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:


N_TRX \(\;\) n_trx


DEFINE TRANSMITTER

N_RECV \(\;\) n_recv
N_TIME \(\;\) n_time
\(\;\;\) Loc-Time Array


DEFINE TRANSMITTER

N_RECV \(\;\) n_recv
N_TIME \(\;\) n_time
\(\;\;\) Loc-Time Array


\(\;\;\;\;\;\; \vdots\)


DEFINE TRANSMITTER

N_RECV \(\;\) n_recv
N_TIME \(\;\) n_time
\(\;\;\) Loc-Time Array

Repeat for number of unique transmitters


../../_images/files_locations.png

Fig. 3.5 Example survey file with various types of transmitters.

3.3.1.1. Parameter Descriptions

  • 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

  • Loc-Time Array: 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 4 columns. The time-locations array is organized as follows:


\(x_1 \;\; y_1 \;\; z_1 \;\; t_1\)
\(x_1 \;\; y_1 \;\; z_1 \;\; t_2\)
\(\; \vdots \;\;\;\;\, \vdots \;\;\;\;\, \vdots \;\;\;\;\, \vdots\)
\(x_1 \;\; y_1 \;\; z_1 \;\; t_{n}\)
\(x_2 \;\; y_2 \;\; z_2 \;\; t_1\)
\(x_2 \;\; y_2 \;\; z_2 \;\; t_2\)
\(\; \vdots \;\;\;\;\, \vdots \;\;\;\;\, \vdots \;\;\;\;\, \vdots\)
\(x_2 \;\; y_2 \;\; z_2 \;\; t_{n}\)
\(\; \vdots \;\;\;\;\, \vdots \;\;\;\;\, \vdots \;\;\;\;\, \vdots\)
\(\; \vdots \;\;\;\;\, \vdots \;\;\;\;\, \vdots \;\;\;\;\, \vdots\)
\(\; \vdots \;\;\;\;\, \vdots \;\;\;\;\, \vdots \;\;\;\;\, \vdots\)
\(x_m \; y_m \; z_m \; t_1\)
\(x_m \; y_m \; z_m \; t_2\)
\(\; \vdots \;\;\;\;\, \vdots \;\;\;\;\, \vdots \;\;\;\;\, \vdots\)
\(x_m \; y_m \; z_m \; t_{n}\)


3.3.1.2. Defining Transmitters

There are two types of transmitters that TDoctree 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:


TRX_LOOP
\(x \;\; y \;\; z \;\; R \;\; \theta \;\; \alpha\)


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:


TRX_LINES
\(N\)
\(x_1 \;\;\; y_1 \;\;\; z_1\)
\(x_2 \;\;\; y_2 \;\;\; z_2\)
\(\; \vdots \;\;\;\;\;\, \vdots \;\;\;\;\;\, \vdots\)
\(x_N \;\; y_N \;\; z_N\)


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