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  • 1
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    Stochastic noise modelling of kinematic orbit positions in the Celestial Mechanics Approach (2020)
    Copernicus
    Details
    Publication Date: 2020-10-20
    Description: Gravity field models may be derived from kinematic orbit positions of Low Earth Orbiting satellites equipped with onboard GPS (Global Positioning System) receivers. An accurate description of the stochastic behaviour of the kinematic positions plays a key role to calculate high quality gravity field solutions. In the Celestial Mechanics Approach (CMA) kinematic positions are used as pseudo-observations to estimate orbit parameters and gravity field coefficients simultaneously. So far, a simplified stochastic model based on epoch-wise covariance information, which may be efficiently derived in the kinematic point positioning process, has been applied. We extend this model by using the fully populated covariance matrix, covering correlations over 50 min. As white noise is generally assumed for the original GPS carrier phase observations, this purely formal variance propagation cannot describe the full noise characteristics introduced by the original observations. Therefore, we sophisticate our model by deriving empirical covariances from the residuals of an orbit fit of the kinematic positions. We process GRACE (Gravity Recovery And Climate Experiment) GPS data of April 2007 to derive gravity field solutions up to degree and order 70. Two different orbit parametrisations, a purely dynamic orbit and a reduced-dynamic orbit with constrained piecewise constant accelerations, are adopted. The resulting gravity fields are solved on a monthly basis using daily orbital arcs. Extending the stochastic model from utilising epoch-wise covariance information to an empirical model, leads to a – expressed in terms of formal errors – more realistic gravity field solution.
    Print ISSN: 1680-7340
    Electronic ISSN: 1680-7359
    Topics: Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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  • 2
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    Evaluation of GPM-DPR precipitation estimates with WegenerNet gauge data (2019)
    Copernicus
    Details
    Publication Date: 2019-09-20
    Description: The core satellite of the Global Precipitation Measurement (GPM) mission provides precipitation observations measured with the Dual-frequency Precipitation Radar (DPR). The precipitation can only be estimated from the radar data, and therefore independent validations using direct precipitation measurements on the ground as a true reference need to be performed. Moreover, the quality and the accuracy of satellite observational data depend on various influencing factors, such as altitude, topography and rainfall type. In this way, a validation may help to minimise those uncertainties. The DPR Level 2 algorithms provide three different sets of radar rain rate estimates: Ku-band-only rain rates, Ka-band-only rain rates, and a product using both the Ku and Ka band. This study presents an evaluation of the three GPM-DPR surface precipitation estimates based on the gridded precipitation data of the WegenerNet, a local-scale terrestrial network of 153 meteorological stations in southeastern Austria. The validation is based on graphical and statistical approaches, using only data where both Ku- and Ka-band measurements are available. The focus lies on the resemblance of the rainfall variability within the whole network and the over- and underestimation of the precipitation through the GPM-DPR. The analysis rests upon 15 rainfall events observed by the GPM-DPR over the WegenerNet in the last 4 years; the meteorological winter is excluded due to technical challenges of snow measurements. The WegenerNet provides between 8 and 12 gauges within each GPM-DPR footprint. Its biases are well studied and corrected; thus, it can be taken as a robust ground reference. This work also includes considerations on the limits of such comparisons between small terrestrial networks with a high density of stations and precipitation observations from a satellite. Our results show that the GPM-DPR estimates basically match with the WegenerNet measurements, but absolute quantities are biased. The three types of radar estimates deliver similar results, where Ku-band and dual-frequency estimates are very close to each other. On a general level, Ka-band precipitation estimates deliver better results due to their greater sensitivity to low rainfall rates.
    Print ISSN: 1867-1381
    Electronic ISSN: 1867-8548
    Topics: Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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  • 3
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    Evaluation of GPM-DPR precipitation estimates with WegenerNet gauge data (2018)
    Copernicus
    Details
    Publication Date: 2018-11-19
    Description: The core satellite of the Global Precipitation Measurement (GPM) mission provides precipitation observations measured with the Dual frequency Precipitation Radar (DPR). The precipitation can only be estimated from the radar data, and therefore, independent validations using direct precipitation observation on the ground as a true reference need to be performed. Moreover, the quality and the accuracy of the measurements depend on various influencing factors. In this way, a validation may help to minimise those uncertainties. The DPR provides three different radar rain rate estimates for the GPM core satellite: Ku-band-only rain rates, Ka-band-only rain rates and a product combining the two frequencies. This study presents an evaluation of the three GPM-DPR surface precipitation estimates based on the gridded precipitation data of the WegenerNet, a local scale terrestrial network of 153 meteorological stations in southeast Austria. The validation is based on a graphical and a statistical approach using only data where both Ku- and Ka-band measurements are available. The data delivered from the WegenerNet are gauge-based gridded rainfall observations; the meteorological winter is excluded due to technical reasons. The focus lies on the resemblance of the variability within the whole network and the over- and underestimation of the precipitation through the GPM-DPR. During the last four years 22 rainfall events were observed by the GPM-DPR over the WegenerNet and the analysis rests upon these rainfall events. The WegenerNet provides a large number of gauges within each GPM-DPR footprint. Its biases are well studied and corrected, thus, it can be taken as a robust ground reference. This work also includes considerations on the limits of such comparisons between small terrestrial networks with a high density of stations and precipitation observations from a satellite. Our results show that the GPM-DPR estimates basically match with the WegenerNet measurements, but absolute quantities are biased. The three types of radar estimates deliver similar results, where Ku-band and dual frequency estimates are very close to each other. On a general level, Ka-band precipitation estimates deliver the best results due to the high number of light rainfall events.
    Electronic ISSN: 1867-8610
    Topics: Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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  • 4
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    Benchmark data for verifying background model implementations in orbit and gravity field determination software (2020)
    Copernicus
    Details
    Publication Date: 2020-12-17
    Description: In the framework of the COmbination Service for Time-variable Gravity fields (COST-G) gravity field solutions from different analysis centres are combined to provide a consolidated solution of improved quality and robustness to the user. As in many other satellite-related sciences, the correct application of background models plays a crucial role in gravity field determination. Therefore, we publish a set of data of various commonly used forces in orbit and gravity field modelling (Earth's gravity field, tides etc.) evaluated along a one day orbit arc of GRACE, together with auxiliary data to enable easy comparisons. The benchmark data is compiled with the GROOPS software by the Institute of Geodesy (IfG) at Graz University of Technology. It is intended to be used as a reference data set and provides the opportunity to test the implementation of these models at various institutions involved in orbit and gravity field determination from satellite tracking data. In view of the COST-G GRACE and GRACE Follow-On gravity field combinations, we document the outcome of the comparison of the background force models for the Bernese GNSS software from AIUB (Astronomical Institute, University of Bern), the EPOS software of the German Research Centre for Geosciences (GFZ), the GINS software, developed and maintained by the Groupe de Recherche de Géodésie Spatiale (GRGS), the GRACE-SIGMA software of the Leibniz University of Hannover (LUH) and the GRASP software also developed at LUH. We consider differences in the force modelling for GRACE (-FO) which are one order of magnitude smaller than the accelerometer noise of about 10−10 m s−2 to be negligible and formulate this as a benchmark for new analysis centres, which are interested to contribute to the COST-G initiative.
    Print ISSN: 1680-7340
    Electronic ISSN: 1680-7359
    Topics: Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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  • 5
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    AIUB-G3P GRACE monthly gravity field solutions (2023)
    GFZ Data Services
    Details
    Publication Date: 2023-03-04
    Description: Abstract
    Description: GRACE monthly gravity field solutions starting from April 2002 to June 2017 up to degree and order 90 computed with the Celestial Mechanics Approach at AIUB. The time series is an updated of AIUB-RL02 GRACE monthly gravity field time series using Level-1B GRACE data and updated background models. The dataset is created within the framework of the G3P - Global Gravity-based Groundwater Product project (https://www.g3p.eu/), this project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 870353.
    Description: Other
    Description: Parameters: product_type = gravity_field earth_gravity_constant = 3.986004415000e+14 radius = 6.378137000000e+06 max_degree = 90 norm = fully_normalized tide_system = tide_free errors = formal
    Keywords: International Center for Global Earth Models ; ICGEM ; Gravity Recovery And Climate Experiment ; GRACE ; GRACE-FO ; Level-2 ; SHM ; Spherical Harmonic Model ; Gravitational Field ; Geopotential ; Gravity Field ; Time variable Gravity Field ; Satellite Geodesy ; EARTH SCIENCE 〉 SOLID EARTH 〉 GRAVITY/GRAVITATIONAL FIELD 〉 GRAVITY
    Type: Dataset , Dataset
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    DATA GFZ
  • 6
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    International Combination Service for Time-variable Gravity Fields (COST-G) Monthly GRACE-FO Series (2020)
    GFZ Data Services
    Details
    Publication Date: 2023-12-01
    Description: Abstract
    Description: Operationally combined monthly gravity fields of the GRACE-FO satellite mission in spherical harmonic representation (Level-2 product) generated by the Combination Service for Time-variable Gravity Fields (COST-G; Jäggi et al. (2020):http://dx.doi.org/10.1007/1345_2020_109), a product center for time-variable gravity fields of IAG's International Gravity Field Service (IGFS). COST-G_GRACE-FO_RL01_OP is a combination of AIUB-GRACE-FO_op, GFZ-RL06 (GFO), GRGS-RL05 (unconstrained solution), ITSG-Grace_op, LUH-GRACE-FO, CSR-RL06 (GFO) and JPL-RL06 (GFO). The original time-series were provided by the analysis centers (ACs) and partner analysis centers (PCs) of COST-G.
    Description: Methods
    Description: COST-G performs a harmonization and quality control of the individual input solutions of the COST-G ACs and PCs. The combination of COST-G_GRACE-FO_RL01_OP is then performed applying variance component estimation on the solution level (Jean et al., 2018): https://doi.org/10.1007/s00190-018-1123-5). The resulting COST-G combined gravity fields are validated assessing their signal and noise content in the spectral and spatial domain (Meyer et al., 2019: https://doi.org/10.1007/s00190-019-01274-6) and by the COST-G Product Evaluation Group (PEG).
    Keywords: COST-G ; IGFS Product Center ; Combined solutions ; Time variable gravity ; EARTH SCIENCE 〉 SOLID EARTH 〉 GRAVITY/GRAVITATIONAL FIELD 〉 GRAVITATIONAL FIELD ; EARTH SCIENCE 〉 SOLID EARTH 〉 GRAVITY/GRAVITATIONAL FIELD 〉 GRAVITY
    Type: Dataset , Dataset
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    DATA GFZ
  • 7
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    AIUB-GRACE-FO-operational - Operational GRACE Follow-On monthly gravity field solutions - release 02 (2023)
    GFZ Data Services
    Details
    Publication Date: 2024-02-06
    Description: Abstract
    Description: Operational GRACE Follow-On monthly gravity field solutions starting from June 2018 up to degree and order 96 computed with the Celestial Mechanics Approach at AIUB (release 02). The time series is a loose continuation of AIUB-RL02 GRACE monthly gravity field time series and is an update of the operational GRACE Follow-On monthly gravity field time series (https://doi.org/10.5880/ICGEM.2020.001) using Level-1B GRACE Follow-On data and operational accelerometer transplant data from TUG (Institute of Geodesy, TU Graz, Working Group Theoretical Geodesy and Satellite Geodesy) and updated modelling strategies concerning data screening and weighting. The time series is reprocessed starting with June 2018. The dataset is created within the framework of the G3P project (https://www.g3p.eu/), this project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 870353. The operational solution of release 02 provides a complete time series of GRACE Follow-on data derived monthly gravity field solutions, is regularly updated with new monthly solutions and features a consistent processing with an advanced noise modelling of GRACE Follow-On data. It is recommened for usage. It is strongly recommended to use release 02 and discontinue using release 01.
    Keywords: Gravity Recovery And Climate Experiment Follow-On (GRACE-FO) ; Level-2 ; SHM ; Spherical Harmonic Model ; Gravitational Field ; Geopotential ; Gravity Field ; Time variable Gravity Field ; Satellite Geodesy ; EARTH SCIENCE 〉 SOLID EARTH 〉 GRAVITY/GRAVITATIONAL FIELD ; EARTH SCIENCE 〉 SOLID EARTH 〉 GRAVITY/GRAVITATIONAL FIELD 〉 GRAVITY
    Type: Dataset , Dataset
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    DATA GFZ
  • 8
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    AIUB-GRACE-FO-operational - Operational GRACE Follow-On monthly gravity field solutions (2020)
    GFZ Data Services
    Details
    Publication Date: 2024-02-06
    Description: Abstract
    Description: Operational GRACE Follow-On monthly gravity field solutions starting from June 2018 up to degree and order 96 computed with the Celestial Mechanics Approach at AIUB. The time series is a loose continuation of AIUB-RL02 GRACE monthly gravity field time series using Level-1B GRACE Follow-On data and operational accelerometer transplant data from IfG (Institute of Geodesy, TU Graz, Working Group Theoretical Geodesy and Satellite Geodesy) and updated background models. The dataset is created within the framework of the G3P project (https://www.g3p.eu/), this project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 870353.
    Keywords: Gravity Recovery And Climate Experiment Follow-On (GRACE-FO) ; Level-2 ; SHM ; Spherical Harmonic Model ; Gravitational Field ; Geopotential ; Gravity Field ; Time variable Gravity Field ; Satellite Geodesy ; EARTH SCIENCE 〉 SOLID EARTH 〉 GRAVITY/GRAVITATIONAL FIELD ; EARTH SCIENCE 〉 SOLID EARTH 〉 GRAVITY/GRAVITATIONAL FIELD 〉 GRAVITY
    Type: Dataset , Dataset
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    DATA GFZ
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