Butterworth Filter

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

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

1D FFT > 1D Filtering
Moving Platform Gravity > Filters > Apply Single FFT Filter

Butterworth filter options

Central wavelength cutoff (in ground units)

Value for the central wavelength cutoff. Default = 1

Script Parameter: FFTBUTTW.WAVEL

Degree of filter

Degree of the filter function. Default = 8

Script Parameter: FFTBUTTW.DEGREE

Low or high pass filter

Select whether to apply a low-pass or high-pass filter. Default = Low

Script Parameter: FFTBUTTW.PASS

Application Notes

The Butterworth filter is ideal for straightforward high-pass and low-pass filtering because it provides easy control over the filter roll-off degree while keeping the central wavenumber fixed. If ringing occurs, reduce the degree until the result is acceptable.

A common, but more complex alternative is the Cosine Filter.

Butterworth Filter

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Parameters:

k₀: Central wavenumber of the filter.

n: Degree of the Butterworth filter function (default = 8).

0/1: Residual/Regional flag indicating whether a residual high-pass or a regional low-pass filter is applied. By default, the system applies a regional filter.