Continuation Filter

Use the Continuation option to apply a Fast-Fourier Transform Continuation filter to a channel.

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

• Geophysics: 1D FFT > 1D Filtering
• Gravity and Terrain Correction: Moving Platform Gravity  > Apply Single FFT Filter

Continuation filter options

Continuation Distance (in ground units)	Continuation distance in ground units (> 0) (Default is 0). Script Parameter: FFTCONT.DIST
Butterworth low-pass (in ground units)	Butterworth low-pass cutoff wavelength (Default is 1). Script Parameter: FFTCONT.LP
Direction (up or down)	Direction for continuation, "Up" or "Down" (Default is Down). Script Parameter: FFTCONT.DIR

Application Notes

Downward Continuation: This is used to enhance the responses from sources at depth by effectively bringing the plane of measurement closer to the sources. Note that it is not theoretically possible to continue through a potential field source. Since short wavelength signals can appear to be from shallow sources, they must be removed to prevent high amplitude and short wavelength noise in the processed data. To do this, set the LP parameter to between 1 and 1.5 times the continuation distance.

Upward Continuation: This is considered a clean filter because it produces almost no side effects that may require the application of other filters or processes to correct. Because of this, it is often used to remove or minimize the effects of shallow sources and noise in grids. Also, upward continued data may be interpreted numerically and with modeling programs. This is not the case for many other filter processes.

Downward Continuation Filter

Parameter:

h Distance in ground_units, to continue down relative to the plane of observation.

 

Upward Continuation Filter

Parameter:

h Distance in ground_units, to continue up relative to the plane of observation.