# 5.1.14. FEM data: GIF file¶

This file is used to specify the transmitters and associated data for a Frequency-domain ElectroMagnetic (FEM) survey. The file is broken down based on the transmitters and requires all data types be present (although they may be filled with an ignore value; see below). The convention is z+down and x+ East and y+ North. Comment lines begin with `!`

. The data line contains 27 columns (x,y,z,E data and H data with uncertainties), but may be filled with ignore flags to denote using only certain data types. Below is the general format:

Parameter definitions:

`flg`

: Any string/value that does not contain actual data. By default, GIFtools will export`NaN`

as the ignore value. The flag`IGNORE`

preceeds this input.`ntrxTimesNfreq`

: Number of transmitters multiplied by the number of frequencies. The flag`N_TRX`

preceeds this input.`TRX_FLAG`

: The \(i^{th}\) transmitter. This line contains the specific transmitter flag and block defining the transmitter. See GIF EM transmitters for specifications on formatting different transmitters.`frq`

: The frequency of the following receivers for the given transmitter. The flag`FREQUENCY`

preceeds this input.`nRec`

: Number of receivers associated with the frequency given above for the given (\(i^{th}\)) transmitter. The flag`N_RECV`

preceeds this input.\(X_{[i,j,k]}\): Easting (m) of the \(k^{th}\) receiver at the \(j^{th}\) frequency for the \(i^{th}\) transmitter.

\(Y_{[i,j,k]}\): Northing (m) of the \(k^{th}\) receiver at the \(j^{th}\) frequency for the \(i^{th}\) transmitter.

\(Z_{[i,j,k]}\): Elevation (m) of the \(k^{th}\) receiver at the \(j^{th}\) frequency for the \(i^{th}\) transmitter.

`Edata`

: 12 columns containing electric-field data and their uncertainties of the \(k^{th}\) receiver at the \(j^{th}\) frequency for the \(i^{th}\) transmitter (in order):\(Ex^r\): Real part of the electric-field component in the Easting direction.

\(Ex^r_{stn}\): Standard deviation of the real part of the electric-field component in the Easting direction. This must be a positive, non-zero number.

\(Ex^i\): Imaginary part of the electric-field component in the Easting direction.

\(Ex^i_{stn}\): Standard deviation of the imaginary part of the electric-field component in the Easting direction. This must be a positive, non-zero number.

\(Ey^r\): Real part of the electric-field component in the Northing direction.

\(Ey^r_{stn}\): Standard deviation of the real part of the electric-field component in the Northing direction. This must be a positive, non-zero number.

\(Ey^i\): Imaginary part of the electric-field component in the Northing direction.

\(Ey^i_{stn}\): Standard deviation of the imaginary part of the electric-field component in the Northing direction. This must be a positive, non-zero number.

\(Ez^r\): Real part of the vertical electric-field component.

\(Ez^r_{stn}\): Standard deviation of the real part of the vertical electric-field component. This must be a positive, non-zero number.

\(Ez^i\): Imaginary part of the vertical electric-field component.

\(Ez^i_{stn}\): Standard deviation of the imaginary part of the vertical electric-field component. This must be a positive, non-zero number.

`Hdata`

: 12 columns containing magnetic-field data and their uncertainties of the \(k^{th}\) receiver at the \(j^{th}\) frequency for the \(i^{th}\) transmitter (in order):\(Hx^r\): Real part of the magnetic-field component in the Easting direction.

\(Hx^r_{stn}\): Standard deviation of the real part of the magnetic-field component in the Easting direction. This must be a positive, non-zero number.

\(Hx^i\): Imaginary part of the magnetic-field component in the Easting direction.

\(Hx^i_{stn}\): Standard deviation of the imaginary part of the magnetic-field component in the Easting direction. This must be a positive, non-zero number.

\(Hy^r\): Real part of the magnetic-field component in the Northing direction.

\(Hy^r_{stn}\): Standard deviation of the real part of the magnetic-field component in the Northing direction. This must be a positive, non-zero number.

\(Hy^i\): Imaginary part of the magnetic-field component in the Northing direction.

\(Hy^i_{stn}\): Standard deviation of the imaginary part of the magnetic-field component in the Northing direction. This must be a positive, non-zero number.

\(Hz^r\): Real part of the vertical magnetic-field component.

\(Hz^r_{stn}\): Standard deviation of the real part of the vertical magnetic-field component. This must be a positive, non-zero number.

\(Hz^i\): Imaginary part of the vertical magnetic-field component.

\(Hz^i_{stn}\): Standard deviation of the imaginary part of the vertical magnetic-field component. This must be a positive, non-zero number.

**NOTE**: Each `FREQUENCY`

flag must be preceded by the transmitter definition, *regardless of whether it is the same as the previous transmitter*. See the DIGHEM example below.

## 5.1.14.1. Examples¶

The following are two examples of data files.

**Example 1**: One transmitter (large loop) at two frequencies of 10 Hz and 50 Hz and one receiver location:

**Example 2**: Co-planar DIGHEM data example. Two transmitters (two loops) at the frequencies of 900, 7200, and 56000 Hz with with only Hz real and imaginary (and standard deviations) given: