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Earth Geoid

The geoid is the equipotential surface of the Earth’s gravity potential that coincides with mean sea level. It’s often represented by “geoid heights”, which indicate the height of the geoid relative to the reference ellipsoid (WGS84 in this case). Negative values indicate that the geoid is below the ellipsoid surface and positive values that it is above. The data are on a regular grid with 0.5 degree spacing and was generated from the spherical harmonic model EIGEN-6C4 [Forste_etal2014].

Out:

<xarray.Dataset>
Dimensions:    (latitude: 361, longitude: 721)
Coordinates:
  * longitude  (longitude) float64 -180.0 -179.5 -179.0 ... 179.0 179.5 180.0
  * latitude   (latitude) float64 -90.0 -89.5 -89.0 -88.5 ... 89.0 89.5 90.0
Data variables:
    geoid      (latitude, longitude) float64 -29.5 -29.5 -29.5 ... 15.37 15.37
Attributes: (12/37)
    generating_institute:  gfz-potsdam
    generating_date:       2018/12/13
    product_type:          gravity_field
    body:                  earth
    modelname:             EIGEN-6C4
    max_used_degree:       1277
    ...                    ...
    maxvalue:              8.4722744E+01 meter
    minvalue:              -1.0625734E+02 meter
    signal_wrms:           3.0584191E+01 meter
    grid_format:           long_lat_value
    attributes:            longitude latitude geoid
    attributes_units:      deg. deg. meter

import cartopy.crs as ccrs
import matplotlib.pyplot as plt

import harmonica as hm

# Load the geoid grid
data = hm.datasets.fetch_geoid_earth()
print(data)

# Make a plot of data using Cartopy
plt.figure(figsize=(10, 10))
ax = plt.axes(projection=ccrs.Orthographic(central_longitude=100))
pc = data.geoid.plot.pcolormesh(ax=ax, transform=ccrs.PlateCarree(), add_colorbar=False)
plt.colorbar(
    pc, label="meters", orientation="horizontal", aspect=50, pad=0.01, shrink=0.6
)
ax.set_title("Geoid heights (EIGEN-6C4)")
ax.coastlines()
plt.show()