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.
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:1104: 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('d34f457e-6f2a-43c4-9c66-99c906d818e6'),
'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 0x781362b61a20>,
<geoh5py.groups.property_group.PropertyGroup at 0x7813681191e0>,
<geoh5py.groups.property_group.PropertyGroup at 0x781368119330>,
<geoh5py.groups.property_group.PropertyGroup at 0x781354d83af0>,
<geoh5py.groups.property_group.PropertyGroup at 0x781354d836d0>,
<geoh5py.groups.property_group.PropertyGroup at 0x781354d83a30>,
<geoh5py.groups.property_group.PropertyGroup at 0x781354391450>,
<geoh5py.groups.property_group.PropertyGroup at 0x781354391c90>]
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('d34f457e-6f2a-43c4-9c66-99c906d818e6'),
'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 0x781354d823b0>,
<geoh5py.data.float_data.FloatData at 0x781368161270>,
<geoh5py.data.float_data.FloatData at 0x781368160d30>],
'Zxx (imaginary)': [<geoh5py.data.float_data.FloatData at 0x78136811a350>,
<geoh5py.data.float_data.FloatData at 0x78136811ac50>,
<geoh5py.data.float_data.FloatData at 0x781354d83370>],
'Zxy (real)': [<geoh5py.data.float_data.FloatData at 0x781354d81bd0>,
<geoh5py.data.float_data.FloatData at 0x781354d837f0>,
<geoh5py.data.float_data.FloatData at 0x781354d83820>],
'Zxy (imaginary)': [<geoh5py.data.float_data.FloatData at 0x781354d81690>,
<geoh5py.data.float_data.FloatData at 0x781354d83340>,
<geoh5py.data.float_data.FloatData at 0x781354d839d0>],
'Zyx (real)': [<geoh5py.data.float_data.FloatData at 0x781354d83dc0>,
<geoh5py.data.float_data.FloatData at 0x781354d83ac0>,
<geoh5py.data.float_data.FloatData at 0x781354390310>],
'Zyx (imaginary)': [<geoh5py.data.float_data.FloatData at 0x781354390610>,
<geoh5py.data.float_data.FloatData at 0x781354390a90>,
<geoh5py.data.float_data.FloatData at 0x781354390ac0>],
'Zyy (real)': [<geoh5py.data.float_data.FloatData at 0x781354390e50>,
<geoh5py.data.float_data.FloatData at 0x7813543903a0>,
<geoh5py.data.float_data.FloatData at 0x781354391330>],
'Zyy (imaginary)': [<geoh5py.data.float_data.FloatData at 0x781354391690>,
<geoh5py.data.float_data.FloatData at 0x781354390c40>,
<geoh5py.data.float_data.FloatData at 0x781354391b70>]}
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()