Combined monthly GRACE-FO gravity fields for a Global Gravity-based Groundwater Product

verfasst von: U. Meyer, M. Lasser, C. Dahle, C. Förste, S. Behzadpour, I. Koch, A. Jäggi
Abstract: The Combination Service for Time-variable Gravity fields (COST-G) operationally provides combinations of monthly Earth gravity field models derived from observations of the microwave ranging instrument of the GRACE Follow-on (GRACE-FO) satellite mission, applying the quality control and combination methodology originally developed by the Horizon 2020 project European Gravity Service for Improved Emergency Management for the data of the GRACE satellites. In the frame of the follow-up Horizon 2020 project Global Gravity-based Groundwater Product (G3P), the GRACE-FO combination is used to derive global grids of groundwater storage anomalies. To meet the user requirements and achieve optimal signal-to-noise ratio, the combination has been further developed and extended to incorporate: • new time-series based on the alternative accelerometer transplant product generated in the frame of the project by the Institute of Geodesy at the Graz University of Technology, which specifically improves the estimation of the C₃₀ coefficient and also reduces the noise at medium to short wavelengths, and • the new time-series AIUB–GRACE-FO–RL02 of monthly GRACE-FO gravity fields, which is derived at the Astronomical Institute of the University of Bern by applying empirical noise modelling techniques. The COST-G quality control confirms the consistency of the contributing GRACE-FO time-series concerning the signal amplitude of seasonal hydrology in large river basins and the secular mass change in polar regions, but it also indicates rather diverse noise characteristics. The difference in the noise levels is taken into account in the combination process by relative weights derived by variance component estimation on the solution level. The weights are expected to be inverse proportional to the noise levels of the individual gravity field solutions. However, this expectation is violated when applying the weighting scheme as developed for the GRACE combination. The reason is found in the high-order coefficients of the gravity field, which are poorly determined from the low–low range-rate observations due to the observation geometry and suffer from aliasing due to the malfunctioning accelerometer onboard one of the GRACE-FO satellites. Hence, for the final G3P-combination a revised weighting scheme is applied where the gravity field coefficients beyond order 60 are excluded from the determination of the weights. The quality of the combined gravity fields is assessed by comparison of the noise content and the signal-to-noise ratio with the individual time-series. Independent validation is provided by the COST-G validation centre at the GFZ German Research Centre for Geosciences, where orbit fits of the low-flying Gravity and steady-state Ocean Circulation Explorer satellite are performed that confirm the high quality of the combined GRACE-FO gravity fields.
Organisationseinheit(en): Institut für Erdmessung
Externe Organisation(en): University of Bern
Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum
Universität Graz
Technische Universität Graz
Typ: Artikel
Journal: Geophysical journal international
Band: 236
Seiten: 456-469
Anzahl der Seiten: 14
ISSN: 0956-540X
Publikationsdatum: 01.01.2024
Publikationsstatus: Veröffentlicht
Peer-reviewed: Ja
ASJC Scopus Sachgebiete: Geophysik, Geochemie und Petrologie
Elektronische Version(en): https://doi.org/10.48350/193577 (Zugang: Offen)
https://doi.org/10.1093/gji/ggad437 (Zugang: Offen)
: Details im Forschungsportal „Research@Leibniz University“

BibTeX

@article{a560f291ab0749dca81a5cd4c4e85d05,
title = "Combined monthly GRACE-FO gravity fields for a Global Gravity-based Groundwater Product",
abstract = "The Combination Service for Time-variable Gravity fields (COST-G) operationally provides combinations of monthly Earth gravity field models derived from observations of the microwave ranging instrument of the GRACE Follow-on (GRACE-FO) satellite mission, applying the quality control and combination methodology originally developed by the Horizon 2020 project European Gravity Service for Improved Emergency Management for the data of the GRACE satellites. In the frame of the follow-up Horizon 2020 project Global Gravity-based Groundwater Product (G3P), the GRACE-FO combination is used to derive global grids of groundwater storage anomalies. To meet the user requirements and achieve optimal signal-to-noise ratio, the combination has been further developed and extended to incorporate: • new time-series based on the alternative accelerometer transplant product generated in the frame of the project by the Institute of Geodesy at the Graz University of Technology, which specifically improves the estimation of the C30 coefficient and also reduces the noise at medium to short wavelengths, and • the new time-series AIUB–GRACE-FO–RL02 of monthly GRACE-FO gravity fields, which is derived at the Astronomical Institute of the University of Bern by applying empirical noise modelling techniques. The COST-G quality control confirms the consistency of the contributing GRACE-FO time-series concerning the signal amplitude of seasonal hydrology in large river basins and the secular mass change in polar regions, but it also indicates rather diverse noise characteristics. The difference in the noise levels is taken into account in the combination process by relative weights derived by variance component estimation on the solution level. The weights are expected to be inverse proportional to the noise levels of the individual gravity field solutions. However, this expectation is violated when applying the weighting scheme as developed for the GRACE combination. The reason is found in the high-order coefficients of the gravity field, which are poorly determined from the low–low range-rate observations due to the observation geometry and suffer from aliasing due to the malfunctioning accelerometer onboard one of the GRACE-FO satellites. Hence, for the final G3P-combination a revised weighting scheme is applied where the gravity field coefficients beyond order 60 are excluded from the determination of the weights. The quality of the combined gravity fields is assessed by comparison of the noise content and the signal-to-noise ratio with the individual time-series. Independent validation is provided by the COST-G validation centre at the GFZ German Research Centre for Geosciences, where orbit fits of the low-flying Gravity and steady-state Ocean Circulation Explorer satellite are performed that confirm the high quality of the combined GRACE-FO gravity fields.",
author = "U. Meyer and M. Lasser and C. Dahle and C. F{\"o}rste and S. Behzadpour and I. Koch and A. J{\"a}ggi",
note = "Funding Information: This project has received funding from the European Union{\textquoteright}s Horizon 2020 research and innovation programme under grant agreement no. 870353. The views expressed herein can in no way be taken to reflect the official opinion of the European Union. The research was also supported by the International Space Science Institute (ISSI) in Bern, through ISSI International Team project 424 (International Combination Service for Time-variable Gravity Field Solutions). UM performed the quality control, combinations and internal validation of the combined time-series and compiled the manuscript; SB provided the G3P-ACT; ML, CD and IK provided specific time-series for the experiments on the G3P-ACT; CF performed the GOCE orbits tests and provided Section and AJ provided supervision of the project. The authors are not aware of any competing interests. ",
year = "2024",
month = jan,
day = "1",
doi = "10.48350/193577",
language = "English",
volume = "236",
pages = "456--469",
journal = "Geophysical journal international",
issn = "0956-540X",
publisher = "Oxford University Press",
number = "1",
}