Vaisala RVP900 - Moment Extraction; Range Averaging and Clutter Microsuppression; Speckle Filter; Threshold Processing

3.3.4 Range Averaging and Clutter Microsuppression
Range averaging can improve the accuracy of the reflectivity measurements.
When this is done, autocorrelations from consecutive range bins are averaged, and the result
is treated as a single bin. This means that the host computer must process fewer range bins.
Range averaging of the autocorrelations may be performed over 2 ...16 bins. Prior to range
averaging, any bins that exceed the selectable clutter-to-signal threshold are discarded. This
prevents isolated strong clutter targets from corrupting the range average, which improves
the sub-clutter visibility.
More Information
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Range Averaging and Clutter Microsuppression (page 200)
3.3.5
Moment Extraction
The autocorrelations are the basis for Doppler moment calculations:
• Mean velocity—From Arg [ R1 ]
• Spectrum width—From |R1| and |R2| assuming Gaussian spectrum
• dBZ—From |R0| with correction for ground clutter, system noise, and gaseous
attenuation. Uses calibration information supplied by host computer
• dBT—Identical to dBZ, but without ground clutter
These standard parameters are output to the host application.
3.3.6
Threshold Processing
RVP900 calculates several parameters that are used to threshold (discard) bins with weak
or corrupted signals. The thresholding parameters are:
• Signal quality index (SQI=|R1|/R0)
• LOG (or incoherent) signal-to-noise ratio (LOG)
• SIG (coherent) signal-to-noise ratio
• CCOR clutter correction
These parameters are computed for each range bin and can be applied in AND/OR logical
expressions, independently for dBZ, V, and W.
3.3.7
Speckle Filter
A speckle filter is a final pass over each output ray, in which isolated, single bins of velocity,
width, or intensity are removed.
There are two speckle removers in RVP900:
• 1D single-ray speckle filter (default)—This is used for any output parameter.
• 2D 3x3 speckle filter—If enabled, this is used for any output parameter.
This eliminates single pixel speckles, which allows the thresholds to be reduced for greater
sensitivity with fewer false alarms (speckles).
RVP900 User Guide M211322EN-J
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