1

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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Algorithm Performance

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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

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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 = 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

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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?