Time-variable gravity fields and ocean mass change from 37 months of kinematic Swarm orbits
Measuring the spatiotemporal variation of ocean mass allows for partitioning of volumetric sea level change, sampled by radar altimeters, into mass-driven and steric parts. The latter is related to ocean heat change and the current Earth's energy imbalance. Since 2002, the Gravity Recovery a...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2018-03-01
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| Series: | Solid Earth |
| Online Access: | https://www.solid-earth.net/9/323/2018/se-9-323-2018.pdf |
| _version_ | 1811216362266165248 |
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| author | C. Lück J. Kusche R. Rietbroek A. Löcher |
| author_facet | C. Lück J. Kusche R. Rietbroek A. Löcher |
| author_sort | C. Lück |
| collection | DOAJ |
| description | Measuring the spatiotemporal variation of ocean mass allows for partitioning
of volumetric sea level change, sampled by radar altimeters, into mass-driven
and steric parts. The latter is related to ocean heat change and the
current Earth's energy imbalance. Since 2002, the Gravity Recovery and Climate
Experiment (GRACE) mission has provided monthly snapshots of the Earth's
time-variable gravity field, from which one can derive ocean mass
variability. However, GRACE has reached the end of its lifetime with data
degradation and several gaps occurred during the last years, and there will
be a prolonged gap until the launch of the follow-on mission GRACE-FO.
Therefore, efforts focus on generating a long and consistent ocean mass time
series by analyzing kinematic orbits from other low-flying satellites, i.e.
extending the GRACE time series.
<br><br>
Here we utilize data from the European Space Agency's (ESA) Swarm Earth
Explorer satellites to derive and investigate ocean mass variations. For this
aim, we use the integral equation approach with short arcs
(Mayer-Gürr, 2006) to compute more than 500 time-variable gravity fields
with different parameterizations from kinematic orbits. We investigate the
potential to bridge the gap between the GRACE and the GRACE-FO mission and to
substitute missing monthly solutions with Swarm results of significantly
lower resolution. Our monthly Swarm solutions have a root mean square error
(RMSE) of 4.0 mm with respect to GRACE, whereas directly estimating
constant, trend, annual, and semiannual (CTAS) signal terms leads to an RMSE
of only 1.7 mm. Concerning monthly gaps, our CTAS Swarm solution
appears better than interpolating existing GRACE data in 13.5 % of
all cases, when artificially removing one solution. In the case of an 18-month
artificial gap, 80.0 % of all CTAS Swarm solutions were found closer
to the observed GRACE data compared to interpolated GRACE data. Furthermore,
we show that precise modeling of non-gravitational forces acting on the
Swarm satellites is the key for reaching these accuracies. Our results have
implications for sea level budget studies, but they may also guide further
research in gravity field analysis schemes, including satellites not
dedicated to gravity field studies. |
| first_indexed | 2024-04-12T06:37:48Z |
| format | Article |
| id | doaj.art-3725228fac30444fa66022ad848f0204 |
| institution | Directory Open Access Journal |
| issn | 1869-9510 1869-9529 |
| language | English |
| last_indexed | 2024-04-12T06:37:48Z |
| publishDate | 2018-03-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Solid Earth |
| spelling | doaj.art-3725228fac30444fa66022ad848f02042022-12-22T03:43:48ZengCopernicus PublicationsSolid Earth1869-95101869-95292018-03-01932333910.5194/se-9-323-2018Time-variable gravity fields and ocean mass change from 37 months of kinematic Swarm orbitsC. Lück0J. Kusche1R. Rietbroek2A. Löcher3Institute of Geodesy and Geoinformation, University of Bonn, Bonn, GermanyInstitute of Geodesy and Geoinformation, University of Bonn, Bonn, GermanyInstitute of Geodesy and Geoinformation, University of Bonn, Bonn, GermanyInstitute of Geodesy and Geoinformation, University of Bonn, Bonn, GermanyMeasuring the spatiotemporal variation of ocean mass allows for partitioning of volumetric sea level change, sampled by radar altimeters, into mass-driven and steric parts. The latter is related to ocean heat change and the current Earth's energy imbalance. Since 2002, the Gravity Recovery and Climate Experiment (GRACE) mission has provided monthly snapshots of the Earth's time-variable gravity field, from which one can derive ocean mass variability. However, GRACE has reached the end of its lifetime with data degradation and several gaps occurred during the last years, and there will be a prolonged gap until the launch of the follow-on mission GRACE-FO. Therefore, efforts focus on generating a long and consistent ocean mass time series by analyzing kinematic orbits from other low-flying satellites, i.e. extending the GRACE time series. <br><br> Here we utilize data from the European Space Agency's (ESA) Swarm Earth Explorer satellites to derive and investigate ocean mass variations. For this aim, we use the integral equation approach with short arcs (Mayer-Gürr, 2006) to compute more than 500 time-variable gravity fields with different parameterizations from kinematic orbits. We investigate the potential to bridge the gap between the GRACE and the GRACE-FO mission and to substitute missing monthly solutions with Swarm results of significantly lower resolution. Our monthly Swarm solutions have a root mean square error (RMSE) of 4.0 mm with respect to GRACE, whereas directly estimating constant, trend, annual, and semiannual (CTAS) signal terms leads to an RMSE of only 1.7 mm. Concerning monthly gaps, our CTAS Swarm solution appears better than interpolating existing GRACE data in 13.5 % of all cases, when artificially removing one solution. In the case of an 18-month artificial gap, 80.0 % of all CTAS Swarm solutions were found closer to the observed GRACE data compared to interpolated GRACE data. Furthermore, we show that precise modeling of non-gravitational forces acting on the Swarm satellites is the key for reaching these accuracies. Our results have implications for sea level budget studies, but they may also guide further research in gravity field analysis schemes, including satellites not dedicated to gravity field studies.https://www.solid-earth.net/9/323/2018/se-9-323-2018.pdf |
| spellingShingle | C. Lück J. Kusche R. Rietbroek A. Löcher Time-variable gravity fields and ocean mass change from 37 months of kinematic Swarm orbits Solid Earth |
| title | Time-variable gravity fields and ocean mass change from 37 months of kinematic Swarm orbits |
| title_full | Time-variable gravity fields and ocean mass change from 37 months of kinematic Swarm orbits |
| title_fullStr | Time-variable gravity fields and ocean mass change from 37 months of kinematic Swarm orbits |
| title_full_unstemmed | Time-variable gravity fields and ocean mass change from 37 months of kinematic Swarm orbits |
| title_short | Time-variable gravity fields and ocean mass change from 37 months of kinematic Swarm orbits |
| title_sort | time variable gravity fields and ocean mass change from 37 months of kinematic swarm orbits |
| url | https://www.solid-earth.net/9/323/2018/se-9-323-2018.pdf |
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