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: