Magnetotellurics

This object can be used to store magnetotelluric (MT) surveys - a natural-source geophysical method. Data are provided in the frequency-domain as point source measurements of either impedances or apparent resistity/phase.

The following example shows how to generate an MT survey with associated data stored in geoh5 format and accessible from Geoscience ANALYST.

from pathlib import Path

import numpy as np

from geoh5py.objects import MTReceivers
from geoh5py.workspace import Workspace


# Create a new project
h5file = Path("my_project.geoh5")
workspace = Workspace(h5file) if h5file.exists() else Workspace.create(h5file)

# Define a synthetic survey with receivers on 2 lines, 60 m apart
x_loc, y_loc = np.meshgrid(np.linspace(-5, 5, 2), np.linspace(0.0, 20.0, 9))
vertices = np.c_[x_loc.ravel(), y_loc.ravel(), np.zeros_like(x_loc).ravel()]

# Create the survey from vertices
mt_survey = MTReceivers.create(workspace, vertices=vertices)

Only receivers are needed to define the survey as MT uses the ambient electromagntic field of the Earth - no transmitters (source) required.

Metadata

Along with the geoh5py.objects.surveys.electromagnetics.magnetotellurics.MTReceivers, the metadata contains all the necessary information to define the geophysical experiment.

mt_survey.metadata

{'EM Dataset': {'Channels': [],
  'Input type': 'Rx only',
  'Property groups': [],
  'Receivers': UUID('ab8d83b1-8f79-4308-82e4-ab229838f71d'),
  'Survey type': 'Magnetotellurics',
  'Unit': 'Hertz (Hz)'}}

Channels

List of frequencies at which the data are provided.

mt_survey.channels = [1.0, 10.0, 100.0]

Input type

Generic label used in the geoh5 standard for all EM survey entities. Restricted to Rx only in the case of natural sources methods.

Property groups

List of module-geoh5py.groups.property_group.PropertyGroups defining the various data components (e.g. Zxx (real), Zxy (imag), …). It is not required to supply all components of the impedance tensor, but it is expected that each component contains a list of data channels of length and in the same order as the Channels (one Data per frequency).

The class method geoh5py.objects.surveys.electromagnetics.base.BaseEMSurvey.add_components_data() can help users add data from nested dictionaries. Below is an example using four components:

# Arbitrary data generator using sine functions
def data_fun(c, f):
    return (c + 1.0) * np.sin(f * np.pi * (x_loc * y_loc).ravel() / 200.0)


# Create a nested dictionary of component and frequency data.
data = {
    component: {
        f"{component}_{freq}": {
            "values": (ff + 1) * 1000.0
            + (cc + 1) * 100.0
            + np.arange(vertices.shape[0])
        }
        for ff, freq in enumerate(mt_survey.channels)
    }
    for cc, component in enumerate(
        [
            "Zxx (real)",
            "Zxx (imaginary)",
            "Zxy (real)",
            "Zxy (imaginary)",
            "Zyx (real)",
            "Zyx (imaginary)",
            "Zyy (real)",
            "Zyy (imaginary)",
        ]
    )
}

mt_survey.add_components_data(data)

[<geoh5py.groups.property_group.PropertyGroup at 0x793cacd72f30>,
 <geoh5py.groups.property_group.PropertyGroup at 0x793cacdd5940>,
 <geoh5py.groups.property_group.PropertyGroup at 0x793cacdd7020>,
 <geoh5py.groups.property_group.PropertyGroup at 0x793cacdd7920>,
 <geoh5py.groups.property_group.PropertyGroup at 0x793cacdd7f20>,
 <geoh5py.groups.property_group.PropertyGroup at 0x793cacc44ad0>,
 <geoh5py.groups.property_group.PropertyGroup at 0x793cacc45340>,
 <geoh5py.groups.property_group.PropertyGroup at 0x793cacc45bb0>]

Metadata are updated immediately to reflect the addition of components:

mt_survey.metadata

{'EM Dataset': {'Channels': [1.0, 10.0, 100.0],
  'Input type': 'Rx only',
  'Property groups': ['Zxx (real)',
   'Zxx (imaginary)',
   'Zxy (real)',
   'Zxy (imaginary)',
   'Zyx (real)',
   'Zyx (imaginary)',
   'Zyy (real)',
   'Zyy (imaginary)'],
  'Receivers': UUID('ab8d83b1-8f79-4308-82e4-ab229838f71d'),
  'Survey type': 'Magnetotellurics',
  'Unit': 'Hertz (Hz)'}}

Data channels associated with each component can be quickly accessed through the geoh5py.objects.surveys.electromagnetics.base.BaseEMSurvey.components property:

mt_survey.components

{'Zxx (real)': [<geoh5py.data.float_data.FloatData at 0x793cacd9b5c0>,
  <geoh5py.data.float_data.FloatData at 0x793cb858ffb0>,
  <geoh5py.data.float_data.FloatData at 0x793cacf0f170>],
 'Zxx (imaginary)': [<geoh5py.data.float_data.FloatData at 0x793cacd266c0>,
  <geoh5py.data.float_data.FloatData at 0x793cd85cec90>,
  <geoh5py.data.float_data.FloatData at 0x793cacdd57c0>],
 'Zxy (real)': [<geoh5py.data.float_data.FloatData at 0x793cacf6acc0>,
  <geoh5py.data.float_data.FloatData at 0x793cacdd6d50>,
  <geoh5py.data.float_data.FloatData at 0x793cacdd6240>],
 'Zxy (imaginary)': [<geoh5py.data.float_data.FloatData at 0x793cacdd57f0>,
  <geoh5py.data.float_data.FloatData at 0x793cacdd7680>,
  <geoh5py.data.float_data.FloatData at 0x793cacdd77d0>],
 'Zyx (real)': [<geoh5py.data.float_data.FloatData at 0x793cacdd6ed0>,
  <geoh5py.data.float_data.FloatData at 0x793cacdd7f80>,
  <geoh5py.data.float_data.FloatData at 0x793cacdd7fb0>],
 'Zyx (imaginary)': [<geoh5py.data.float_data.FloatData at 0x793cacdd7800>,
  <geoh5py.data.float_data.FloatData at 0x793cacc44860>,
  <geoh5py.data.float_data.FloatData at 0x793cacc44080>],
 'Zyy (real)': [<geoh5py.data.float_data.FloatData at 0x793cacc44050>,
  <geoh5py.data.float_data.FloatData at 0x793cacc450d0>,
  <geoh5py.data.float_data.FloatData at 0x793cacc45220>],
 'Zyy (imaginary)': [<geoh5py.data.float_data.FloatData at 0x793cacc448f0>,
  <geoh5py.data.float_data.FloatData at 0x793cacc45940>,
  <geoh5py.data.float_data.FloatData at 0x793cacc45a90>]}

Receivers

Generic label used in the geoh5 standard for EM survey to identify the receiver entity. Restricted to itself in the case of MTReceivers.

Survey type

Label identifier for Magnetotellurics survey type.

Unit

Units for frequency sampling of the data: Hertz (Hz), KiloHertz (kHz), MegaHertz (MHz) or Gigahertz (GHz).

workspace.close()