Displays

The twin satellites of the Gravity Recovery and Climate Experiment (GRACE) Follow-On mission were successfully launched in May-2018. The primary objective of the mission is to continue the 15-year GRACE (2002-2017) global data record of Earth’s monthly mass changes. These measurements have become an indispensable tool to quantify and track Earth’s water movement and surface mass changes across the planet. Monitoring changes in ice sheets and glaciers, near-surface and underground water storage, the amount of water in large lakes and rivers, as well as changes in sea level and ocean currents provides an integrated global view of how Earth’s water cycle and energy balance are evolving.

In this presentation we will present the current mission status, including instrument and flight system performance, discuss science data quality and performance as well as recent science results from the first two years of observations, and address data continuity from GRACE to GRACE Follow-On.

How to cite: Flechtner, F., Landerer, F., Save, H., Dahle, C., Bettadbur, S., Watkins, M., and Webb, F.: NASA and GFZ GRACE Follow-On Mission: Status, Science, Advances, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3077, https://doi.org/10.5194/egusphere-egu2020-3077, 2020.

Due to the battery issue, the Gravity Recovery and Climate Experiment (GRACE) mission unfortunately came to an end in October 2017 after providing more than 15 years of mass transport information of our changing planet. To continue to monitoring the mass transport in the Earth system, the GRACE Follow-On (GRACE-FO) was launched in May 2018. As a new feature of GRACE-FO, a Laser Ranging Interferometer (LRI) was equipped to measure the inter-satellite range at a nanometer level. Since May 2019, GRACE-FO Level-1B observations have been made available to our community. Using the GRACE-FO Level-1B observations without laser ranging information, preliminary GRACE-FO gravity field solutions from Center for Space Research (CSR), GeoForschungsZentrum (GFZ), Jet Propulsion Laboratory (JPL) and Graz University of Technology have been released. Incorporating laser ranging observations into gravity field determination, a preliminary time series of GRACE-FO gravity field solutions has been derived from Tongji University in collaboration with University of Bonn. In this paper, the signal and noise of our gravity field solutions are analyzed and compared to those from other research groups. Our results show that the laser ranging observations with a sampling rate of 2s are able to improve gravity field solutions by about 7% in terms of geoid degree variances up to degree and order 96 as compared to the K-Band ranging data with a sampling rate of 5s.

How to cite: Chen, Q., Shen, Y., Zhang, X., and Kusche, J.: Preliminary GRACE-FO gravity field solutions from Tongji University, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7707, https://doi.org/10.5194/egusphere-egu2020-7707, 2020.

The GRACE Follow-On (GRACE-FO) mission, launched on May 22, 2018, is continuing the unprecedented mass anomaly time-series started by the GRACE mission. The 18 year record of global mass change fields have become indispensable to track the movement of water in the Earth System and monitor changes in the ice sheets, glaciers, surface water, ground water, sea level, ocean currents etc.

The traditional GRACE and GRACE-FO mascon solutions produced at the Center for Space Research uses the range-rate measurement from the intersatellite K-band ranging (KBR) data. In this paper we present techniques for computing alternate mascon solutions using range-acceleration measurements from the K-band ranging system. We discuss the comparison in techniques used and the results produced using SST range-rate vs range-acceleration data. GRACE-FO carries a technology demonstration of Laser Ranging Interferometer (LRI) system which offers a 10x improvement in the ranging measurement system. We discuss the comparison of the technique, parameterization and the resulting mascon solution derived using range-acceleration data from the KBR and LRI system.

How to cite: Save, H., Bettadpur, S., Poole, S., Pie, N., and Nagel, P.: Comparing GRACE-FO Mascon Solutions Computed Using Range-Rate vs Range-Acceleration Data from K-Band Ranging (KBR) and Laser Ranging Interferometer (LRI) , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11664, https://doi.org/10.5194/egusphere-egu2020-11664, 2020.

How to cite: Allgeyer, S., McQueen, H., and Tregoning, P.: Comparison between Laser Ranging Interferometer and K/Ka band Ranging instruments. , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6368, https://doi.org/10.5194/egusphere-egu2020-6368, 2020.

In GRACE-FO (Gravity Recovery and Climate Experiment Follow-on) mission, similar to its predecessor GRACE, the twin satellites are equipped with three-axis accelerometers, measuring the non-gravitational forces. After one month in orbit, the GRACE-D accelerometer data degraded and its measurements were replaced by synthetic accelerometer data, the so-called transplant data, officially generated by the Jet Propulsion Laboratory (JPL). The transplant data was derived from the GRACE-C accelerometer measurements, by applying a time and attitude corrections and adding model-based residual accelerations due to thruster firings on GRACE-D.

For the ITSG-Grace2018 GRACE-FO release, the gravity field recovery is based on the use of in-house Level-1B accelerometer data (ACT1B) using the provided Level-1A data products. In this work, we present a novel approach to recover the ACT1B data by (a) implementing the state-of-the-art non-gravitational force models and (b) applying additional force model corrections.

The preliminary results show the improved ACT1B data not only contributed to a noise reduction but also improved the estimates of the C20 and C30 coefficients. We show that the offset between SLR (Satellite Laser Ranging) and GRACE-FO derived C20 and C30 time series can be reduced remarkably by the use of the new accelerometer product, demonstrating the merit of this new approach.

How to cite: Behzadpour, S., Mayer-Gürr, T., Kvas, A., Krauss, S., Strasser, S., and Süsser-Rechberger, B.: GRACE-FO accelerometer data recovery within ITSG-Grace2018 data processing, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3017, https://doi.org/10.5194/egusphere-egu2020-3017, 2020.

GRACE and GRACE-Follow On are the standard tools for observing the time variable gravity field. Unfortunately, there is no overlap of the two time series of monthly gravity field solutions due to the ending of the GRACE mission in 2017 before the first monthly solutions of GRACE-Follow On became available in June 2018. Thus, there is a need for an intermediate technique that will bridge the gap between the two missions and will allow 1) for a continued and uninterrupted time series of mass observations and 2) to compare, cross-validate and link the two time series. As a bridging technology hlSST/SLR combinations are arguably the most promising candidate. We presented earlier combinations of those based on 41 kinematic orbit products of 27 satellites and 9 SLR satellites. Here, we progress to the next step and present results where we use the combined hlSST/SLR solution within a Kalman environment to link GRACE to GRACE-Follow On via the hlSST/SLR time series. The combination is conducted on coefficient level: after reducing the climatology derived from GRACE, a modified continuous Wiener process acceleration (CWPA) model is employed as the driving dynamic model of the Kalman filter for the prediction step. Subsequently the predicted time step is updated by (residual) observations when available. The resulting time series is thus complete for all months starting from April 2002 till today. We will discuss the benefit and limitations of the approach. The research is conducted within the framework of the International Gravity Field Service (IGFS) product center (COST-G) which is dedicated to the combination of monthly global gravity field models.

How to cite: Weigelt, M., Jäggi, A., and Meyer, U.: Bridging the gap – linking GRACE and GRACE-Follow On by hlSST and SLR, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15173, https://doi.org/10.5194/egusphere-egu2020-15173, 2020.

We present a method of analysing inter-satellite tracking data for detecting short-term (sub-monthly) gravitational changes from GRACE and GRACE Follow-On.  The method is based on the residual range-rate data with respect to the reference range-rate computed with dynamic orbital state vectors.  Then, we apply a numerical differentiation to compute range-acceleration residuals.  We found that the range-acceleration residuals are near-perfectly correlated with the line-of-sight gravity difference (LGD) between two spacecrafts and the transfer (admittance) function between them can be determined regardless of time and space (Ghobadi-Far et al., 2018, JGR-Solid Earth, https://doi.org/10.1029/2018JB016088).  The transfer function, to be applied directly to range-acceleration residuals, enables accurate LGD determination with the error of 0.15 nm/s^2 over the frequency band higher than 1 mHz (5 cycles-per-revolution), whereas the actual GRACE measurement error is several times larger.

In this presentation, we present two new geophysical applications to examine high-frequency gravitational changes at times scales of significantly less than one month; Gravitational observation of tsunamis triggered by the 2004 Sumatra, 2010 Maule, and 2011 Tohoku earthquakes and transient gravitational changes due to Earth’s free oscillation excited by the 2004 earthquake.  Lastly, we present new results from GRACE Follow-On KBR and LRI inter-satellite ranging data. 

How to cite: Han, S.-C., Ghobadi Far, K., Sauber, J., Mccullough, C., Wiese, D., and Landerer, F.: Along-track analysis of GRACE and GRACE Follow-On KBR and LRI data for new science applications, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21426, https://doi.org/10.5194/egusphere-egu2020-21426, 2020.

Over the recent years, the computation of temporally high-resolution (daily) GRACE gravity field solutions has advanced as an alternative to the processing of monthly models. In this presentation we will show that recent processing improvements incorporated in the latest version of daily gravity field models (ITSG-Grace2018) now allow for the investigation of water flux signals on the continents down to time scales of a few days.

Time variations in terrestrial water storage derived from GRACE can be related to atmospheric net-fluxes of precipitation (P), evapotranspiration (E) and lateral runoff (R) via the terrestrial water balance equation, which makes GRACE a new and completely independent data set for constraining hydro-meteorological observations and the output of atmospheric reanalyses.

In our study, band-pass filtered water fluxes are derived from the daily GRACE water storage time series by first applying a numerical differentiation filter and subsequent high-pass filtering to isolate fluxes at periods between 5 and 30 days. We can show that on these time scales GRACE is able to identify quality differences between different global reanalyses, e.g. the improvements in the latest reanalysis ERA5 of the European Centre for Medium-Range Weather Forecasts (ECWMF) over its direct predecessor ERA-Interim.

We can further demonstrate that only the very recent progress in GRACE data processing has enabled the use of daily GRACE time series for such an evaluation of high-frequency atmospheric fluxes. The accuracy of the previous daily GRACE time series ITSG-Grace2016 would not have been sufficient to carry out such an assessment.

How to cite: Eicker, A., Jensen, L., Wöhnke, V., Kvas, A., Dobslaw, H., Mayer-Gürr, T., and Dill, R.: Can daily GRACE gravity field models be used to evaluate short-term hydro-meteorological signals over the continents?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18050, https://doi.org/10.5194/egusphere-egu2020-18050, 2020.

Following the ESA CCI Sea Level Budget Closure (SLBC) project's work of 2017–2019, we present updated time-series of

• Global Ocean Mass Change (OMC) and
• Continental Mass Change (CMC),

both including continuous measurements by GRACE-FO. By least-squares adjusting a multi-parameter fit to monthly resolved OMC, we estimate the linear trend of Global Ocean mass change over all presently available GRACE/-FO months since April 2002 to be 2.41 ± 0.22 mm/a, with an acceleration of 0.10 mm a^-2 over the same period.

A systematic analysis of the computed ocean response ("monthly fingerprints") to on-shore mass changes by means of solving the sea level equation implies that the common method of re-scaling the 'inner' buffered ocean may lead to OMC overestimations up to 10 per cent. We present this effect as a function of coastal buffer width for a global and for a 'truncated' global ocean (Lat ≤ ±65°), since the latter case, as seen e.g. in conjunction with radar altimetry, can lead to more than five per cent overestimated OMC. Furthermore, the use of coastal buffers seems to induce phase bias in the annual oscillation, which may explain the observed phase shift in the monthly budget between GRACE OMC and the sum of contributing continental components (i.e. ice sheets, glaciers, land water storage).

As a supplementary product of the SLBC project, we present GRACE/-FO derived mass change series 2002-04/present for continents (excluding Greenland and Antarctica). Consistent integration of out-leaking signal over coastal buffer zones, and subtraction of GAD-corrected mean OMC therein, leads to agreement with independently-assessed joint land water and glacier mass change data, well within uncertainty bounds.

How to cite: Gutknecht, B. D., Groh, A., Cáceres, D., and Horwath, M.: Assessing Global Ocean and Continental Mass Change from 17 years of GRACE/-FO: the role of coastal buffer zones, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18038, https://doi.org/10.5194/egusphere-egu2020-18038, 2020.

The total water storage change (TWSC) data record from the GRACE mission has found numerous applications in hydrology, oceanography, cryosphere, solid Earth and sea level research, and climate sciences. However, GRACE was only launched in 2002 and it lasted until 2017 with an increasing number of missing data, while GRACE-FO continued in May 2018. There will be no TWSC data within a gap of at least 11 months, and no GRACE-like data exists prior to 2002. As a result the current data record is not sufficiently long to for validating climate model predictions even for the long-term mean of TWSC, let alone for the probability of extreme events.

In this contribution we will discuss ways to reconstruct terrestrial TWSC from either geodetic or hydrometeorological data, or possibly from a combination. We will present new reconstructions of TWSC from 1992 onwards from satellite laser ranging (SLR) and from statistical learning methods, discuss various approaches, and compare to conventional SLR solutions, the Humphrey (2019) statistical reconstruction, and to GRACE in the more recent time frame. We show that both geodetic SLR analysis and/or multilinear regression or machine learning approaches can be successfully applied in a regularized framework where spatial modes from a GRACE-era TWSC decomposition inform the reconstructions. We show that these reconstructions reproduce many phenomena seen in modelling studies beyond the seasonal cycle; e.g. the suspected gradual onset of Greenland mass loss around 1998-2000, increase ocean mass rate since about 2011, or the presence of ENSO events.

How to cite: Kusche, J., Löcher, A., Fupeng, L., and Rietbroek, R.: GRACE-like gridded reconstructions of total water storage change from SLR and statistical techniques, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2229, https://doi.org/10.5194/egusphere-egu2020-2229, 2020.

The 2017-2027 US National Academy of Sciences Decadal Survey for Earth Science and Applications from Space classified mass change as one of five designated observables having the highest priority in terms of Earth observations required to better understand the Earth system over the next decade.  In response to this designation, NASA initiated multi-center studies with an overarching goal of defining observing system architectures for each designated observable.  Here, we discuss the progress made and future plans for the Mass Change Designated Observable study. Progress includes the development of a Science and Applications Traceability Matrix, a tool that links science objectives to measurement techniques and accuracies,  for the 15 science and applications objectives listed in the Decadal Survey, as well as the definition of as many as three different architectural classes for which to achieve those objectives.  We will describe the Value Framework that is under way to assess and evaluate each observing system architectural option.  Preliminary results assessing the science value versus cost/risk of observing system architectures will be presented. In addition, future plans for the Mass Change Designated Observable Study will be discussed.

How to cite: Wiese, D., Boening, C., Zlotnicki, V., Luthcke, S., Loomis, B., Rodell, M., Sauber, J., Bearden, D., Chrone, J., Horner, S., Webb, F., Bienstock, B., and Tsaoussi, L.: The NASA Mass Change Designated Observable Study: Progress and Future Plans, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12077, https://doi.org/10.5194/egusphere-egu2020-12077, 2020.

The Bender configuration comprises of two GRACE-like pairs, one in a polar orbit and the other in an inclined orbit. While the polar pair covers the entire globe, the inclined pair does not cover the higher latitudes. Similarly, the polar orbit due to its north-south orientation is able to capture features that are predominantly oriented in the east-west direction, but the inclined pair does not have any such issues. In this scenario, we would like to know the signal contribution of the polar and inclined pairs to the different spherical harmonic coefficients. Furthermore, this contribution analysis will enable us to understand the strengths and weaknesses of the GRACE(-FO) mission. In this study we use simulated data for analysing the signal contribution of the two pairs of satellites.

How to cite: Devaraju, B., Yadav, A., and Weigelt, M.: Signal contribution of the polar and the inclined pairs in a Bender configuration, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21085, https://doi.org/10.5194/egusphere-egu2020-21085, 2020.

Data from the US and German Gravity Recovery And Climate Experiment (GRACE) showed indications of pre-, co-, and post-seismic mass redistributions associated with earthquakes down to a magnitude of 8.3 Mw. These demonstrated state-of-the-art capabilities in obtaining high spatial resolution space-based gravimetry, and helped to improve understanding of mantle rheology, potentially even providing a route to developing early warning capabilities for future seismic events. We describe a new mission concept, GRAvity observations by Vertical Laser ranging (GRAVL), which aims to extend the earthquake detection limit down to magnitude 6.5 Mw, significantly increasing the number of observable events.

GRAVL directly measures the radial component of the acceleration vector via “high-low” inter-satellite laser ranging, increasing gravity field sensitivity. A constellation of Low-Earth Orbit (LEO) satellites act as test masses, equipped with reflectors and high precision accelerometers to account for non-gravitational forces. Two or more larger satellites are placed above these, in Geostationary or Medium Earth Orbit (GEO / MEO), and measure the distance to the LEO satellites via time-of-flight measurement of a laser pulse. To do this, the GEO/MEO spacecraft are each equipped with a laser, telescope and detector, and additionally require highly  accurate timing systems to enable ranging accuracy down to sub-micron precision. To detect co-seismic mass redistribution events of the desired magnitude, we determine a gravity field measurement requirement of order 0.1 µGal at a spatial resolution of approximately 100 km over a 3-day revisit interval. These are challenging requirements, and we will discuss possible approaches to achieving them.

The GRAVL mission concept was developed during the FFG/ESA Alpbach Summer School 2019 by a team of science and engineering students, and further refined using the Concurrent Engineering approach during the Post-Alpbach Summer School Event at ESA Academy's Training and Learning Facility at ESEC-Galaxia in Belgium.

How to cite: Woodwark, J. and Stefko, M. and the GRAVL development team: GRAVL: a new satellite mission concept aiming to detect earthquakes with a magnitude of 6.5 Mw and higher, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8304, https://doi.org/10.5194/egusphere-egu2020-8304, 2020.

In the context of an increased public interest in climate-relevant processes, a number of studies on Next Generation Gravity Missions (NGGMs) have been commissioned to better map mass transport processes on Earth. On the basis of the successfully completed gravity field missions CHAMP, GOCE and GRACE as well as the current satellite mission GRACE-FO, different concepts were examined for their feasibility and economic efficiency. The focus is on increasing the spatiotemporal resolution while simultaneously reducing the known error effects such as the aliasing of temporal gravity fields due to under-sampling of signals and uncertainties in ocean tide models. An additional inclined pair to a GRACE-like satellite pair (Bender constellation) is the most promising solution. Since the costs for a realization of the Bender constellation are very high, this contribution focuses on alternative concepts in the form of different constellations and formations of small satellites. The latter includes both satellite pairs and chains consisting of trailing satellites. The aim is to provide a cost-effective alternative to the previous gravity field satellites while simultaneously increasing the spatiotemporal resolution and minimizing the above mentioned error effects. In numerical closed-loop simulations, different scenarios will be performed which differ in orbit parameters like shape and number of orbits, the number of satellites per orbit and their distance to each other as well as the number of inter-satellite links. Additionally, the impacts from the co-parametrization of non-tidal temporal gravity field signal and ocean tides on the gravity field solutions, obtained by the different concepts, will be investigated. 

How to cite: Pfaffenzeller, N., Pail, R., and Yunck, T.: Simulation study on future gravity missions with constellations and formations of small satellites , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10103, https://doi.org/10.5194/egusphere-egu2020-10103, 2020.

The Atmosphere and Ocean non-tidal De-aliasing Level-1B (AOD1B) product is widely used internationally to correct for transient effects of atmosphere-ocean mass variability on Earth satellites at in particular low altitudes. The most recent release 06 is given every 3 hours in Stokes coefficients expanded up to degree and order 180. It is based on ERA-Interim and ECMWF operational data for the atmosphere, and simulations with the global general ocean circulation model MPIOM consistently forced with fields from the same atmospheric data-set. RL06 was introduced in the year 2016 and is routinely updated every 24 hours with all data-sets for the previous calendar day.

Based on a stationary error assessment for AOD1B RL06 that might be also used to explicitly characterize uncertainties of AOD1B in the gravity field estimation process, we present preliminary numerical experiments with the TP10 configuration of MPIOM in preparation of a new AOD1B version 07 which is planned to be released in the year 2021. Those experiments test effects of (i) the new hourly atmospheric forcing data-set from the latest reanalysis ERA-5 of ECMWF; (ii) a revised bathymetry in particular around Antarctica that also includes cavities underneath the ice-shelves; and the consideration of shielding effects of the ice cover; and (iii) the consequences of self-attraction and loading feedbacks on the ocean dynamics. Results will be discussed in terms of differences with respect to RL06, in situ ocean observations, and alternative model data-sets.

How to cite: Shihora, L., Poropat, L., and Dobslaw, H.: Towards AOD1B RL07, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2596, https://doi.org/10.5194/egusphere-egu2020-2596, 2020.

Gridded terrestrial water storage (TWS) observed by GRACE or GRACE-FO typically show a spatial error structure that is anisotropic (direction depending), non-homogeneous (latitude depending), and non-stationary (time depending).

We will introduce a new covariance model characterizing this error behavior analytically with a direction depending Bessel function of the first kind. The anisotropy of this function is governed by a shape parameter allowing for longer correlation lengths in longitudinal than in latitudinal direction. The wave-effect of the Bessel function allows us to account for the residuals of the GRACE striping errors. Both size as well as shape parameters of the Bessel function vary smoothly with latitude. These variations are implemented via even Legendre polynomials. The non-stationarity of the covariance is modeled with time-varying point variances. The validity of this covariance model on the sphere was thoroughly tested with a Monte-Carlo approach.

First, we apply this covariance model to 5 years of simulated GRACE data (Flechtner et al., 2016) where true errors are readily available from the differences of the synthetic input and the finally recovered gravity fields. For the 50 largest discharge basins, we obtain more realistic time series uncertainties than from propagating the formal errors associated with the Stokes coefficients. For smaller basins, however, the covariance model tends to provide overly pessimistic uncertainty estimates.

Second, the model is adapted to real GRACE and GRACE-FO data to obtain realistic error covariance information for arbitrarily shaped basins from globally gridded error information. We will show the current plans to update GFZ’s GravIS portal (http://gravis.gfz-potsdam.de/home) so that area- and time-dependent error information which is critically important for the assimilation of GRACE-based TWS data into numerical models will become readily available to the user community.

How to cite: Thomas, M., Boergens, E., Dobslaw, H., Dill, R., Dahle, C., and Flechtner, F.: A spatial covariance model for GRACE and GRACE-FO terrestrial water storage data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8032, https://doi.org/10.5194/egusphere-egu2020-8032, 2020.

The GRACE Follow-On (GRACE-FO) mission was successfully launched on May 22^nd, 2018 and continues the 15-year data record of monthly global mass changes from the GRACE mission (2002-2017). The German Research Centre for Geosciences (GFZ) as part of the GRACE/GRACE-FO Science Data System (SDS) has recently reprocessed the complete GRACE mission data (RL06 in the SDS nomenclature). These RL06 processing standards serve as common baseline for the continuation with GRACE-FO data.

This presentation provides an overview of the current processing status and the validation of the GFZ GRACE/GRACE-FO RL06 gravity field products. Besides its Level-2 products (monthly sets of spherical harmonic coefficients representing the Earth's gravity potential), GFZ additionally generates user-friendly Level-3 products in collaboration with the Alfred-Wegener-Institut (AWI) and TU Dresden. These Level-3 data products comprise dedicated mass anomaly products of terrestrial water storage over non-glaciated regions, bottom pressure variations in the oceans and ice mass changes in Antarctica and Greenland, available via GFZ's Gravity Information Service (GravIS) portal (http://gravis.gfz-potsdam.de/).

How to cite: Dahle, C., Murböck, M., Flechtner, F., König, R., Dobslaw, H., Boergens, E., Sasgen, I., and Groh, A.: Status of GFZ's GRACE/GRACE-FO RL06 Level-2 and Level-3 Data Products, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10273, https://doi.org/10.5194/egusphere-egu2020-10273, 2020.

Today's state-of-the-art gravity missions GRACE and GRACE-FO monitor the Earth's gravitational field in high temporal and spatial resolution. The resulting time series of gravitational fields serves various geophysical applications. It is however recommended to replace the C(2,0) coefficients, which describe the change of the Earth's oblateness, by those determined by Satellite Laser Ranging (SLR) to geodetic satellites. There are also discussions ongoing on the C(2,1), S(2,1) and C(3,0) coefficients. Current research shows that a combination of GRACE and GRACE-FO with SLR can lead to an improvement of the determination of the low degree coefficients in view of certain geophysical applications. This contribution gives an insight into the recent research at the Helmholtz Center Potsdam - German Research Center for Geosciences (GFZ) on various methods for the multi-technique combination on normal equation level and discusses the effects on the low degree spherical harmonics.

How to cite: Koenig, R., Schreiner, P., and Dahle, C.: On the determination of low degree harmonics by combining SLR with GRACE / GRACE-FO, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19563, https://doi.org/10.5194/egusphere-egu2020-19563, 2020.

The central hypothesis of the Research Unit (RU) NEROGRAV (New Refined Observations of Climate Change from Spaceborne Gravity Missions), funded for three years by the German Research Foundation DFG, reads: only by concurrently improving and better understanding of sensor data, background models, and processing strategies of satellite gravimetry, the resolution, accuracy, and long-term consistency of mass transport series from satellite gravimetry can be significantly increased; and only in that case the potential of future technological sensor developments can be fully exploited. Two of the individual projects (IPs) within the RU work on stochastic modeling for GRACE and GRACE-FO gravity field determination. TU München and TU Berlin are responsible for IP4 (OSTPAG: optimized space-time parameterization for GRACE and GRACE-FO data analysis), where besides optimal parameterization the focus is on the stochastic modeling of the key observations, i.e. GRACE and GRACE-FO inter-satellite ranging and accelerometer observations, in a simulation (TU München) and real data (TU Berlin) environment. IP5 (ISTORE: improved stochastic modeling in GRACE/GRACE-FO real data processing), which GFZ is responsible for, works on the optimal utilization of the stochastic properties of the main GRACE and GRACE-FO observation types and the main background models.

This presentation gives first insights into the TU Berlin and GFZ results of these two IPs which are both related on stochastic modeling for real data processing based on GFZ GRACE and GRACE-FO RL06 processing. We present the analyses of K-band inter-satellite range observations and corresponding residuals of three test years of GRACE and GRACE-FO real data in the time and frequency domain. Based on the residual analysis we show results of the effects of different filter matrices, which take into account the stochastic properties of the range observations in order to decorrelate them. The stochastic modeling of the background models starts with Monte-Carlo simulations on background model errors of atmospheric and oceanic mass variations. Different representations of variance-covariance matrices of this model information are tested as input for real GRACE data processing and their effect on gravity field determination are analyzed.

How to cite: Murböck, M., Natalia, P., Christoph, D., Karl-Hans, N., Frank, F., and König, R.: The research unit NEROGRAV: first results on stochastic modeling for gravity field determination with real GRACE and GRACE-FO data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8622, https://doi.org/10.5194/egusphere-egu2020-8622, 2020.

Developing meaningful uncertainty quantifications for GRACE or GRACE-FO derived products, e.g. water storage anomalies, requires a robust understanding of the information and noise content in the observables employed in their estimation.

The stochastic models for GRACE and GRACE-FO K-Band, LRI, and GPS carrier phase and pseudorange observables employed in upcoming JPL solutions, along with notes on their implementation and development, will be presented. Within these models, the time-domain correlations for each of the observations are estimated, and then applied in the least squares estimate of monthly gravity field solutions. Reproducing results from other groups, the resulting formal errors of monthly solutions are improved.

It is envisioned that possible new Level 3 products can make these improved uncertainty quantifications accessible to the GRACE user community at large. Possible specifications for such products will be presented, and feedback from the community and discussion will be appreciated.

How to cite: Ellmer, M., Wiese, D., McCullough, C., Yuan, D.-N., and Fahnestock, E.: Implementation of GRACE and GRACE-FO observation covariance estimates at JPL, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11953, https://doi.org/10.5194/egusphere-egu2020-11953, 2020.

One of the valuable products of the Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) mission is a centimeter-accuracy orbit of the GOCE satellite called the precise science orbit (PSO). This orbit, delivered by the European Space Agency (ESA), was the reference for the GOCE orbit modeling using the piecewise constant acceleration approach. Besides initial conditions, the piecewise constant accelerations (i.e. empirical accelerations) were estimated in the radial, along-track and cross-track direction, employing the dedicated package called Torun Orbit Processor (TOP). The TOP software is based on the classical least squares adjustment including the Cowell 8-th order numerical integration for an orbit prediction and the orbit improvement module, taking into account the gravity field model and the background models (BM) describing gravitational and non-gravitational perturbing forces. The positions of GOCE satellite on the reduced-dynamic PSO orbit were treated as observations in the orbit improvement process. A measure of the fit of estimated arcs and their accuracy was the RMS of the residuals between the estimated orbits and the corresponding reference ones. Different variants of the orbit estimation were obtained for the shorter  arcs (22.5, 45, 90 and 180 minutes)  and for the longer 1-day arcs. The solution variants were determined for different numbers of the estimated piecewise constant accelerations. Moreover, these numbers were different for the radial, along-track and cross-track direction. The obtained solutions depend on a kind of computational mode – with and without the BM models in the GOCE orbit modeling using the estimated piecewise constant accelerations. Additionally, for selected solutions, the distributions of the residuals in the aforementioned directions along the estimated arcs are presented. 

How to cite: Bobojć, A.: Efficiency of the piecewise constant acceleration modeling - GOCE case study , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1378, https://doi.org/10.5194/egusphere-egu2020-1378, 2020.

ONERA (the French Aerospace Lab) is developing, manufacturing and testing ultra-sensitive electrostatic accelerometer for space application. ONERA has procured the accelerometer for all the previous gravity missions (GRACE, GOCE, GRACE-FO) and works to improve the scientific return of the instruments.

One way is to propose an accelerometer with 3 sensitive linear acceleration measurements as well as 3 angular acceleration measurements for the attitude control or reconstruction. Two different configurations are proposed: CubSTAR, a miniaturized version with low accuracy but adapted for constellation or nanosat; and MicroSTAR, a high accuracy accelerometer.

CubSTAR accelerometer is a small volume instrument with the same performance on the 3 axes, the baseline being 20x20x20mm proof-mass in a 15x15x20cm volume envelope. A prototype was manufactured and tested during a drop-tower test. Moreover this prototype will be tested in vibration environment to check its good mechanical behavior.

MicroSTAR accelerometer is designed with a disruptive mechanical concept allowing using a 30x30x30mm proof-mass, with the same high-performance on the 3 axes. Modal and dynamic analyses have been performed and a prototype is under manufacturing.  

How to cite: Dalin, M., Lebat, V., Boulanger, D., Liorzou, F., Christophe, B., Rodrigues, M., and Huynh, P.-A.: ONERA accelerometers for future gravity mission, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5721, https://doi.org/10.5194/egusphere-egu2020-5721, 2020.

On May 22, 2020, the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO), will celebrate two years of successful in-orbit operation. The primary goal of this satellite mission is to provide information about time variations of the Earth’s gravity field. This is possible due to precise orbit determination and inter-satellite ranging by determining the relative clock alignment of the USOs, precise attitude determination and accelerometry. High quality satellite observations are one of the fundamental requirements for successful gravity field recovery. NASA/Caltech Jet Propulsion Laboratory is the official Level-1 data processing and analysis center. The GRACE-FO Level-1 data are currently being processed with software version V04. This software will be used also for final reprocessing of the GRACE (2002-2017) Level-1 data. Here we present the analysis of two years of GRACE-FO sensor data as well as a preview of the reprocessed GRACE data, and discuss the measurement performance.

How to cite: Bandikova, T., Wen, H. Y., Paik, M., Bertiger, W., Miller, M., Harvey, N., McCullough, C., Finch, C., Byun, S., Kuang, D., Landerer, F., and Boening, C.: V04 Level-1 data processing status for GRACE and GRACE Follow-On, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10626, https://doi.org/10.5194/egusphere-egu2020-10626, 2020.

Precise LEO satellite orbit determination(OD) and Earth gravity field modeling are researched in this study.

Firstly, on the basis of Precise Point Positioning Ambiguity Resolution(PPPAR), a kinematic LEO satellite OD algorithm based on the epoch-difference and post-facto iteration is introduced, which plays a vital rule in the detection of the phase cycle slip to achieve the best orbit accuracy. The experiments of GRACE satellite OD with zero-difference IF combination observations spanning one year of 2010 show that, compared to the JPL reference orbits, the daily average 3D RMS is generally below 5.0cm for the float solution, while that is below 4.0cm for the fixed solution.

Secondly, to solve the problem that specific a-priori information like earth gravity field model must be involved in LEO’ reduced dynamic OD, the simultaneous solution method, which is specially on the relation with the kinematic OD and reduced dynamic OD, is used and the carrier-range, which can be recovered from phase observations once the kinematic OD process using Integer Ambiguity Resolution (IAR) technology is carried out, is naturally applied to this method. With the experiments based on the data over a period of the year of 2010, comes some evacuations, including the external checks on the accuracy of the orbits and the analysis on the earth gravity model. The numerical results show that, compared to the JPL reference orbits, the 3D RMS is below 3.0cm and the RMS is below 2.0cm for each component. As for the accuracy of gravity field model, compared to some contemporary significant earth gravity model, the model of the single month solution behaves very well below the 60 degree of the gravity field’s coefficients, while over the 60 degree, only the UTCSR model quite corresponds to the model computed by this method. Therefore, due to the promotion of the orbital accuracy and gravity field model, we suggest that the recovered carrier-range should be implemented in the simultaneous method for the better product solution of the LEO’s missions.

How to cite: Gao, G., Zou, X., Zhang, S., and Liu, B.: Precise LEO satellite orbit determination and Earth gravity field modeling with carrier-range method, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3976, https://doi.org/10.5194/egusphere-egu2020-3976, 2020.

In Next Generation Gravity Missions (NGGM) the Laser Ranging Interferometer (LRI) is applied to measure inter-satellite range rate with nanometer-level precision. Thereby the precision of numerical orbit integration must be higher or at least same as that of LRI and the currently widely-used double-precision orbit integration technique cannot meet the numerical requirements of LRI measurements. Considering quadruple-precision orbit integration arithmetic is time consuming, we propose a hybrid-precision numerical orbit integration technique, in which the double- and quadruple-precision arithmetic is employed in the increment calculation part and orbit propagation part, respectively. Since the round-off errors are not sensitive to the time-demanding increment calculation but to the least time-consuming orbit propagation, the proposed hybrid-precision numerical orbit integration technique is as efficient as the double-precision orbit integration technique, and as precise as the quadruple-precision orbit integration. By using hybrid-precision orbit integration technique, the range rate precision is easily achieved at 10-12m/s in either nominal or Encke form, and furthermore the sub-nanometer-level range precision is obtainable in the Encke form with reference orbit selected as the best-fit one. Therefore, the hybrid-precision orbit integration technique is suggested to be used in the gravity field solutions for NGGM.

How to cite: Nie, Y., Shen, Y., and Chen, Q.: A Hybrid-Precision Numerical Orbit Integration Technique for Next Generation Gravity Missions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12622, https://doi.org/10.5194/egusphere-egu2020-12622, 2020.

How to cite: Lasser, M., Mayer-Gürr, T., Kvas, A., Koch, I., Lemoine, J.-M., Neumayer, K. H., Dahle, C., Flechtner, F., Flury, J., Meyer, U., and Jäggi, A.: Benchmark data for verifying background model implementations in orbit and gravity field determination software, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18877, https://doi.org/10.5194/egusphere-egu2020-18877, 2020.

At the time of presentation, nearly two years of flight data from the joint NASA/GFZ GRACE Folllow-On mission will have been collected. In this time, gravity field models have been produced using two independent inter-satellite tracking systems - the MWI and the LRI using radio and optical interferometry, respectively. The data have been analyzed over more than two complete cycles of the sun relative to the orbit plane, allowing a characterization of the environmental impacts on the flight data. Extended duration of analyses have also permitted an assessment of the GRACE-FO data relative to the corresponding GRACE data.

This poster presents the status and lessons learned from two years of estimation of Earth gravity field models from the GRACE-FO data at the science data system component at the University of Texas Center for Space Research.

How to cite: Bettadpur, S., Save, H., Nagel, P., Pie, N., Poole, S., Kang, Z., and Wang, F.: Gravity Field Estimation from GRACE Follow-On Data: Results from CSR Analyses, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11686, https://doi.org/10.5194/egusphere-egu2020-11686, 2020.

The dual-satellite mission GRACE Follow-On (GRACE-FO) was launched in May 2018 as the successor of the Gravity Recovery And Climate Experiment (GRACE). In May 2019 first level 1 data products were made available to the community and are now published regularly. These products, among others, include orbits, accelerometer measurements, star camera data and micron and sub-micron precise inter-satellite range measurements. The data products are used by different groups to compute estimates of monthly gravity fields of the Earth. The in-house developed GRACE-SIGMA software is used at the Institut of Geodesy/Leibniz University Hannover for the estimation of monthly gravity fields. Several parts of the software’s processing chain, such as background modeling, were updated recently and different parametrization scenarios were tested. First solutions were estimated based on laser ranging interferometer measurements. Moreover, different orbit types, such as reduced-dynamic and kinematic, were tested. In this contribution, we present the influence of these updates and tests on the quality of the gravity fields. The obtained solutions are assessed in terms of error degree standard deviations and post-fit residuals of the inter-satellite measurements.

How to cite: Koch, I., Duwe, M., Flury, J., and Shabanloui, A.: Processing of GRACE-FO satellite-to-satellite tracking data using the GRACE-SIGMA software, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20851, https://doi.org/10.5194/egusphere-egu2020-20851, 2020.

In this study, we investigate systematic errors in our temporal gravity solutions computed using the improved energy balance approach (EBA) (Shang et al. 2015) by reprocessing the GRACE JPL RL03 L1B data product. Our processing consists of two steps: the first part is the estimation of in-situ geopotential differences (GPD) at the satellite altitude using the energy balance formalism, the second part is the estimation of spherical harmonic coefficients (SHCs) of the global temporal gravity field model using the estimated GPDs. The first step includes daily dynamic orbit reconstruction by readjusting the reduced-dynamic (GNV1B) orbit considering the reference model, and estimating the accelerometer calibration parameters. This is coupled with the alignment of the intersatellite velocity pitch from KBR range rate observations. Due to the strategy of using KBR range-rate in our processing algorithm, the estimation of in-situ geopotential differences (GPD) includes both the systematic errors and the high-frequency noise that result from the range-rate observations. Since estimated GPDs are linearly connected with the spherical harmonic coefficients (SHCs) of the global gravity field model, our temporal models are affected by these errors, especially in high-degree coefficients of the temporal gravity field solutions (from n=25 to n=60).

In order to increase our solution accuracy, we fit additional empirical parameters for different arc lengths to mitigate the systematic errors in our GPD estimates, thus improving our temporal gravity field solutions. Our EBA approach GRACE monthly gravity field models are validated by comparisons to the official L2 data products, including the official solutions from CSR (Bettadpur et al., 2018), JPL (Yuan et al., 2018) and GFZ (Dahle et al., 2018).

How to cite: Uz, M., Akyılmaz, O., Kusche, J., Shum, C., Üstün, A., and Zhang, Y.: Investigation of systematic errors in GRACE temporal gravity field solutions using the Improved Energy Balance Approach, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11504, https://doi.org/10.5194/egusphere-egu2020-11504, 2020.

Planning is underway for development of the next NASA Mass Change satellite mission, as identified in the National Science Foundation’s 2017-2027 Decadal Survey for Earth Science and Applications from Space  (Decadal Survey). NASA has identified a Mass Change Designated Observable (MCDO) Study Team to evaluate satellite mission architectures that could optimally support a range of science and applications needs of user communities (both research and operational) of future mass change missions (i.e., successors to the GRACE and GRACE Follow On missions). The primary science objective of the MCDO, as identified in the Decadal Survey, is the continued measurement of changes in the Earth’s dynamic gravity field over time. The Decadal Survey also emphasizes applications of the mission data products as a major focus, in addition to science outcomes. 

Operational use and societal benefit derived from the GRACE and GRACE FO data and information products demonstrate the value of these missions. Applications include drought monitoring, quantification of groundwater depletion, flood prediction, and thermal expansion of the ocean, which contributes to sea level rise, to name a few. In order to effectively identify the observational product requirements of future gravity mission applications data users and to develop actionable objectives for mission design, a Mass Change Mission Applications survey was developed. Information on user needs, current uses, and capabilities derived from the survey have provided insights as to desired or required spatial scales, data latency, data formats, and technical capabilities of the users, as well as how to prioritize tradeoffs. The survey focused on evaluating the needs of a broad range of existing and potential user communities in order to incorporate these needs into mission design and architecture studies that are underway.

The survey comprises general questions about requirements for a given application, and data use and demographic information to help characterize aspects of the user community. Analyses of the survey results are now being used to inform potential mission architecture designs, evaluate tradeoffs, and ensure that the data products are optimized for a broad user community.

How to cite: Srinivasan, M., Rodell, M., Reager, J., Doorn, B., and Rogers, L.: A User Needs Assessment for the next Mass Change Satellite Mission , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12732, https://doi.org/10.5194/egusphere-egu2020-12732, 2020.

The "MARVEL gravity and reference frame mission" proposal has been selected by CNES for the start of a pre-phase A study. 
MARVEL aims at reaching in one single mission two major and complementary goals:
- The monitoring of mass transfers within the Earth system with increased precision,
- The realization, at the millimeter level, of the terrestrial reference frame.

In the nominal configuration, a LEO satellite (400 - 450 km) in polar orbit, acting as a gravity sensor, performs optical ranging measurements on two MEO satellites (7000 km) orbiting on the same plane. The MEO satellites are equiped with the four geodetic techniques (GNSS, SLR, DORIS, VLBI), in order to meet the GGOS Earth reference frame accuracy objectives.

We also propose two alternative (and less costly) configurations, where only the first goal is fully reached:
- one by replacing the MEO satellites by two or more cubesats on the same orbit,
- the second one by using specially equipped GNSS satellites as targets for the LEO optical ranging measurements.

In any case, the goal of monitoring mass change with enhanced precision is attained through the use of high-low SST laser tracking.

We will present in detail the different configurations proposed and present the simulation plan for this pre-phase A study.

How to cite: Lemoine, J.-M. and Mandea, M. and the MARVEL Team: The MARVEL gravity and reference frame mission proposal, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13359, https://doi.org/10.5194/egusphere-egu2020-13359, 2020.

We perform Next Gerataion Gravity Mission (NGGM) simulations over a 12-year operational period by including in the background gravity field the time-dependent gravity anomalies caused by different earthquake scenarios and considering different sources of error on 28-day mean gravity field solutions: the instrumental errors of the interferometer and accelerometers, the time depenendent background model and the atmosphere-ocean dealiasing. In order to assess whether the observational errors mask or not the earthquake-induced gravity signals, we assume known the background gravity field and the spatial and temporal pattern of the earthquake-induced gravity anomalies. Then, for each earthquake, we estimate the amplitude of its gravity anomaly by inverting the NGGM synthetic data time series and we check its consistency with the expected amplitude, as well as with the null hypothesis. In order to investigate case studies representative of the main earthquake characteristics and their compliance with the NGGM specifications, we have considered normal, inverse and strike-slip focal mechanisms striking with different angles with respect to the polar orbit, reaching the Earth surface and in depth, occurring inland, off-shore and close to the coastlines and at the beginning (2-4 years), at the middle (5-7 years) and at the end (8-10 years) of the 12-year operational period. The fault dimensions and slip distribution vary with the seismic moment magnitude and are prescribed according to the circular fault model by Eshelby (1957). Furthermore, we also consider two different rheological stratifications with asthenospheric viscosity of 10¹⁸ and 10¹⁹ Pa s. In order to discuss whether the earthquake signal can be discriminated from other geophysical processes (like atmosphere, ocean, hydrology and glacial isostatic adjustment), we also perform the same inversion but, this time, its amplitude is estimated jointly with the time dependent background gravity field, which we simply model using static values, trends and periodical functions.

How to cite: Cambiotti, G., Douch, K., Cesare, S., Anselmi, A., Sneeuw, N., Marotta, A. M., and Sabadini, R.: On the earthquake detectability by the Next Generation Gravity Mission (NGGM), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12821, https://doi.org/10.5194/egusphere-egu2020-12821, 2020.

Within this contribution we present the new experimental combined global gravity field model XGM2020. Key feature of this model is the rigorous combination of the latest GOCO06s satellite-only model with global terrestrial gravity anomalies on normal equation level, up to d/o 2159, using individual observation weights. To provide a maximum resolution, the model is further extended to d/o 5400 by applying block diagonal techniques.

To attain the high resolution, the incorporated terrestrial dataset is composed of three different data sources: Over land 15´ gravity anomalies (by courtesy of NGA) are augmented with topographic information, and over the oceans gravity anomalies derived from altimetry are used.  Corresponding normal equations are computed from these data sets either as full or as block diagonal systems.

Special emphasis is given to the novel processing techniques needed for very high-resolution gravity field modelling. As such the spheroidal harmonics play a central role, as well as the stable calculation of associated Legendre polynomials up to very high d/o. Also, a new technique for the optimal low-pass filtering of terrestrial gravity datasets is presented.

On the computational side, solving dense normal equation systems up to d/o 2159 means dealing with matrices of the size of about 158TB. Handling with matrices of such a size is very demanding, even for today’s largest supercomputers. Thus, sophisticated parallelized algorithms with focus on load balancing are crucial for a successful and efficient calculation.

How to cite: Zingerle, P., Pail, R., and Gruber, T.: High-resolution combined global gravity field modelling – The d/o 5,400 XGM2020 model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16447, https://doi.org/10.5194/egusphere-egu2020-16447, 2020.

Sea level change is an important indicator of global warming. In order to predict future sea level changes, it becomes more and more important to understand the complex contribution of different components (steric changes, melting of ice sheets and glaciers, hydrology,…) to the total sea level change on global and regional scales.

To distinguish between steric and mass-related sea level changes, we consider (1) satellite altimetry, which measures total sea level change, and (2) Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GRACE-FO) data to derive mass changes within the Earth system. The information of both methods can be combined in a joint inversion approach to derive the individual components of sea level change. However, there is a gap of 11 months between GRACE and GRACE-FO and there are numerous (bi-)monthly gaps since 2011, which means that there is no dedicated gravity field mission to derive ocean mass changes during these times.

In this contribution, we use time-variable gravity field data from the Swarm satellite mission and Satellite Laser Ranging (SLR) as an additional source of information on mass changes within the inversion approach. Thus, we are able to derive inversion results even in times without GRACE(-FO), albeit at the expense of an inevitably lower spatial resolution. We compare results with GRACE(-FO) data to those without GRACE(-FO) data. Furthermore, we quantify the leverage of Swarm and SLR on the low-resolution mass signal at basin scale in the combined inversion approach during the GRACE(-FO) lifetime.

How to cite: Lück, C., Uebbing, B., Löcher, A., Rietbroek, R., Kusche, J., Androsov, A., Schröter, J., Danilov, S., and Yakhontova, A.: Can Swarm and SLR contribute to closing the global sea level budget?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3378, https://doi.org/10.5194/egusphere-egu2020-3378, 2020.

Monitoring environmental hazards, due to natural and anthropogenic causes, is one of the important issues, which requires proper data, models, and cross-validation of the results. The geodetic satellite missions, e.g. the Gravity Recovery and Climate Experiment (GRACE) and Sentinel-1, are very useful in this aspect. GRACE missions are dedicated to model the temporal variations of the Earth’s gravity field and mass transportation in the Earth’s surface, whereas Sentinel-1 collects Synthetic Aperture Radar (SAR) data which enables us to measure the ground movements accurately. Extraction of large volumes of water and oil decreases the reservoir pressure, form compaction and consequently land subsidence occurs which can be analyzed by both GRACE and Sentinel-1 data. In this paper, large-scale groundwater storage (GWS) changes are studied using the GRACE monthly gravity field models together with different hydrological models over the major oil reservoirs in Sudan, i.e. Heglig, Bamboo, Neem, Diffra and Unity-area oil fields. Then we correlate the results with the available oil wells production data for the period of 2003-2012. In addition, using the only freely available Sentinel-1 data, collected between November 2015 and April 2019, the ground surface deformation associated with this oil and water depletion is studied. Due to the lack of terrestrial geodetic monitoring data in Sudan, the use of GRACE and Sentinel-1 satellite data is very valuable to monitor water and oil storage changes and their associated land subsidence over our region of interest. Our results show that there is a significant correlation between the GRACE-based GWS change and extracted oil and water volumes. The trend of GWS changes due to water and oil depletion ranged from -18.5 to -6.2 mm/year using the CSR GRACE monthly solutions and the best tested hydrological model in this study. Moreover, our Sentinel-1 SAR data analysis using Persistent Scatterer Interferometry (PSI) method shows high rate of subsidence i.e. -24.5, -23.8, -14.2 and -6 mm/year over Heglig, Neem, Diffra and Unity-area oil fields respectively. The results of this study can help us to control the integrity and safety of operations and infrastructure in that region, as well as to study the groundwater/oil storage behavior.

How to cite: Gido, N., Amin, H., Bagherbandi, M., and Nilfouroushan, F.: Satellite monitoring of mass changes and ground subsidence in Sudan’s oil fields using GRACE and Sentinel-1 data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4710, https://doi.org/10.5194/egusphere-egu2020-4710, 2020.

Satellite missions Gravity Field and Climate Experiment (GRACE) and its successor (GRACE-FO) plays very important role in nowadays research in geodesy, geophysics, hydrology, oceanography, glaciology and climatology. Various research centres adopted different procedures for processing the GRACE/GRACE-FO measurements in order to get the main final product – the global monthly gravity field model. Until now there have been developed and published two fundamentally different approaches to this problem. The first is well-known approach of spherical harmonic analysis and the second is more recent and more direct approach called in literature MASCON (Mass Concentration). The purpose of this contribution is to compare existing MASCON global monthly gravity field models with the selected models based on spherical harmonic approach. Comparison is performed in selected river basins and also in selected polar region. Chosen river basins differ both in size and seasonal changes of continental water storage to cover more situations. Comparison of different filtered versions of spherical harmonic solutions (DDK1 – DDK7) with MASCON solution is also performed in one of the analysed river basins. Differences are analysed and advantages and drawbacks of two approaches and of particular models are discussed.

How to cite: Janák, J., Novák, A., and Korekáčová, B.: MASCON versus spherical harmonic solutions to global monthly time varying gravity field, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21563, https://doi.org/10.5194/egusphere-egu2020-21563, 2020.

Presently, Gravity Recovery and Climate Experiment (GRACE) mission data is widely used in various fields of science. The longest satellite gravimetric mission regularly explored changes of the gravity field from April 2002 to October 2017. Nowadays, its follow-on mission (GRACE-FO) observes gravity changes from May 2018, providing new greater research opportunities. In the following research, we present a completely new vertical deformations changes model of the first 14 months GRACE-FO observations. The study’s aim is to reduce the signal noise left after Gauss spatial smoothing. In this study, we use monthly gravity field in spherical harmonics form up to degree and order 96, provided by three different centers, i.e. the NASA’s Jet Propulsion Laboratory (JPL), the German Research Center for Geosciences (GFZ) and the Center for Space Research (CSR). In following study, we use all sets of data (JPL, GFZ and CSR) to test three various algorithms: (1) coefficient-wise and (2) field-wise non-iterative weighting methods and further, (3) estimation by iterative variance component method.  Finally, we obtain joined spherical harmonics changes by a weighted average scheme, which are converted to Earth crust vertical deformations. The used weighting methods reduce root mean square scatter of monthly deformation fields by nearly 5% for continental areas (excluding Amazon basin and Hudson Bay region) and by 10-15% changes for the ocean areas. However, with respect to each new-created model, differences in monthly deformation changes are in the range from ±3 mm to ±6 mm depending on the data center (JPL, GFZ or CSR). Furthermore, the analysis of signal information contained in each degree allows us to assess the quality of the created models. The highest signal variations in our models occur up to the degree and order 25. Additionally, the high differences in the signal are obtained for sectoral harmonics up to the maximum degree. Analysis showed that the applied field-wise weights much more effectively remove remaining noise after spatial averaging than per-order/degree weighting. Whereas, the obtained results indicate that observations provided by GFZ center have the smallest weights for each algorithm.

How to cite: Lenczuk, A., Klos, A., and Bogusz, J.: Determination of homogenous GRACE FOLLOW-ON monthly displacements based on available solutions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-380, https://doi.org/10.5194/egusphere-egu2020-380, 2020.

Groundwater plays a major role in the hydrological processes driven by climate change and human activities, particularly in upper mountainous basins. The Jinsha River Basin (JRB) is the uppermost region of the Yangtze River and the largest hydropower production region in China. With the construction of artificial cascade reservoirs increasing in this region, the annual and seasonal flows are changing and affecting the water cycles. Here, we first infer the groundwater storage changes (GWSC), accounting for sediment transport in JRB, by combining the Gravity Recovery and Climate Experiment (GRACE) mission, hydrologic models and in situ data. The results indicate: (1) the average estimation of the GWSC trend, accounting for sediment transport in JRB, is 0.76±0.10 cm/year during the period 2003–2015, and the contribution of sediment transport accounts for 15%; (2) precipitation (P), evapotranspiration (ET), soil moisture change (SMC), GWSC and land water storage changes (LWSC) show clear seasonal cycles; the interannual trends of LWSC and GWSC increase, but P, runoff (R), surface water storage change (SWSC) and SMC decrease, and ET remains basically unchanged; (3) the main contributor to the increase in LWSC in JRB is GWSC, and the increased GWSC may be dominated by human activities, such as cascade damming, and climate variations (such as snow and glacier melt due to increased temperatures). This study can provide valuable information regarding JRB in China for understanding GWSC patterns and exploring their implications for regional water management.

How to cite: Chao, N.: Groundwater storage change in the Jinsha River basin from GRACE, hydrologic models, and in situ data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1281, https://doi.org/10.5194/egusphere-egu2020-1281, 2020.

In this study, we use temporal solutions of the Gravity Recovery and Climate Experiment (GRACE) satellite mission to study the surface mass variations of hydrological origin in North America. The most recent release (RL06) of GRACE Level 2 data from three processing centers (CSR, JPL, GFZ) and mascon products are used in a combination scheme to produce estimates of terrestrial water storage (TWS) changes for the period 2002–2016. The land hydrology signal is isolated from GRACE data by removing the contribution of two major non-hydrologic processes, i.e., the glacial isostatic adjustment (GIA) and the ice mass melting from the glaciated areas of Alaska, Greenland and the Canadian Arctic.

The examination of long-term TWS trends revealed strong signatures of the 2011–2015 droughts in California and Texas, as well as accumulation of TWS in the central part of North America. Negative long-term TWS trends associated with ice melting were found around the Hudson Bay region. The TWS changes are dominated by a strong annual and semi-annual signal with higher magnitude in Alaska and along the west coast of North America.

An additional study on the estimation of groundwater storage (GWS) changes is performed using the Global Land Data Assimilation System (GLDAS) model. The GLDAS data are pre-filtered using the same strategy as GRACE data to ensure spectral consistency between them. The general behavior of GWS agrees well with the TWS, especially in terms of positive long-term GWS trends in central North America and strong annual signal in Alaska. Positive GWS trends are also identified in the east US coast.

How to cite: Sideris, M. and Piretzidis, D.: An analysis of terrestrial water and groundwater storage changes in North America using recent GRACE products, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2478, https://doi.org/10.5194/egusphere-egu2020-2478, 2020.

The mesoscale ocean gyres within polar oceans, including Ross Gyre (RG), Weddell Gyre (WG) and Beaufort Gyre (BG), are important features of the polar climate and ocean systems. However, they are not well observed by satellite altimetry because of their high latitudes and wintertime sea-ice coverage. We employ the GRACE satellite’s time-variable gravity (TVG) dataset from the Centre National d'Etudes Spatiales/Groupe de Recherches de Géodésie Spatiale (CNES/GRGS) Release 03 solutions at nominal 10-day sampling between July 2002 to June 2016, to investigate the non-seasonal and high-frequency variations of the three gyres, a feat demonstrated in a previous work by Yu and Chao (2018) for studying the Argentine Gyre. We solve the empirical orthogonal functions (EOF) and confirm their barotropic structure and find the sea level variations in the RG and WG are strongly correlated with the Antarctic Oscillation (AAO) and the El Nino-Southern Oscillation (ENSO), and that in the BG is correlated with salinity changes and ENSO. Different from the Argentine Gyre, there are no short-period oscillations of dipole pattern within the three subpolar gyres based on the complex EOF (CEOF) analysis from GRACE data. The fact that GRACE does observe these signals, while the de-aliasing background ocean model (whose predictions were removed before-hand in the employed GRACE data) fails to, ascertains that GRACE TVG data can shed light on the ocean gyre variabilities unavailable by satellite altimetry and at spatial and temporal resolutions higher than practiced hitherto.

How to cite: Gao, C. and Chao, B. F.: Variations of Subpolar Ocean Gyres Observed by the GRACE Time-Variable Gravity: Antarctic Ross/Weddell and Arctic Beaufort Gyres, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4022, https://doi.org/10.5194/egusphere-egu2020-4022, 2020.

The Amur River, with a total length of 4440 kilometers, is one of the major Asian rivers as well as the tenth largest river in the world flowing through China, Mongolia and Russia. As one of the high latitude rivers, the characteristics of terrestrial water storage(TWS) in Amur Drainage Basin are different from those in the middle and low latitude rivers. Its runoff is influenced by precipitation as well as the ice melt water, in this case, the research on this region has a unique scientific significance. In this study, Gravity Recovery and Climate Experiment(GRACE) time-varying gravity data is used to inverse the change of TWS in order to study the seasonal and interannual change of water storage in Amur Drainage Basin. By introducing Global Land Data Assimilation System(GLDAS) hydrological model and Global Precipitation Measurement(GPM) precipitation data, we can get the mass change of ice and snow of this area with water balance method. The result shows that the mass change of ice and snow detected by GRACE fits well with the trend of temperature. Which means GRACE combined with multi-source data has the ability to detect the change of ice and snow in high latitude rivers during the ice age.

How to cite: Xu, Z. and Wang, Z.: Ice mass change in the Amur Drainage Basin estimated from multi-source observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8170, https://doi.org/10.5194/egusphere-egu2020-8170, 2020.

         The Tibetan Plateau (TP) experiences complex mass transfer and redistribution due to the effects from internal earth dynamics and external climate change, such as, land water change, crustal uplift, surface denudation, and Moho interface change. These phenomenas are accompanied by the gravity field change and could be observed by the Gravity Recovery and Climate Experiment (GRACE). This study applies GRACE data to estimate the corresponding mass changes expressed by water equivalent height (EWH) anomaly of the TP. In addition, we use ICESat data and hydrological models to estimate the effects of hydrological factors (lake, glaciers, snow, soil moisture, and groundwater), to separate them from the comprehensive mass field to obtain the tectonic information. The total hydrological contribution to the average EWH change is -0.30±0.21 cm/yr. We further estimate the rates of tectonic uplift and denudation based on GNSS and denudation, with results of 0.71±0.46 mm/yr and 0.38±0.10 mm/yr, respectively. Removing the effects of hydrological change, surface displacements and GIA from the GRACE data, we obtain the EWH change contributed from interior mass change of 0.21±0.27 cm/yr, which is equivalent to a mean Moho interface uplift rate of 3.63±4.32 mm/yr. Final results show that the crustal thickness of the northern TP is thinning because of the upwelling of Moho interface and the southern TP is thickening along with Moho deepening, coinciding with the tomographic results.

Key words: the Tibetan plateau, mass transfer, land water change, Moho interface change, GRACE

How to cite: Rao, W. and Sun, W.: Estimating the changes in the Moho interface beneath the Tibetan Plateau based on GRACE data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4537, https://doi.org/10.5194/egusphere-egu2020-4537, 2020.

Global Positioning System (GPS) observations are able to resolve Earth’s surface vertical deformation which originates among others from continental hydrological mass changes. Although long-term signals and seasonal changes of hydrology loading are well-captured by GPS observations, it is still unanswered whether GPS detects also the short-term hydrology-related deformations or not. In this presentation, we use predictions of vertical deformations from a GRACE (Gravity Recovery and Climate Experiment)-assimilating land surface model to separate deterministic and stochastic parts of GPS height changes observed by a set of 221 European EPN (EUREF Permanent GNSS Network) stations. This approach is compared to conventional harmonic functions approach, in which deterministic and stochastic parts are separated by pre-defined annual and semi-annual periods. For the stochastic parts associated with two methods, the noise parameters (spectral indices and amplitudes of power-law noise) are estimated using the Maximum Likelihood Estimation (MLE). Comparing original GPS displacements to displacements reduced for hydrological loading, we notice that annual and semi-annual frequencies are significantly explained by the hydrological model, resulting 60% reduction on average in amplitudes. This means that large part of seasonal crustal deformation arises from hydrological loading or unloading of the lithosphere. We find that the annual and semi-annual peaks are greatly reduced (72% on average) once conventional harmonic functions approach is used instead of GRACE-assimilating hydrological model, but no physical interpretation can be made here since it is difficult to identify the magnitude of each individual processes contributing to seasonal changes. The GRACE-assimilated model can remove the effect of high-frequency hydrological deformations, producing residuals with spectrum closer to the white noise process. Many oscillations present in GPS displacements at periods between 15 and 90 days are well-explained by GRACE-assimilating deformation model. We find the greatest improvement in noise parameters for stations located in the eastern and central regions of Europe, encompassing the Rhine, Elbe, Danube and Oder drainage basins where hydrological mass changes are relatively larger comparing to western Europe. Using GRACE-assimilated model as a deterministic part of GPS displacement time series, we provide a totally new estimates of noise parameters for European sites, which has never been presented before. Our results show that GRACE-assimilating water storage re-analyses can provide essential information for obtaining improved unbiased estimates of GPS vertical velocity, including their uncertainty, which are essential for a range of applications such as upcoming reference frame realizations.

How to cite: Klos, A., A. Karegar, M., Kusche, J., and Springer, A.: How much of GPS noise refers to hydrology loading? An insight from GRACE-assimilating hydrological modeling, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5697, https://doi.org/10.5194/egusphere-egu2020-5697, 2020.

The Gravity Recovery and Climate Experiment (GRACE) mission, since 2002, has measured total water storage change (TWSC) and interpreted drought patterns in an unparalleled way. Nevertheless, there are still few sources could be used to understand drought patterns prior to the GRACE era. Here we derived multi-decadal climate-driven TWSC grids and used them to interpret drought patterns (1993-2019) over the Amazon basin. The correlations of climate-driven TWSC as compared to GRACE, GRACE Follow-on, and Swarm TWSC are 0.95, 0.92, and 0.77 in Amazon at grid scale (0.5° resolution). The drought patterns assessed by the climate-driven TWSC are consistent to those interpreted by the Palmer Drought Severity Index and GRACE TWSC. We also found that the 1998 and 2016 drought events in Amazon, both induced by the strong El Niño events, show similar drought patterns. This study provides a new perspective for interpreting long-term drought patterns prior to the GRACE period.

How to cite: Li, F., Wang, Z., Chao, N., Liang, W., Tian, K., and Gao, Y.: Drought Patterns over the Amazon River Basin (1993-2019) as Interpreted by the Climate-driven Total Water Storage Change Fields, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6236, https://doi.org/10.5194/egusphere-egu2020-6236, 2020.

Viscoelastic relaxation is generally considered as the dominant process of the long-term post-seismic deformation, while viscoelastic characteristic relaxation time represents the time scale of deformation caused by viscoelastic relaxation effect after the earthquake. The subduction earthquakes which occurred at the boundary of the ocean and continental plates often release greater stress, and the stress relaxation of mantle materials is more significant due to the response to viscoelasticity. Satellite gravity mission GRACE (gravity recovery and climate experience) is able to observe the corresponding co-seismic and post-seismic gravity changes. Therefore, in this study, we use the monthly gravity field model data of GRACE RL06 to study the post-seismic gravity changes of 2011 Tohoku earthquake and 2004 Sumatra earthquake. After removing the influence of sea level changes, GIA changes and GLDAS on the seasonal precipitation changes in the land area, as well as the sea water correction, we get the post-seismic deformation only related to the deformation of the solid earth. Then we use the attenuation function to fit each grid value and obtain the spatial distribution of viscoelastic characteristic relaxation time after rejecting the afterslip from the total post-seismic deformation. Thus，we can capture  the viscous structure in the subduction area.

How to cite: Ji, Y., Sun, W., and Tang, H.: Spatial Distribution of Viscoelastic Relaxation Following a Subduction Earthquake, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6756, https://doi.org/10.5194/egusphere-egu2020-6756, 2020.

The GRACE mascon solutions, called the advanced products of GRACE data, are widely used in cryosphere science or hydrology research. It has been demonstrated that the mascon solutions have the same or better performances compared with the spherical harmonic (SH) solutions at the basin scale. However, although the mascon solutions are expected to have the ability to recover the transient gravity signals due to large earthquakes, few studies have investigated the performances of the mascon solutions in studying seismic deformations systematically. In this study, we attempt to examine the performances of the mascon solutions for transient gravity signals induced by three M9 class earthquakes: the 2011 Tohoku-Oki, 2004 Sumatra and 2010 Chile earthquakes, and compare them with the SH solutions and theoretical gravity changes modelled by dislocation theory. We analyse the co-seismic gravity changes and conclude that the mascon solutions contain almost identical information as the SH solutions and can retrieve the co-seismic gravity change signals in the resolutions equivalent to the Gaussian filter radii of 210~270 km. However, the mascon solutions have other strengthening gravity change signals, with magnitudes that are the same order as that of the SH solutions and contain pre-seismic gravity change signals in the Tohoku earthquake. These strengthening and pre-seismic signals are both considered artificially introduced noise due to the mathematical treatment before releasing rather than real geophysical signals.

How to cite: Zhang, L., Tang, H., Chang, L., and Sun, W.: The Performances of GRACE Mascon Solutions in Studying Seismic Deformations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8819, https://doi.org/10.5194/egusphere-egu2020-8819, 2020.

Low Earth Orbit (LEO) satellites are subject to numerous disturbances related to the Earth’s upper ionosphere. Perturbations induced by the activity of the electromagnetic field (EM) at the upper ionospheric layers have not been fully understood yet. This study focuses on the disturbances shown on GRACE-FO accelerometer measurements when the EM field was disturbed by an intense geomagnetic storm occurred on August 2018. A thorough analysis of the accelerometer measurements of GRACE-C as well as the magnetic and electric field measurements from Swarm constellation is conducted, to enlighten their impulse-response relationship. We derive the temporal variations of the magnetic field by removing the main static field and we calculate the Poynting vector employing the Swarm magnetic field measurements and electric field data, by implementing rigorous data analyses to analyze the spatiotemporal characteristics of the energy flow of the electromagnetic field. Results show that GRACE-C accelerometer measurements are highly disturbed in the higher latitudes especially near the auroral regions. The signature of the spatial temporal variations of the magnetic field and the Poynting vector demonstrates very similar behaviour with GRACE-C disturbances. Cross wavelet analysis between Poynting vector and GRACE-C accelerometer disturbances shows a very strong coherence. With the two LEO missions, i.e. GRACE-FO and Swarm, orbiting the Earth in very similar orbits, further analysis towards integrating their measurements will enhance our understanding of the interaction of LEO satellites with the space environment and how this interaction is depicted in their measurements.

How to cite: Tzamali, M., Peidou, A., and Pagiatakis, S.: GRACE-FO and Swarm integrated data analysis reveals ionospheric disturbances on the accelerometer measurements, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12931, https://doi.org/10.5194/egusphere-egu2020-12931, 2020.

As opposed to the level 1B release 5 GOCE gravitational gradient data, the newly reprocessed release 6 gradients provide reduced noise amplitudes in the low frequency-range, leading to reduced noise amplitudes of the derived gravity field models at large spatial scales, where temporal variations of the Earth’s gravity field have their highest amplitudes. This is the motivation to test the release 6 gradients for their ability to resolve temporal gravity variations.

For the gravity field processing, we apply a conventional spherical harmonics approach using the time-wise (TIM) processing method as well as a mass concentration (mascon) approach using point masses as base elements, which are grouped to land or ocean mascons by taking into account the coastlines.

By means of a closed-loop simulation study, we find that the colored instrument noise of the GOCE gravitational gradiometer introduces noise amplitudes into the derived gravity field models that lie above the amplitude of the gravity trend signal accumulated over 5 years. This indicates that detecting gravity variations taking place during the four-year GOCE data period from GOCE gradients only is challenging.

Using real GOCE data, we test bimonthly gradiometry-only gravity field models computed by both the spherical harmonic and the mascon approach for gravity signals that are resolved by GRACE data, being the temporal signals due to the ice mass trends in Greenland and Antarctica and the 2011 earthquake in Japan. Besides, corresponding GRACE/GOCE combination models are used to test whether the incorporation of GOCE data increases the resolution of temporal gravity signals.

We found that high-amplitude long-wavelength noise prevented the detection of temporal gravity variations among the bimonthly GOCE-only models. Using the SH approach, it was possible to detect the mean trend signal contained in the data by averaging multiple bimonthly models and considering their difference to a reference model. Using the mascon approach, trend signals contained in GOCE data could be recovered by including a GRACE model truncated to d/o 45 in a GRACE/GOCE combination model and thus let the GOCE data determine the short-scale signal structures instead of GRACE.

Finally, compared to the temporal gravity signal as resolved by GRACE data, no significant benefit of using or incorporating GOCE gravitational gradient data was found. The reason are the still rather high noise amplitudes in the derived models at large spatial scales, where the considered signal is strongest.

In order to detect temporal gravity variations in satellite gravitational gradiometry data, the measurement noise amplitudes in the low-frequency range would need to be reduced.

How to cite: Heller, B., Siegismund, F., Pail, R., and Gruber, T.: Temporal gravity variations in GOCE release 6 gravitational gradients, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2563, https://doi.org/10.5194/egusphere-egu2020-2563, 2020.