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Curtin University

GGMplus 200m-resolution maps
of Earth's gravity field

A showcase of unprecedented
GGMplus resolution:
Gravity over the Himalayas
Himalayas
2 km resolution. Click for larger image
Himalayas
1 km resolution. Click for larger image
Himalayas
500 m resolution.
Click for larger image
Himalayas
200 m resolution.
Mount Everest in the centre.
Click for larger image

General

Watch GGMplus video      Go to image gallery      Go to download area

GGMplus (Global Gravity Model plus, cf. Hirt et al. 2013) provides maps and data of Earth’s gravity at 200 m resolution for all land and near-coastal areas of our planet between +- 60o latitude. Past gravity field modelling efforts either placed focus on global coverage with limited resolution or on representation of local detail over regionally limited areas. GGMplus is the first model of Earth’s gravity field to reach local resolution with near-global coverage, thus uniting both foci.

GGMplus describes the Earth’s gravity field in terms of frequently used functionals (i) gravity accelerations, (ii) gravity disturbances, (iii) North-South and East-West deflections of the vertical, and (iv) quasigeoid heights at 3,062,677,383 points at 7.2 arc-sec spatial resolution.

GGMplus data coverage
GGMplus data coverage. Click for larger image

GGMplus is constructed as a composite of GRACE and GOCE satellite gravity, EGM2008 and short-scale topographic gravity effects. The model was developed using advanced computing resources and evaluation methods, which reduced the equivalent of about 80 years of standard CPU time to less than 2 months processing time to create GGMplus. GGMplus is a joint gravity field initiative of Curtin University and Technical University Munich (TUM, Germany), endorsed by Commission 2 of the International Association of Geodesy, and supported by the Australian Research Council, TUM’s Institute of Advanced Study and the Western Australian iVEC supercomputing facility.

Watch the GGMplus making-of video and explore gravity over different parts of Earth.

African Continent
GGMplus gravity over Africa.
Click for larger image
South American Continent
GGMplus gravity over South America.
Click for larger image

Construction

GGMplus is a composite gravity field model that is based on GRACE and GOCE information (providing the spatial scales of 10000 down to ~100 km), EGM2008 (scales of 100 km to ~10 km) and topographic gravity effects from RTM-forward-modelling (~10 km to ~250 m). In particular, GGMplus incorporates

  • 7 years of GRACE satellite data (ITG2010s by University of Bonn, Mayer-Guerr et al. 2010)
  • 2 years of GOCE satellite data (4th-generation TIM-4 release by European Space Agency, Pail et al. 2011),
  • The EGM2008 global gravity model (by US National Geospatial Intelligence Agency, Pavlis et al. 2012)
  • 7.5 arc-sec SRTM topography data (V4.1 release, Jarvis et al. 2008)
  • 30 arc-sec SRTM30_PLUS bathymetry data (V7.0 release, Becker et al. 2009) over near-coastal areas.

GRACE/GOCE and EGM2008 were combined and evaluated at the Earth’s topography in spectral band 2 to 2190 using the gradient approach to fifth-order (Hirt 2012). SRTM topography and SRTM30_PLUS bathymetry were high-pass filtered and used as data source for forward-modelling of short-scale gravity effects using a variant of the RTM approach (Hirt 2013). The conversion of high-pass-filtered topography/bathymetry to gravity effects required brute-force numerical prism integration of gravity-effects (Forsberg 1984). This task was accomplished through massive parallelisation and use of advanced computational resources of the iVEC supercomputing facility.

For further information on the construction of GGMplus, see Hirt et al., 2013.

What’s available?
Gravity
Gravity
Gravity
Gravity
Gravity
The panels show the five GGMplus
gravity functionals provided
over the Mount Everest area.

Data access and software

Data access

The GGMplus gravity field model is freely available from our FTP-Server. Due to its total size of 75 GB, the model is partitioned and distributed in 881 binary files of 5 deg x 5 deg size for each functional (gravity accelerations, gravity disturbances). A list of all tiles can be accessed here

Format description

Each 5 deg x 5 deg tile contains 2500x2500 grid points in centre-of-cell representation. The grid resolution is 0.002 deg (7.2 arc seconds) with the grid equally spaced in terms of geodetic (GRS80) latitude and longitude.

Depending on the functional, data is stored either in 2-byte integer big-endian format (int16, ieee-be), or 4-byte big-endian format (int32, ieee-be). Vertical deflections (xi, eta) and gravity disturbances (dg) are in 2-byte format, quasigeoid heights and gravity accelerations in 4-byte format. The file sizes are 12,208 KB and 24,416 KB, respectively. The readme-document provides full details on the file formats.

Free software

Matlab scripts are available for seamless access and interpolation of the GGMplus functionals. Instructions on the use of these scripts is provided in the file headers.

Contact and Feedback

For further information or if you want to provide feedback please contact c.hirt@curtin.edu.au

Acknowledgement

This work is supported by the Australian Research Council (Grant DP120102441) and Western Australia’s iVEC supercomputing facility. All data providers are kindly acknowledged.

References

Becker et al. (2009) Global Bathymetry and Elevation Data at 30 Arc Seconds Resolution: SRTM30_PLUS. Marine Geodesy 32(4), 355-371.

Forsberg R (1984) A study of terrain reductions, density anomalies and geophysical inversion methods in gravity field modelling. Report 355, Department of Geodetic Science and Surveying, Ohio State University, Columbus.

Hirt C. (2012) Efficient and accurate high-degree spherical harmonic synthesis of gravity field functionals at the Earth's surface using the gradient approach. Journal of Geodesy 86(9), 729-744. [pdf]

Hirt C. (2013) RTM gravity forward-modeling using topography/bathymetry data to improve high-degree global geopotential models in the coastal zone, Marine Geodesy 36(2), 1-20. [pdf]

Hirt, C., S.J. Claessens, T. Fecher, M. Kuhn, R. Pail, M. Rexer (2013) New ultrahigh-resolution picture of Earth's gravity field, Geophysical Research Letters, Vol 40, doi: 10.1002/grl.50838 [pdf]

Jarvis A, Reuter HI, Nelson A Guevara E (2008) Hole-filled SRTM for the globe Version 4. Available from the CGIAR-SXI SRTM 90m database: http://srtm.csi.cgiar.org

Mayer-Gurr T, E Kurtenbach, A Eicker (2010) The ITG GRACE 2010 model,
http://www.igg.uni-bonn.de/apmg/index.php?id=itg-grace2010.

Pail, R. et al. (2011) First GOCE gravity field models derived by three different approaches, Journal of Geodesy 85(11), 819-843.

Pavlis, N.K., S.A. Holmes, S.C. Kenyon, and J.K. Factor (2012) The development and evaluation of the Earth Gravitational Model 2008 (EGM2008). Journal of Geophysical Research 117, B04406.

Disclaimer

Neither Curtin University nor any of its staff accept any liability in connection with the use of data and models provided here. Neither Curtin University nor any of its staff make any warranty of fitness, completeness, usefulness and accuracy of the data and models for any intended or unintended purpose.