Vaisala RVP900 - Table 55 Threshold Qualifiers

ID Criterion Name Pass Criterion
CCOR
Clutter Correction CCOR > threshold
SIG
Weather Signal Power SIG > threshold
PMI
Polarimetric Meteo Index PMI > threshold
Each qualification criterion can be switched on and o independently, and the threshold
levels (for example, SQI
thresh
) can each be set independently. Also, each
qualifier test can
be AND'd and OR'd with any other. This allows very complex thresholds criteria to be
constructed as required. The following table shows the threshold qualifiers.
Table 55 Threshold Qualifiers
Threshold Qualifier Description Default Value
LOG
A measure of signal strength that is usually used for the
thresholding of reflectivity data.
0.75 dB
SQI
Typically used for velocity and width thresholding since it is
a measure of the coherency. It is a number between 0 ... 1
(dimensionless), where 0 is perfect white noise and 1 is a
pure tone (perfect Doppler signal).
0.4
CCOR
The clutter correction threshold is typically used to reject
measurements when the clutter in a range bin is very strong
(i.e., when the calculated CCOR is a large negative number
in dB). The appropriate value depends on the coherency of
the radar system.
Threshold values lower than the default (more negative)
reject fewer clutter bins. Threshold values closer to 0 reject
more clutter bins.
-18 dB.
SIG
Typically used only for thresholding the spectrum width to
assure that the signal power is strong enough for an
accurate width measurement.
If R
2
processing is used, this can usually be reduced to 5 dB
for width thresholding.
5 dB
PMI
Typically used to reject echoes that are identified as
inconsistent with the preferred hypothesis of precipitation.
Identification is based on combined interpretation of
polarimetric measurements of reflectivity, dierential
reflectivity, dierential phase and co-polar correlation
coecient by the HydroClass pre-classifier.
0.45
The following table shows the default threshold combinations for each of the parameters
that can be selected for output from RVP900:
RVP900 User Guide M211322EN-J
208