EGM2008 Global Earth Geoid

_images/GMT_geoid.jpg

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):

EGM2008 Global Earth Geoid. An asterisk denotes tiled datasets.

Code

Dimensions

Reg

Size

Description

01d

360 x 180

g,p

99 KB

1 arc degree global EGM2008 geoid (1 min @ 111 km)

30m

720 x 360

g,p

324 KB

30 arc minute global EGM2008 geoid (1 min @ 55 km)

20m

1080 x 540

g,p

664 KB

20 arc minute global EGM2008 geoid (1 min @ 37 km)

15m

1440 x 720

g,p

1.1 MB

15 arc minute global EGM2008 geoid (1 min @ 28 km)

10m

2160 x 1080

g,p

2.9 MB

10 arc minute global EGM2008 geoid (1 min @ 18 km)

06m

3600 x 1800

g,p

5.9 MB

6 arc minute global EGM2008 geoid (1 min @ 10 km)

05m*

4320 x 2160

g,p

8.1 MB

5 arc minute global EGM2008 geoid (1 min @ 9 km)

04m*

5400 x 2700

g,p

11 MB

4 arc minute global EGM2008 geoid (1 min @ 7.5 km)

03m*

7200 x 3600

g,p

20 MB

3 arc minute global EGM2008 geoid (1 min @ 5.6 km)

02m*

10800 x 5400

g,p

34 MB

2 arc minute global EGM2008 geoid (1 min @ 3.7 km)

01m*

21600 x 10800

p

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

  1. Pavlis, N.K., Holmes, S.A., Kenyon, S.C. and Factor, J.K., 2012: [https://doi.org/10.1029/2011JB008916].