Rock-Water-Ice topographic-isostatic gravity field model

In the framework of the REAL GOCE project, a high-resolution spherical harmonic representation of the Earth's topographic-isostatic gravitational potential has been derived at the Geodetic Institute of the Karlsruhe Institute of Technology (KIT). The so-called Rock-Water-Ice model (RWI model) is based on a three-layer decomposition of the topography with variable density
values and a modified Airy-Heiskanen concept incorporating seismic Moho depths.

Overview:

 

Release 2012:

  • RWI_TOPO_2012: Spherical harmonic representation of the Earth's topographic gravitational potential (N=1800)
  • RWI_ISOS_2012: Spherical harmonic representation of the Earth's isostatic gravitational potential (N=1800)
  • RWI_TOIS_2012: Spherical harmonic representation of the Earth's topographic-isostatic gravitational potential (N=1800)

 

 Vzz gravity gradient component of RWI_TOIS_2012 at the satellite altitude of GOCE

RWI model

 

Main features:

  • Three-layer decomposition of the topography using the 5′×5′ topographic database DTM2006.0 (Pavlis et al. 2007)
  • Rigorous separate modeling of rock, water, and ice masses with layer-specific density values
    • Rock: 2670 kg m-3, Water: 1000 kg m-3, Ice: 920 kg m-3
  • Avoidance of geometry changes compared to classical condensation methods (e.g. rock-equivalent heights)
  • Ellipsoidal arrangement of the topography using the GRS80 ellipsoid as height reference surface
  • Adapted and modified Airy-Heiskanen isostatic concept
  • Incorporation of seismic Moho depths derived from the CRUST2.0 model (Bassin et al. 2000)
  • Location-dependent estimation of the crust–mantle density contrast

 Further details are provided in Grombein et al. (2014).

Processing:

  • Forward modelling in the space domain using tesseroid mass bodies (Grombein et al. 2013)
  • Transformation of global gridded values to the frequency domain by applying harmonic analysis up to degree and order 1800

 

Model versions and download at ICGEM (DOI: 10.5880/ICGEM.2014.001):

  • Spherical harmonic coefficients of the RWI 2012 models are provided by three versions
    (GM = 3.986004415e+14 m3 s-2, a = 6378136.3 m):
     
    Topographic potential RWI_TOPO_2012 Download
    Isostatic potential RWI_ISOS_2012 Download
    Topographic-isostatic potential RWI_TOIS_2012 Download

  • To allow the evaluation of the RWI 2012 models by synthesis software that by default subtracts the coefficients of a normal gravity field, three additional versions are available:
     
    Topographic potential + GRS80 RWI_TOPO_2012_plusGRS80 Download
    Isostatic potential + GRS80 RWI_ISOS_2012_plusGRS80 Download
    Topographic-isostatic potential + GRS80 RWI_TOIS_2012_plusGRS80 Download

    where the zonal harmonic coefficients of the GRS80 normal gravity field are added to the coefficients of the RWI model


  • Please acknowledge the use of the RWI 2012 models by citing Grombein et al. (2014)

 

Release 2015:

  • RWI_TOPO_2015: Updated spherical harmonic representation of the Earth's topographic gravitational potential (N=2190)
  • REQ_TOPO_2015: Consistent rock-equivalent version using condensed DTM-heights (N=2190)

 

 

Main features:

  • Three-layer decomposition of the topography using the new 1′×1′ Earth2014 topography model (Hirt and Rexer 2015)
  • Rigorous separate modeling of rock, water, and ice masses with layer-specific density values
    • Rock: 2670 kg m-3, Water: 1030 kg m-3 (Ocean), 1000 kg m-3 (Inland)    , Ice: 917 kg m-3
  • Ellipsoidal arrangement of the topography using the GRS80 ellipsoid + geoid undulations as height reference surface
  • Additional compilation of a consistent rock-equivalent version REQ_TOPO_2015, in which DTM-heights of water and ice masses are condensed to the constant rock density 2670 kg m-3

Further details are provided in Grombein et al. (2016).

 

Processing:

  • Forward modelling in the space domain using tesseroid mass bodies (Grombein et al. 2013)
  • Transformation of global gridded values to the frequency domain by applying harmonic analysis up to degree and order 2190

 

Model versions and download at ICGEM (DOI: 10.5880/ICGEM.2015.001):

  • Spherical harmonic coefficients of the RWI 2015 models are provided by two versions
    (GM = 3.986004415e+14 m3 s-2, a = 6378136.3 m):
     
    Topographic potential RWI_TOPO_2015 Download
    Topographic potential
    (using rock-equivalent heights)    		 REQ_TOPO_2015 Download

  • To allow the evaluation of the RWI 2015 models by synthesis software that by default subtracts the coefficients of a normal gravity field, two additional versions are available:
     
    Topographic potential + GRS80 RWI_TOPO_2015_plusGRS80 Download
    Topographic potential + GRS80
    (using rock-equivalent heights)    		 REQ_TOPO_2015_plusGRS80 Download

    where the zonal harmonic coefficients of the GRS80 normal gravity field are added to the coefficients of the RWI model


  • Please acknowledge the use of the RWI 2015 models by citing Grombein et al. (2016)

 

References:

  • Bassin, C.; Laske, G.; Masters, G. (2000): The current limits of resolution for surface wave tomography in North America. EOS Trans AGU, 81. F897

  • Grombein, T.; Seitz, K.; Heck, B. (2013): Optimized formulas for the gravitational field of a tesseroid. Journal of Geodesy 87(7):645–660, DOI: 10.1007/s00190-013-0636-1

  • Grombein, T.; Luo, X.; Seitz, K.; Heck, B. (2014): A wavelet-based assessment of topographic-isostatic reductions for GOCE gravity gradients. Surveys in Geophysics 35(4):959–982, DOI: 10.1007/s10712-014-9283-1

  • Grombein, T.; Seitz, K.; Heck, B. (2016): The Rock-Water-Ice topographic gravity field model RWI_TOPO_2015 and its comparison to a conventional rock-equivalent version. Surveys in Geophysics 37(5):937–976, DOI: 10.1007/s10712-016-9376-0

  • Hirt, C.; Rexer, M. (2015): Earth2014: 1 arc-min shape, topography, bedrock and ice-sheet models – Available as gridded data and degree-10,800 spherical harmonics. International Journal of Applied Earth Observation and Geoinformation 39:103–112, DOI: 10.1016/j.jag.2015.03.001

  • Pavlis, N.K.; Factor, J.K.; Holmes, S.A. (2007): Terrain-related gravimetric quantities computed for the next EGM. Proc. 1st Int. Symposium IGFS: Gravity Field of the Earth, Special Issue 18, 318–323.

 

Contact:

Dr.-Ing. Thomas Grombein

 

Acknowledgement:

This research was funded by the German Federal Ministry of Education and Research under grant number 03G0726F within the REAL GOCE project of the GEOTECHNOLOGIEN Programme.