User manual

Code: ENIGMA III User Manual
Edition: 1 Revision: 4
Date: 19/12/2008
Page: 12/97
2.1.6 Adjusting reflectivity thresholds
Uncorrected reflectivity data (UZ) is not corrected for clutter. In order to compare the influence of
threshold adjustments for corrected reflectivity data (CZ), open two A-Scopes or PPI's. One for
uncorrected reflectivity and one for corrected reflectivity.
2.1.6.1 NOISE Threshold Parameter
This threshold [dB] rejects corrected reflectivity data, which is n dB above the noise floor. The noise
floor was obtained from noise sampling.
In the Extended parameter dialog in FrogRT
● Set the noise threshold (Typically the threshold is set to 0.5..2 dB)
● Select NOISE for CZ threshold flags
● Click on Apply
Observe the two displays for UZ and CZ data. The CZ data should present a „clean“ picture without
noise. Fine-tune the noise threshold setting.
2.1.6.2 Clutter threshold Parameter
Two parameters in the extended SDP settings are related to clutter processing and thresholding:
2.1.6.2.1 CCOR Threshold:
The CCOR threshold is selectable from 0 dB .. -90 dB. The clutter power is obtained from the 4th.order
clutter filter or from the frequency domain processing. If the clutter power is less than the CCOR
threshold, reflectivity data may be thresholded (=rejected), if the appropriate CZ threshold flag CCOR is
enabled (CCOR is always negative as it is the Clutter Correction value in dB).
2.1.6.2.2 IQ clutter filter
The 4th. order high pass clutter filter can be configured to have different cutoff frequencies. All filters
have a stop band attenuation of 40 dB (or 50 dB depending on the selected filter set).
Allpass filter means no filtering. It does not remove any clutter. Filter IQ1 has the lowest cutoff
frequency, filter IQ7 has the highest cutoff frequency. Filter IQ1 is the „smoothest“ filter type, which will
probably reject little clutter, whereas filter type IQ7 will remove most of the clutter. Unfortunately,
weather and clutter spectra overlap, so it is important to select a clutter filter, which offers a good
compromise. From experience, IQ2..IQ4 should be selected for a first step.
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