Earth gravity grid at 10 arc-minute resolution

The grid is grid-node registered and stored in netCDF with CF-compliant metadata. The gravity values are derived from the EIGEN-6C4 spherical harmonic model. Here “gravity” refers to the combined gravitational and centrifugal accelerations.

The data are calculated uniformly at 10 km above the WGS84 ellipsoid.

Original source: EIGEN-6C4 model

Pre-processing: Source code for preparation of the original dataset for redistribution in Ensaio

import pygmt
import xarray as xr

import ensaio

Download and cache the data and return the path to it on disk.

fname = ensaio.fetch_earth_gravity(version=1)
print(fname)

/home/runner/work/_temp/cache/ensaio/v1/earth-gravity-10arcmin.nc

Load the netCDF grid with xarray.

data = xr.load_dataarray(fname)
data

<xarray.DataArray 'gravity' (latitude: 1081, longitude: 2161)>
array([[980106.5 , 980106.5 , 980106.5 , ..., 980106.5 , 980106.5 ,
        980106.5 ],
       [980108.25, 980108.25, 980108.25, ..., 980108.25, 980108.25,
        980108.25],
       [980108.8 , 980108.8 , 980108.8 , ..., 980108.75, 980108.75,
        980108.8 ],
       ...,
       [980153.8 , 980153.75, 980153.6 , ..., 980153.94, 980153.8 ,
        980153.8 ],
       [980160.44, 980160.44, 980160.44, ..., 980160.44, 980160.44,
        980160.44],
       [980157.5 , 980157.5 , 980157.5 , ..., 980157.5 , 980157.5 ,
        980157.5 ]], dtype=float32)
Coordinates:
  * longitude  (longitude) float64 -180.0 -179.8 -179.7 ... 179.7 179.8 180.0
  * latitude   (latitude) float64 -90.0 -89.83 -89.67 -89.5 ... 89.67 89.83 90.0
    height     (latitude, longitude) float32 1e+04 1e+04 1e+04 ... 1e+04 1e+04
Attributes:
    Conventions:     CF-1.8
    title:           Gravity acceleration (EIGEN-6C4) at a constant geometric...
    crs:             WGS84
    source:          Generated from the EIGEN-6C4 model by the ICGEM Calculat...
    license:         Creative Commons Attribution 4.0 International Licence
    references:      https://doi.org/10.5880/icgem.2015.1
    long_name:       gravity acceleration
    description:     magnitude of the gravity acceleration vector (gravitatio...
    units:           mGal
    actual_range:    [974748.6 980201.9]
    icgem_metadata:  generating_institute: gfz-potsdam\ngenerating_date: 2021...

xarray.DataArray

'gravity'

• latitude: 1081
• longitude: 2161

• 9.801e+05 9.801e+05 9.801e+05 ... 9.802e+05 9.802e+05 9.802e+05

  array([[980106.5 , 980106.5 , 980106.5 , ..., 980106.5 , 980106.5 ,
          980106.5 ],
         [980108.25, 980108.25, 980108.25, ..., 980108.25, 980108.25,
          980108.25],
         [980108.8 , 980108.8 , 980108.8 , ..., 980108.75, 980108.75,
          980108.8 ],
         ...,
         [980153.8 , 980153.75, 980153.6 , ..., 980153.94, 980153.8 ,
          980153.8 ],
         [980160.44, 980160.44, 980160.44, ..., 980160.44, 980160.44,
          980160.44],
         [980157.5 , 980157.5 , 980157.5 , ..., 980157.5 , 980157.5 ,
          980157.5 ]], dtype=float32)

• Coordinates: (3)
  • longitude
    (longitude)
    float64
    -180.0 -179.8 ... 179.8 180.0

    long_name :

    longitude

    standard_name :

    longitude

    units :

    degrees_east

    actual_range :

    [-180. 180.]

    array([-180.      , -179.833333, -179.666667, ...,  179.666667,  179.833333,
            180.      ])

  • latitude
    (latitude)
    float64
    -90.0 -89.83 -89.67 ... 89.83 90.0

    long_name :

    latitude

    standard_name :

    latitude

    units :

    degrees_north

    actual_range :

    [-90. 90.]

    array([-90.      , -89.833333, -89.666667, ...,  89.666667,  89.833333,
            90.      ])

  • height
    (latitude, longitude)
    float32
    1e+04 1e+04 1e+04 ... 1e+04 1e+04

    long_name :

    geometric height

    standard_name :

    height_above_reference_ellipsoid

    description :

    height of gravity computation points above the WGS84 ellipsoid

    units :

    m

    actual_range :

    [10000. 10000.]

    array([[10000., 10000., 10000., ..., 10000., 10000., 10000.],
           [10000., 10000., 10000., ..., 10000., 10000., 10000.],
           [10000., 10000., 10000., ..., 10000., 10000., 10000.],
           ...,
           [10000., 10000., 10000., ..., 10000., 10000., 10000.],
           [10000., 10000., 10000., ..., 10000., 10000., 10000.],
           [10000., 10000., 10000., ..., 10000., 10000., 10000.]],
          dtype=float32)

• Indexes: (2)
  • longitude
    PandasIndex

    PandasIndex(Index([             -180.0, -179.83333333333334, -179.66666666666666,
                        -179.5, -179.33333333333334, -179.16666666666666,
                        -179.0, -178.83333333333334, -178.66666666666666,
                        -178.5,
           ...
                         178.5,  178.66666666666663,  178.83333333333331,
                         179.0,  179.16666666666663,  179.33333333333331,
                         179.5,  179.66666666666663,  179.83333333333331,
                         180.0],
          dtype='float64', name='longitude', length=2161))

  • latitude
    PandasIndex

    PandasIndex(Index([             -90.0, -89.83333333333333, -89.66666666666667,
                        -89.5, -89.33333333333333, -89.16666666666667,
                        -89.0, -88.83333333333333, -88.66666666666667,
                        -88.5,
           ...
                         88.5,  88.66666666666666,  88.83333333333331,
                         89.0,  89.16666666666666,  89.33333333333331,
                         89.5,  89.66666666666666,  89.83333333333331,
                         90.0],
          dtype='float64', name='latitude', length=1081))

• Attributes: (11)

  Conventions :

  CF-1.8

  title :

  Gravity acceleration (EIGEN-6C4) at a constant geometric height

  crs :

  WGS84

  source :

  Generated from the EIGEN-6C4 model by the ICGEM Calculation Service (http://icgem.gfz-potsdam.de)

  license :

  Creative Commons Attribution 4.0 International Licence

  references :

  https://doi.org/10.5880/icgem.2015.1

  long_name :

  gravity acceleration

  description :

  magnitude of the gravity acceleration vector (gravitational + centrifugal)

  units :

  mGal

  actual_range :

  [974748.6 980201.9]

  icgem_metadata :

  generating_institute: gfz-potsdam generating_date: 2021/06/11 product_type: gravity_field body: earth modelname: EIGEN-6C4 max_used_degree: 720 gentlecut: 540 to 720 tide_system: tide_free functional: gravity_ell (centrifugal term included) unit: mgal refsysname: WGS84 gmrefpot: 3.98600441800E+14 m**3/s**2 radiusrefpot: 6378137.000 m flatrefpot: 3.352810664747480E-03 (1/298.25722356300) omegarefpot: 7.29211500000E-05 1/s long_lat_unit: degree latlimit_north: 90.000000000000 latlimit_south: -90.000000000000 longlimit_west: -180.00000000000 longlimit_east: 180.00000000000 gridstep: 0.16666666666667 height_over_ell: 10000.0000 m latitude_parallels: 1081 longitude_parallels: 2161 number_of_gridpoints: 2336041 gapvalue: 9999999.0000 weighted_mean: 9.7667904E+05 mgal maxvalue: 9.8020189E+05 mgal minvalue: 9.7474860E+05 mgal signal_wrms: 1.5468191E+03 mgal grid_format: long_lat_value attributes: longitude latitude gravity_ell attributes_units: deg. deg. mgal

Make a PyGMT pseudo-color map of the grid in a Mollweide projection.

fig = pygmt.Figure()
fig.basemap(
    region="g",
    projection="W15c",
    frame=True,
)
fig.grdimage(data, cmap="viridis", shading="+nt0.5")
fig.colorbar(frame='af+l"gravity [mGal]"')
fig.coast(shorelines=True, resolution="c", area_thresh=1e4)
fig.show()