1. NEXRAD Data Quality Optimization AP Clutter Mitigation Scheme
Cathy Kessinger
Scott Ellis, Joe Van Andel, John Hubbert, Greg Meymaris, Mike Dixon
Research Applications Laboratory/ Earth Observing Systems
28 April 2005
NEXRAD TAC Meeting

2. AP Clutter Mitigation Scheme
Objective -- automatic detection and suppression of AP clutter to improve hydrology and aviation products for the WSR-88D
Approach:
Separate clutter from precipitation return using the Radar Echo Classifier (REC)
AP Clutter Detection Algorithm (REC-APDA)
Precipitation Detection Algorithm (REC-PDA)
Current: remove clutter gates during RPG processing
Future: Transition REC to ORDA and remove clutter in spectral domain
28 April 2005
NEXRAD TAC Meeting

3. ORPG Radar Echo Classifier (REC)
REC-APDA classifies return from clutter
REC-PDA classifies return from precipitation
Fuzzy logic, data fusion algorithms
Independent from each other
Moment data (Z, V, W) are input
Likelihood field is output (0-100%)
Run in RPG
REC-APDA deployed Fall 2002
REC-PDA to be deployed in future
28 April 2005
NEXRAD TAC Meeting

4. AP Clutter Mitigation Scheme
Enhanced Precipitation Preprocessor (EPRE)
Builds the Hybrid Scan Reflectivity (HSR) for input into radar-derived rainfall algorithm
REC-APDA used as quality control (QC) for clutter
If clutter detected (REC-APDA>50%), next elevation angle used for HSR
28 April 2005
NEXRAD TAC Meeting

5. Modification to EPRE QC
Installed ORPG Common Operating Development Environment (CODE) at NCAR
REC-PDA ported to CODE
EPRE modified
QC does extra check w/ REC-PDA
For gate to be rejected it must:
Be clutter (REC-APDA > 50%), OR
Not be precipitation (REC-PDA < 50%)
Have run a few, selected cases using this new QC
Results look very favorable
More testing needed
28 April 2005
NEXRAD TAC Meeting

6. REC-APDA and REC-PDA results
Radial velocity
Reflectivity
REC-APDA
REC-PDA
AP clutter
St. Louis KLSX
1 Nov 2004
Note:
REC-APDA finds clutter
REC-PDA finds precipitation (not clutter)
28 April 2005
NEXRAD TAC Meeting

7. REC-APDA and REC-PDA results
In mixed clutter and precipitation cases,
REC-APDA gives a missed detection (REC-APDA<50%)
REC-PDA does not classify it as precipitation (REC-PDA<50%)
2nd QC check for EPRE
Better HSR results
Recall, for gate to be rejected it must:
Be clutter (REC-APDA > 50%) OR
Not be precipitation (REC-PDA < 50%)
Radial velocity
Reflectivity
Clutter mixed with weather
REC-APDA
REC-PDA
28 April 2005
NEXRAD TAC Meeting

8. HSR using only REC-APDA
28 April 2005
NEXRAD TAC Meeting

9. HSR using REC-PDA and REC-APDA
28 April 2005
NEXRAD TAC Meeting

10. Summary of RPG REC
Adding REC-PDA to EPRE quality control checks will improve quality of Hybrid Scan Reflectivity
28 April 2005
NEXRAD TAC Meeting

11. Migration from RPG into ORDA
ORDA allows spectral processing techniques
Moving REC-APDA to ORDA will allow clutter filter control – only filter the clutter targets, not precipitation
Preliminary Spectral REC-APDA coded
LegacyRDA
ORPG
Moments
I & Q
Products
AP Clutter Control
a) Old ORPG-based Scheme
ORDA
Corrected Moments
REC
b) New ORDA-based Scheme
SZ Alg.
(NP Clutter)
Uncorrected
Spectral Variables
Clutter or
Precipitation
28 April 2005
Result: Stratiform precipitation is retained!!
NEXRAD TAC Meeting

12. Spectral Variables in REC
With ORDA, input spectral domain variables into REC
Variables under test include:
F(gi) = power at the gi velocity index
Cp = ∑ [F(g0) + F(g-1) + F(g+1)] (power at 0th coefficient, blue region)
Pnz = ∑ [F(g-3) + F(g-2) + F(g+2) + F(g+3)] (power near 0th coefficient, green region)
Ptot = ∑ F(gi) where i = -n to +n (total power, summation of all gi)
Ratio 1 = Cp/(Ptot – Cp)
Ratio 2 = Cp/Pnz g0
g-1 g1
g-2 g2
g-3 g3
Clutter
Precipitation
g-i
g+i
28 April 2005
NEXRAD TAC Meeting

13. Ratios 1 and 2 Definitions: Precipitation has values near zero
Ratio 1 = Cp/(Ptot – Cp)
Ratio 2 = Cp/Pnz
Precipitation has values near zero
Clutter has high values
Membership functions devised for APDA and ran through REC
Comparison made:
Original APDA (without SW field)
Adding Ratio1 and 2 as additional feature fields
Adding Ratio 1 and 2 and removing the VE and SDVE feature fields
Ratio 1
Ratio 2
Reflectivity
Radial Velocity
NP Clutter
Precipitation
28 April 2005
NEXRAD TAC Meeting

14. High Mag of Previous Slide
APDA + Ratio1 + Ratio2
Original APDA
(no SW)
Velocity
Power
APDA + Ratio1 + Ratio2
No Doppler
Blue oblongs: precipitation only
Red oblongs: clutter only
Adding spectral variables improves the APDA performance
Discrimination between precipitation return and clutter is improved
28 April 2005
NEXRAD TAC Meeting

15. Spectral REC-APDA Preliminary version of Spectral REC
Uses same feature fields as ORPG REC-APDA
Spectral variables will be added soon
Local area is 2 beams on either side, 8 gates long
In the example shown in following slides, the clutter filter is enabled only where the REC-APDA identifies the echo as clutter or mixed clutter and precipitation
Purely precipitation echoes are not clutter-filtered
28 April 2005
NEXRAD TAC Meeting

16. Unfiltered Moment Data: S-Pol at Marshall, CO
Time series data collected on March 28, 2004
Low PRF (320 Hz), gate spacing 225 m, 0.5 deg elevation
Zero m/s
Mixed
Mixed
Mixed
Zero m/s
Reflectivity
28 April 2005
Radial Velocity
NEXRAD TAC Meeting
Spectrum Width

17. Filtered Moment Data: S-Pol at Marshall, CO
Spectral REC-APDA identifies clutter
GMAP removes it
Zero m/s
Mixed
Mixed
Mixed
Zero m/s
Reflectivity
28 April 2005
Radial Velocity
NEXRAD TAC Meeting
Spectrum Width

18. Summary Moving the REC-APDA to the ORDA allows:
Spectral variables to be used
Provides better clutter/precipitation discrimination
Better preserve stratiform precipitation near zero m/s
Clutter filter only applied to clutter and mixed clutter/precipitation echoes
Filters not applied to purely precipitation echoes
28 April 2005
NEXRAD TAC Meeting