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Discussion papers
https://doi.org/10.5194/essd-2019-158
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/essd-2019-158
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: data description paper 01 Oct 2019

Submitted as: data description paper | 01 Oct 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Earth System Science Data (ESSD).

Multi-approach gravity field models from Swarm GPS data

João Teixeira Encarnaco1,2, Pieter Visser1, Daniel Arnold3, Ales Bezdek4, Eelco Doornbos5, Matthias Ellmer6, Junyi Guo8, Jose van den IJssel1, Elisabetta Iorfida1, Adrian Jaggi3, Jaroslav Klokocnik4, Sandro Krauss7, Xinyuan Mao3, Torsten Mayer-Gurr7, Ulrich Meyer3, Josef Sebera4, C. K. Shum8,9, Chaoyang Zhang8, and Yu Zhang8 João Teixeira Encarnaco et al.
  • 1Delft University of Technology, Faculty of Aerospace Engineering, Kluyverweg 1, 2629 HS, Delft, the Netherlands
  • 2Center for Space Research, The University of Texas at Austin, 3925 West Braker Lane, Suite 200 Austin, Texas, USA
  • 3Astronomical Institute of the University of Bern, Sidlerstrasse 5, 3012 Bern, Switzerland
  • 4Astronomical Institute of the Czech Academy of Sciences, Friˇcova 298, 251 65 Ondˇrejov, Czech Republic
  • 5Royal Netherlands Meteorological Institute, Utrechtseweg 297, 3731 GA De Bilt, the Netherlands
  • 6Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
  • 7Institute of Geodesy of the Graz University of Technology, Steyergasse 30/III, 8010 Graz, Austria
  • 8School of Earth Sciences of The Ohio State University, 125 Oval Dr S, Columbus, OH 43210, USA
  • 9Institute of Geodesy and Geophysics, Chinese Academy of Sciences, Wuhan, China

Abstract. Although the knowledge of the gravity of the Earth has improved considerably with CHAMP, GRACE and GOCE satellite missions, the geophysical community has identified the need for the continued monitoring of the time-variable component with the purpose of estimating the hydrological and glaciological yearly cycles and long-term trends. Currently, the GRACE-FO satellites are the sole dedicated provider of these data, while previously the GRACE mission fulfilled that role for 15 years. There is a data gap spanning from July 2017 to May 2018 between the end of the GRACE mission and start the of GRACE-FO, while the Swarm satellites have collected gravimetric data with their GPS receivers since December 2013.

We present high-quality gravity field models from Swarm data that constitute an alternative and independent source of gravimetric data, which could help alleviate the consequences of the 10-month gap between GRACE and GRACE-FO, as well as the short gaps in the existing GRACE and GRACE-FO monthly time series. The geodetic community has realized that the combination of different gravity field solutions is superior to any individual model and set up a Combination Service of Time-variable Gravity Fields (COST-G) under the umbrella of the International Gravity Field Service (IGFS), part of the International Association of Geodesy (IAG).

We exploit this fact and deliver to the highest quality monthly-independent gravity field models, resulting from the combination of four different gravity field estimation approaches.

All solutions are unconstrained and estimated independently from month to month. We tested the added value of including Kinematic Baselines (KBs) in our estimation of Gravity Field Models (GFMs) and conclude that there is no significant improvement.

The non-gravitational accelerations measured by the accelerometer on-board Swarm-C were also included in our processing to determine if this would improve the quality of the GFMs, but observed that is only the case when the amplitude of the non-gravitational accelerations is higher than during the current quiet period in solar activity.

Using GRACE data for comparison, we demonstrate that the geophysical signal in the Swarm gravity field models is largely restricted to Spherical Harmonic degrees below 12.

A 750 km smoothing radius is suitable to retrieve the temporal variations of Earth’s gravity field over land areas since mid-2015 with roughly 4 cm Equivalent Water Height (EWH) agreement with respect to a GRACE-derived parametric model. Over ocean areas, we illustrate that a more intense smoothing with 3000 km radius is necessary to resolve large scale gravity variations, which agree with the aforementioned parametric model under 2 cm EWH, while at these spatial scales the model represents variations with amplitudes between 2 and 3.5 cm EWH.

The agreement with GRACE and GRACE-FO over nine selected large basins under analyses is 1.19 cm, 0.60 cm/year and 0.75 in terms of temporal mean, trend and correlation coefficient, respectively.

João Teixeira Encarnaco et al.
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João Teixeira Encarnaco et al.
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Multi-approach Gravity Field Models from Swarm GPS data J. Encarnacao, P. Visser, A. Jaeggi, A. Bezdek, T. Mayer-Gürr, C. K. Shum, D. Arnold, E. Doornbos, M. Elmer, J. Guo, J. van den IJssel, E. Iorfida, J. Klokocnik, S. Krauss, X. Mao, U. Meyer, J. Sebera, C. Zhang, and Y. Zhang https://doi.org/10.5880/ICGEM.2019.006

João Teixeira Encarnaco et al.
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