3.3.1. Survey and Locations File¶
The survey and locations file is used to predict synthetic field data (forward modeling). This file contains all necessary survey information including: the number of transmitters, transmitter geometry, observation locations and frequencies.
Note
Bolded entries are fixed flags recognized by the Fortran codes and blue hyperlinked entries are values/regular expressions specified by the user
The lines of the survey file are formatted as follows:
Fig. 3.6 Example survey file with various types of transmitters.¶
3.3.1.1. Parameter Descriptions¶
n_trx: The total number of unique transmitter-frequency pairs. Example: N_TRX 3
n_nodes: The number of nodes defining a particular transmitter loop. Note that:
xi yi zi: This refers to the X (Easting), Y (Northing) and Z (elevation) locations of the nodes defining the transmitter loop. Transmitters are defined using a left-handed coordinate system. Which means you must define a horizontal transmitter loop in the clockwise direction for a dipole moment in the vertical direction.
fi: The frequency (in Hz) at which the subsequent set of measurements are made.
n_recv: The number of receivers collecting field observations at a particular frequency for a particular transmitter.
Loc Array: Contains the X (Easting), Y (Northing) and Z (elevation) locations for measurements at a particular frequency for a particular transmitter. It has dimensions n_recv \(\times\) 3.
3.3.1.2. Defining Transmitters¶
There are three types of transmitters that E3D survey files can use
3.3.1.2.1. 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
3.3.1.2.2. Large 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_ORIG is a flag that must be entered
\(N\) is the number of nodes (# segments = N-1)
\(x_i, \; y_i, \; z_i\) are Easting, Northing and elevation locations for the nodes
3.3.1.2.3. Arbitrary source¶
Using this transmitter type, we can define both inductive sources (by closing the loop) or grounded sources (by not closing 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 = N-1)
\(x_i, \; y_i, \; z_i\) are Easting, Northing and elevation locations for the nodes