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('34e3536f-58e1-4fcd-96bb-722c9195d1d3'),
  '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 0x7720ae04fb00>,
 <geoh5py.groups.property_group.PropertyGroup at 0x7720ff3aa720>,
 <geoh5py.groups.property_group.PropertyGroup at 0x7720ae0b23f0>,
 <geoh5py.groups.property_group.PropertyGroup at 0x7720ae0b2c90>,
 <geoh5py.groups.property_group.PropertyGroup at 0x7720ae0b3590>,
 <geoh5py.groups.property_group.PropertyGroup at 0x7720ae0b3e90>,
 <geoh5py.groups.property_group.PropertyGroup at 0x7720adf1c710>,
 <geoh5py.groups.property_group.PropertyGroup at 0x7720adf1d010>]

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('34e3536f-58e1-4fcd-96bb-722c9195d1d3'),
  '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 0x7720ae17c2f0>,
  <geoh5py.data.float_data.FloatData at 0x7720ae00e5a0>,
  <geoh5py.data.float_data.FloatData at 0x7720ed42e1b0>],
 'Zxx (imaginary)': [<geoh5py.data.float_data.FloatData at 0x7720ec1f7440>,
  <geoh5py.data.float_data.FloatData at 0x7720aef52960>,
  <geoh5py.data.float_data.FloatData at 0x7720ae17d070>],
 'Zxy (real)': [<geoh5py.data.float_data.FloatData at 0x7720af131b20>,
  <geoh5py.data.float_data.FloatData at 0x7720ae06e210>,
  <geoh5py.data.float_data.FloatData at 0x7720ae0b1760>],
 'Zxy (imaginary)': [<geoh5py.data.float_data.FloatData at 0x7720ae06f5f0>,
  <geoh5py.data.float_data.FloatData at 0x7720ae0b2a80>,
  <geoh5py.data.float_data.FloatData at 0x7720ae0b2b40>],
 'Zyx (real)': [<geoh5py.data.float_data.FloatData at 0x7720ae0b22a0>,
  <geoh5py.data.float_data.FloatData at 0x7720ae0b32f0>,
  <geoh5py.data.float_data.FloatData at 0x7720ae0b3440>],
 'Zyx (imaginary)': [<geoh5py.data.float_data.FloatData at 0x7720ae0b2b70>,
  <geoh5py.data.float_data.FloatData at 0x7720ae0b3bf0>,
  <geoh5py.data.float_data.FloatData at 0x7720ae0b3d40>],
 'Zyy (real)': [<geoh5py.data.float_data.FloatData at 0x7720ae0b3470>,
  <geoh5py.data.float_data.FloatData at 0x7720ae0b3ec0>,
  <geoh5py.data.float_data.FloatData at 0x7720adf1c5c0>],
 'Zyy (imaginary)': [<geoh5py.data.float_data.FloatData at 0x7720ae0b3b90>,
  <geoh5py.data.float_data.FloatData at 0x7720adf1ce00>,
  <geoh5py.data.float_data.FloatData at 0x7720adf1cec0>]}

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()