NCAR ACTIVITY UPDATE

1. NCAR ACTIVITY UPDATE NEXRAD TAC MEETING28-29 April 2005 John Hubbert, Cathy Kessinger Mike Dixon, Scott Ellis, Greg Meymaris and Joe Van Andel National Center for Atmospheric Research, Boulder CO Sponsored by The Radar Operations Center, Norman OK

2. NCAR UPDATE • S-Pol back from NAME (Mexico) and Barbuda (Caribbean: no picnic) • S-Pol undergoing refurbishment: motors, gears, receiver/processor, generators, most subsystems • RVP8 took dual pol time series in NAME and it will likely be the main processor on S-Pol. • NCAR is cooperating with the ROC on S-Pol transmitter upgrades. Would like to be WSR-88D compatible. • S-Pol will be set up at Marshall this June and participate in a refractivity experiment in conjunction with CSU-CHILL and Denver NEXRAD

3. REFRACTT Experiment Summer 2005 Transition of Radar Refractivity to Operational Radars Refractivity Experiment For H2O Research And Collaborative operational Technology Transfer Rita Roberts, NCAR OS&T Briefing, 6 April 2004

4. Refractt Experimental Set Up • S-Pol, CSU-CHILL and KFTG will attempt to make coordinated refractivity measurements and integrate the water vapor information for storm initiation studies (this has not been done before). • NCAR has revived the old A1 recorder and will install it on KFTG. • NCAR will help CSU with the refractivity algorithm (along with Fabry).

5. Northeastern Colorado REFRACTT- Summer 2005 Plan is to collect KFTG refractivity data intermittently in summer 2005. Pawnee CSU CHILL staff are very interested in being able to produce refractivity fields from their CHILL and Pawnee radars. CSU-CHILL and S-Pol will potentially be available in July and August. CSU-CHILL S-Pol KFTG

6. N = 77.6 P + 3.73 x 105e TT2 What is a Refractivity measurement? • Refractivity of clear air is described by the following equation: where P is pressure, T is temperature, e is water vapor and N is the index of refraction. • For warm weather, water vapor dominates the equation. • As radar waves propagate through clear air the amount of phase shift per kilometer strongly depends on the index of refraction; the higher the index of refraction the more phase shift occurs. • The amount of phase shift between two clutter targets along a radar radial can be monitored by the radar (and automatically is by any coherent radar) and thus water vapor content can be estimated.

7. Goals of REFRACTT • Demonstrate feasibility on operational radars and motivate • NWS and FAA to install refractivity on WSR-88D and TDWR. • Demonstrate forecast improvement in models and very • short period forecasting techniques over a larger domain. • Improve basic understanding of the role of water vapor • in convective storm initiation and storm evolution. • This is technology transfer of IHOP results to the • operational community. In October 2003 the Technical Advisory Committee (TAC) to the U.S. NEXRAD Program were unanimously in support of REFRACTT goals

8. IHOP Radar Refractivity Estimates Compared to Surface Mesonet Stations Station 10 km West of S-Pol Station 20 km east of S-Pol radar Mixing ratio (g/kg) C. Pettet, T. Weckwerth, F. Fabry, J. Wilson, 2003

9. Why is it so important to have operational radars produce a refractivity field? • Potentially yield high resolution (both spacial and temporal) estimates of moisture information out to 40-60 km. • Refractivity provides information on boundary layer moisture that is crucial for forecasting thunderstorm initiation and evolution. • Refractivity data collected at all radar sites will provide important boundary layer observations for data assimilation schemes, NWP models, forecast guidance (expert) and aviation systems. • Forecasters want it!

10. EVOLUTION OF REC STEP1: Made possible by the new processing power of RVP8 OLD REC in RPG AP Detection Precip. Detection (EPRE) Sea Clutter Detection ORDA New ORPG AP Detection and Correction IN REAL TIME Precip. Detection (EPRE) Sea Clutter Detection Residual Clutter Detection

11. EVOLUTION of REC:COMBINATION of REC and PID STEP2: Using dual pol data REC Spatial Variances and Fuzzy Logic PID Dual Polarization Gate by Gate Fuzzy Logic SUPER REC • Spatial Variances • Dual Pol. Variables • Spectral Variables • Spectra versus Range

12. Zdr Calibration

13. CSU-CHILL

14. Calibration Measurables Sun Measurement Limitations: • Receive chain only • One power level Test Pulse Limitations: • Insertion losses • Very accurate calibration of source • Very accurate calibration of attenuators • Stability & maintenance of test equipment TX Power Measurement Limitations: • Insertion losses • Very accurate calibration of power meters • Stability & maintenance of test equipment

15. Zdr Calibration • Using test measurements: • Is there another way? • Use reciprocity: (scattering matrix) This means H and V crosspolar power measurements are equal!

16. Non Obtrusive Zdr Calibration (i.e., no test/monitoring equipment) (TX H, receive V) (TX V, receive H)

17. S-Pol (and now CHILL) Block Diagram RCO RCX Thus, there are now 4 separate electrical paths

18. Very Minor Complication Zdr calibration equation becomes: Where S1, S2 are the “copolar” and “crosspolar” sun calibration ratio numbers (see Hubbert et al., Studies of the Polarimetric Covariance Matrix: Part I Calibration Methodology, JTECH, 2003)

19. CSU-CHILL Scatter Plot of Crosspolar Powers Transmit V receive H Transmit H receive V

20. Mean and Standard Deviation of Crosspolar Power Plot

21. The Crosspolar power ratio as a Function of Received Power This results from using H and V receivers (in contrast to CO and CROSS receivers).

22. CHILL Experimental Data

23. Scatter Plot of S-Pol Crosspolar Powers

24. Mean Differences of Crosspolar Powers (3 dB bins)

25. PPI plots of Z, VR, uncorrected ZDR, and corrected ZDR Z (dBZ) VR(ms-1) ZDR correction = 0.36 dB ZDR, uncorrected (dB) ZDR, corrected (dB)

26. Histogram: uncorrected ZDR in cloud and drizzle Mean ZDR = -0.32 dB

27. Histogram: corrected ZDR in cloud and drizzle Mean ZDR = 0.04 dB

28. Histogram: uncorrected ZDR in Bragg scatter Mean ZDR = -0.44 dB

29. Histogram: corrected ZDR in Bragg scatter Mean ZDR = -0.08 dB

30. NEXRAD Zdr Calibration Verification & S-Pol • S-Pol can point vertically and use the fact that precipitation scatterers are isotropically oriented at vertical incidence. • Thus Zdr should be zero dB and this is regarded as truth for calibration verification.

31. S-Pol Polarization Switch Can directly swap in a Magic T

32. Proposed High Power Front End • Allows horizontal, vertical or simultaneous RF transmission • COST: switch $2000, wave guide: $400 to $500

33. Super Resolution Data and SZ Phase coding • Are they compatible?

34. Test Set: Concatenated PPI Scans

35. Power Normal resolution Super resolution Rectangular window, no SZ phase coding 64 Point Versus 32 Point Resolution

36. 64 Point Versus 32 Point Resolution Velocity Normal resolution Super resolution Rectangular window, no SZ phase coding

37. Hanning and Blackman Window Functions P1 P2 P3 Pw/Pt P2/Pt P2/(P1+P2+P3) Pt = Total rectangular area Pw = area under the window Most power (91.9% and 97%) come from the center half of points

38. Azimuth EXAMPLE: 64 Point Sliding Window 64 pts. 64 pts. 64 pts. 64 pts. (4) (1) (2) (3) Time samples Typical sampling strategy: non over lapping time series. 64 pts. 64 pts. 64 pts. 64 pts. (1) (3) (5) (7) (2) 64 pts. (4) 64 pts. (6) 64 pts. Time samples Sliding window sampling strategy: over lapping time series. • i.e., the 64 point sample window slides 32 points at a time

39. Super Res. Versus 64 Point Sliding Window Power 32 pt. rectangular window 64 pt. sliding Hanning window: No SZ

40. Blackman versus Hanning Power 64 pt. sliding Blackman window. No SZ 64 pt. sliding Hanning window. No SZ

41. Super Res. Versus 64 Point Sliding Window Velocity 32 pt. rectangular window, i.e., super resolution 64 pt. sliding Hanning window. No SZ.

42. NOW APPLY SZ PHASE CODING • The concatenated PPI scans are now overlaid and separated via the SZ algorithm. • Results compared to the moments calculated from the non overlaid data.

43. Strong and Weak Trip Echo Areas

44. Sliding Window with SZ Phase Coding Power 64 point sliding Hanning window, i.e, “super resolution” 64 point sliding Hanning window with SZ No SZ SZ phase coding used to separate overlay

45. Comparison: 32 pt vs 64 pt Sliding Window Power 32 point rectangular window, i.e, “super resolution” 64 point sliding Hanning window SZ phase coding used to separate overlay

46. Sliding Window with SZ Phase Coding Velocity 64 point rectangular window, i.e, “super resolution” 64 point sliding Hanning window with SZ SZ phase coding used to separate overlay

47. 32 pt Super Res. Versus 64 pt. Sliding Window Super Res. Velocity 32 pt. rectangular window, i.e. super resolution 64 pt. sliding Hanning window, i.e., pseudo super resolution With SZ With SZ Note the significant increase in image speckle for the 32 point velocity calculations. Thus by accepting a small amount of image smearing one gains significant improvement in standard error of velocity estimates.

48. NCAR’s NEXRAD DATA QUALITY PROGRAM • See:http://www.atd.ucar.edu/rsf/NEXRAD/index.html for publication and presentation downloads & further info. Thank You!