1 Sebastian Torres NEXRAD Range-Velocity Ambiguity Mitigation Staggered PRT and Phase Coding Algorithms on the KOUN Research Radar

2 Part One Research RDA (RRDA) Capabilities

3 VCP Definitions Legacy VCP definition –RPG Message 7 ICD RDA/RPG (Doc. # A) –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

4 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

5 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

6 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 (M p ) –Examples Standard staggered pattern: T 1, T 2, T 1, T 2, … –PRI 1 = 1, M 1 = 1, PRI 2 = 2, M 2 = 1, M p = 32 Block staggered pattern: T 4, T 4, T 2, T 2, T 2, T 4, T 4, T 2, T 2, T 2, … –PRI 1 = 4, M 1 = 2, PRI 2 = 2, M 2 = 3, M p = 10

7 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 T 1 /T 2 ratios Requirements for different r a Resolution given by 9.6 MHz clock

8 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: 1 st trip decoding Staggered PRT: full processing with simple GCF

9 Part Two RRDA Implementation of the Staggered PRT Algorithm

10 Assumptions Transmission sequence alternates two PRT’s for a total of M pulses N 1 and N 2 are range gates for T 1 and T 2 No echoes beyond max(r a1, r a2 ) –Overlay of “short” into “long” –Echoes extending beyond max(r a1,r a2 ) can be censored Does not assume: –M is even –T 1 /T 2 is rational –T 1 < T 2 In what follows T 1 < T 2 for clarity

11 Inputs Time-series data V(n,m) = I(n,m) + jQ(n,m) 0 < m < M 0 < n < N 1 for even m 0 < n < N 2 for odd m Associated metadata GCF Maps Adaptation Data As in legacy PSP

12 Outputs Base data –Reflectivity Z(n), for 0 < n < N 2 –Doppler velocity v(n), for 0 < n < N 1 –Doppler spectrum with w(n), for 0 < n < N 1 Z is computed through r a2 v and w are computed through r a1 –Could include censored data up to r a2

13 Algorithm 1.Suppress interference Legacy PSP algorithm 2.Compute powers and correlations P 1, R 1 for short range sweeps P 2, R 2 for long range sweeps T1T1 T2T2 T1T1

14 Algorithm 3.Apply GCF: DC removal Compute time-series mean: V m Remove |V m | 2 from P 1, P 2, R 1, and R 2 Use bypass map –Could use Sachidananda’s GCF (Rep. 3 & 4) 4.Suppress point clutter Legacy PSP algorithm 5.Compute Doppler velocities v 1 based on R 1 v 2 based on R 2

15 Algorithm 6.De-alias v 1 using v 2 Use v 1 and v 2 to determine Nyquist interval De-alias v 1 Close to MMSE for SD(v 1 ) >> SD(v 2 ) 7.Compute Doppler spectrum widths w based on P 2 and R 2 (Zrnić and Mahapatra, 1985)

16 Algorithm 8.Compute combined Echo power (N 2 ) 9.Compute Reflectivity Legacy PSP algorithm 10.Determine Significant Returns for Z Use reflectivity threshold T1T1 T2T2

17 Algorithm 11.Compute individual Echo powers (N 1, N 2 ) 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 T1T1 T2T2

18 Algorithm Performance v a1 = 22.58m s -1, v a2 = 15.06m s -1, v a = m s -1 Staggered PRT Velocity De-aliasing

19 Algorithm Performance

20 Future Work Sophisticated GCF –Spectral (Reports 3 and 4) –Others (Regression?) One-overlaid resolution –Sachidananda and Zrnic, 2003 Extension beyond r a2 –For T 1 /T 2 = 2/3 up to 2r a1

21 Part Three Preliminary Case Studies

22 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)

23 02/13/ :58 GMT KTLX VCP 11 KOUN Staggered 336/466 EL = 0.5 deg

24 02/13/2003 KTLX VCP 11 KOUN Staggered 336/466 Recalibrated EL = 0.5 deg

25 02/13/2003 KTLX VCP 11 Needs Split Cut KOUN Staggered 336/466 No need for Split Cut EL = 0.5 deg v a = m s -1 v a = m s -1

26 02/13/2003 KTLX VCP 11 KOUN Staggered 336/466 EL = 0.5 deg

27 02/13/ :58 GMT KTLX VCP 11 KOUN Staggered 336/466 EL = 1.5 deg

28 02/13/2003 v a = m s -1 v a = m s -1 KTLX VCP 11 KOUN Staggered 336/466 EL = 1.5 deg

29 02/13/ :42 GMT KTLX VCP 11 KOUN Staggered 336/466 EL = 0.5 deg

30 02/13/2003 KOUN Staggered 336/466 GCF ON w/censoring KOUN Staggered 336/466 GCF OFF KOUN Staggered 336/466 GCF ON

31 02/13/2003 v a = m s -1 v a = m s -1 KTLX VCP 11 KOUN Staggered 336/466 EL = 0.5 deg

32 02/13/2003 KOUN Staggered 336/466 GCF ON w/censoring KOUN Staggered 336/466 GCF OFF KOUN Staggered 336/466 GCF ON

33 02/13/2003 KTLX VCP 11 KOUN Staggered 336/466 EL = 0.5 deg

34 02/13/2003 KOUN Staggered 336/466 GCF ON w/censoring KOUN Staggered 336/466 GCF OFF KOUN Staggered 336/466 GCF ON

35 02/13/ :42 GMT KTLX VCP 11 KOUN Staggered 336/466 EL = 1.5 deg

36 02/13/2003 KTLX VCP 11 KOUN Staggered 336/466 EL = 1.5 deg v a = m s -1 v a = m s -1

37 03/17/ :39 GMT KTLX VCP 11 KOUN Staggered 184/276 EL = 0.5 deg

38 03/17/2003 KTLX VCP 11 KOUN Staggered 184/276 EL = 0.5 deg v a = m s -1 v a = m s -1

39 03/17/2003 KTLX VCP 11 KOUN Staggered 184/276 EL = 0.5 deg

40 03/17/2003 KTLX VCP 11 KOUN Staggered 184/276 EL = 0.5 deg v a = m s -1 v a = m s -1

41 03/17/2003 KTLX VCP 11 KOUN Staggered 184/276 EL = 0.5 deg

42 03/17/ :44 GMT KTLX VCP 11 KOUN Staggered 336/466 EL = 0.5 deg

43 03/17/2003 v a = m s -1 v a = m s -1 KTLX VCP 11 KOUN Staggered 336/466 EL = 0.5 deg

44 03/17/ :44 GMT KTLX VCP 11 KOUN Staggered 240/360 EL = 2.5 deg

45 03/17/2003 KTLX VCP 11 KOUN Staggered 240/360 EL = 2.5 deg v a = m s -1 v a = m s -1

46 03/17/2003 KTLX VCP 11 KOUN Staggered 240/360 EL = 2.5 deg

47 04/06/ :37 GMT KTLX VCP 11 KOUN Staggered 184/276 EL = 1.5 deg

48 04/06/2003 KTLX VCP 11 KOUN Staggered 184/276 EL = 1.5 deg v a = m s -1 v a = m s -1

49 04/06/2003 KOUN Legacy  v computation KOUN R(T 2 )/R(T 1 )  v computation

50 04/06/ :42 GMT KTLX VCP 11 KOUN Staggered 240/360 EL = 1.5 deg

51 04/06/2003 KTLX VCP 11 KOUN Staggered 240/360 EL = 1.5 deg v a = m s -1 v a = m s -1

52 R/V Ambiguity Mitigation Techniques v a = m s -1 v a = m s -1 KOUN Phase Coding (SZ-2) KOUN Staggered 184/276 EL = 1.5 deg

53 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(T 1, T 2 ) –Use at lower elevations?