clean-ap update cl utter e nvironment an alysis using a daptive p rocessing sebastián torres and...
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CLEAN-AP UpdateClutter Environment Analysis using Adaptive Processing
Sebastián Torres and David Warde CIMMS/The University of Oklahoma
and National Severe Storms Laboratory/NOAA
NEXRAD TACNorman, OK
29 August, 2012
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CLEAN-AP is a novel real-time, automatic, integrated technique for ground clutter detection and filtering that produces meteorological data with improved quality while meeting NEXRAD technical requirements.
what is CLEAN-AP?
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While CLEAN-AP can deal with normal- (NP) and anomalous-propagation (AP) clutter, it is not a mitigation technique for moving clutter such as airplanes, cars, or wind turbines.
what is CLEAN-AP not?
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• Developed concept (Spring ‘08)– Filed invention disclosure with OU’s OTD
• Evaluated performance using simulations (Spring ‘08)• Implemented in real time on the NWRT PAR (Fall ‘08) • Compared with current WSR-88D clutter mitigation (Fall
‘09)– KEMX (Tucson, AZ), KTLX (Oklahoma City, OK), KABX (Albuquerque, NM), KCRI
(ROC testbed)
• Presented at November 2009 TAC meeting– initially presented CLEAN-AP
• “… the technique shows potential utility…”, “… encouraged by early results…”• “… [have not] shown the scientific details behind the algorithm…”• “… [need] case comparisons with CMD…”
• Extended to dual-polarization (Spring ‘10)– KOUN (S-band) and OU’ (C-band)
• Developed clutter model (Spring ‘10)– Form/Function/Fit for RVP8
milestones (I)
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• Presented at fall 2010 ROC/NSSL/NCAR TIM– presented more technical details and data cases– received positive feedback from ROC eng and agency reps
• Delivered CLEAN-AP algorithm description (Fall ’10)– NSSL Report 14 (confidential attachment)
• Extended to staggered PRT (Fall ‘10)• Presented at March 2011 TAC meeting
– decision briefing• “The TAC members agreed to move forward with conducting
an engineering evaluation on CLEAN AP.”
• Documented CLEAN-AP performance (Winter ’11)– NSSL Report 15
• Delivered SPRT CLEAN-AP algorithmdescription (Spring ’12)
– NSSL Report 16 (confidential)
milestones (II)
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Ground Clutter Filtering
Ground Clutter Filtering
Ground Clutter Detection
Ground Clutter Detection
Unfiltered data
Filtered data
clutter mitigation at the RDA
Control
CMDCMD
GMAPGMAP
CLEAN-AP
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CLEAN-AP’s core: the ASDlag-1 autocorrelation spectral density
• For periodic signals: F1(k) = F0(k) ej2k/M
– S1(k) = F0*(k) F0(k) ej2k/M =S (k) ej2k/M
– the ASD is the PSD with linear phase
sample time
10 M2 M1
V0
V1
window & DFT
F1
window & DFT F0
S1(k) = F0*(k)F1(k)
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MeasuredTrue
v
v
ASD
v
v
ASD
v
PSD
Ground Clutter
v
PSD
Weatherv
v
ASD
v
v
ASD
Leakage
Leakage
nothing is ideal…
Spectral leakage in the measured ASD is the basis for clutter detection in CLEAN-AP
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how does CLEAN-AP work? Integrated Detection and Filtering
• Estimate CNR• Select appropriate data
window• Compute ASD• Identify components
with clutter contamination
– Phase of ASD is near zero due to leakage effect
• Remove clutter• Reconstruct weather
• ASD is used to estimate meteorological variables
v
v
|ASD|
zero phase
DC
Arg(ASD)
PSD
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Performance Summary
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data window selectionCLEAN-AP vs. GMAP
More aggressive data windows contain spectral leakage but increase variance of estimates
better suppression
lower variance
GMAP
%
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notch width selectionCLEAN-AP vs. GMAP
CLEAN-AP uses magnitude and phase for improved notch width determination
better suppression
lower bias
NW determination
mag phase
GMAP CLEAN-AP
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CLEAN-AP has more clutter suppression and less variance of estimates
Clutter SuppressionDoppler Mode
CLEAN-AP GMAP
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CLEAN-AP has a more robust notch width determination that results in smaller biases
Reflectivity (Power) BiasDoppler Mode
CLEAN-AP GMAP
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Case Examples
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• Ground-clutter suppression– Due to the mountainous terrain close to the
radar, KEMX data exhibited “hot spots” (clutter residue) after the initial release of CMD (B11). This led to a few software changes (B11 fixed)
KEMX Tucson, AZCan you see the mountains?
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KEMX Reflectivity
Unfiltered CMD+GMAP (B11 fixed)CLEAN-AP
CLEAN-AP mitigates both weak and strong clutter contamination
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KEMX Tucson, AZCLEAN-AP Performance
CLEAN-AP adapts to clutter environment
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CLEAN-APPower Removed
CLEAN-APWindow Used
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• Zero-isodop loss– Weather with narrow spectrum width and near
zero velocity has nearly the same spectrum as clutter
KCRI Norman, OKWhat happened to the zero-isodop?
if it looks like a duck… 19
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KCRIReflectivity
Unfiltered UnfilteredCLEAN-APCMD+GMAP (B11
fixed)
CLEAN-AP better preserves the zero isodop
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KCRIVelocity
CLEAN-AP better preserves the zero isodop
Unfiltered UnfilteredCLEAN-AP CMD+GMAP (B11)
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• Support implementation on the ORDA• Support engineering evaluation • Investigate using dual-pol information to
improve detection performance• Investigate using H and V channels to
determine the filter’s notch width– This also applies to
the current filter
Future Work
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CLEAN-AP is a novel real-time, automatic, integrated technique for ground clutter mitigation that produces meteorological data with improved quality while meeting NEXRAD technical requirements.
In March 2011, the TAC endorsedits engineering evaluation on the WSR-88D.
Summary
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back up slides
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• CLEAN-AP is automatic– no need for user intervention– real-time ground-clutter detection– no need for clutter maps
• CLEAN-AP produces data withimproved quality
– adaptive data windowing finds a good compromise between clutter suppression and data quality
• CLEAN-AP meets NEXRAD requirements– improved clutter suppression– requirements (Z) met with as few as 8 samples
• CLEAN-AP is integrated– one algorithm for ground clutter detection and filtering– gate-by-gate operation
the CLEAN-AP filter (I)
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• CLEAN-AP “sets the stage” for further spectral processing
– phase provides useful information– immune to biases from circular convolution
• CLEAN-AP is operational on the NWRT PAR– running in real-time since Sep 2008– performance informally evaluated by meteorologists
and forecasters (PARISE experiments)
• CLEAN-AP is compatible with current and future upgrades
– SZ-2, super resolution, dual pol., hybrid SW,– SPRT, range oversampling, etc.
the CLEAN-AP filter (II)
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KEMX
Clutter Map (Pwr Rmvd > 10 dB)Clutter Map (Pwr Rmvd > 20 dB)
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• Snow event with embedded storms
KTLX Oklahoma City, OKWhere is the zero?
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KTLXReflectivity
Unfiltered CLEAN-AP
Where is the zero isodop?
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KTLXVelocity
Unfiltered CLEAN-AP
No detectable zero isodop loss
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KOUN What about dual polarization?
ReflectivityDifferential ReflectivityCorrelation CoefficientDifferential Phase
CLEAN-AP is compatible with dual polarization
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