User manual

Code: ENIGMA III User Manual
Edition: 1 Revision: 4
Date: 19/12/2008
Page: 23/97
2.4.2 Frequency domain filtering
For frequency domain filtering several different algorithms have been implemented the algorithm can be
chosen with the parameter InterpolationMode.
2.4.2.1 DC Cancelation
This is the simplest frequency domain filter. It is basically a highpass filter
(like the timedomain IIR filter) with infinite stopband attenuation.
According to the specified filter width the taps around frequency 0 are
zeroed. The filter is not adaptive and might introduce ringing (Gibbs
Phenomenon)
2.4.2.2 Half plane subtraction
Half plane (Passarelli et al 1981) subtraction removes symetric
components around zero from the spectrum. This includes the symetric
clutter peaks and sidelobes and unfortunately weather echoes with zero
radial velocity. This filter is adaptive.
2.4.2.3 Interpolation
Beginning at frequency zero the minimum is searched (in both directions)
up to a maximum width (see filter number). The center pixels are
discarded and replaced by a linear interpolation. This filter is adaptive.
2.4.2.4 Dual slope search interpolation
This filter works similar to the interpolation above. The difference is that it
tries to interpolate across the first sidelobe (introduced by the strong clutter
target). This filter is adaptive.
GAMIC Proprietary
Illustration 17: DC
cancelation
Illustration 18: Spectrum
interpolation