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International Combination Service for Time-variable Gravity Fields (COST-G) Monthly GRACE/GRACE-FO RL02 Series

Second release of combined monthly gravity fields of the GRACE and GRACE-FO satellite missions in spherical harmonic representation (Level-2 product) generated by the Combination Service for Time-variable Gravity Fields (COST-G; Jäggi et al., 2020), a product center for time-variable gravity fields of IAG's International Gravity Field Service (IGFS). COST-G RL02 is a combination of gravity field time series provided by the following analysis centers (ACs) and partner analysis centers (PCs) of COST-G: ACs: - GFZ Helmholtz Centre for Geosciences: GFZ RL06 (GRACE), GFZ RL06.3 (GRACE-FO) - Graz University of Technology, Institute of Geodesy: ITSG-Grace2018 (GRACE), ITSG-Grace_op (GRACE-FO) - Centre National d’Etudes Spatiales, Groupe de Recherche de Geodesie Spatiale: CNES_GRGS_RL05_CHOL (GRACE & GRACE-FO) - Astronomical Institute University of Bern: AIUB-RL03 (GRACE), AIUB-GRACE-FO_rl02op (GRACE-FO) - Leibniz Universität Hannover: LUH-GRACE-2020 (GRACE), LUH-GRACE-FO-2020 (GRACE-FO) - Innovation Academy for Precision Measurement Science and Technology, Chinese Academy of Sciences: APM-SYSU (GRACE) - HuaZhong University of Science and Technology: HUST-Grace2024 (GRACE & GRACE-FO) - Southern University of Science and Technology, Department of Earth and Space Sciences: SUSTech2025 (GRACE) - Tongji University, College of Surveying and Geo-informatics: Tongji-Grace2022 (GRACE) PCs: - Center for Space Research at University of Texas: CSR RL06 (GRACE), CSR RL06.3 (GRACE-FO) - NASA Jet Propulsion Laboratory: JPL RL06 (GRACE), JPL RL06.3 (GRACE-FO) --------------------------------------------------------------------------------------------- Version History: 4 July 2025: Release of Version 2.1. This is an update of Version 2.0 of the same data set including the following changes: Replacement of Tongji-Grace-Costg (nonofficial release) by Tongji-Grace2022; replacement of HUST-Grace2023 (nonofficial release) by HUST-Grace2024 (currently also not yet officially released); use of GFZ RL06.3, CSR RL06.3, JPL RL06.3 and CNES_GRGS_RL05_CHOL for the entire GRACE-FO period. 25 April 2025: Initial release of the data (Version 2.0).

Superconducting Gravimeter Data from Serrahn - Level 1

The International Geodynamics and Earth Tide Service (IGETS) was established in 2015 by the International Association of Geodesy (IAG). IGETS continues the activities of the Global Geodynamics Project (GGP, 1997-2015) to provide support to geodetic and geophysical research activities using superconducting gravimeter (SG) data within the context of an international network. The SG site “Serrahn” is located in the TERENO Observatory in the nort-eastern German lowlands. The observatory contributes to investigating the regional impact of climate and land use change. At the IGETS site Serrahn, the mean annual temperature is 8.8 °C and mean annual precipitation is 591 mm. The land cover is mainly characterized as a mixed forest, dominated by European beech and Scots pine. Influenced by the last glaciation in an outwash close to the terminal morraine, the uppermost soil layer of the site consists of aeolian sands up to a depth of 450 cm, followed by coarser sandy material with intercalated till layers. The unconfined groundwater level is at about 14 m below surface. There is hardly any human activity (e.g., traffic) at this quiet forest site. The nearest town is Neustrelitz at a distance of 5 km. Since December 2017, the superconducting gravimeter iGrav-033 is operated outdoors at this forest location (Latitude: 53.3392 N, Longitude: 13.17413 E, Elevation: 79.60 m). The gravimeter is installed in a dedicated field enclosure on top of a concrete pillar with an area of 1.1 m x 1.1 m at an elevation of 0.80 m above the terrain surface. The pillar has been build to a depth of 2.00 m below the surface. One additional pillar (also 1.1 m x 1.1 m, at surface level) is located right next to the iGrav installation and is used for repeated observations with absolute gravimeters (AG). At the site, meteorological (precipitation, air temperature, humidity, air pressure) and hydrological (groundwater, soil moisture, sapflow, throughfall) parameters are monitored by different sensors. Raw gravity and local atmospheric pressure records sampled at second intervals and the same records decimated at 1‐minute samples are provided as Level 1 products to the IGETS network.

Superconducting Gravimeter Data from Buchholz, Eifel - Level 1

The International Geodynamics and Earth Tides Service (IGETS) was established in 2015 by the International Association of Geodesy IAG. IGETS continues the activities of the Global Geodynamics Project (GGP) between 1997 and 2015 to provide support to geodetic and geophysical research activities using superconducting gravimeter (SG) data within the context of an international network. As part of this network, the Eifel Gravimetric Observatory Germany (EIGOG) was established by the GFZ Helmholtz Centre for Geosciences in August 2025. Continuous time-varying gravity and atmospheric pressure data from the SG at EIGOG are integrated in the IGETS data base hosted by GFZ. The EIGOG observatory is located at the Buchholz Provostry (Propstei Buchholz) in the municipality of Burgbrohl. It is part of a multiparameter station for the monitoring and analysis of seismic and volcanic signals within the Central European Volcanic Province Observatory (CVO) in the Eifel region. Additional sensors at Buchholz are GNSS, InSAR corner reflector, seismometer, tiltmeter, groundwater level and a weather station. The operation and maintenance of the EIGOG instrumentation is done by staff of the GFZ. EIGOG is a high precision gravimetric observatory with the dual-sphere OSG D037 manufactured by GWR Instruments as core instrument, one of the two SGs operating at Sutherland, South Africa, until December 2024 (Förste et al., 2016, http://doi.org/10.5880/igets.su.l1.001). The time series of gravity and barometric pressure from the OSG D037 starts in August 2025. The SG is active and the time series is kept up to date regularly with a time delay of a few months. The time sampling of the raw gravity and barometric pressure data of IGETS Level 1 is 1 second and 1 minute. For a detailed description of the IGETS data base and the provided files see Voigt et al. (2016, http://doi.org/10.2312/GFZ.b103-16087).

gravitools - A collection of tools to analyze gravimeter data

This Python package is a collaborative effort by the gravity Metrology group at the German Federal Agency for Carthography and Geoesy (BKG) and the Hydrology section at GFZ Helmholtz Centre for Geosciences. It comprises functionalities and features around the respectively new instrument type of a Quantum Gravimeter (here AQG). New (standardized) instrument data format additional to new measurement and processing concepts lead to the first collection of scripts and now complete python package for a fully-featured analysis of AQG data. This encompasses live-monitoring while the instrument is actually measuring (with enhanced functionality than what is provided by the manufacturer), data processing, visualizations as well as archiving data, fulfilling the idea of reproducible data within FAIR principles. Many of these functionalities and concepts also apply to other gravimeter types. It is thus planned to include also access and processing of data for these other devices (starting in the near future with CG-6 relative gravimeters). This package is actively maintained and developed. If you are interested in contributing, please do not hesitate to contact us. Please find instructions for its installation and usage in the documentation or git repository, linked in the left panel. gravitools is listed in the python standard repository database "PyPi". Some highlight features, available in the first official stable release are: • Read and process raw data of the Exail Absolute Quantum Gravimeter (AQG) • Apply standardized or customized AQG data processing and outlier detection • Read and write processed datasets with metadata to .nc-files in NETCDF4-format • Handle Earth orientation parameters (EOP) from iers.org for polar motion correction • Visualize data with matplotlib • CLI for standard processing of AQG raw data to .nc-file • Dashboard for real-time processing and visualization during measurements (on AQG laptop) • Dashboard includes a proposed standard template for a measurement protocol • Standardized, easy-to-read and modify config files for processing options and reproducible data handling • Generation of PDF reports from individual measurements

Post-processed GRACE/GRACE-FO Geopotential GSM Coefficients COST-G RL02 (Level-2B Product)

Post-processed GRACE/GRACE-FO spherical harmonic coefficients of COST-G RL02 Level-2 GSM products representing an estimate of Earth's gravity field variations during the specified timespan. Post-processing steps comprise: (1) subtraction of a long-term mean field; (2) optionally, decorrelation and smoothing with VDK filter (anisotropic filter taking the actual error covariance information of the underlying GSM coefficients into account, see Horvath et al. (2018)); (3) replacement of coefficients C20 and C30 (only for the months within the period from 2016/11 through 2017/06) and its formal standard deviations by values estimated from a combination of GRACE/GRACE-FO and Satellite Laser Ranging (SLR); (4) subtraction of linear trend caused by Glacial Isostatic Adjustment (GIA) as provided by a numerical model; (5) insertion of geocenter coefficients (C10, C11, S11); and (6) removal of estimated aliased signal of the S2 tide (161 days period). These coefficients represent signals caused by water mass redistribution over the continents and in the oceans. These post-processed GRACE/GRACE-FO GSM products are denoted as Level-2B products. There are multiple variants of Level-2B products available that differ by the characteristics of the anisotropic filter applied. These variants are distinguishable by the following strings in the product file names: - 'NFIL': Level-2B product is not filtered - 'VDK1': Level-2B product is filtered with VDK1 - 'VDK2': Level-2B product is filtered with VDK2 - 'VDK3': Level-2B product is filtered with VDK3 - 'VDK4': Level-2B product is filtered with VDK4 - 'VDK5': Level-2B product is filtered with VDK5 - 'VDK6': Level-2B product is filtered with VDK6 - 'VDK7': Level-2B product is filtered with VDK7 - 'VDK8': Level-2B product is filtered with VDK8 The individual auxiliary data sets and models used during the post-processing steps mentioned above are provided as well (in the aux_data folder): - 'GRAVIS-2B_COSTG_0200_2002095-2020091_NFIL_0001.gz': Long-term mean field calculated as unweighted average of the 183 available GFZ RL06 GSM products in the period from 2002/04 through 2020/03 - 'GRAVIS-2B_COSTG_0200_GRACE+SLR_LOW_DEGREES_0001.dat': Time series of coefficients C20, C30, C21 and S21 estimated from a combination of GRACE/GRACE-FO and SLR - 'GRAVIS-2B_COSTG_0200_GIA_ICE-6G_D_VM5a_0001.gz': Model from Peltier et al. (2018) for subtraction of linear trend caused by GIA - 'GRAVIS-2B_COSTG_0200_GEOCENTER_0001.dat': Time series with geocenter coefficients estimated from COST-G RL02.1 Further information about the Level-2B products and the auxiliary data is provided in the header of the corresponding data files. --------------------------------------------------------------------------------------------- Version History: 22 July 2025: Initial release of the data (Version 0001).

3D-SCS: Three-dimensional lithospheric-scale structural and density model of the South China Sea

We present a comprehensive 3D lithospheric-scale model of the South China Sea region (SCS), which reveals the structural configuration of the area. This model delineates seven distinct geological units: (1) seawater, (2) sedimentary cover, (3) continental crystalline crust, (4) oceanic crust, (5) upper lithospheric mantle, (6) lower lithospheric mantle, and (7) sub-lithospheric mantle. The model covers an area of 960 km × 1260 km and reach down to a depth of 250 km. It is provided as uniformly spaced grids with 10 km intervals for each unit. The geometries and density distributions within the crust have been compiled and interpolated from a variety of datasets, predominantly seismic data (see section 6). To eliminate boundary effects, the model boundaries have been extended by more than 500 km in all horizontal directions, incorporating additional constraining data from the extended region. Additionally, we provide gridded gravity field data, a density voxel cube for the sub-lithospheric mantle, and relevant tomography data. Notably, the density of the lower lithospheric mantle was derived from 3D gravity inversion modeling.

Ellipsoidal Harmonic Forward Model derived from Earth2014 topographies up to d/o 7200: EHFM_Earth_7200

The model named EHFM_Earth_7200 was derived by layer-based forward modeling technique in ellipsoidal harmonics, the maximum degree of this model reaches 7200. The relief information was provided by Earth2014 relief model. EHFM_Earth_7200 provides very detailed (~3 km) information for the Earth’s short-scale gravity field, and it is expected to be able to augment or refine existing global gravity models. To meet the existing standard, here we provide spherical harmonic coefficients, which are transformed from original ellipsoidal harmonic coefficients. The maximum degree of the spherical harmonic coefficients is 7300.

The Uruguayan gravimetric geoid: UruGeoide110

The Uruguayan gravimetric geoid model UruGeoide110 was calculated by the Military Geographic Institute (IGM) in 2023. The extent is from 29.5° S to 35.5° S in latitude, and 52.5° W to 59.5° W in longitude, covering parts of Argentina and Brazil, with a grid resolution of 1´ x 1´. The geodetic reference system is SIRGAS ROU-98 (the reference ellipsoid is GRS80). The model is a combination of the EIGEN-6C4 geopotential model up to degree and order of 720, 10,429 land gravimetric stations plus 10,089 free air gravity anomalies in marine areas, based on the DTU13 model. The terrain data at the final 90 m resolution was taken from a 2017 Lidar survey in Uruguay with a 2.5 m initial resolution and SRTM (V2) for the external terrestrial data. The DT18 bathymetry model was used for the marine areas. Due to the total terrain data points (about 104 million), the overall area was divided into 4 overlapped blocks in the framework of the remove-compute-restore procedure. The reduced height anomalies were computed from the reduced gravity anomalies with Stokes 1D FFT and Wong Gore´s kernel modification (170-180 degrees). After adding back the residual terrain model effects and the contribution of the global geopotential model, the obtained quasi-geoid was transformed into a geoid model via Bouguer anomalies, even if the difference between the two models is just a few mm. A comparison with 51 GNSS/levelling stations shows a standard deviation of 10 cm. The geoid model is provided in ISG format 2.0 (ISG Format Specifications), while the file in its original data format is available at the model ISG webpage.

The Uruguayan gravimetric quasi-geoid: UruQGeoide110

The Uruguayan gravimetric quasi-geoid model UruQGeoide110 was calculated by the Military Geographic Institute (IGM) in 2023. The extent is from 29.5° S to 35.5° S in latitude, and 52.5° W to 59.5° W in longitude, covering parts of Argentina and Brazil, with a grid resolution of 1´ x 1´. The geodetic reference system is SIRGAS ROU-98 (the reference ellipsoid is GRS80). The model is a combination of the EIGEN-6C4 geopotential model up to degree and order of 720, 10,429 land gravimetric stations plus 10,089 free air gravity anomalies in marine areas, based on the DTU13 model. The terrain data at the final 90 m resolution was taken from a 2017 Lidar survey in Uruguay with a 2.5 m initial resolution and SRTM (V2) for the external terrestrial data. The DT18 bathymetry model was used for the marine areas. Due to the total terrain data points (about 104 million), the overall area was divided into 4 overlapped blocks in the framework of the remove-compute-restore procedure. The reduced height anomalies were computed from the reduced gravity anomalies with Stokes 1D FFT and Wong Gore´s kernel modification (170-180 degrees) and the quasi-geoid model was finally obtained by adding back the residual terrain model effects and the contribution of the global geopotential model. The geoid model is provided in ISG format 2.0 (ISG Format Specifications), while the file in its original data format is available at the model ISG webpage.

Superconducting Gravimeter Data from Pecný - Level 2 pre-processed by station operators

The International Geodynamics and Earth Tide Service (IGETS) was established in 2015 by the International Association of Geodesy (IAG). IGETS continues the activities of the Global Geodynamics Project (GGP, 1997-2015) to provide support to geodetic and geophysical research activities using superconducting gravimeter (SG) data within the context of an international network. Raw gravity and local atmospheric pressure records sampled at second and the same records decimated at 1‐minute samples are provided as Level 1 products of the IGETS network for the Pecný station (https://doi.org/10.5880/igets.pe.l1.001). The corrected 1-minute samples have been prepared by operators of the station, from raw decimated 1-minute samples, by following steps: 1) The 1-minute samples have been used to compute residual gravity signal by using the SG calibration factor and applying corrections from tides, atmosphere and polar motion. 2) These data have been associated with auxiliary data from the SG (Dewar Pressure, Tx/Ty balance, Neck temperature etc.) and information from LOG files. 3) Gaps have been created in the residual gravity signal according to auxiliary data and log files. Moreover, gaps were created also for large disturbances, where the residual signal exceeding 20 nm/s^2. 4) Gaps up to 24 hours were filled by a linear fit. 5) Spikes exceeding 5 nm/s^2 were removed by using TSOFT. 6) Steps were applied only in exceptional cases in accordance with LOG files. 7) The cleaned residual signal was converted to corrected 1-minute samples by using the same corrections and the calibration factor as used in 1). Therefore, the corrected 1-minute signal is again in units as the raw data (Volt). Note, since 31 October 2017, the OSG-050 is running at new site (NGL - new gravimetric laboratory at Pecný) according to https://doi.org/10.5880/igets.pe.l1.001.

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