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

28 April 2005 NEXRAD TAC Meeting Slide 1

Cathy Kessinger

Scott Ellis, Joe Van Andel, John Hubbert,

Greg Meymaris, Mike Dixon

NEXRAD Data Quality Optimization

AP Clutter Mitigation Scheme

Research Applications Laboratory/ Earth Observing Systems



• 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


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



• 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


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


REC-APDA and REC-PDA results

• St. Louis KLSX– 1 Nov 2004

• Note: – REC-APDA finds

clutter

– REC-PDA finds precipitation (not clutter)

Radial velocity Reflectivity

REC-APDA REC-PDA

AP clutter


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

REC-APDA REC-PDA

Clutter mixed with

weather


HSR using only REC-APDA


HSR using REC-PDA and REC-APDA


Summary of RPG REC

• Adding REC-PDA to EPRE quality control checks will improve quality of Hybrid Scan Reflectivity


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

Result: Stratiform precipitation is retained!!

LegacyRDA

ORPGMomentsI & Q Products

AP Clutter Control

a) Old ORPG-based Scheme

ORDACorrected Moments

I & Q

ORPGREC

Products

AP Clutter Control

b) New ORDA-based Scheme

SZ Alg.

(NP Clutter)

RECUncorrectedMoments

Spectral Variables

REC

Clutter orPrecipitation

REC


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

g0g-1 g1g-2 g2g-3 g3

Clutter

Precipitation

g-i g+i


Ratios 1 and 2

Ratio 1 Ratio 2

Reflectivity Radial Velocity

NP Clutter

Precipitation

• 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


PowerVelocity

High Mag of Previous Slide

Original APDA(no SW)

APDA + Ratio1 + Ratio2APDA + Ratio1 + Ratio2No Doppler

• Blue oblongs: precipitation only

• Red oblongs: clutter only

• Adding spectral variables improves the APDA performance– Discrimination between

precipitation return and clutter is improved


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


• Time series data collected on March 28, 2004

• Low PRF (320 Hz), gate spacing 225 m, 0.5 deg elevation

Unfiltered Moment Data: S-Pol at Marshall, CO

Reflectivity Radial Velocity Spectrum Width

Zero m/s

Zero m/s

Mixed Mixed Mixed


• Spectral REC-APDA identifies clutter

• GMAP removes it

Filtered Moment Data: S-Pol at Marshall, CO

Reflectivity Radial Velocity Spectrum Width

Mixed

Zero m/s

Zero m/s

Mixed Mixed


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

Documents

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