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Horizontal LP-filter
is a low-pass filter operating along the profile, in the
antenna’s moving direction. It is designed for the fast signal variable suppression and
slow signal variable extraction (e.g. those from layer boundaries). The algorithm used
here ensures that the averaged trace in a definite window shall replace the input profile
trace which is positioned in the mid-window location. The resulting trace thus obtained
shall be recorded in a relevant profile position. The window width shall be an input
parameter for this procedure.
Horizontal HP-filter
– high-pass filter acting along the profile in the antenna
movement direction. Intended for profile extensive signals suppression and for rapidly
varying signals extraction (e.g. from small-size objects, pipes, etc.). The algorithm used
here operates so that the trace resulting from accumulation and normalization in a
definite window is subtracted from the output profile trace whose position corresponds
to the middle of the window. The trace thus obtained is recorded in a respective profile
position. The window width is the input parameter for the procedure. If you don’t wish
the procedure to remove the direct sounding signal, specify the height of the window
wherein subtraction will be made.
Ormsby bandpass –
a bandpass filter acting along a trace. Designed for low-
frequency interference and signal’s high-frequency components suppression. The
algorithm used here comprises three steps: application of direct FFT (fast Fourier
transform) for transition from the time domain into the frequency domain, of low-
frequency and high-frequency trace spectrum components suppression, and application
of reverse FFT for transition from the frequency domain into the time domain. Input
parameters for this procedure include suppression/pass frequencies in the low-
frequency and high-frequency regions of the frequency axis. The name of the filter is
determined by cosine approximation between specified points of the frequency axis.
Setting of cut off and pass by frequencies is made in the dialog box manually with their
indication directly on averaged spectrum of file displayed by red line. Filter’s
frequency response is displayed by blue line and output signal spectrum – by the green
colored line. Filter’s desired frequency response setup is performed by moving filter’s
cut-off and bandwidth frequencies on the frequency axis with the mouse observing the
shape of spectrum at the output of the filter. Setting the required cut-off and bandwidth
frequencies may be done directly in the small boxes at the bottom of the dialog box.
Desired spectrum part may be expanded for the more accurate cut-off and bandwidth
setup using
and
buttons.
Fig. 11.2. Example of spectral procedure effect. Left - original profile; right - result.
