pygmt.datasets.load_earth_magnetic_anomaly

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

Load the Earth magnetic anomaly datasets in various resolutions.

Earth Magnetic Anomaly Model (EMAG2)	World Digital Magnetic Anomaly Map (WDMAM)

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 processing function or plotting method. 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 the grid registration type (p for pixel registration or g for gridline registration).

The default color palette tables (CPTs) for this dataset are @earth_mag.cpt for data_source="emag2" and data_source="emag2_4km", and @earth_wdmam.cpt for data_source="wdmam". The dataset-specific CPT is implicitly used when passing in the file name of the dataset to any grid plotting method if no CPT is explicitly specified. When the dataset is loaded and plotted as an xarray.DataArray object, the default CPT is ignored, and GMT’s default CPT (turbo) is used. To use the dataset-specific CPT, you need to explicitly set cmap="@earth_mag.cpt" or cmap="@earth_wdmam.cpt".

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 about available datasets, including version information and references.

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". The "02m" resolution is not available for data_source="wdmam".

• 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 (Literal['gridline', 'pixel', None], default: None) – Grid registration type. Either "pixel" for pixel registration or "gridline" for gridline registration. Default is None, means "gridline" for all resolutions except "02m" for data_source="emag2" or data_source="emag2_4km", which are "pixel" only.

• data_source (Literal['emag2', 'emag2_4km', 'wdmam'], default: 'emag2') –

  Select the source of the magnetic anomaly data. Available options are:

  • "emag2": EMAG2 Earth Magnetic Anomaly Model. It only includes data observed at 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 Tesla (nT).

Note

The registration and coordinate system type of the returned xarray.DataArray grid can be accessed via the GMT accessors (i.e., grid.gmt.registration and grid.gmt.gtype respectively). However, these properties may be lost after specific grid operations (such as slicing) and will need to be manually set before passing the grid to any PyGMT data processing or plotting functions. Refer to pygmt.GMTDataArrayAccessor for detailed explanations and workarounds.

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"
... )