pygmt.datasets.load_earth_magnetic_anomaly

pygmt.datasets.load_earth_magnetic_anomaly(resolution='01d', region=None, registration=None, data_source='emag2')

Load an Earth magnetic anomaly grid in various resolutions.

The grids are downloaded to a user data directory (usually ~/.gmt/server/earth/earth_mag/, ~/.gmt/server/earth/earth_mag4km/, or ~/.gmt/server/earth/earth_wdmam/) the first time you invoke this function. Afterwards, it will load the grid from the data directory. So you’ll need an internet connection the first time around.

These grids can also be accessed by passing in the file name @earth_mag_type_res[_reg] to any grid plotting/processing function. earth_mag_type is the GMT name for the dataset. The available options are earth_mag, earth_mag4km, and earth_wdmam. res is the grid resolution (see below), and reg is grid registration type (p for pixel registration or g for gridline registration).

Refer to https://www.generic-mapping-tools.org/remote-datasets/earth-mag.html and https://www.generic-mapping-tools.org/remote-datasets/earth-wdmam.html for more details.

Parameters

• resolution (str) – The grid resolution. The suffix d and m stand for arc-degrees and arc-minutes. It can be "01d", "30m", "20m", "15m", "10m", "06m", "05m", "04m", "03m", or "02m".

• region (str or list) – The subregion of the grid to load, in the form of a list [xmin, xmax, ymin, ymax] or a string xmin/xmax/ymin/ymax. Required for grids with resolutions higher than 5 arc-minutes (i.e., "05m").

• registration (str) – Grid registration type. Either "pixel" for pixel registration or "gridline" for gridline registration. Default is "gridline" for all resolutions except "02m" which is "pixel" only.

• data_source (str) –

  Select the source of the magnetic anomaly data.

  Available options:

  • emag2 : EMAG2 Global Earth Magnetic Anomaly Model [Default option]. Only includes data is observed from sea level over oceanic regions. See https://www.generic-mapping-tools.org/remote-datasets/earth-mag.html.

  • emag2_4km : Use a version of EMAG2 where all observations are relative to an altitude of 4 km above the geoid and include data over land.

  • wdmam : World Digital Magnetic Anomaly Map (WDMAM). See https://www.generic-mapping-tools.org/remote-datasets/earth-wdmam.html

Returns

grid (xarray.DataArray) – The Earth magnetic anomaly grid. Coordinates are latitude and longitude in degrees. Units are in nano Teslas (nT).

Note

The xarray.DataArray grid doesn’t support slice operation, for Earth magnetic anomaly with resolutions of 5 arc-minutes or higher, which are stored as smaller tiles.

Examples

>>> from pygmt.datasets import load_earth_magnetic_anomaly
>>> # load the default grid (gridline-registered 1 arc-degree grid)
>>> grid = load_earth_magnetic_anomaly()
>>> # load the 30 arc-minutes grid with "gridline" registration
>>> grid = load_earth_magnetic_anomaly(
...     resolution="30m", registration="gridline"
... )
>>> # load high-resolution (5 arc-minutes) grid for a specific region
>>> grid = load_earth_magnetic_anomaly(
...     resolution="05m",
...     region=[120, 160, 30, 60],
...     registration="gridline",
... )
>>> # load the 20 arc-minutes grid of the emag2_4km dataset
>>> grid = load_earth_magnetic_anomaly(
...     resolution="20m", registration="gridline", data_source="emag2_4km"
... )
>>> # load the 20 arc-minutes grid of the WDMAM dataset
>>> grid = load_earth_magnetic_anomaly(
...     resolution="20m", registration="gridline", data_source="wdmam"
... )