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Sebastian Torres
NEXRAD Range-Velocity Ambiguity Mitigation
Staggered PRT andPhase Coding
Algorithms on the KOUN Research Radar
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Part One
Research RDA (RRDA) Capabilities
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VCP Definitions
• Legacy VCP definition– RPG Message 7
• ICD RDA/RPG (Doc. # 2620002A)
– Provision for• Waveform Type
– Constant or Random Phase
• Waveform Configuration– Staggered Pulse Pair
• Not supported on the WSR-88D!
– No provision for systematic phase codes– No provision for staggered pattern definition
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VCP Definitions
• RRDA VCP definition– Concurrent with NPI and Homeland Security
Experiment• High-resolution data• Horizontal raster, vertical raster, searchlight scans
– Backward compatible with Legacy definition for supported modes
– R/V mitigation techniques are specified on a scan-by-scan basis
• Proposed VCP for R/V
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VCP Definitions
• Phase Coding Features– Can specify phase coding sequence number
for each scan• Standard (or predefined)• Downloadable
– Proposed new RPG Message to define phase coding sequence
» Sequence length» Phases specified as multiples of 2/128
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VCP Definitions
• Staggered PRT Features– Can specify patterns using
• Up to 3 PRI’s• A pulse count (M) for each PRI• An overall pattern count (Mp)
– Examples• Standard staggered pattern:
T1, T2, T1, T2, …– PRI1 = 1, M1 = 1, PRI2 = 2, M2 = 1, Mp = 32
• Block staggered pattern: T4, T4, T2, T2, T2, T4, T4, T2, T2, T2, …
– PRI1 = 4, M1 = 2, PRI2 = 2, M2 = 3, Mp = 10
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Hardware Enhancements
• Synchronizer– Phase coding of transmitted pulses
• Uses legacy phase shifter (7 bits)
– Generation of staggered pulse patterns– Generation of expanded set of PRTs
• Legacy has limited set
• Requirements for precise T1/T2 ratios
• Requirements for different ra
• Resolution given by 9.6 MHz clock
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Software Enhancements
• Archive I Recorder– Handling of variable range-sweep sizes– Associated tools to handle phase-coded and
staggered PRT data
• Signal Processing– SimSPS model
• Rapid prototyping
– Real-time implementation• Phase coding: 1st trip decoding• Staggered PRT: full processing with simple GCF
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Part Two
RRDA Implementation of the Staggered PRT Algorithm
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Assumptions
• Transmission sequence alternates two PRT’s for a total of M pulses
• N1 and N2 are range gates for T1 and T2
• No echoes beyond max(ra1, ra2)– Overlay of “short” into “long”– Echoes extending beyond max(ra1,ra2) can be censored
• Does not assume:– M is even– T1/T2 is rational– T1 < T2
• In what follows T1 < T2 for clarity
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Inputs
• Time-series dataV(n,m) = I(n,m) + jQ(n,m)
0 < m < M0 < n < N1 for even m0 < n < N2 for odd m
• Associated metadata
• GCF Maps
• Adaptation DataAs in legacy PSP
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Outputs
• Base data– Reflectivity
Z(n), for 0 < n < N2
– Doppler velocityv(n), for 0 < n < N1
– Doppler spectrum withw(n), for 0 < n < N1
• Z is computed through ra2
• v and w are computed through ra1
– Could include censored data up to ra2
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Algorithm
1. Suppress interference• Legacy PSP algorithm
2. Compute powers and correlations
• P1, R1 for short range sweeps
• P2, R2 for long range sweeps
T1 T2 T1
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Algorithm
3. Apply GCF: DC removal• Compute time-series mean: Vm
• Remove |Vm |2 from P1, P2, R1, and R2
• Use bypass map– Could use Sachidananda’s GCF (Rep. 3 & 4)
4. Suppress point clutter• Legacy PSP algorithm
5. Compute Doppler velocities• v1 based on R1
• v2 based on R2
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Algorithm
6. De-alias v1 using v2
• Use v1 and v2 to determine Nyquist interval
• De-alias v1
• Close to MMSE for SD(v1) >> SD(v2)
7. Compute Doppler spectrum widths• w based on P2 and R2
(Zrnić and Mahapatra, 1985)
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Algorithm
8. Compute combined Echo power (N2)
9. Compute Reflectivity• Legacy PSP algorithm
10.Determine Significant Returns for Z• Use reflectivity threshold
T1 T2
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Algorithm
11. Compute individual Echo powers (N1, N2)
12. Determine overlaid echoes
• Overlaid echoes do not bias v, but act as noise• Use overlaid threshold• Could use Sachidananda’s overlaid resolution scheme
13. Determine Significant Returns for v and w• Use velocity and width thresholds
T1 T2
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Algorithm Performance
va1 = 22.58m s-1, va2 = 15.06m s-1, va = 45.17 m s-1
Staggered PRT Velocity De-aliasing
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Future Work
• Sophisticated GCF– Spectral (Reports 3 and 4)– Others (Regression?)
• One-overlaid resolution– Sachidananda and Zrnic, 2003
• Extension beyond ra2
– For T1/T2 = 2/3 up to 2ra1
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Part Three
Preliminary Case Studies
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Case Data
• Data acquired with RRDA archive I recorder• Staggered PRT
– Custom VCP’s alternating uniform and staggered PRT scans at 3 elevations
• Phase Coding– ROC/NSSL VCP’s alternating non-phase-coded and
phase-coded scans at 2 elevations
• Proposed VCP for R/V Ambiguity Mitigation– Phase coding at lower elevations, staggered PRT at
higher elevations (Report 6)
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02/13/2003
20:58 GMT
KTLXVCP 11
KOUNStaggered 336/466
EL = 0.5 deg
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02/13/2003
KTLXVCP 11
KOUNStaggered 336/466
Recalibrated
EL = 0.5 deg
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02/13/2003
KTLXVCP 11
Needs Split Cut
KOUNStaggered 336/466
No need for Split Cut
EL = 0.5 deg
va = 28.08 m s-1 va = 31.96 m s-1
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02/13/2003
KTLXVCP 11
KOUNStaggered 336/466
EL = 0.5 deg
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02/13/2003
20:58 GMT
KTLXVCP 11
KOUNStaggered 336/466
EL = 1.5 deg
28
02/13/2003
va = 28.08 m s-1 va = 31.96 m s-1
KTLXVCP 11
KOUNStaggered 336/466
EL = 1.5 deg
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02/13/2003
22:42 GMT
KTLXVCP 11
KOUNStaggered 336/466
EL = 0.5 deg
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02/13/2003
KOUNStaggered 336/466
GCF ON w/censoring
KOUNStaggered 336/466
GCF OFF
KOUNStaggered 336/466
GCF ON
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02/13/2003
va = 28.08 m s-1 va = 31.96 m s-1
KTLXVCP 11
KOUNStaggered 336/466
EL = 0.5 deg
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02/13/2003
KOUNStaggered 336/466
GCF ON w/censoring
KOUNStaggered 336/466
GCF OFF
KOUNStaggered 336/466
GCF ON
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02/13/2003
KTLXVCP 11
KOUNStaggered 336/466
EL = 0.5 deg
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02/13/2003
KOUNStaggered 336/466
GCF ON w/censoring
KOUNStaggered 336/466
GCF OFF
KOUNStaggered 336/466
GCF ON
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02/13/2003
22:42 GMT
KTLXVCP 11
KOUNStaggered 336/466
EL = 1.5 deg
36
02/13/2003
KTLXVCP 11
KOUNStaggered 336/466
EL = 1.5 deg
va = 28.08 m s-1 va = 31.96 m s-1
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03/17/2003
21:39 GMT
KTLXVCP 11
KOUNStaggered 184/276
EL = 0.5 deg
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03/17/2003
KTLXVCP 11
KOUNStaggered 184/276
EL = 0.5 deg
va = 28.08 m s-1 va = 45.17 m s-1
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03/17/2003
KTLXVCP 11
KOUNStaggered 184/276
EL = 0.5 deg
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03/17/2003
KTLXVCP 11
KOUNStaggered 184/276
EL = 0.5 deg
va = 28.08 m s-1 va = 45.17 m s-1
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03/17/2003
KTLXVCP 11
KOUNStaggered 184/276
EL = 0.5 deg
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03/17/2003
21:44 GMT
KTLXVCP 11
KOUNStaggered 336/466
EL = 0.5 deg
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03/17/2003
va = 28.08 m s-1 va = 31.96 m s-1
KTLXVCP 11
KOUNStaggered 336/466
EL = 0.5 deg
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03/17/2003
22:44 GMT
KTLXVCP 11
KOUNStaggered 240/360
EL = 2.5 deg
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03/17/2003
KTLXVCP 11
KOUNStaggered 240/360
EL = 2.5 deg
va = 28.08 m s-1 va = 34.63 m s-1
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03/17/2003
KTLXVCP 11
KOUNStaggered 240/360
EL = 2.5 deg
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04/06/2003
04:37 GMT
KTLXVCP 11
KOUNStaggered 184/276
EL = 1.5 deg
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04/06/2003
KTLXVCP 11
KOUNStaggered 184/276
EL = 1.5 deg
va = 28.08 m s-1 va = 45.17 m s-1
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04/06/2003
KOUNLegacy v computation
KOUNR(T2)/R(T1) v computation
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04/06/2003
04:42 GMT
KTLXVCP 11
KOUNStaggered 240/360
EL = 1.5 deg
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04/06/2003
KTLXVCP 11
KOUNStaggered 240/360
EL = 1.5 deg
va = 28.08 m s-1 va = 34.63 m s-1
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R/V Ambiguity Mitigation Techniques
va = 35.52 m s-1 va = 45.17 m s-1
KOUNPhase Coding (SZ-2)
KOUNStaggered 184/276
EL = 1.5 deg
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Conclusions
• RRDA dedicated to WSR-88D evolution– Flexible synchronizer and signal processor– Archive I recorder– Development tools
• Staggered PRT is the choice for upper elevations– Complete separation in time: f(T1, T2)
– Use at lower elevations?
