G4.1 | Satellite Gravimetry: Data Analysis, Results and Future Mission Concepts
EDI
Satellite Gravimetry: Data Analysis, Results and Future Mission Concepts
Convener: Christoph Dahle | Co-conveners: Saniya Behzadpour, Ulrich Meyer, Christina Strohmenger
Orals
| Thu, 18 Apr, 08:30–12:25 (CEST)
 
Room D1
Posters on site
| Attendance Fri, 19 Apr, 10:45–12:30 (CEST) | Display Fri, 19 Apr, 08:30–12:30
 
Hall X2
Posters virtual
| Attendance Fri, 19 Apr, 14:00–15:45 (CEST) | Display Fri, 19 Apr, 08:30–18:00
 
vHall X2
Orals |
Thu, 08:30
Fri, 10:45
Fri, 14:00
For more than two decades, satellite missions dedicated to the determination of the Earth's gravity field have enabled a wide variety of studies related to climate research as well as other geophysical or geodetic applications. Continuing the successful, more than 15 years long data record of the Gravity Recovery and Climate Experiment (GRACE, 2002-2017) mission, its Follow-on mission GRACE-FO, launched in May 2018, is currently in orbit providing fundamental observations to monitor global gravity variations from space. Regarding the computation of high-resolution static gravity field models of the Earth and oceanic applications, the Gravity field and steady-state Ocean Circulation Explorer (GOCE, 2009-2013) mission plays an indispensable role. Complementary to these dedicated missions, observations from other non-dedicated missions such as Swarm as well as satellite laser ranging (SLR) have shown to be of significant importance, either to bridge gaps in the GRACE/GRACE-FO time series or to improve gravity field models and scientific results derived thereof. The important role of satellite gravimetry in monitoring the Earth from space has led to various ongoing initiatives preparing for future gravity missions, including simulation studies, the definition of user and mission requirements and the investigation of potential measurement equipment and orbit scenarios.

This session solicits contributions about:
(1) Results from satellite gravimetry missions as well as from non-dedicated satellite missions in terms of
- data analyses to retrieve time-variable and static global gravity field models,
- combination synergies, and
- Earth science applications.
(2) The status and study results for future gravity field missions.

Orals: Thu, 18 Apr | Room D1

Chairpersons: Christoph Dahle, Christina Strohmenger
08:30–08:35
GRACE/GRACE-FO: Gravity Field Processing
08:35–08:45
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EGU24-7426
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Highlight
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On-site presentation
Frank Flechtner, Felix Landerer, Himanshu Save, Christopher Mccullough, Christoph Dahle, Srinivas Bettadpur, Robert Gaston, and Krzysztof Snopek

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.

08:45–08:55
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EGU24-16789
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On-site presentation
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Michael Murböck, Christoph Dahle, Natalia Panafidina, Markus Hauk, Josefine Wilms, Karl-Hans Neumayer, and Frank Flechtner

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 field 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 last year.

At present, we primarily work towards the completion of an optimized stochastic modeling for GRACE and GRACE-FO gravity field determination. This includes the extension of the stochastic instrument error models, the optimization of the combination of the different observations, and the inclusion of tidal and temporally changing non-tidal background model error variance-covariance matrices in the adjustment process.

This presentation provides an overview of the main outcomes of these advanced processing strategies. We discuss details on stochastic modeling of non-tidal atmospheric-oceanic background models including the assessment of temporal correlations and will present preliminary RL07 Level-2 results in the spectral and spatial domain in comparison with the standard GFZ GRACE/GRACE-FO RL06 time series.

How to cite: Murböck, M., Dahle, C., Panafidina, N., Hauk, M., Wilms, J., Neumayer, K.-H., and Flechtner, F.: Advanced processing strategies for a future GFZ GRACE/GRACE-FO Level-2 data release, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16789, https://doi.org/10.5194/egusphere-egu24-16789, 2024.

08:55–09:05
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EGU24-8595
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ECS
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On-site presentation
Moritz Huckfeldt, Florian Wöske, Benny Rievers, and Meike List

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.

09:05–09:15
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EGU24-3692
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ECS
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On-site presentation
Yufeng Nie, Jianli Chen, Yunzhong Shen, and Qiujie Chen

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.

09:15–09:25
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EGU24-15115
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ECS
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On-site presentation
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Martin Lasser, Ulrich Meyer, Daniel Arnold, and Adrian Jäggi

We study temporal gravity field determination from GRACE Follow-On satellite-to-satellite tracking data using the inter-satellite link of the K-Band Ranging System (KBR) and kinematic positions of the satellites as observations and pseudo-observations, respectively. In addition, we introduce the range-rate observations collected by the Laser Ranging System (LRI) as further observation group. We compute our solutions with the Celestial Mechanics Approach using next to the kinematic positions either only LRI range-rate observations or combining them with the KBR derived range-rate data by the means of Variance Component Estimation (VCE).

The stochastic noise of the KBR and LRI data is modelled with an empirical description of the noise based on the post-fit residuals between the final GRACE Follow-On orbits, that are co-estimated together with the gravity field, and the observations, expressed in position residuals to the kinematic positions and in KBR and/or LRI range-rate residuals. We validate the LRI-only and KBR+LRI monthly solutions by comparing them with the KBR-only derived models from the operational GRACE Follow-On processing at the AIUB, by examining the stochastic behaviour of respective post-fit residuals and by inspecting  areas where a low noise is expected. Last but not least, we investigate the influence of LRI-only and KBR+LRI monthly gravity field solutions in a  combination of monthly gravity fields based on other approaches as it is done by the Combination Service for Time-variable Gravity fields (COST-G) and make use of noise and signal assessment applying the quality control tools routinely used in the frame of COST-G.

How to cite: Lasser, M., Meyer, U., Arnold, D., and Jäggi, A.: Integration of laser ranging range-rate observations into the GRACE Follow-On processing at the AIUB, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15115, https://doi.org/10.5194/egusphere-egu24-15115, 2024.

09:25–09:35
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EGU24-11987
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ECS
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Virtual presentation
Mathias Duwe, Igor Koch, and Jakob Flury

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.

GRACE/GRACE-FO: Applications
09:35–09:45
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EGU24-6953
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ECS
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On-site presentation
Kunpu Ji, Yunzhong Shen, Lin Zhang, Qiujie Chen, Lizhi Lou, and Lianbi Yao

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.

09:45–09:55
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EGU24-18889
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On-site presentation
Pavel Ditmar

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.

09:55–10:05
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EGU24-680
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ECS
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On-site presentation
Komali Bharath Narayana Reddy and Balaji Devaraju

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.

10:05–10:15
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EGU24-5322
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ECS
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On-site presentation
Junyang Gou, Lara Börger, Michael Schindelegger, and Benedikt Soja

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.

Coffee break
Chairpersons: Ulrich Meyer, Christoph Dahle
Next Generation Gravity Missions
10:45–10:55
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EGU24-11271
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Highlight
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On-site presentation
Ilias Daras, Luca Massotti, Philip Willemsen, Guenther March, Michael Francois, and Bernardo Carnicero Dominguez

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.


[1] Pail, R., Bingham, R., Braitenberg, C. et al. Science and User Needs for Observing Global Mass Transport to Understand Global Change and to Benefit Society. Surv Geophys 36, 743–772 (2015). https://doi.org/10.1007/s10712-015-9348-9

[2] Terrestrial Water Storage ECV Requirements: The 2022 GCOS ECVs Requirements (GCOS 245)

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.

10:55–11:05
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EGU24-19340
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On-site presentation
Carla Braitenberg, Anna Fantoni, Gerardo Maurizio, and Alberto Pastorutti

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.

11:05–11:15
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EGU24-10995
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ECS
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On-site presentation
Philipp Zingerle, Roland Pail, Thomas Gruber, and Ilias Daras

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.

11:15–11:25
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EGU24-16638
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On-site presentation
MAGIC – investigating a solution for a worst-case scenario
(withdrawn)
Matthias Weigelt
11:25–11:35
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EGU24-3215
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ECS
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On-site presentation
Niusha Saadat, Srinivas Bettadpur, Christopher McCullough, and Peter Nagel

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.

11:35–11:45
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EGU24-6951
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On-site presentation
Srinivas Bettadpur, Furun Wang, NIcholas Childress, Ben Krichman, and Geethu Jacob

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.

11:45–11:55
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EGU24-8268
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ECS
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On-site presentation
Malte Misfeldt, Vitali Mueller, and Gerhard Heinzel

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.

11:55–12:05
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EGU24-17380
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ECS
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On-site presentation
|
Laura Müller, Vitali Müller, Malte Misfeldt, and Gerhard Heinzel

GRACE-FO was launched almost six years ago, following the successful GRACE mission. Measuring changes in the Earth's mass distribution is useful for climate research, such as monitoring melting ice caps or changes in groundwater storage. The Earth's gravitational field causes distance variations between the two twin satellites, which are measured by a Microwave Instrument (MWI) and a Laser Ranging Interferometer (LRI). This first inter-satellite laser interferometer provides reliable measurements with lower noise than the MWI and has therefore been selected as the main science instrument for future gravity missions.

Here we present the current status and results of a novel LRI Level 0/1A data simulator developed to support studies for future missions and to verify and improve the current LRI1B processing chain. The main inputs to the simulator are satellite orbit files with position and velocity and attitude data sets, which are transformed into LRI Level 0/1A data files, taking into account relativistic effects, phase wrapping, tilt-to-length coupling and many other noise sources. The output data format is equivalent to the raw phase or ranging data from GRACE-FO. The Level 1A data can then be further processed to Level 1B using the same software used for the GRACE-FO LRI flight data processing. We explain our strategy to validate the results and to identify and address limitations in the Level-1A simulator and in our Level-1B flight data processing chain, e.g. by using specially tailored orbit sets.

We conclude that the simulator is capable of deriving realistic LRI Level 0/1A data that can be further processed to Level 1B, and that the simulator has led to improvements in our GRACE-FO LRI Level 1B processing.

How to cite: Müller, L., Müller, V., Misfeldt, M., and Heinzel, G.: Novel LRI Level 0/1A Data Simulator, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17380, https://doi.org/10.5194/egusphere-egu24-17380, 2024.

De-aliasing Models
12:05–12:15
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EGU24-15143
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On-site presentation
Christian Mielke, Anne Springer, and Jürgen Kusche

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.

12:15–12:25
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EGU24-7181
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ECS
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On-site presentation
Yinglun Bai, Qiujie Chen, and Yunzhong Shen

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.

Posters on site: Fri, 19 Apr, 10:45–12:30 | Hall X2

Display time: Fri, 19 Apr, 08:30–Fri, 19 Apr, 12:30
Chairperson: Christoph Dahle
X2.10
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EGU24-7548
Adrian Jaeggi, Ulrich Meyer, Martin Lasser, Frank Flechtner, Christoph Dahle, Eva Boergens, Torsten Mayer-Gürr, Felix Öhlinger, Jean-Michel Lemoine, Stéphane Bourgogne, Thorben Döhne, Hao Zhou, Jianjun Ran, Qiujie Chen, Changqing Wang, and Wei Feng

In 2019 the Combination Service for Time-variable Gravity fields (COST-G) started its operation with the first release of combined monthly GRACE gravity field models. Meanwhile almost five years have passed, while new experience was gained with the operational combination of the monthly gravity field models of the successor mission GRACE-FO, which has triggered a review of the weighting scheme and consequently a second release of GRACE-FO models in 2023. Moreover, the COST-G consortium has been in close cooperation with new GRACE/GRACE-FO analysis centers from China since spring 2020, which recently provided time-series of unconstrained models, covering the whole GRACE period, as it is requested by the COST-G processing standards. After careful evaluation of all individual time-series the whole GRACE time-series has now been recombined based on the new weighting scheme and also taking into account the contributions of the new COST-G analysis centers APM-SYSU, HUST, SUSTech and Tongji. We present the COST-G GRACE RL02 and also show latest results of the operational GRACE-FO combination.

How to cite: Jaeggi, A., Meyer, U., Lasser, M., Flechtner, F., Dahle, C., Boergens, E., Mayer-Gürr, T., Öhlinger, F., Lemoine, J.-M., Bourgogne, S., Döhne, T., Zhou, H., Ran, J., Chen, Q., Wang, C., and Feng, W.: The COST-G GRACE RL02, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7548, https://doi.org/10.5194/egusphere-egu24-7548, 2024.

X2.11
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EGU24-5715
Sergei Rudenko, Denise Dettmering, Mathis Bloßfeld, and Julian Zeitlhöfler

Gravitational forces are the major forces acting on near-Earth orbiting (e.g., altimetry) satellites. Recently published Earth’s gravity field models used within the satellite precise orbit determination (POD) comprise observations of GRACE (Gravity Recovery And Climate Experiment) and GRACE-FO (GRACE-Follow-On), gravity field satellite missions between 2002 until 2017 and since 2018, respectively. In this presentation, we perform a review of selected Earth’s time-variable gravity field models developed in the past ten years (2014-2023). We analyze also the POD results obtained for selected altimetry satellites, namely, TOPEX/Poseidon, Jason-1, Jason-2, and Jason-3 at the time interval from 1992 to 2023 using various Earth’s gravity field models. A special focus is put on the CNES/GRGS mean gravity field models of releases 2 to 5, including the latest CNES_GRGS.RL05MF_COMBINED_GRACE_SLR_DORIS model. The impact of these models is assessed for different orbit parameters as well as the root-mean-square and mean values of Satellite Laser Ranging observation residuals and orbit differences. Furthermore, the impact of these models on altimetry (single- and multi-satellite) sea surface height crossover differences is investigated. From these crossover differences, radial errors and geographically-correlated mean errors are derived and analyzed. The results are used to conclude on the accuracy of current Earth’s time-variable gravity field models when used for the POD of altimetry satellites.

How to cite: Rudenko, S., Dettmering, D., Bloßfeld, M., and Zeitlhöfler, J.: Impact of new Earth’s time-variable gravity field models on orbits of altimetry satellites, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5715, https://doi.org/10.5194/egusphere-egu24-5715, 2024.

X2.12
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EGU24-12539
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ECS
Chaoyang Zhang, Byron Tapley, Himanshu Save, Peter Nagel, Zhigui Kang, Steven Poole, Mark Tamisiea, and Furun Wang

The fifteen and half years long GRACE temporal gravity data has greatly contributed to interdisciplinary studies especially in climate and solid Earth sciences. To further improve the noise level and error characteristic of the GRACE temporal gravity solutions, as well as provide an archival record for supporting a multidecade mass change measurement based on measurement continuity between the GRACE and GRACE Follow-On mission, the GRACE RL07 re-processing has been carried out at CSR. We will use an initial version of the GRACE Level1B  data (i.e. version 04P), updated background models, new GPS observation strategy and improved observation noise model for the RL07 re-processing. In this poster, we will present preliminary results from the GRACE RL07 re-processing and compare them with the GRACE RL06 solutions using different metrics.       

How to cite: Zhang, C., Tapley, B., Save, H., Nagel, P., Kang, Z., Poole, S., Tamisiea, M., and Wang, F.: Preliminary CSR GRACE RL07 re-processing results , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12539, https://doi.org/10.5194/egusphere-egu24-12539, 2024.

X2.13
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EGU24-10401
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ECS
Felix Öhlinger and Torsten Mayer-Gürr

Gravity field recovery using GRACE-FO observations requires the reduction of non-conservative forces usually measured by the onboard accelerometer in the center of mass of each spacecraft. The accelerometer of GRACE-D degraded significantly in June 2018 showing increased noise levels by orders of magnitude and common mode errors on all acceleration components. However, the quality of the accelerometer measurements is vital for accurately estimating the Earth’s gravity field. The standard approach to account for the degraded data of GRACE-D is to replace the measurements with synthetic data, the so-called transplant data. At Graz University of Technology (TUG) a very effective procedure to estimate such an accelerometer transplant was developed adopting a remove-restore approach (Behzadpour, 2021). Hereby, data from GRACE-C and non-conservative force models are used to substitute GRACE-D data. Since then the effort was made to further improve the TUG transplant product.

Effects that need to be considered are on the one hand the increased solar activity as we are approaching the peak of solar cycle 25 which makes it harder to estimate an accurate transplant product by using force models and on the other hand influences such as thruster leakage which occurs on both GRACE-C and GRACE-D. Investigations that were carried out comprise the adaption of the physical properties of the satellite’s surface elements and the consideration of bias jumps at each thruster firing. The bias jumps for GRACE-C were corrected before the transplant process and with the use of actual GRACE-D data thruster leakage and some residual drag acceleration was restored for GRACE-D.

How to cite: Öhlinger, F. and Mayer-Gürr, T.: Improved alternative GRACE-FO accelerometer transplant product computed at Graz University of Technology (TUG), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10401, https://doi.org/10.5194/egusphere-egu24-10401, 2024.

X2.14
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EGU24-17286
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ECS
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Pallavi Bekal, Malte Misfeldt, Laura Müller, Vitali Müller, and Gerhard Heinzel

The Laser Ranging Interferometer (LRI) is a technology demonstrator instrument on board the GRACE-FO twin-satellite mission that has been in orbit since 2018. It uses laser interferometry to measure the range between the two satellites (GF1 and GF2) with a nanometer level of accuracy. The gravity field measurements using the ranging data quantify the spatial and temporal variation in the Earth's mass distribution.

The change in the range measured by the LRI has gravitational and non-gravitational origins. Many non-gravitational effects, like atmospheric drag and thruster firings, are known and can be delineated from the LRI data. However, other sporadic instantaneous changes in the range are described as possible momentum transfer events (MTEs) candidates. Some potential sources are meteoroids and space debris's physical impacts on the spacecraft. 

To analyze MTE candidates, we first present the process of detecting them by correlating the LRI ∆v with that of the accelerometer (ACC) for both GRACE-FO spacecraft. Through this, 129 events were found on GF1 and 138 in GF2 between mid-2018 and the end of 2022. Some events show a better correlation between LRI and ACC data than others. Hence, further analysis is conducted by categorizing them accordingly and studying their spatial distribution and periodicity. The occurrence of many events coincides with the period of the beta angle of the sun. Structural changes in the spacecraft could cause these events upon exposure to solar radiation. However, many events have ∆v < 5 × 10 −8 m/s, which is too low to be considered an MTE. They are instead categorized as disturbances to the spacecraft. The origin of these remains unknown.

Furthermore, simulations are performed using the ESA MASTER v8.0.3 to render the number of events per year that cause MTEs via physical impact during the same observation period. The observed events are consistent with the simulation for ∆v ≥ 5 × 10 −8 m/s. 

This analysis is beneficial in creating a repository of known effects in the first-ever space laser interferometer. In future missions, the knowledge of these occurrences in the LRI and ACC data will be helpful during post-processing.

How to cite: Bekal, P., Misfeldt, M., Müller, L., Müller, V., and Heinzel, G.: Momentum Transfer Events and Other Disturbances in LRI Data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17286, https://doi.org/10.5194/egusphere-egu24-17286, 2024.

X2.15
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EGU24-16530
Josefine Wilms, Markus Hauk, Christoph Dahle, Michael Murboeck, Natalia Panafidina, and Frank Flechtner

GFZ has performed various full-scale simulations within the ESA NGGM/MAGIC Science Support Study, including instrument noise and background model error assumptions. The focus was set on developing and applying extended parameterization techniques for improved de-aliasing of short-term mass variations.

The impact of using model uncertainties was investigated for ocean tide and non-tidal atmospheric and oceanic background models. As part of the DFG Research Unit NEROGRAV covariances of model uncertainties were computed and during gravity field retrieval model corrections were co-estimated using this prior covariance information. In principle, model errors are absorbed by the additional co-estimated parameters, and gravity field estimation is thereby improved.

First, simulations with only ocean tide errors and only non-tidal background model errors were performed separately for one month to assess the error reduction obtained for each. Finally, ocean tide and non-tidal errors were included together in a full noise simulation and compared to the processing strategy that did not include co-estimation of background model errors.

The novel optimized method was then also applied for monthly gravity field retrieval over one year, showing improvements for each month. The estimated residual ocean tides from this 1-year simulation were then used to calculate an improved ocean tide model optimized for gravity field recovery.

In addition, monthly solutions, obtained with co-estimation of background model errors, have been calculated for the inclined pair alone using regularization for the not-covered polar regions and compared to double pair solutions for latitudes lower than +/- 70 degrees.

How to cite: Wilms, J., Hauk, M., Dahle, C., Murboeck, M., Panafidina, N., and Flechtner, F.: Gravity field recovery using co-estimation of background model errors to improve de-aliasing capabilities of the MAGIC double-pair constellation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16530, https://doi.org/10.5194/egusphere-egu24-16530, 2024.

X2.16
|
EGU24-2909
Anna Maria Marotta, Riccardo Barzaghi, Carla Braitenberg, Luca Brocca, Gabriele Cambiotti, Stefania Camici, Stefano Casotto, Carlo Iapige De Gaetani, Angelo De Min, Maurizio Fedi, Alberto Pastorutti, Tommaso Pivetta, Mirko Reguzzoni, Umberto Riccardi, Lorenzo Rossi, Roberto Sabadini, Simona Zoffoli, Giovanni Paolo Blasone, and Francesco Longo

The substantial improvement in spatio-temporal accuracy that will be provided by the ESA NGGM/MAGIC mission will make it possible to take a decisive step forward in our knowledge of the dynamics of the main physical processes involving the different compartments of the Earth.

Since every physical process that occurs within each terrestrial compartment involves a redistribution of mass and therefore a signal of gravity, the project intends to provide results of impact and breakthroughs in the modeling and understanding of the dynamics of Solid Earth and Fluid Earth processes, the latter including the water stored in continents and oceans, as well as in geodesy.

Methodologies will be developed that link gravity signals from the various compartments of the Earth to the MAGIC raw data, finally linking each terrestrial compartment with the two pairs of satellites, the core of MAGIC.

The partnership proposing the project includes researchers from different Universities and Research Institutions and has all the skills in the various sectors mentioned above, from its assets in basic science to the application ones.

The following activities are planned:

- Modeling of the gravitational effects of slow tectonics and seismic cycle

- Modeling of the gravitational effects from volcanic processes

- Development of methodologies of compact imaging/inversion for the estimation of mass changes

- Tidal and ocean circulation models for gravity signal and generation of L2 data

- Precipitation and river flow models, hydrological models for the TWSA

- High resolution background gravity and gravity anomaly error determination and E2E simulations for geophysical processes detectability.

Among the objectives of these activities, common to all partners, there will be in particular that of verifying that the spatio-temporal resolution of MAGIC allows to satisfy the requirements necessary to extract from the mission data the gravity signal that allows a significant advance in the basic research and related applications in the various geophysical and geodetic components.

The project is funded by the Italian Space Agency - ASI.

How to cite: Marotta, A. M., Barzaghi, R., Braitenberg, C., Brocca, L., Cambiotti, G., Camici, S., Casotto, S., De Gaetani, C. I., De Min, A., Fedi, M., Pastorutti, A., Pivetta, T., Reguzzoni, M., Riccardi, U., Rossi, L., Sabadini, R., Zoffoli, S., Blasone, G. P., and Longo, F.: The “NGGM-MAGIC: A breakthrough in the understanding of the dynamics of the Earth” project, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2909, https://doi.org/10.5194/egusphere-egu24-2909, 2024.

X2.17
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EGU24-12435
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ECS
Yihao Yan, Vitali Müller, Gerhard Heinzel, Changqing Wang, and Zitong Zhu

The GRACE-like gravity satellites are designed to provide accurate measurements of the global time-varying gravity field, allowing to monitor the changes in the distribution of the Earth's mass caused, for example, by climate change. The gravity information is encoded in the line-of-sight vector, which is given by the position difference between the satellites. The key observable of GRACE and GRACE follow-on is the change in length of the LOS vector, measured by dedicated ranging instruments (K-band ranging system (KBR) or laser ranging interferometer (LRI)). However, the orientation of the LOS vector is measured with some precision using GNSS/GPS, which limits the accuracy of the gravity field maps. To overcome this problem, we propose the use of a dedicated angular velocity sensing (AVS) system that tracks the changes in the orientation of the line of sight with respect to the inertial frame. The angular velocity vector of the LOS has two independent components, yaw and pitch, which we introduce as additional observations in the gravity field recovery process. We firstly show how the AVS and range observables can be used to reconstruct the 3-dimensional differential acceleration vector. Then we find that the inversion results with AVS and regular ranging can mitigate the effect of AOD errors and significantly improve the accuracy of the gravity fields if more accurate AVS observations are available than currently provided by GNSS/GPS orbits. One potential way to achieve more accurate AVS observations is to use differential wavefront sensing (DWS) to accurately measure the orientation of the accelerometer test masses with respect to the platform, giving lower noise than the conventional star cameras, and combine these measurements with the DWS measurements from the inter-satellite laser interferometer to obtain the orientation of the LOS with respect to the inertial frame. With a DWS noise level of 0.1 nrad/√Hz, a single pair of GRACE satellites can achieve the same accuracy as a four-satellite Bender configuration. This study provides a promising alternative to the development of multiple satellite pairs to improve the accuracy of gravity missions.

How to cite: Yan, Y., Müller, V., Heinzel, G., Wang, C., and Zhu, Z.: What can we expect from angular velocity sensing for future gravity missions?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12435, https://doi.org/10.5194/egusphere-egu24-12435, 2024.

X2.18
|
EGU24-21808
Satellite Gravity Gradiometry Sensitivity Analysis
(withdrawn after no-show)
Anthony Purcell and Paul Tregoning
X2.19
|
EGU24-7389
|
ECS
Jianhua Chen, Qiujie Chen, Yunzhong Shen, Xingfu Zhang, and Yufeng Nie

The Satellite Gravity Gradiometry (SGG) data from the Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite demonstrated unprecedented accuracy in estimating the gravity field model across medium and long wavelengths. However, the GOCE satellite re-entered Earth’s atmosphere in Nov. 2013. Leveraging SGG data for gravity field estimation will be a prominent research focus within the Next-Generation Gravity Mission (NGGM) to enhance further the spatial resolution and accuracy of solved gravity field models. During the final 15 months of the GOCE mission, there was a notable reduction in orbital altitude from 259.5 to 229 km. This decline provides essential data for assessing how different orbital altitudes affect static gravity field estimation. Based on Tongji-GMMG2021S (Gravity field Model from Multi-Gravity observation [Satellites]), this paper conducts a quantitative analysis, leading to the following conclusions: (1) The Tongji-GMMG2021S model derived from reprocessed Level-1b SGG data and the normal equation of Tongji-Grace02s, exhibits spatial and accuracy levels comparable to those of the GOCO06s model. (2) The contribution analysis at the normal matrix level shows that SGG data primarily contributes between 95 and 260 degrees to the Tongji-GMMG2021S normal matrix. (3) In terms of the geoid grid height difference to the Tongji-GMMG2021S model in the spatial domain, the period of Low Orbital Altitude from Aug. 2012 to Oct. 2013 significantly contributes to reducing residuals compared to the period of Higher Orbital Altitude from Nov. 2009 to Jul. 2012. These findings also provide a valuable reference for balancing the orbital altitude of NGGMs, the lifespan of NGGMs operational and the accuracy of the gravity field models.

How to cite: Chen, J., Chen, Q., Shen, Y., Zhang, X., and Nie, Y.: Contribution Analysis of the SGG Observation from Different GOCE Orbital Altitudes to Static Gravity Field Solution, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7389, https://doi.org/10.5194/egusphere-egu24-7389, 2024.

X2.20
|
EGU24-1914
|
ECS
Samuel Milki Yadeta, Walyeldeen Godah, Malgorzata Szelachowska, Wojciech Jarmołowski, and Paweł Wielgosz

The determination of geodetic heights with high accuracy is one of the main tasks in geodesy. In 2015, a resolution for definition of International Height Reference System (IHRS) and its realization by International Height Reference Frame (IHRF) was released by the International Association of Geodesy (IAG). In the recent few years, intensive efforts have been devoted to develop the IHRF and its temporal changes. The main goal of the proposed study is to analyze temporal variations of geodetic height changes at the locations of proposed IHRF sites using data from Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GRACE-FO) satellite missions, tide gauges, and space geodetic techniques, i.e. GNSS, SLR, VLBI, and DORIS.

Monthly GRACE/GRACE-FO-based Global Geopotential Models were utilized to estimate temporal variations of ellipsoidal height at proposed IHRF sites. Moreover, geodetic height changes were obtained from the aforementioned space geodetic techniques and tide gauge stations that co-located with the proposed IHRF sites. Then, the seasonal decomposition method and Discrete Fourier Transform were implemented to analyze time series of obtained geodetic height change. Based on the results, seasonal and long-term components of geodetic height variations at the proposed IHRF sites were determined, analyzed, and discussed according to the contemporary requirements for the definition of the IHRF, as well as the precise levelling measurements.

Keywords: GRACE/GRACE-FO satellite missions, space geodetic techniques, tide gauge, reference system/frame, geodetic height

How to cite: Yadeta, S. M., Godah, W., Szelachowska, M., Jarmołowski, W., and Wielgosz, P.: On the analysis of geodetic height changes obtained using different observation techniques at proposed IHRF sites, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1914, https://doi.org/10.5194/egusphere-egu24-1914, 2024.

X2.21
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EGU24-4465
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ECS
Zhongtian Ma, Robert Tenzer, and Hok-Sum Fok

The Gravity Recovery and Climate Experiment (GRACE) has played an important role in sea level observations over the last few decades. However, regional-scale studies of this phenomenon are still challenging due to the potential land-to-ocean leakage along coastlines. In this study, we utilized the Spherical Slepian Functions (SSF) to inverse the regional sea level signal within the South China Sea by incorporating an optimal coastal buffering zone into transform procedures of the original GRACE spherical harmonics (SH). By synthesizing the time series of oceanic and coastal areas with different trends, annual amplitudes and phases, the SSF-inversed signal with a 1° buffering zone was found to be more consistent with synthesized time series than traditional SH-inversed results. Then, the spatiotemporal characteristics of seasonal and residual sea level variations were further analyzed and compared with results from traditional GRACE SH product, GRACE Mascon resolution, the Estimating the Ocean Circulation and Climate (ECCO) model, and the difference between altimetry and a steric sea level model (i.e., Altimetry-Steric data). Temporal analysis shows that the trend and the phase of regional sea level signal within the South China Sea with the 1° buffering zone using the GRACE SSF was 0.28 cm/yr and 108° respectively, which generally agrees with other sea level solutions. However, the SSF-inversed mass sea level amplitude of 4.63 cm was larger (smaller) than that obtained from the SH (Mascon) method by approximately 0.7 cm (0.6 cm), showing relatively better consistency with the 4.47 cm from the ECCO model and 4.23 cm from the Altimetry-Steric data. For the spatial analysis, an extremely high amplitude of sea level signal at the centre of the Gulf of Thailand due to seasonal alternating circulations was observed in all data, except for the GRACE SH solution, which significantly underestimated the signal due to a smoothing effect of filtering. Besides, the SFF-inversed GRACE exceptionally observed an apparent seasonality of sea level signal near the mouth of the Pearl River with an amplitude of ~ 8 cm. Furthermore, the sea level signal along the eastern coasts and the Sunda Shelf was out-of-phase for SSF GRACE and Altimetry-steric data, probably due to the interaction of active tropical eddies nearby. The potential inter-annual sea level variability was also analyzed by decomposing the residual time series through the Multivariate Singular Spectrum Analysis (MSSA) method. Results show that the highest cross-correlation between the decomposed modes of GRACE Mascon mass sea level and Southern Oscillation Index (SOI) reached 0.52 with a time lag of 2 months, considerably larger than 0.14 from GRACE SSF. This finding can be explained by the fact that most of the truncated Spherical Slepian functions capture short-term signals that are mainly attributed to seasonal changes. Consequently, it is difficult to distinguish between a relatively small long-term signal and noise. This may also explain the irregular spatial distribution in the GRACE SSF sea level trends. Nevertheless, this study demonstrates a feasibility of using the Spherical Slepian functions in modelling of mass sea level signal over a medium-sized sea.

How to cite: Ma, Z., Tenzer, R., and Fok, H.-S.: Estimating spatio-temporal characteristics of sea level variations of the South China Sea using the Spherical Slepian functions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4465, https://doi.org/10.5194/egusphere-egu24-4465, 2024.

X2.22
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EGU24-11024
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ECS
Le Liu and Michael Schindelegger

Significant resources have been and are continuing to be devoted to monitor variability in the North Atlantic Meridional Overturning Circulation (AMOC), an essential component of the climate system. Transport mooring arrays are one means of choice, but given their confinement to individual latitudes, complementary large-scale observations are desirable. Here we follow lines of previous research and explore whether ocean bottom pressure (OBP) estimates from present and future satellite gravimetry missions can add useful constraints on interannual AMOC variability between 25°N and 55°N. Central to these considerations are OBP signals along the continental slope of the basin’s western boundary, which—in principle—allow for recovery of geostrophic AMOC variability above 1000 m, between 1000–3000 m, and in some latitudes also below 3000 m. We apply the geostrophic calculation to latest GRACE (Gravity Recovery and Climate Experiment) monthly OBP solutions, in part to document current system capabilities and highlight known shortcomings (e.g., coarse horizontal resolution and data noise). Despite these issues, there are tentative signs of robust and meridionally connected transport variations at latitudes of the New England continental slope (between 35°N and 42°N), including a positive anomaly of ~2 Sverdrup between 2006 and 2012 below 1000 m. We further assess the feasibility of recovering AMOC variability from boundary pressures in high-resolution coupled climate models. These datasets provide useful information on the variance of the involved quantities as well as locations (i.e., depths and latitudes) where accurate knowledge of OBP changes is most important. Insights gained here will be used in upcoming closed-loop orbit simulations that will make special allowance for mass change recovery on the continental slope through dedicated parameterizations in the gravity field estimation.

How to cite: Liu, L. and Schindelegger, M.: Recovering North Atlantic meridional transport variability from bottom pressure anomalies – a revisit, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11024, https://doi.org/10.5194/egusphere-egu24-11024, 2024.

X2.23
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EGU24-8356
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ECS
Bart Root and Cedric Thieulot

With the GRACE-FO mission well underway and the plans of the MAGIC/NGGM mission in the future, there will be several decades of satellite gravity change data available. Both periodic and secular mass changes are studied with this data, mostly surface mass changes like hydrology, ice melt, Glacial Isostatic Adjustment, and large Earthquakes. With the increasing time period of the gravity data set, smaller variation in the signal can be detected, especially linear secular changes. One of the processes that would result in small secular gravity rate is the mass change due to mantle convection.

We perform various sensitivity analysis studies to understand the added benefit of detecting mantle convection with satellite gravity change observations. A fast stoke solver (FLAPS) is developed that is based on an axisymmetric half annulus geometry. A density and viscosity structure can inserted as well as test anomalies to understand the effect of the mantle flow on the gravity change observations. The model evolves over 50 years after which the difference between the initial and final state is computed. This will also give the rate of change information. Realistic Earth models (PREM) as well as synthetic models are tested to better understand the sensitivity of the gravity change data.

The gravity change observations are sensitive to the absolute viscosity state of the mantle. This is contrary to dynamic topography and geoid data, which do not have this sensitivity and studies using these data always have an ambiguity wrt. viscosity state. Moreover, it seems that the gravity change data is more sensitive to the lower mantle of the Earth. This sensitivity can be very helpful in further exploration of Core-Mantle Boundary structures. The modelled magnitude of the gravity change linked to global mantle convection seems to be larger then the formal error estimates of the GRACE and GRACE-FO instrumentation. A longer acquisition period will reduce the secular errors in the ocean, atmosphere and tidal correction models, such that eventually mantle convection can be studied directly by satellite gravimetry.

How to cite: Root, B. and Thieulot, C.: Sensitivity analysis on gravity change data in order to observe mantle convection, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8356, https://doi.org/10.5194/egusphere-egu24-8356, 2024.

X2.24
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EGU24-17911
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ECS
Kazuma Nakakoji, Yoshiyuki Tanaka, Volker Klemann, and Zdeněk Martinec

Space geodetic techniques such as GNSS have been used to observe co- and post-seismic crustal deformation in subduction zones with high spatio-temporal resolution. However, it is difficult to observe such crustal deformations in oceanic regions. Satellite gravimetry, on the other hand, can detect co- and post-seismic mass changes both over land and ocean. However, the spatio-temporal resolution of these satellites is insufficient to distinguish co- and post-seismic effects. The planned MAGIC mission aims to achieve a 3-day, 100 km resolution, enabling their separation. This advancement is expected to provide a more precise understanding of the mechanisms of post-seismic deformations following major earthquakes.

 

Geodetic observations have so far shown that there are three mechanisms of post-seismic deformations: afterslip, poroelastic rebound, and viscoelastic relaxation. The last one, viscoelastic relaxation has not been considered to contribute to short-term deformations unlike other two mechanisms. However, seafloor geodetic observations after the 2011 Tohoku earthquake captured the characteristic deformation even one year after the earthquake, which cannot be interpreted without a contribution of viscoelastic relaxation. Geophysical models that reproduce such viscoelastic relaxation have been proposed considering surface topography and 3D viscoelastic and density structure including a subducting oceanic slab. However, there are only a few models incorporating a nonlinear rheology to calculate post-seismic gravity changes. In the nonlinear case, the effective viscosity changes in space and time with stress evolution. In particular, co-seismic high stress changes lead to low effective viscosity, which promotes short-term viscoelastic relaxation after an earthquake. Hence, it is essential to discuss the extent to which this mechanism can be constrained when satellite gravity data with high spatio-temporal resolution become available by MAGIC.

 

Previous physical models to calculate post-seismic deformation have often treated the self-gravitation effects only approximately or ignored it. To represent the effects naturally, we have developed a spectral finite-element method based on a spherical earth model with a 3D viscosity distribution for a linear rheology. In this study, we extend this method to a nonlinear rheology. This method computes the deformation in the time domain. Therefore, one can easily obtain the deformation for the nonlinear case by evaluating effective viscosity at each time step without major changes in the algorithm for the linear case. In the presentation, the spectral finite element method will be introduced, and numerical results will be shown, including viscosity distributions corresponding to co-seismic stress changes and their time evolution, and gravity signals reflecting a nonlinear rheology.

How to cite: Nakakoji, K., Tanaka, Y., Klemann, V., and Martinec, Z.: Development of a calculation method for viscoelastic relaxation incorporating nonlinear rheology in a self-gravitating spherical Earth model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17911, https://doi.org/10.5194/egusphere-egu24-17911, 2024.

Posters virtual: Fri, 19 Apr, 14:00–15:45 | vHall X2

Display time: Fri, 19 Apr, 08:30–Fri, 19 Apr, 18:00
Chairperson: Christina Strohmenger
vX2.2
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EGU24-12760
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ECS
Chiachun angela Liang, Isabella Velicogna, Geruo Aa, and Tyler Sutterley

Consensus from mass balance studies published in the past decade revealed an increase in mass loss from the Antarctic Ice Sheet. However, independent methods (e.g., gravity, altimetry, and mass budget) for determining the rate of mass loss disagree about the magnitude and uncertainty of estimates for East Antarctica. This discrepancy is largely due to the size of East Antarctica, the low signal-to-noise ratios of existing sensors, and the confluence of uncertainties for each method. As a result, ice sheet models may not be well-constrained to make future projections of ice mass change and sea level change. Here, we combine GRACE/GRACE-FO, ICESat/ICESat-2, and GPS observations and extend Velicogna et al. (2002) iterative algorithm to improve the estimate of the Antarctic mass balance. We add outputs from surface mass balance (SMB) and firn models to satellite altimetry, time-variable gravity, and GPS measurements. We evaluate the sensitivity of the approach to realistic ice mass spatial and time distributions using an effective density map derived from ICESat-2 data, and reconstructions of SMB and firn depth from climate model outputs. Our result provides information on how the GPS network could be completed to resolve major uncertainties, obtain a better glacial isostatic adjustment (GIA), and a better estimate of ice mass balance.

How to cite: Liang, C. A., Velicogna, I., Aa, G., and Sutterley, T.: An iterative method combining GRACE/GRACE- FO, ICESat/ICESat-2, GPS, and SMB from climate model outputs to improve Antarctic mass balance and GIA, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12760, https://doi.org/10.5194/egusphere-egu24-12760, 2024.

vX2.3
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EGU24-14290
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ECS
Hongjuan Yu, Lin Zhang, and Yong Zhang

The publicly available SLR-derived monthly Earth’s oblateness C20 (or J2) time series exhibits varying levels of noise or systematic errors depending on the processing strategies used during estimation. We propose the use of two strategies, variance component estimate (VCE) and equal weighting (EW), to combine the SLR-derived J2 time series from four internationally renowned institutions. The resulting combined J2 time series is theoretically expected to demonstrate enhanced quality by reducing noise and systematic errors compared to individual contributions. These two combined solutions alongside four individual solutions are then discussed by analyzing their effects on global and local mass changes, thus exploring the potential for an optimized J2 time series in GRACE applications. The two combined SLR-derived J2 time series can assess the accuracy of the GRACE-derived J2 time series, which has shown poor but progressively improving accuracy. Results indicate that the RL06 version model of GRACE-derived J2 significantly outperforms the RL05 version, thus rendering the 160-day ocean tide effect in RL06 negligible. Moreover, significant discrepancies and lower quality among the various institutions' GRACE-derived J2 lead to Antarctic/Greenland ice sheet mass change estimates notably deviating from SLR-derived results. Therefore, upon replacing the GRACE-derived J2 time series with the VCE-combined SLR-J2 time series, the difference between the calculated mass change of the Antarctic/Greenland ice sheet and the RACMO2.3p2 model is theoretically the smallest, displaying the highest correlation coefficient between them.

How to cite: Yu, H., Zhang, L., and Zhang, Y.: Combination and analysis of the SLR monthly Earth’s oblateness variation solutions from different processing strategies, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14290, https://doi.org/10.5194/egusphere-egu24-14290, 2024.