# 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: