3.3.4. Observations File
The observations contains the set of field measurements used in the inversion. This file contains all necessary survey information including: the number of transmitters, transmitter geometry, observation locations, frequencies, observed fields and uncertainties.
Note
Bolded entries are fixed flags recognized by the Fortran codes and blue hyperlinked entries are values/regular expressions specified by the user
3.3.4.1. Standard TEM Data
Here we describe the observed data file when inverting Cartesian components of the fields (E, H and dB/dt). The lines the observations file are formatted as follows:
3.3.4.2. TEM SAM Data
Here we describe the observed data file when inverting SAM data. The lines the observations file are formatted as follows:
3.3.4.3. Parameter Descriptions
vx vy vz: The x, y and z components of the unit vector defining the direction of the Earth’s magnetic field. This line is only used when inverting SAM data. Note that z is +ve downward and therefore vz is positive if the field is going into the Earth.
reg_exp: A regular expression denoting which data are ignored during the inversion; examples include -9999 and NaN
n_trx: The total number of unique transmitters. Example: N_TRX 3
n_recv: The number of receivers collecting field observations for a particular transmitter.
n_time: The number of time channels for each receiver
Data Array: Contains the X (Easting), Y (Northing), Z (elevation) locations, time channels, data and uncertainties for all receivers for a particular transmitter. Depending on whether you are inverting standard TEM data or SAM data, the structure of the data array will be different; see standard TEM data array or SAM data array.
3.3.4.4. Defining Transmitters
There are two types of transmitters that H3DTD v2 survey files can use. These were defined in the survey file section.
3.3.4.5. Data Arrays
3.3.4.5.1. Standard TEM Data
Contains the X (Easting), Y (Northing), Z (elevation) locations and time channels for all receivers for a particular transmitter. It has has n_recv \(\times\) n_time rows and 22 columns. The time-locations array is organized as follows:
such that \(E \; data\) is in units V/m and is comprised of 6 columns:
\(H \; data\) is in units A/m and is comprised of 6 columns:
and \(dB/dt \; data\) is in units T/s and is comprised of 6 columns:
Important
The data are represented in a left-handed coordinate system where X is Easting, Y is Northing and Z is +ve downward.
The vertical component of dB/dt is represented using \(\mathbf{-dB_z/dt}\) !!! This is done due to a common plotting convention. The associated uncertainties are still positive values however!
3.3.4.5.2. TEM SAM Data
Contains the X (Easting), Y (Northing), Z (elevation) locations and time channels for all receivers for a particular transmitter. It has has n_recv \(\times\) n_time rows and 6 columns. The time-locations array is organized as follows:
where \(H_a\) is a placeholder for a SAM datum and \(Unc\) is a placeholder for its uncertainty. For H3DTD v2, SAM data is the projection of the anomalous magnetic field intensity (H-field) onto the direction of the Earth’s magnetic field.