervals. However, up until now, the parametrization of the gravity field within these intervals usually only accounts for a static behavior, resembling a step function in the time domain. Obviously, such a behavior is unnatural and does not follow the actual progression of the gravity field. So, even if sufficient temporal resolution would be available, temporal aliasing will not be fully mitigated due to this mis-parametrization. In this contribution we will thus investigate the impact of a direct time-variable parametrization through continuous spline-functions. On the example of a fictive 6-pair mission, we show how such a spline parametrization with daily support points can be applied: firstly, we prove that the spline parametrization allows numerically stable and correct solution based on a closed loop scenario without residual (sub-daily) temporal aliasing. Secondly, based on a more realistic scenario with sub-daily temporal gravity signal, we also highlight the (theoretical) limitations of a 6-pair mission due to the still very dominant temporal aliasing (from sub-daily signal sources). This work is supported by the ESA QSG4EMT study in collaboration with Politecnico di Milano, Delft University of Technology, HafenCity University Hamburg, University of Bonn and University of Trieste.

How to cite: Zingerle, P., Pail, R., Gruber, T., and Daras, I.: Future satellite gravity field missions – Impact of a direct time-variable parametrization, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10995, https://doi.org/10.5194/egusphere-egu24-10995, 2024.

Satellite gravimetry missions continue to provide data to produce high resolution gravity models of the Earth for over 20 years. The Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) exemplifies the current state-of-the-art mission architecture. GRACE-FO consists of a pair of twin satellites flying in the same orbit with an onboard laser ranging interferometer (LRI) system and GNSS receivers. The LRI is used for accurately tracking low-low satellite range change. The GNSS receivers are used for high-low SST to GNSS satellites, contributing information for satellite positioning, timing, and long-wavelength gravity field information.

We present results from a numerical simulation study to characterize the contributions of various high low SST observation architectures relative to the GRACE-FO configuration. These include gravity fields estimated with only high-low SST observations as well as fields with combined high-low and low-low SST observations. Other aspects of the setup such as measurement observables, bias parameterization, and noise characteristics are evaluated to better understand how high-low SST and its errors impact gravity field estimation. We anticipate the results to be useful in the architecture and science data analysis algorithms for future mass change missions.

How to cite: Saadat, N., Bettadpur, S., McCullough, C., and Nagel, P.: A Quantitative Analysis of the Contributions of High-Low Satellite-to-Satellite Tracking (SST) Observations used for Gravity Field Estimation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3215, https://doi.org/10.5194/egusphere-egu24-3215, 2024.

Considerable research is underway in the satellite geodesy, spaceflight engineering, and high-precision metrology community that brings to bear modern technology to next generation mass-change estimation. This is motivated by a consensus community desire for ever increasing resolution and accuracy of global mass change - an essential climate variable - for understanding and inference of the Earth system at all spatio-temporal scales.

The infusion of high-precision modern technology brings with it additional challenges in the data analysis including fundamental enabling analyses such as attitude and orbit determination, modeling of the observation and its connection to the gravity field parameters, and estimation techniques to maximize the fidelity of spatial patterns and signal amplitudes in estimated mass-change fields.

In this paper, we report on our investigations into the mechanisms of aliasing - one of the most visible challenges in mass-change estimation from satellite gravity observations. In prior work, we have presented symptomatic assessments of how aliasing can have orthogonal impacts on gravity field estimated from low-low satellite-to-satellite (SST) tracking and from gravity gradiometry (GG), and shown how a combination of the two in a hybrid configuration can offer the best of both techniques. In this follow-up paper, we present results of closer investigations into the mechanisms of aliasing and their differential impacts on SST and GG, and what this suggests for mitigation in future multi-technique mass-change measurement environment. These results form the basis for recommendations of analysis techniques such as appropriate modifications to the variational methods, scoping the requirements on prior knowledge of rapid mass variability that is the principal cause of aliasing errors, and their mitigation in estimation techniques.

How to cite: Bettadpur, S., Wang, F., Childress, N., Krichman, B., and Jacob, G.: Analysis challenges for spaceborne multi-technique mass-change measurement: Mechanisms and mitigation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6951, https://doi.org/10.5194/egusphere-egu24-6951, 2024.

The GRACE-FO mission was launched in 2018 and has been providing valuable data since then. However, developments for future missions have been initiated: the US-German GRACE-C Mission with a planned launch in 2028 and the ESA-led Next Generation Gravity Mission (NGGM) with a launch window around 2031. Both use laser interferometers as their primary and only inter-satellite ranging instruments. Accurate knowledge of the laser wavelength, or equivalently the laser frequency, is required to convert the measured phase to a range with a unit of meters.

In GRACE-FO, this conversion (or scale) factor can be determined with the main microwave ranging instrument. However, future missions will require a dedicated wavelength or scale factor readout. Additional phase modulations to be applied to the laser light, in parallel with the conventional cavity locking scheme, have been proposed by the Australian National University (ANU) to achieve such a readout. This technique is now being implemented as a novel Scale Factor Unit (SFU) for the Laser Ranging Interferometer (LRI) onboard the GRACE-C mission, and is also being investigated for the European Laser Tracking Instrument (LTI) of NGGM.

In this talk we will explain the measurement principle, show first results from a breadboard setup of our Scale Factor Measurement System (SFMS) and give an outlook on the next steps towards an implementation for the NGGM LTI.

How to cite: Misfeldt, M., Mueller, V., and Heinzel, G.: Investigations on the Scale Factor Readout of the Laser Interferometer aboard NGGM, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8268, https://doi.org/10.5194/egusphere-egu24-8268, 2024.

Hydrometeorological extreme events, such as heavy rainfall, can cause a rapid increase in local water storage over a short period of time. The duration, magnitude, and area of the event, as well as the runoff of the affected region, determine the life span of these water mass changes. This leads to temporal aliasing, which, along with instrument noise, poses a significant challenge to improving the accuracy and resolution of satellite gravimetry products from GRACE, GRACE Follow-On, and next-generation gravity missions (NGGM). The current Atmospheric Ocean Dealiasing (AOD) products can remove tidal and sub-monthly non-tidal mass variations in the ocean and atmosphere from the level-1 GRACE/-FO data. However, the reanalysis and forecast datasets underlying these AOD products only have a limited temporal and spatial resolution and do not include high-frequency hydrological mass variations and liquid cloud water content of atmospheric mass, that can significantly increase during hydrometeorological extreme events.

The research group New Refined Observations of Climate Change from Spaceborne Gravity Missions (NEROGRAV), funded by the German Research Foundation (DFG), aims at improving GRACE/-FO data products by developing new analysis methods and modeling approaches. This includes a revision of existing geophysical background models as well as their spatial-temporal parameterization. Within this research group we investigate how hydrometeorological extreme events are mapping into GRACE/-FO level-1 data. In this study, we provide statistics on events that may affect GRACE/-FO/NGGM observations and are not accounted for in current AOD products. Using a 3D connected component algorithm, we determine the duration, magnitude, and area of these events for multiple test years over the entire GRACE/-FO observation time span from 2002 to 2023. As expected, the majority of hydrometeorological extreme events take place in tropical regions and areas that are frequently impacted by typhoons, hurricanes, and monsoon rains such as Japan, northern India, and around the Gulf of Mexico. Additionally, we found an increasing number of events over Europe that could significantly impact GRACE/-FO/NGGM observations. Overall, the number of events per year more than doubles from the start to the end of the observation period, which is likely due to climate change. We suspect that the GRACE-FO LRI measurement is sensitive to instantaneous precipitation and liquid cloud water content during overfly for a significant number of these extreme events. Hence, we anticipate an increased probability of NGGM observations being affected by such events, particularly in the context of ongoing climate change. Therefore, we recommend that upcoming dealiasing procedures carefully consider these events.

How to cite: Mielke, C., Springer, A., and Kusche, J.: Statistical assessment of temporal aliasing in GRACE/-FO and NGGM induced by hydrometeorological extremes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15143, https://doi.org/10.5194/egusphere-egu24-15143, 2024.

Despite the increasing accuracies of GRACE/GRACE-FO gravity field models through worldwide endeavors, the temporal aliasing effect caused by the imperfect background models used in gravity field modelling is still a crucial factor that degrades the quality of gravity field solutions. Recognizing the significant impact of temporal resolution in atmospheric de-aliasing models, this study specifically explores its influence on gravity field modeling across frequency, spectral, and spatial domains. Analysis indicates that elevating the temporal resolution from 3 hours to 1 hour has a negligible impact on gravity solutions in both frequency and spectral domains, and this effect is smaller than the variations caused by employing different atmospheric datasets. Nevertheless, in the spatial domain, increasing temporal resolution proves effective in mitigating LRI range-rate residuals, particularly in specific regions of the Southern Hemisphere at mid- and high-latitudes. Mass changes, expressed in Equivalent Water Height (EWH) and derived through P₄M₆ filtering, reveal that the maximum RMS value of spatial differences resulting from enhanced temporal resolution in atmospheric de-aliasing models can reach ~13.4mm in the sub-region of the Congo River Basin. However, using different atmospheric datasets can lead to a maximum difference of ~16.5mm. For the Amazon River Basin, the corresponding maximum discrepancy is ~18.1mm, and that caused by improving temporal resolution is ~9.4mm. Subsequently, the Congo River Basin is divided into several sub-regions using a lat-lon regular grid with a spatial resolution of 3 degrees. The subsequent time series results of mass changes reveal that the maximum contribution of temporal resolution and changes in the atmospheric datasets can reach 11.09% and 21.24%, respectively. These findings underscore the importance of accounting for temporal resolution in de-aliasing products when investigating mass changes at a regional scale.

How to cite: Bai, Y., Chen, Q., and Shen, Y.: Comparisons of Temporal Resolution of Atmospheric De-aliasing Products for the Analysis of Gravity Field Estimation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7181, https://doi.org/10.5194/egusphere-egu24-7181, 2024.