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Signals of Mass Redistribution at the South African Gravimeter Site SAGOS

  • C. KronerEmail author
  • S. Werth
  • H. Pflug
  • A. Güntner
  • B. Creutzfeldt
  • M. Thomas
  • H. Dobslaw
  • P. Fourie
  • P. H. Charles
Conference paper
Part of the International Association of Geodesy Symposia book series (IAG SYMPOSIA, volume 136)

Abstract

The superconducting gravimeter (SG) operating at the South African Geodynamic Observatory Sutherland (SAGOS) is one of the few instruments installed in the southern hemisphere and presently still the only one of its kind on the African continent. SAGOS is located in the Karoo, a semi-arid area with an average annual precipitation of 200–400 mm. The distance to the ocean is approx. 220 km.

A local hydrology-related seasonal effect on gravity is clearly seen in the SG record. Its general order of magnitude is estimated to be about 4–10 nm/s2. A large-scale hydrological influence in a similar order of magnitude or even larger (up to 60 nm/s2 peak-to-peak) is inferred from global hydrological models for the years 2003–2007. Significant contributions are found for the southern coast, the central Cape region, and the basin of the Orange river. Contributing basins with larger distance comprise the areas of Okavango/Sambesi, Congo, and eastern Africa. Between SG data, temporal GRACE gravity field solutions, and the gravity effect derived from global hydrological models clear differences exist. Among others, the deviations between the hydrological models can be traced to deviations in the gravity effect originating from the Okavango basin and the central Cape region.

Gravity residuals reduced for changes in continental water storage are compared to the gravity effect caused by non-tidal oceanic mass changes. A rudimentary correlation between observed variations and modeled effect is found.

The peak-to-peak amplitude of the modeled effects amounts to 15 nm/s2 for the years 2001–2008. After reducing the SG data for this oceanic effect the variation of the residuals decreases by 9%.

The present findings indicate the suitability of the SG observations at Sutherland for studies on mass transport phenomena in the South African region.

Keywords

Gravity Change Gravity Residual Superconducting Gravimeter Global Land Data Assimilation System Soil Moisture Variation 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Notes

Acknowledgements

We thank P. Döll, the GGFC Special Bureau for Hydrology, and NOAA for providing data of the global hydrological models used in this study. The provision of the weekly GRACE gravity field and MASCON solutions by GFZ-ISDC and NASA is gratefully acknowledged. Our thanks also go to two anonymous reviewers for their support.

References

  1. Chen X-D, Kroner C, Sun H-P, Abe M, Zhou J, Yan H, Wziontek H (2009) Determination of gravimetric parameters of the gravity pole tide using observations recorded with superconducting gravimeters. J Geodyn 48(3–5):348–353CrossRefGoogle Scholar
  2. Crossley D, Hinderer J, Boy J-P (2005) Time variation of the European gravity field from superconducting gravimeters. Geophys J Int 161(2):257–264CrossRefGoogle Scholar
  3. Dobslaw H, Thomas M (2007) Simulation and observation of global ocean mass anomalies. J Geophys Res 112:C05040CrossRefGoogle Scholar
  4. Döll P, Kaspar F, Lehner B (2003) A global hydrological model for deriving water availability indicators: model tuning and validation. J Hydrol 270:105–134CrossRefGoogle Scholar
  5. Dziewonski AM, Anderson DL (1981) Preliminary reference earth model (PREM). Phys Earth Planet Int 25(4):297–367CrossRefGoogle Scholar
  6. Essler KJ, Milton SJ, Dean WRJ (2006) Karoo Veld – ecology and management. BRIZA Publications, Pretoria, 214Google Scholar
  7. Farrell WE (1972) Deformation of the earth by surface loads. Rev Geophys 10:761–797CrossRefGoogle Scholar
  8. Francis O, Dehant V (1987) Recomputation of the Green’s functions for tidal loading estimations. Bulletin d’Information des Marées Terrestres 100:6962–6986Google Scholar
  9. Güntner A, Stuck J, Werth S, Döll P, Verzano K, Merz B (2007) A global analysis of temporal and spatial variations in continental water storage. Water Resour Res 43(5):W05416CrossRefGoogle Scholar
  10. Hinderer J, Andersen O, Lemoine F, Crossley D, Boy JP (2006) Seasonal changes in the European gravity field from GRACE: A comparison with superconducting gravimeters and hydrology model predictions. J Geodyn 41(1–3):59–68CrossRefGoogle Scholar
  11. Kroner C, Thomas M, Dobslaw H, Abe M, Weise A (2009) Seasonal effects of non-tidal oceanic mass shifts in observations with superconducting gravimeters. J Geodyn 48(3–5):354–359CrossRefGoogle Scholar
  12. Neumeyer J, Barthelmes F, Kroner C, Petrovic S, Schmidt R, Virtanen H, Wilmes H (2008) Analysis of gravity field variations derived from superconducting gravimeter recordings, GRACE satellite and hydrological models at selected European sites. Earth, Planets Space 60:1–14Google Scholar
  13. Rodell M, Houser PR, Jambor U, Gottschalck J, Mitchell K, Meng C-M, Arsenault K, Cosgrove B, Radakovich J, Bosilovich M, Entin JK, Walker JP, Lohmann P, Toll D (2004) The global land data assimilation system. Bull Am Meteorol Soc 85(3):381–394CrossRefGoogle Scholar
  14. Weise A, Kroner C, Abe M, Ihde J, Jentzsch G, Naujoks M, Wilmes H, Wziontek H (2009) Terrestrial gravity observations with superconducting gravimeters for validation of satellite-derived (GRACE) gravity variations. J Geodyn 48(3–5):325–330CrossRefGoogle Scholar

Copyright information

© Springer-Verlag Berlin Heidelberg 2012

Authors and Affiliations

  • C. Kroner
    • 1
    Email author
  • S. Werth
    • 2
  • H. Pflug
    • 3
  • A. Güntner
    • 3
  • B. Creutzfeldt
    • 3
  • M. Thomas
    • 3
  • H. Dobslaw
    • 3
  • P. Fourie
    • 4
  • P. H. Charles
    • 4
  1. 1.Physikalisch-Technische Bundesanstalt BraunschweigBraunschweigGermany
  2. 2.Institute of Earth and Environmental ScienceUniversity of PotsdamPotsdam-GolmGermany
  3. 3.Helmholtz Centre Potsdam GFZ German Research Centre for GeosciencesPotsdamGermany
  4. 4.South African Astronomical ObservatoryObservatorySouth Africa

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