Threshold qualifiers
For data quality control, each RVP10 output parameter can be qualified, that is, accepted or rejected for output, based on threshold criteria:
| ID | Criterion name | Pass criterion |
|---|---|---|
| LOG | (Signal+Noise)-to-Noise Ratio | LOG > threshold |
| SQI | Signal Quality Index | SQI > threshold |
| 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 off independently, and the threshold levels (for example, SQIthresh
) can each be set independently. Also, each qualifier test can be OR'd with
any other. This allows very complex threshold criteria to be constructed as required. The
following table shows the 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). ). It may also be used to identify and remove 2nd trip echo and RF interference. | 0.4 |
| CCOR |
The clutter correction threshold is typically used to reject measurements when the clutter in a range bin is very strong compared to the non-clutter signal (that is, 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 |
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, differential reflectivity, differential phase and co-polar correlation coefficient by the HydroClass pre-classifier. PMI is typically applied to reflectivity data. | 0.45 |
The following table shows the default threshold combinations for each of the parameters that can be selected for output from RVP10:
| Parameter | Description | Threshold |
|---|---|---|
| dBZ | Reflectivity with clutter correction | LOG , CCOR, SQI,PMI |
| dBT | Reflectivity without clutter correction | LOG |
| V | Mean velocity | SQI , CCOR |
| W | Spectrum width | SQI , CCOR, SIG |
| Dual Pol | Differential reflectivity | LOG |