Magnetic anomaly grid of the Lightning Creek Sill Complex, Australia

This is a section of an airborne survey acquired in 1990 by the Queensland Government, Australia. The grid has 50 m resolution (UTM coordinates) and is at a uniform orthometric height of 500 m.

Original source: Geophysical Acquisition & Processing Section 2019. MIM Data from Mt Isa Inlier, QLD (P1029), magnetic line data, AWAGS levelled. Geoscience Australia, Canberra

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_lightning_creek_magnetic(version=1)
print(fname)

/home/runner/work/_temp/cache/ensaio/v1/lightning-creek-magnetic-grid.nc

Load the netCDF grid with xarray

data = xr.load_dataarray(fname)
data

<xarray.DataArray 'total_field_anomaly' (northing: 370, easting: 346)> Size: 1MB
array([[  34.99995117,   36.19995117,   36.69995117, ..., -101.10004883,
        -100.40004883,  -99.60004883],
       [  36.49995117,   37.59995117,   37.99995117, ..., -102.20004883,
        -101.50004883, -100.70004883],
       [  37.09995117,   38.19995117,   38.59995117, ..., -103.30004883,
        -102.60004883, -101.90004883],
       ...,
       [ 182.79995117,  172.39995117,  160.79995117, ...,    0.79995117,
         -24.20004883,  -41.80004883],
       [ 182.09995117,  172.59995117,  161.39995117, ...,    5.99995117,
         -21.50004883,  -41.00004883],
       [ 178.79995117,  170.39995117,  160.29995117, ...,   11.39995117,
         -16.00004883,  -35.80004883]])
Coordinates:
  * easting   (easting) float64 3kB 4.655e+05 4.656e+05 ... 4.827e+05 4.828e+05
  * northing  (northing) float64 3kB 7.576e+06 7.576e+06 ... 7.595e+06 7.595e+06
    height    (northing, easting) float64 1MB 500.0 500.0 500.0 ... 500.0 500.0
Attributes:
    Conventions:   CF-1.8
    title:         Magnetic total-field anomaly of the Lightning Creek sill c...
    crs:           proj=utm zone=54 south datum=WGS84 units=m no_defs ellps=W...
    source:        Interpolated from airborne magnetic line data using gradie...
    license:       Creative Commons Attribution 4.0 International Licence
    references:    Geophysical Acquisition & Processing Section 2019. MIM Dat...
    long_name:     total-field magnetic anomaly
    units:         nT
    actual_range:  [-1785.  3798.]

xarray.DataArray

'total_field_anomaly'

• northing: 370
• easting: 346

• 35.0 36.2 36.7 36.6 36.3 35.6 ... 113.1 78.6 43.7 11.4 -16.0 -35.8

  array([[  34.99995117,   36.19995117,   36.69995117, ..., -101.10004883,
          -100.40004883,  -99.60004883],
         [  36.49995117,   37.59995117,   37.99995117, ..., -102.20004883,
          -101.50004883, -100.70004883],
         [  37.09995117,   38.19995117,   38.59995117, ..., -103.30004883,
          -102.60004883, -101.90004883],
         ...,
         [ 182.79995117,  172.39995117,  160.79995117, ...,    0.79995117,
           -24.20004883,  -41.80004883],
         [ 182.09995117,  172.59995117,  161.39995117, ...,    5.99995117,
           -21.50004883,  -41.00004883],
         [ 178.79995117,  170.39995117,  160.29995117, ...,   11.39995117,
           -16.00004883,  -35.80004883]])

• Coordinates: (3)
  • easting
    (easting)
    float64
    4.655e+05 4.656e+05 ... 4.828e+05

    long_name :

    UTM easting

    standard_name :

    projection_x_coordinate

    units :

    m

    actual_range :

    [465533.31767977 482783.31767977]

    array([465533.31768, 465583.31768, 465633.31768, ..., 482683.31768,
           482733.31768, 482783.31768])

  • northing
    (northing)
    float64
    7.576e+06 7.576e+06 ... 7.595e+06

    long_name :

    UTM northing

    standard_name :

    projection_y_coordinate

    units :

    m

    actual_range :

    [7576368.82029097 7594818.82029097]

    array([7576368.820291, 7576418.820291, 7576468.820291, ..., 7594718.820291,
           7594768.820291, 7594818.820291])

  • height
    (northing, easting)
    float64
    500.0 500.0 500.0 ... 500.0 500.0

    long_name :

    orthometric height

    standard_name :

    height_above_geopotential_datum

    units :

    m

    actual_range :

    [500. 500.]

    array([[500., 500., 500., ..., 500., 500., 500.],
           [500., 500., 500., ..., 500., 500., 500.],
           [500., 500., 500., ..., 500., 500., 500.],
           ...,
           [500., 500., 500., ..., 500., 500., 500.],
           [500., 500., 500., ..., 500., 500., 500.],
           [500., 500., 500., ..., 500., 500., 500.]])

• Indexes: (2)
  • easting
    PandasIndex

    PandasIndex(Index([465533.31767976715, 465583.31767976715, 465633.31767976715,
           465683.31767976715, 465733.31767976715, 465783.31767976715,
           465833.31767976715, 465883.31767976715, 465933.31767976715,
           465983.31767976715,
           ...
           482333.31767976715, 482383.31767976715, 482433.31767976715,
           482483.31767976715, 482533.31767976715, 482583.31767976715,
           482633.31767976715, 482683.31767976715, 482733.31767976715,
           482783.31767976715],
          dtype='float64', name='easting', length=346))

  • northing
    PandasIndex

    PandasIndex(Index([7576368.82029097, 7576418.82029097, 7576468.82029097, 7576518.82029097,
           7576568.82029097, 7576618.82029097, 7576668.82029097, 7576718.82029097,
           7576768.82029097, 7576818.82029097,
           ...
           7594368.82029097, 7594418.82029097, 7594468.82029097, 7594518.82029097,
           7594568.82029097, 7594618.82029097, 7594668.82029097, 7594718.82029097,
           7594768.82029097, 7594818.82029097],
          dtype='float64', name='northing', length=370))

• Attributes: (9)

  Conventions :

  CF-1.8

  title :

  Magnetic total-field anomaly of the Lightning Creek sill complex, Australia

  crs :

  proj=utm zone=54 south datum=WGS84 units=m no_defs ellps=WGS84 towgs84=0,0,0

  source :

  Interpolated from airborne magnetic line data using gradient-boosted equivalent sources

  license :

  Creative Commons Attribution 4.0 International Licence

  references :

  Geophysical Acquisition & Processing Section 2019. MIM Data from Mt Isa Inlier, QLD (P1029), magnetic line data, AWAGS levelled. Geoscience Australia, Canberra. http://pid.geoscience.gov.au/dataset/ga/142419

  long_name :

  total-field magnetic anomaly

  units :

  nT

  actual_range :

  [-1785. 3798.]

Make a PyGMT pseudo-color map of the total field magnetic anomaly.

fig = pygmt.Figure()
scale = 2500
pygmt.makecpt(cmap="polar+h", series=[-scale, scale], background=True)
fig.grdimage(
    grid=data,
    cmap=True,
    shading="+a45+nt0.1",
    projection="X15c/17c",
    frame="af",
)
fig.colorbar(
    frame='af+l"total field magnetic anomaly [nT]"',
    position="JBC+h+o0/1c+e",
)
fig.show()

The anomaly at the top right is the Lightning Creek sill complex.