1. Sebastian Torres NEXRAD Range-Velocity Ambiguity Mitigation Fall 2004 – Technical Interchange Meeting

2. Part One Recap of last TIM

3. Surprise! GMAP GMAP adopted as the ORDA GCF in FY04 Ice et al. (2004) performed initial assessment –Blackman window required for 50 dB+ suppression –Input noise required for small number of samples Devoted good part of FY04 to study GMAP –Implemented in MATLAB from source code

4. Yet Another Windows ® Update Window choice –Sachidananda et al. (1998) recommended using von Hann window –Blackman window is more aggressive Larger standard error of estimates (needs to be quantified) Recommendation: Consider an adaptive scheme that uses the presence/strength of clutter for window selection

5. Let’s Make Some Noise Noise estimation –A rank order noise estimation algorithm is invoked if noise is not provided to GMAP –Filter notch width depends on noise level A good noise estimate is critical for the filter’s performance –SZ(8/64) phase coded out-of-trip echoes appear as noise –Recommendation: Provide reliable noise estimate to GMAP

6. Filling the Void Spectral reconstruction –GMAP fills notched spectrum using Gaussian interpolation Biases are minimized Process assumes coherent signal spectrum –Recommendation: Clutter with strong signal: use spectral reconstruction Clutter not with strong signal: bypass spectral reconstruction (notch filter) –GMAP modification: enable/disable spectral reconstruction

7. It’s just a phase… Time-series reconstruction –GMAP operates in the power spectrum domain Phase information is lost –SZ-2 requires time-series for cohering process –Recommendation: Save unfiltered phase spectrum and use zeroes in the gap GMAP modification: return number of spectral components with clutter

8. SZ-2 Clutter Filtering (I) Conditions for filtering –Determined by maps Bypass map Clutter censor zones –Determined by clutter strength Clutter power is not available in maps GMAP removed power is a good estimate of clutter power only for CSR > 0 dB –Recommendation: Use maps as in legacy WSR-88D Use total power if clutter is not with the two strongest trips

9. SZ-2 Clutter Filtering (II) Sequence of operations –Clutter must be removed first Cohere to trip with clutter Apply GMAP Censoring –Recommendation: Do not recover weak signal if clutter is not with the strong signal

10. Part Two Status of the SZ-2 Algorithm

11. SZ-2 Evolution Initial recommendation on Aug 15, 2003 Interim recommendation on May, 2004 –Incorporation of GMAP (with a couple of modifications) –Ability to handle clutter in any trip –PNF optimization –Spectrum width computation New recommendation on June 1, 2004 –GCF bypassing using CSR (in addition to maps) –New censoring rules and refined thresholds Thresholds may require further refinement after operational tests Errata on June 22, 2004

12. Scan Strategy Long PRT (non phase coded) used to retrieve –Filtered powers –GMAP removed powers –Spectrum widths Short PRT (phase coded) used to retrieve –Strong and weak trip velocities –Strong trip spectrum width Weak trip spectrum width from the long PRT scan

13. The SZ-2 Algorithm (I) Determine overlaid trips Determine clutter location(s): 3 cases Window time series If needed, filter clutter –Cohere to trip with clutter –Apply GMAP range 1 st trip2 nd trip3 rd trip4 th trip PLPL P th P1P1 P2P2 P3P3 P4P4 Long PRT powers are clutter filtered

14. The SZ-2 Algorithm (II) Determine strong and weak trips –Cohere to trips with recoverable signals –Compute autocorrelations Cohere to strong trip Compute strong trip velocity Apply PNF Strong trip cohered Weak trip modulated PNF vvsvs

15. The SZ-2 Algorithm (III) Cohere to weak trip Compute weak trip velocity Compute strong and weak trip powers Compute strong trip spectrum width Censor unrecoverable data –Eight censoring rules –Recommendation: Censoring thresholds should be in adaptation data

16. SZ-2 Censoring Three types of returns –Significant –Overlaid-like (purple haze) –Noise-like (not shown on displays) SZ-2 censoring occurs in –Doppler velocities –Spectrum widths

17. SZ-2 Censoring Rules (I) Noise-like cells –(1) Low SNR in the long-PRT scan Cells with non-significant powers are not considered as candidates for recovery during the short-PRT scan K SNR is specified in the VCP definition –(2) Low SNR in the short-PRT scan Takes care of advection between long- and short- PRT scans K SNR is specified in the VCP definition

18. SZ-2 Censoring Rules (II) Overlaid-like cells –(3) Low SNR* Out-of-trip signals appear as noise Thresholds for strong and weak trips are K s and K w –(4) Weak trip not recoverable Recovery region from plots of SD(v 2 ) in the S 1 /S 2 vs.  n1 plane Different regions for narrow and wide weak-trip spectrum widths Recoverable Unrecoverable

19. SZ-2 Censoring Rules (III) Overlaid-like cells (cont’d) –(5) High CSR Strong clutter residue makes recovery of overlaid signals very difficult Thresholds for the strong and weak trips are K CSR1 and K CSR2 –(6) Clutter location Weak trip recovery only feasible is clutter is with strong trip

20. SZ-2 Censoring Rules (IV) Overlaid-like cells (cont’d) –(7) Large weak trip spectrum widths Spectrum widths are derived from long-PRT  v saturates at ~4.8 m/s with PRT #1 Threshold is  v,max –(8) Triple or quadruple overlay SZ-2 can recover at most two overlaid trips Third or fourth strongest trips are censored

21. Future Enhancements Proposed SZ-2 algorithm provides significant improvement compared to legacy algorithms Identified 4 areas for further improvements –Use of GMAP without spectral reconstruction –AP clutter suppression –Recovery of overlaid echoes with comparable powers –Weak trip spectrum width computation Need more research –Cost-benefit analyses

22. Part Three Performance of the SZ-2 Algorithm Case Examples

23. Set Up Data collected with KOUN radar –RRDA with analog or digital receiver –Experimental VCP, lowest elevation angles, 5 scans at each elevation angle Non PC, long PRT Non PC, medium PRT PC, medium PRT Non PC, short PRT PC, short PRT Proposed SZ-2 algorithm (June 04) completely implemented in MATLAB

24. Stratiform Precipitation v a = 35.5 m s -1, r a = 117 kmv a = 8.9 m s -1, r a = 466 km Reflectivity Long PRT EL = 0.5 deg 10/08/02 15:11 GMT Legacy Velocity Short PRT

25. Stratiform Precipitation v a = 35.5 m s -1, r a = 117 km SZ-2 Velocity Short PRT EL = 0.5 deg 10/08/02 15:11 GMT Legacy Velocity Short PRT

26. Stratiform Precipitation v a = 35.5 m s -1, r a = 117 km SZ-2 Velocity Short PRT EL = 0.5 deg 10/08/02 15:11 GMT SZ-2 Censoring Short PRT

27. Stratiform Precipitation v a = 35.5 m s -1, r a = 117 km SZ-2 Velocity Short PRT EL = 0.5 deg 10/08/02 15:11 GMT SZ-2 Censoring* Short PRT

28. Stratiform Precipitation v a = 23.7 m s -1, r a = 175 km SZ-2 Velocity Medium PRT EL = 0.5 deg 10/08/02 15:11 GMT Legacy Velocity Medium PRT

29. Stratiform Precipitation v a = 23.7 m s -1, r a = 175 km SZ-2 Velocity Medium PRT EL = 0.5 deg 10/08/02 15:11 GMT SZ-2 Censoring Medium PRT

30. Stratiform Precipitation v a = 23.7 m s -1, r a = 175 km SZ-2 Velocity Medium PRT EL = 0.5 deg 10/08/02 15:11 GMT SZ-2 Censoring* Medium PRT

31. Convective Precipitation v a = 35.5 m s -1, r a = 117 kmv a = 8.9 m s -1, r a = 466 km Reflectivity Long PRT EL = 0.5 deg 05/17/03 0:39 GMT Legacy Velocity Short PRT

32. Convective Precipitation v a = 35.5 m s -1, r a = 117 km SZ-2 Velocity Short PRT EL = 0.5 deg 05/17/03 0:39 GMT Legacy Velocity Short PRT

33. Convective Precipitation v a = 35.5 m s -1, r a = 117 km SZ-2 Velocity Short PRT EL = 0.5 deg 05/17/03 0:39 GMT SZ-2 Censoring Short PRT

34. Convective Precipitation v a = 23.7 m s -1, r a = 175 km SZ-2 Velocity Medium PRT EL = 0.5 deg 05/17/03 0:39 GMT Legacy Velocity Medium PRT

35. Convective Precipitation v a = 23.7 m s -1, r a = 175 km SZ-2 Velocity Medium PRT EL = 0.5 deg 05/17/03 0:39 GMT SZ-2 Censoring Medium PRT

36. Squall Line v a = 35.5 m s -1, r a = 117 kmv a = 8.9 m s -1, r a = 466 km Reflectivity Long PRT EL = 0.5 deg 06/11/03 6:44 GMT Legacy Velocity Short PRT

37. Squall Line v a = 35.5 m s -1, r a = 117 km SZ-2 Velocity Short PRT EL = 0.5 deg 06/11/03 6:44 GMT Legacy Velocity Short PRT

38. Squall Line v a = 35.5 m s -1, r a = 117 km SZ-2 Velocity Short PRT EL = 0.5 deg 06/11/03 6:44 GMT SZ-2 Censoring Short PRT

39. Squall Line v a = 23.7 m s -1, r a = 175 km SZ-2 Velocity Medium PRT EL = 0.5 deg 06/11/03 6:44 GMT Legacy Velocity Medium PRT

40. Squall Line v a = 23.7 m s -1, r a = 175 km SZ-2 Velocity Medium PRT EL = 0.5 deg 06/11/03 6:44 GMT SZ-2 Censoring Medium PRT

41. MCS-Squall Line v a = 35.5 m s -1, r a = 117 kmv a = 8.9 m s -1, r a = 466 km Reflectivity Long PRT EL = 1.5 deg 06/26/03 3:14 GMT Legacy Velocity Short PRT

42. MCS-Squall Line v a = 35.5 m s -1, r a = 117 km SZ-2 Velocity Short PRT EL = 1.5 deg 06/26/03 3:14 GMT Legacy Velocity Short PRT

43. MCS-Squall Line v a = 35.5 m s -1, r a = 117 km SZ-2 Velocity Short PRT EL = 1.5 deg 06/26/03 3:14 GMT SZ-2 Censoring Short PRT

44. The End