Continuation Filter

Use the Continuation option to apply a Fast Fourier Transform (FFT) continuation filter to a channel.

The filter option is available with the following extensions and menus:

Continuation filter options

Continuation distance
(in ground units)

Continuation distance in ground units (> 0). Default = 0

Script Parameter: FFTCONT.DIST

Butterworth low-pass
(in ground units)

Low-pass cutoff wavelength for Butterworth filter. Default = 1

Script Parameter: FFTCONT.LP

Direction (up or down)

Direction for continuation: Up or Down. Default = Down

Script Parameter: FFTCONT.DIR

Application Notes

Downward Continuation

Used to enhance responses from deep sources by effectively moving the observation plane closer to them.

  • It is not theoretically possible to continue through a potential field source.

  • Short-wavelength signals can mimic shallow sources and must be removed to avoid high-amplitude, short wavelength noise.

  • To reduce noise, set the LP parameter to 1–1.5 times the continuation distance.

Upward Continuation

Considered a clean filter with minimal side effects, often used to remove or minimize the effects of shallow sources and noise in grids.

  • Upward continued data can be interpreted numerically and modeled, unlike many other filter processes.

Downward Continuation Filter

h: Distance (ground units) to continue down relative to the plane of observation.

Upward Continuation Filter

h: Distance (ground units) to continue up relative to the plane of observation.

See Also: