watex.view.TPlot.plotSkew#

TPlot.plotSkew(method='Bahr', view='skew', mode=None, threshold_line=None, show_average_sensistivity=True, suppress_outliers=True, **plot_kws)[source]#

Plot phase sensistive skew visualization

‘Skew’ is also knwown as the conventional asymmetry parameter based on the Z magnitude.

Mosly, the EM signal is influenced by several factors such as the dimensionality of the propagation medium and the physical anomalies, which can distort theEM field both locally and regionally. The distortion of Z was determined from the quantification of its asymmetry and the deviation from the conditions that define its dimensionality. The parameters used for this purpose are all rotational invariant because the Z components involved in its definition are independent of the orientation system used. The conventional asymmetry parameter based on the Z magnitude is the skew defined by Swift (1967) [1] and Bahr (1991) [2].

Parameters

  • method (str, default='Bahr':) –

    Kind of correction. Can be:

    • swift for the remove distorsion proposed by Swift in 1967. The value close to 0. assume the 1D and 2D structures, and 3D otherwise. However, In general case, the electrical structure of \(\eta < 0.4\) can be treated as a 2D medium.

    • bahr for the remove distorsion proposed by Bahr in 1991. The latter threshold is set to 0.3. Above this value the structures is 3D.

  • view (str, default='skew') – phase sensistive visualization. Can be rotational invariant invariant. In fact, setting to mu or invariant does not change any interpretation when since the distortion of Z are all rotational invariant whether using the Bahr or swift methods.

  • mode (str, optional) – X-axis coordinates for visualisation. plot either 'frequency' or 'periods'. The default is 'frequency'

  • threshold_line (float, optional) –

    Visualize th threshold line. Can be [‘bahr’, ‘swift’, ‘both’]:

    • Note that when method is set to swift, the value close to close to \(0.\) assume the 1D and 2D structures (\(\eta <0.4\)), and 3D otherwise( \(\eta >0.4\)). The threshold line for swift is set to \(0.4\).

    • when method is set to Bahr, \(\eta > 0.3\) is 3D structures, between \([0.1 - 0.3]\) assumes modified 3D/2D structures whereas \(<0.1\) 1D, 2D or distorted 2D.

  • show_average_sensistivity (bool, default=True) – Display the averaged value of skew data at all -frequencies. Value can help a dimensionality interpretation purposes.

  • suppress_outliers (bool, default=True) – Remove the outliers in the data if exists. It uses the Inter Quartile Range (IQR) approach. See the documentation of watex.utils.remove_outliers(). This is useful for clear interpretation using the skew threshold value.

See also

watex.methods.EMAP.skew

For mathematical skew Bahr and Swift concept formulations.

watex.utils.plot_skew

For phase sensistive skew visualization - naive plot.

Examples

>>> import watex
>>> test_data = watex.fetch_data ('edis', samples =37, return_data =True )
>>> watex.TPlot(fig_size =(10,  4), marker ='x').fit(
    test_data).plotSkew(method ='swift', threshold_line=True)

References

1

Swift, C., 1967. A magnetotelluric investigation of an electrical conductivity anomaly in the southwestern United States. Ph.D. Thesis, MIT Press. Cambridge.

2

Bahr, K., 1991. Geological noise in magnetotelluric data: a classification of distortion types. Physics of the Earth and Planetary Interiors 66 (1–2), 24–38.