Magnetotellurics

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.

mtSurvey

import numpy as np

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


# Create a new project
workspace = Workspace("my_project.geoh5")

# 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)

/home/docs/checkouts/readthedocs.org/user_builds/mirageoscience-geoh5py/conda/latest/lib/python3.10/site-packages/geoh5py/workspace/workspace.py:1107: UserWarning: From version 0.8.0, the 'h5file' attribute must be a string or path to an existing file, or user must call the 'create' method. We will attempt to `save` the file for you, but this behaviour will be removed in future releases.
  warnings.warn(

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 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('da016898-3def-4208-aa40-26ede065ffed'),
  '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 PropertyGroups defining the various data components (e.g. Zxx (real), Zxy (imag), …). It is not required to supply all components of the impedence 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 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 0x72ee6432e140>,
 <geoh5py.groups.property_group.PropertyGroup at 0x72ee5c1ace20>,
 <geoh5py.groups.property_group.PropertyGroup at 0x72ee5c1ae8f0>,
 <geoh5py.groups.property_group.PropertyGroup at 0x72ee5c1af160>,
 <geoh5py.groups.property_group.PropertyGroup at 0x72ee5c1aedd0>,
 <geoh5py.groups.property_group.PropertyGroup at 0x72ee5c1ad1e0>,
 <geoh5py.groups.property_group.PropertyGroup at 0x72ee5c1afd60>,
 <geoh5py.groups.property_group.PropertyGroup at 0x72ee5c0f85e0>]

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('da016898-3def-4208-aa40-26ede065ffed'),
  'Survey type': 'Magnetotellurics',
  'Unit': 'Hertz (Hz)'}}

Data channels associated with each component can be quickly accessed through the BaseEMSurvey.components property:

mt_survey.components

{'Zxx (real)': [<geoh5py.data.float_data.FloatData at 0x72ee6432e260>,
  <geoh5py.data.float_data.FloatData at 0x72ee6430f850>,
  <geoh5py.data.float_data.FloatData at 0x72ee6432eec0>],
 'Zxx (imaginary)': [<geoh5py.data.float_data.FloatData at 0x72ee6432e680>,
  <geoh5py.data.float_data.FloatData at 0x72ee5c1ae0e0>,
  <geoh5py.data.float_data.FloatData at 0x72ee5c1acbe0>],
 'Zxy (real)': [<geoh5py.data.float_data.FloatData at 0x72ee5c1acdc0>,
  <geoh5py.data.float_data.FloatData at 0x72ee5c1adc00>,
  <geoh5py.data.float_data.FloatData at 0x72ee5c1ae7d0>],
 'Zxy (imaginary)': [<geoh5py.data.float_data.FloatData at 0x72ee5c1acc10>,
  <geoh5py.data.float_data.FloatData at 0x72ee5c1aea10>,
  <geoh5py.data.float_data.FloatData at 0x72ee5c1af040>],
 'Zyx (real)': [<geoh5py.data.float_data.FloatData at 0x72ee5c1ae7a0>,
  <geoh5py.data.float_data.FloatData at 0x72ee5c1af2b0>,
  <geoh5py.data.float_data.FloatData at 0x72ee5c1aecb0>],
 'Zyx (imaginary)': [<geoh5py.data.float_data.FloatData at 0x72ee5c1af1c0>,
  <geoh5py.data.float_data.FloatData at 0x72ee5c1aea40>,
  <geoh5py.data.float_data.FloatData at 0x72ee5c1acac0>],
 'Zyy (real)': [<geoh5py.data.float_data.FloatData at 0x72ee5c1aec80>,
  <geoh5py.data.float_data.FloatData at 0x72ee5c1ae230>,
  <geoh5py.data.float_data.FloatData at 0x72ee5c1afc40>],
 'Zyy (imaginary)': [<geoh5py.data.float_data.FloatData at 0x72ee5c1aca30>,
  <geoh5py.data.float_data.FloatData at 0x72ee5c1afe80>,
  <geoh5py.data.float_data.FloatData at 0x72ee5c1afb80>]}

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()
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