EGM2008 Earth Geoid
Geodynamics studies have an interest in the Earth’s geoid. The US National Geospatial-Intelligence Agency’s Office of Geomatics provide spherical harmonics models for the geopotential. The latest EGM2008 [Pavlis et al., 2012] geoid model is now available for remote use in GMT.
Usage
You access a global geoid grid by specifying the special name
@earth_geoid[_rru[_reg]]
The following codes for rru and the optional reg are supported (dimensions are listed for pixel-registered grids; gridline-registered grids increment dimensions by one):
Code |
Dimensions |
Reg |
Size |
Description |
|---|---|---|---|---|
01d |
360 x 180 |
g,p |
98 KB |
1 arc degree global EGM2008 geoid (1 min @ 315 km) |
30m |
720 x 360 |
g,p |
320 KB |
30 arc minute global EGM2008 geoid (1 min @ 157 km) |
20m |
1080 x 540 |
g,p |
658 KB |
20 arc minute global EGM2008 geoid (1 min @ 105 km) |
15m |
1440 x 720 |
g,p |
1.1 MB |
15 arc minute global EGM2008 geoid (1 min @ 79 km) |
10m |
2160 x 1080 |
g,p |
2.3 MB |
10 arc minute global EGM2008 geoid (1 min @ 52 km) |
06m |
3600 x 1800 |
g,p |
5.9 MB |
6 arc minute global EGM2008 geoid (1 min @ 32 km) |
05m* |
4320 x 2160 |
g,p |
8.0 MB |
5 arc minute global EGM2008 geoid (1 min @ 26 km) |
04m* |
5400 x 2700 |
g,p |
11 MB |
4 arc minute global EGM2008 geoid (1 min @ 21 km) |
03m* |
7200 x 3600 |
g,p |
20 MB |
3 arc minute global EGM2008 geoid (1 min @ 16 km) |
02m* |
10800 x 5400 |
g,p |
34 MB |
2 arc minute global EGM2008 geoid (1 min @ 11 km) |
01m* |
21600 x 10800 |
g |
100 MB |
1 arc minute global EGM2008 geoid (1 min original) |
See GMT remote dataset usage for when resolution codes are optional or required.
All of these data will, when downloaded, be placed in your ~/.gmt/server directory, with
the earth_geoid files being placed in an earth/earth_geoid sub-directory. If you do not
specify a CPT, the default CPT for this dataset (the GMT master turbo CPT) will be used.
Technical Information
We scale and reformat the original data to take up very little space so that downloads from the servers are as fast as possible. For the geoid grid this means we chose 0.01 m as the smallest data unit, which is well below the uncertainties in the model. Data are scaled and shifted to fit in a short integer grid that is highly compressed by netCDF lossless compression and chunking. The data are reported in meters.
Data References
Pavlis, N.K., Holmes, S.A., Kenyon, S.C. and Factor, J.K., 2012: [https://doi.org/10.1029/2011JB008916].