Upload
errol
View
48
Download
0
Tags:
Embed Size (px)
DESCRIPTION
Staggered PRT Update Part I. Sebastián Torres and David Warde CIMMS/The University of Oklahoma and National Severe Storms Laboratory/NOAA. NEXRAD TAC Norman, OK 29 August, 2012. Why Staggered PRT?. Less “Purple haze” : larger r a Less Velocity aliasing : larger v a. - PowerPoint PPT Presentation
Citation preview
Staggered PRT Update
Part I
Sebastián Torres and David Warde CIMMS/The University of Oklahoma
and National Severe Storms Laboratory/NOAA
NEXRAD TACNorman, OK
29 August, 2012
Why Staggered PRT?• Less “Purple haze”: larger ra
• Less Velocity aliasing: larger va
Doppler Velocity from KTLXBatch Mode
Doppler Velocity from KOUNStaggered PRT
2
Early SPRT Concerns• Extending the range coverage– Overlaid echoes
• Extending the Nyquist velocity– Velocity dealiasing algorithm– Catastrophic errors
• Defining scanning strategies– PRT selection– Dwell-time selection
• Mitigating ground-clutter contamination
3
SPRT Range Coverage
ra,2
ra,1
ra,2
ra,1
ra,2-ra,1
Batc
hSP
RT
ra,L 2ra,S
ra,S
2ra,S
ra,S
ra,2
ra,1
Reflectivity Doppler Var. Polarimetric Var.
4No “purple haze”
possibleSome “purple haze”
possiblekey: vs.
SPRT Velocity Dealiasing• Velocities are estimated for each PRT– v1 are estimated from the short-PRT pairs– v2 are estimated from the long-PRT pairs
• Maximum unambiguous velocities for the short and long PRT pairs are different
– Velocities v1 and v2 alias in different ways• The true (de-aliased) velocity can be obtained by
“analyzing” how v1 and v2 alias
T1 T2
timeT1 T2
…R1
R2 R1 R2
5
“Catastrophic” Velocity Errors• A “catastrophic error” occurs if errors of
estimates are so large that v1 and v2 cannot be properly dealiased
– These appear as speckles in the velocity fields
– Catastrophic errors are more likely for wider normalized spectrum widths
– The ORPG velocity dealiasing algorithm has been modified to mitigate these
6
ORPG Legacy Velocity Dealiasing
KCRI - 31 March 2008
3.1 degNo Dealiasing
KCRI - 31 March 2008
3.1 degBaseline
Dealiasing
KCRI - 31 March 2008
3.1 degModified
Dealiasing
(courtesy of David Zittel, ROC)
7
Milestones• 2003: 2/3 PRT ratio with DC filter
– NSSL Report 7• 2005: SACHI filter (standalone)
– NSSL Report 9• 2007: Informal presentation to ROC DQ Team• 2008: Any PRT ratio with DC filter
– Last NEXRAD TAC informational briefing– NSSL Report 12
• 2009: 2/3 PRT ratio with SACHI filter– Stand-alone algorithm description delivered on 03/09
• 2009: 2/3 PRT ratio with SACHI filter and overlaid echo recovery– Stand-alone algorithm description delivered on 07/09– NSSL Report 13
• 2010: Extension to dual polarization– Last NSSL/NCAR/ROC TIM briefing– NSSL Report 14
• 2012: CLEAN-AP– NSSL Report 16
8
2012 SPRT Algorithm Description• Dual-pol extension– H- and V-channel processing– Spectral moments and
polarimetric variables• CLEAN-AP integration– Detection and filtering functions– Modular description to facilitate
future uniform-PRT implementation• Recovery of overlaid echoes– Allows using shorter PRTs for better
performance
9
ROC’s 3-Phase Approach
SPRT (NSSL)
DPT2 (SIGMET)
Algorithm Selection
Engineering Implementation
Operational Implementation
DC Removal GCF
RPG Velocity
Dealiasing Algorithm
Spectral GCF
Scanning Strategies
10
Batch PRT vs. Staggered PRT Reflectivity
(courtesy of D. Saxion, ROC)11
BATCHSPRT
Batch PRT vs. Staggered PRT Doppler Velocity
(courtesy of D. Saxion, ROC)12
BATCHSPRT
VCPs for SPRT• Careful VCP design for SPRT is needed– SPRT algorithm performance is more intimately
tied to acquisition parameters• Ground clutter suppression• Catastrophic errors
– More trade-offs than with other techniques• We want everything we have and more!
• SPRT can complement SZ-2 in VCPsthat achieve a “complete solution” for the mitigation of R/V ambiguities
13
Legacy Mitigation Strategy
0.5°
1.5°
19.5°
Long-PRT scan followed by short-PRT scan.Long-PRT reflectivities are used to unfold short-PRT velocities (at most, strongest overlaid trip can be recovered)
Alternating batches of long- and short-PRT pulses. Long-PRT reflectivities are used to unfold short-PRT velocities(at most, strongest overlaid trip can be recovered)
Split Cuts2 scans at each elevation angle
Batch PRT
1 scan at each elevation angle
Uniform PRT
1 scan at each elevation angle7.0°
14
Evolutionary Mitigation Strategy
0.5°
1.5°
19.5°
Long-PRT scan followed by phase-coded short-PRT scan.Long-PRT reflectivities are used to unfold short-PRT velocities (two strongest overlaid trips can be recovered) (ORDA Build 9)
Phase coding (SZ-2)2 scans at each elevation angle
Staggered PRT
1 scan at each elevation angle
Uniform PRT (Legacy)
1 scan at each elevation angle7.0°
Alternating long- and short-PRT pulses.
Range-unfolded reflectivities and velocities with good maximum unambiguous velocity (ORDA Build 14+)
15
Staggered PRT
1 scan at each elevation angle
What does a good VCP look like?
16
T1 = 1.6 msT2 = 2.4 msM = 28
SPRT
T1 = 1.23 msT2 = 1.84 msM = 40
SPRTSPRT
T1 = 1.6 msT2 = 2.4 msM = 28
TL = 3.11 msTS = 0.98 msML = 6, MS = 41
Batch(~ same dwell times)
Choosing the PRTs• PRT ratio: 2/3– Not required but recommended for initial
implementation• Choose the PRTs as short as possible– The proposed SPRT
algorithm can handle overlaid echoes
– Maximum overlay condition result in shortest PRTs
• ra,2 = rmax T2 = 2rmax /c
17
Choosing the Dwell Times• Dwell times must be chosen to…– Meet meteorological-variable variance
requirements– Meet ground-clutter suppression requirements– Satisfy operational needs for short update
times
18
Standard vs. Proposed VCP 221
Same update time Larger va
Reduced “purple haze” for v and v
No “purple haze” for Z, ZDR, DP, and HV
Lower variance of Z compared to batchSlightly increased variance of v
19
Future Work• Document performance of CLEAN-AP for SPRT– Similar to what was done for SACHI
• Support implementation of SPRT on the ORDA• Support engineering evaluation of SPRT• Support ORPG 2D-VDA modifications for SPRT– Similar to what was done for legacy VDA
• Support VCP design for SPRT• Investigate advantages of
other PRT ratios– Algorithm already generalized to
work with any PRT ratio20
Summary• SPRT is a mature technique– dual-pol extension– CLEAN-AP integration
• Algorithm description delivered to the ROC in April ‘12
• SPRT improves– range coverage
• less purple haze for v and v , no purple haze for the polarimetric variables
– velocity measurements• significantly less velocity aliasing
– data quality• reflectivity and polarimetric variables with lower variance
• SPRT is expected to replace Batch and Doppler waveforms in R/V ambiguity mitigation VCPs
21
Backup Slides
Another great example
Batch Mode SPRTDoppler Velocity (04 Mar 2004)
23
Case I: April 22, 2004 – 2.5 deg
Batch ModeVCP 11
ra = 147 kmva = 28.8 m/s
Doppler VelocityStaggered PRT(2/3, same DT)
ra = 184 kmva = 45.1 m/s
Doppler Velocity
Reflectivity
ra = 276 km
24
Case II: June 30, 2004 – 1.5 deg
Staggered PRT(2/3, same DT)
ra = 240 kmva = 34.7 m/s
Doppler VelocityBatch Mode
VCP 11
ra = 147 kmva = 28.8 m/s
Doppler Velocity
Reflectivity
ra = 360 km
25
Case III: March 3, 2004 – 2.5 deg
Batch ModeVCP 11
ra = 147 kmva = 28.8 m/s
Doppler VelocityStaggered PRT(2/3, same DT)
ra = 184 kmva = 45.1 m/s
Doppler Velocity
Reflectivity
ra = 276 km
26
Staggered PRT Processing
• Reflectivity and polarimetric-variable estimation– Segment I: short PRT samples– Segment II: short and long PRT samples– Segment III: long PRT samples
• Velocity and spectrum width estimation– Segment I: overlaid echoes on one sample of every pair
• No bias for “dominant” echo– Segment II: clean pairs– Segment III: overlaid echoes on one sample of every pair
• Non-dominant echo must be censored!27
T1 T2
I II I II III I
= 2/3R1 R2R1
R2R1R2