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Introduction to the Dual-Polarized WSR-88D.pptx

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Introduction to the Dual-Polarized WSR-88D.pptx Powered By Docstoc
					Introduction to the Dual­Polarized 
             WSR­88D
                    
             Don Burgess
        OU CIMMS/NSSL (Ret.)


        Storm-Scale Data Assimilation Workshop
                     October 2011
    Explaining Dual-Polarization
Dual-polarization radars emit EM waves with horizontal and
vertical polarizations.




- Alternating H & V Transmission requires an expensive fast switch and
longer acquisition times
        WSR­88D Dual­Polarization Upgrade




• Simultaneous Transmission And Reception (STAR); Slant 45


• Transmit at 45o, receive at both horizontal and vertical
• There is a PROBLEM!
        WSR­88D Dual­Polarization Upgrade




• Simultaneous Transmission And Reception (STAR); Slant 45


• Transmit at 45o, receive at both horizontal and vertical
• There is a PROBLEM! Split the power; 3-dB sensitivity loss
List of New WSR­88D Dual­                       Pol  Outputs
• 3 New Variables (like moments)
  – Differential Reflectivity (ZDR;    Zdr)
  – Correlation Coefficient (CC;      Rhv )
  – Specific Differential Phase (KDP;         Kdp )
• 3 New Algorithms
  – Melting Layer
  – Hydrometeor Classification
  – QPE
• 9 NEW Precipitation Estimation
     Display Products
  New Product #1: Differential Reflectivity (ZDR)

           Definition                Possible      Units     Abbreviated Name
                                     Range of
                                      Values
Measure of the log of the ratio of   -4 to 10     Decibels         ZDR
the horizontal to vertical power                    (dB)
            returns




                                                Horizontal Reflectivity

                                                 Vertical Reflectivity
    ZDR Physical Interpretation

        Spherical                 Horizontally                  Vertically
(drizzle, small hail, etc.)        Oriented                     Oriented
                              (rain, melting hail, etc.)   (i.e. vertically oriented
                                                                  ice crystals)
            Pv                              Pv                        Pv

   Ph                           Ph
                                                                 Ph




        Zh ~ Zv                      Zh > Z v                   Zh < Z v




    ZDR     ~    0 dB             ZDR > 0 dB                  ZDR < 0 dB
Typical ZDR Values for Various Targets
    New Product #2 Correlation Coefficient (CC)

           Definition               Possible   Units   Abbreviated Name
                                    Range of
                                     Values
   Measure of similarly of the       0 to 1    None       CC (AWIPS)
   horizontally and vertically                          ρHV (Literature)
polarized pulse behavior within a
          pulse volume
                   CC Physical Interpretation
   Non-Meteorological               Metr (Uniform)              Metr (Non-Uniform)
   (birds, insects, etc.)          (rain, snow, etc.)         (hail, melting snow, etc.)




Shapes are complex and        Shapes are fairly simple       Shapes can be complex and
highly variable. Horizontal   and do not vary much.          are mixed phase.
and vertical pulses will      Horizontal and vertical        Horizontal and vertical
behave very differently       pulses behave very             pulses behave somewhat
with these objects            similarly with these objects   differently with these
                                                             objects



      Low CC (< 0.85)              High CC (> 0.97)          Moderate CC (0.85 to 0.95)
Correlation Coefficient (CC   ) Typical Values




               Non-Precip        Precip
   New Product #3: Differential Phase
  Specific Differential Phase Shift (KDP)


• Definition: gradient of the difference between
  phase shift in the horizontal and vertical
  directions
• Units: degrees per kilometer ( o/km)




              Differential phase shift 
     What ΦDP Means


t6



                      ΦDP
      KDP Has Big Advantages               

• Immune to partial beam blockage, attenuation,
  radar calibration , presence of hail
• Used primarily for rainfall estimation and
  locating heavy rain




          Gradients Most Important
                = KDP!!!
                       Typical Values :: KDP




v The main difference between ZH and KDP is that ZH gets contributions from all
hydrometeors, including those comprised of ice, whereas KDP is not sensitive to ice particles.
v Almost linearly related to rainfall rate
v KDP is great at indicating high amounts of liquid precipitation
    Melting Layer  Detection Algorithm

• Run in the RPG
• Mixed phase hydrometeors: Easy detection
  for dual-pol!
  – Z typically increases (bright band)
  – ZDR and KDP definitely increase
  – Coexistence of ice and water will reduce the
    correlation coefficient (CC ~ 0.9-0.8)
• Algorithm overlay product for top and
  bottom of melting layer
• User Selectable MLDA, RUC, Sounding
ML Product in AWIPS
   Hydrometeor Classification Algorithm (HCA)
          • Run in RPG
          • Algorithm makes best guess of dominant radar
            echo type for each gate
             – Display Product for each radar elevation
               angle
          • Based on Fuzzy Logic
          • Tornado debris category to be added
Lgt/mod    Heavy            “Big                Ice       Dry    Wet              AP or
                    Hail            Graupel                            Unknown             Biological
  rain      rain           drops”             crystals   snow   snow             Clutter




                   Current Classification Options
• SOO-DOH
         20000 ft MSL
  Images\kcri_0.5_HC_20080408_0638.
  png
      Hydrometeor Classification
        Algorithm Challenges
• Run in the RPG

• Verification Limitations: We need the A10 aircraft

• “Fuzzy” Logic; assumes Zdr Accuracy

• Typical Radar sampling limitations (snow at 2000 ft AGL
  may not be snow at the surface)
      Dual­Pol QPE Algorithm
• Run in the RPG
• Uses Z, Zdr, Kdp
• 9 new products
   – Match Legacy PPS
   – Instantaneous Rate
   – User Selectable (Up to 10 durations) for
     the NWS
   – Difference products
• Legacy Products still available
The WSR­88D Dual­   Pol  Upgrade
     WSR-88D Dual-Pol Calibration


• Dual-Pol calibration is more complex than Legacy
  calibration
   – Zdr calibration
   – Initial System PHIdp calibration
   – Components/outputs are temperature sensitive
• Initial system PHIdp calibration working well
• Zdr calibration still under investigation
   – Full system calibration
       • Vertical pointing = NO
       • Cross-polar calibration = Not Yet
   – We think Zdr not calibrated to < 0.1 dB
           “Investigate System ZDR” Basics


 •   Part of “ZDR” comes from the system
     –   Different losses in H & V transmit and receive paths
     –   ZDR true = ZDR measured - ZDR sys

 •   ZDR sys initially measured during off-line calibration, then
     adjusted for drift over time


         ZDR sys = Initial ZDR        sys   + drift compensation
Updated each          Offline calibration            Retrace + 8 hr check
volume scan
0.99<R   hv ;   Range: 20-60 km; Elevation: 2.4 deg; Height < 2.5 km




    0.65 dB observed value



                                          Zdr sys error = .42 dB

0.23 dB expected value
0.99<R   hv ;   Range: 20-60 km; Elevation: 2.4 deg; Height < 2.5 km




   0.45 dB observed value



                                          Zdr sys error = .22 dB
0.23 dB expected value
         The WSR­88D Upgrade Deployment

•   All WSR-88Ds upgraded 2010
    -2012 = NO
•   10-14 days radar downtime
    during upgrade
•   System Test: Apr 10 – Sep 10
    •   KOUN: April 2010
•   Ops Test: Sep 10 – May 11
    •   Vance: Feb 2011
•   Beta Test: Jun 11 – Aug 11
    •   Wichita: June 2011
    •   Phoenix: June 2011
    •   Pittsburgh: July 2011
    •   Morehead City: July 2011
•   Full Deployment: Sep 2011 to
    Apr 2013
                                                    Sep 26, 2011




 Legend
      Deployment Complete
      Deployment In Progress
      Deployment Scheduled
Radar coverage shown is at 10,000 ft AGL or below
                                                    Jan 2, 2012




 Legend
      Deployment Complete
      Deployment In Progress
      Deployment Scheduled
Radar coverage shown is at 10,000 ft AGL or below
                                                    Jun 18, 2012




 Legend
      Deployment Complete
      Deployment In Progress
      Deployment Scheduled
Radar coverage shown is at 10,000 ft AGL or below
                                                    Dec 01, 2012




 Legend
      Deployment Complete
      Deployment In Progress
      Deployment Scheduled
Radar coverage shown is at 10,000 ft AGL or below
                                                    Apr 22, 2013




 Legend
      Deployment Complete
      Deployment In Progress
      Deployment Scheduled
Radar coverage shown is at 10,000 ft AGL or below
Life Gets More Complicated With 5
       -cm and 3-cm Radar
            The Result for 5­CM & 3­CM




• Scattering response different for
 shorter wavelengths (above)
• ZDR and KDP are different at the
        shorter wavelengths (right)
                            Summary
• WSR-88D Dual-Pol deployment underway;
  lots of data in 2012
• More work needed on dp calibration and dp
  algorithms
• Some model verification work with dp data
  can be done soon
• Lots of model verification work with dp data
  can be done with time
• How will dual-pol information be
  assimilated into models?
   •   Assimilate dual-pol variables?
   •   Assimilate dp algorithm output?
   •   Drop size and ice distributions?
   •   Something else?
Questions?
              Impacts of radar wavelength

                                                            Fields of measured Z, Z DR , and Φ      DP
                                                            at C and S bands for the storm on
                                                            03/10/2009 at 0309 UTC .

                                                            El(C) = 0.41°, El(S) = 0.48°. C-band
                                                            radar is at X = 0, Y = 0.

                                                            The areas of visible negative bias of
                                                            Z caused by attenuation at C band
                                                            are marked as A and B (left top
                                                            panel).




Taken from: Gu, et al. (   conditionally accepted to JAMC   )
      Those Darn Laws of Physics Again
•   The Full Radar Equation is Ugly
•   Radar Scattering Cross-Section Equation is Ugly
•   We Simplify Things at 10-cm Wavelength
•   10-cm: Rayleigh Approximation
    – Scattering by particles whose radii are ~1/10 of the radar
      wavelength or smaller
• 5-cm & 3-cm we must use the full Mie
  Scattering Equation…the Ugly Equation
             Important Information
• The fundamentals of this presentation and other Dual-
  Polarization training materials for outreach (NWS, media,
  others) are at:
   – http://www.wdtb.noaa.gov/modules/dualpol/index.htm

				
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