Cathy Kessinger Scott Ellis, Joe Van Andel, John Hubbert, Greg Meymaris, Mike Dixon

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 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 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 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 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 NEXRAD TAC Meeting

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

7. REC-APDA and REC-PDA results Radial velocity Reflectivity • 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%) Clutter mixed with weather REC-APDA REC-PDA NEXRAD TAC Meeting

8. HSR using only REC-APDA NEXRAD TAC Meeting

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

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

11. Migration from RPG into ORDA a) Old ORPG-based Scheme ORPG LegacyRDA I & Q Moments Products REC AP Clutter Control b) New ORDA-based Scheme ORDA Corrected Moments Products ORPG REC Uncorrected Moments I & Q REC SZ Alg. (NP Clutter) REC Spectral Variables Clutter or Precipitation AP Clutter Control • 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 NEXRAD TAC Meeting Result: Stratiform precipitation is retained!!

12. Spectral Variables in REC Clutter Precipitation g-i g-3 g-2 g-1 g0 g1 g2 g3 g+i • 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 NEXRAD TAC Meeting

13. Ratios 1 and 2 Reflectivity Radial Velocity Precipitation NP Clutter Ratio 1 Ratio 2 • Definitions: • 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 NEXRAD TAC Meeting

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