Vaisala RVP900 - Signal+Noise) to Noise Ratio (LOG Threshold); Thresholding; Threshold Qualifiers; Table 54 Threshold Quality Criteria

Autocorrelation Equation Description
R
0
, R
1
,R
2
 = 10log
2

0
 2
+ 
The SIG is computed based on the
SNR.
The signal power S is determined
as described in 7.4.7 Clutter
Correction (CCOR threshold)
(page 205).
7.4.9 (Signal+Noise) to Noise Ratio (LOG Threshold)
The LOG threshold parameter is calculated to provide a signal strength estimate that is
useful for qualifying reflectivity.
For historical reasons, the LOG threshold is not the true SNR (whose dB representation can
be both positive and negative) but rather, the ratio of (Signal + Noise) to Noise, which
always has a positive representation in dB. Specifically:
 = 10log

0

(when applied to the dBT parameter)
 = 10log

0

(when applied to the other parameter)
7.5
Thresholding
RVP900 can accept or reject incoming real time data to remove range bins. Rejected data
may include that with:
• Weak signal power
• Unreliable estimates of Doppler parameters
• Polarimetric parameters that suggest echo is of undesired origin, for example not
precipitation
This process is called thresholding. IRIS provides
flexibility for thresholding to provide clean
displays, promote ecient execution and transmission of the products, and reduce the
amount of tape and disk space required to hold compressed data and product archives.
7.5.1
Threshold Qualifiers
For data quality control, each RVP900 output parameter can be qualified, that is, accepted
or rejected for output, based on threshold criteria:
Table 54 Threshold Quality Criteria
ID Criterion Name Pass Criterion
LOG
(Signal+Noise)-to-Noise Ratio LOG > threshold
SQI
Signal Quality Index SQI > threshold
Chapter 7 – Processing Algorithms
207