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Dual-Polarization Radar Technology

Dual-Polarization Radar Technology. Photo courtesy of NSSL. Acknowledgements. Paul Schlatter and Andrew Wood @ NWS Warning Decision Training Branch Norman, OK http://www.wdtb.noaa.gov/courses/dualpol/outreach/. What Is Dual-Polarization Radar Technology Exactly?.

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Dual-Polarization Radar Technology

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  1. Dual-Polarization Radar Technology Photo courtesy of NSSL

  2. Acknowledgements Paul Schlatter and Andrew Wood @ NWS Warning Decision Training Branch Norman, OK http://www.wdtb.noaa.gov/courses/dualpol/outreach/

  3. What Is Dual-Polarization Radar Technology Exactly?

  4. Why Is Dual-Polarization Technology Important? Conventional Radar Dual-Polarization Radar –=Size (|+–) = Shape σ(|+–) =Variety –=Size Conventional radar tells us about the size of objects Dual-polarization radar tells us about the size, shape, & variety of objects

  5. Highlights of How Dual-pol Data Will Aid Decision Makers • Improved detection and mitigation ofnon-weather echoes (insects, clutter, etc.) • Melting layer identification • Hydrometeor classification (precip type) • New severe storm signatures • Better precipitation estimation

  6. List of New Products via Dual-Pol • Differential Reflectivity (ZDR) • Correlation Coefficient (CC) • Hydrometeor Classification Algorithm (HCA) • Melting Layer Detection Algorithm (MLDA) • Specific Differential Phase (KDP) • 9 NEW Precipitation Estimation Products

  7. Differential Reflectivity (ZDR) • Simple definition: • Ratio of Horizontally and Vertically Oriented Power Returns • Size and shape dependent • Values of -2 to +6 dB

  8. Differential Reflectivity (ZDR) ZDR < 0 Indicates the presence of large liquid drops. Most horizontal ZDR ~ 0 Indicates large hail or hail shafts without a lot of liquid water

  9. Physical Interpretation Pv Pv Pv Ph Ph Ph Zh ~ Zv Zh > Zv Zh < Zv

  10. Reflectivity vs ZDR Is there hail and if so where is it, exactly? Area of ZDR ~ 0 (blues)

  11. Updraft Detection • “ZDR columns”: regions of liquid water found above the environmental 0oC height (freezing level) • Water droplets “flattened” by intense updraft (ZDR > 0)

  12. Differential Reflectivity (ZDR) • Simple definition: • Measures the relationship between the horizontal and vertical power returns • ZDR is useful for: • Detecting the presence of liquid drops (especially large drops) • Detecting updrafts containing liquid water above the freezing layer • Detecting severe-sized hail

  13. Correlation Coefficient (CC) • Simple definition: The VARIETY or DIVERSITY of shapes reflected back to the radar “Spectrum width” for reflectivity Values range from 0 to 1

  14. What Do We Mean by Variety? Small Variety Example When the radar detects objects similar in size and type, the correlation coefficient is high

  15. What Do We Mean by Variety? Large Variety Example When the radar detects a variety of object sizes and types, the correlation coefficient is lower

  16. Physical Interpretation

  17. Melting Layer Helps both aviation & surface transportation better resolve precipitation type issues Identifies areas of icing Frozen Melting Liquid

  18. Winter Precip Are all these precip types the same? Right is uniform (either all rain or all snow) Center and left are mixed precip

  19. PrecipvsNonPrecip • Chaff, AP/Ground Clutter, Birds/Insects Standard Reflectivity (Z) Correlation Coefficient(CC)

  20. PrecipvsNonPrecip Developing Showers Biological Targets 0.5o Base Reflectivity 0.5o Correlation Coefficient

  21. Very Large Hail Detection Is there very large hail here? Area of low CC

  22. Correlation Coefficient (CC) • Simple definition: • Measure of similarity between the horizontally and vertically oriented pulses in a volume (VARIETY) • Lower CC values useful for identifying: • Non-weather targets • Melting layer • Very large hail

  23. Hydrometeor Classification Algorithm (HCA) • Simple definition: • Uses “fuzzy logic” algorithm to make a best guess at radar echo classification on every elevation angle scan • Combines ZDR, CC and other data • HCA is useful for: • Identifying precipitation type • Hail detection • Biological target detection • Ground clutter removal

  24. Algorithm makes best guess of dominant radar echo type For every radar elevation angle Hydrometeor Classification Algorithm Lgt/mod rain Heavy rain Hail “Big drops” Graupel Ice crystals Dry snow Wet snow Unknown AP or Clutter Biological Currently 11 Classification Options

  25. Hydrometeor Classification Algorithm

  26. SOO-DOH Images\kcri_0.5_HC_20080408_0638.png 20000 ft MSL

  27. Summary • Dual-Polarization Radar: • Provides more information about observed targets (i.e., size, shape, & variety) • Allows forecasters to make better decisions (hopefully) about issuing products • Enables your local office to improve service during hazardous weather Big Drops Hail Mixed w/Rain Heavy Rain Rain

  28. Ken Drozd NWS Tucson 520-670-5156 x 223 Kenneth.drozd@noaa.gov

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