3.3.1. Locations File
The locations file is used to predict synthetic field data (forward modeling) using h3dtd_v2.exe. This file defines the number of transmitters, transmitter geometry and the observation locations. Along with the time gates file, this defines all necessary survey information.
Note
Bolded entries are fixed flags recognized by the Fortran codes and blue hyperlinked entries are values/regular expressions specified by the user
3.3.1.1. Standard TEM Data
This is used to model the Cartesian components of the fields (E, H and dB/dt). The lines of the survey file in this case are formatted as follows:
Fig. 3.4 Example survey file with various types of transmitters.
3.3.1.2. TEM SAM Data
This is used to model the Sub-audio magnetic (SAM) data. The lines of the survey file in this case are formatted as follows:
3.3.1.3. 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 modeling SAM data. Note that z is +ve downward and therefore vz is positive if the field is going into the Earth
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.
Locations Array: Contains the X (Easting), Y (Northing), Z (elevation) locations for all receivers associated with a particular transmitter. The TEM response will be predicted at all times defined in the time gates file . Thus for a single given transmitter, the locations array is organized as follows:
3.3.1.4. Defining Transmitters
There are two types of transmitters that TDoctree survey files can use
3.3.1.4.1. Circular loop transmitter
This is an inductive source. The circular loop transmitter is defined using two lines:
- where
TRX_LOOP is a flag that must be entered
\(x\) is the Easting, \(y\) is the Northing and \(z\) is the elevation location of the center of the loop
\(R\) is the radius of the loop
\(\theta\) is the azimuthal angle in degrees. A horizontal loop is defined by \(\theta = 0\)
\(\alpha\) is the clockwise angle from northing in degrees
3.3.1.4.2. Custom inductive source
Here, we define the inductive source using a set of wire segments. When defining this type of transmitter, you must close the loop. The block defining this transmitter is given by:
- where
TRX_LINES is a flag that must be entered
\(N\) is the number of nodes (# segments - 1)
\(x_i, \; y_i \; z_i\) are Easting, Northing and elevation locations for the nodes
3.3.1.4.3. Custom galvanic source
Galvanic sources are also defined using a set of wire segments with TRX_LINES ; except here we do not close the wire path. The block defining this transmitter is given by:
- where
TRX_LINES is a flag that must be entered
\(N\) is the number of nodes (# segments - 1)
\(x_i, \; y_i \; z_i\) are Easting, Northing and elevation locations for the nodes