Apply Single FFT Filter

Use the Apply Single FFT Filter option (geogxnet.dll(Geosoft.GX.FFT1D.FFT1DFiltering;RunGravityFilters)*) from the menu Moving Platform Gravity > Filters to apply a single 1D Fast Fourier Transform (FFT) filter to a channel.

Apply Single FFT Filter dialog options

Channel to filter

Name of the input channel to filter.

Script Parameter: FFT1MULT.IN

Output channel

Name of the output channel (created if does not exist).

Script Parameter: FFT1MULT.OUT

Filter to apply

Select the filter to apply. The parameters for the selected filter will be displayed below and will vary depending on the filter chosen.

The following filters can be selected:

  • Apparent density calculation
  • Apparent susceptibility calculation
  • Band-pass
  • Butterworth
  • Continuation
  • Cosine roll-off
  • Gaussian
  • Horizontal derivative
  • Horizontal integration
  • High-pass
  • Low-pass
  • Reduce to magnetic pole
  • Resistance capacitance
  • Vertical derivative
  • Vertical integration

Script Parameter: FFT1MULT.FILTER

More

Distance increment

Specify the distance increment in ground units. If not specified, the nominal data spacing will be used.

Script Parameter: FFT1MULT.SAMPINCR

Interpolation method

Select the Interpolation method: Minimum Curvature, Linear, or Akima.

Script Parameter: FFT1MULT.METHOD

Application Notes

*GX.NET tools are embedded in the geogxnet.dll file located in the \Geosoft\Desktop Applications\bin folder. To run this GX interactively (outside the menu), navigate to the bin directory and specify the GX.NET tool in the required format. See the Run GX topic for more guidance.

The dialog applies a single filter in a one process:

  1. Data is Fourier Transformed (FT) to the wavenumber domain.

  2. The selected filter is applied.

  3. Data is Inverse Fourier Transformed (IFT) back to the spatial domain.

FFT Sampling Parameters (distance Increment and interpolation method) ensure proper sampling for 1D FFT.

  • If your data has variable spacing between samples (e.g., ground-based surveys), the default Minimum Curvature method may introduce artifacts in the filtered output.

  • To avoid this—or if artifacts occur—use Linear interpolation or specify an appropriate distance increment.

The relevant parameters for the selected filter will be displayed for input.

Finding Help for a Specific Filter

Once you select a filter in the Apply Single Filter dialog, click Help to view detailed information for that filter. You can also click the filter links provided below.

See Also: