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Z dr CALIBRATION

Z dr CALIBRATION. Technical Interchange Meeting 18-19 October 2010. John Hubbert, Mike Dixon, Scott Ellis, Greg Meymaris. National Center for Atmospheric Research Boulder, Colorado (hubbert@ucar.edu). Z dr Calibration. S HH. Z dr Calibration. S VH. Z dr Calibration.

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Z dr CALIBRATION

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  1. Zdr CALIBRATION Technical Interchange Meeting 18-19 October 2010 John Hubbert, Mike Dixon, Scott Ellis, Greg Meymaris National Center for Atmospheric Research Boulder, Colorado (hubbert@ucar.edu)

  2. Zdr Calibration SHH

  3. Zdr Calibration SVH

  4. Zdr Calibration

  5. Non Obtrusive Zdr Calibration (i.e., no test/monitoring equipment)

  6. Front End for S-Pol Dummy Load H Magic-T Fast switch V Dummy Load TX Advantage: Only H and only V paths are identical to simultaneous H/V paths. The is not true for NEXRAD!

  7. WSR88-D Block Diagram I&Q (H) Test plane H Receiver NEXRAD Switching Network TX V Receiver I&Q (V) S S

  8. Zdr Cal. For NEXRAD only only S S

  9. Zdr Cal. For NEXRAD S only PH PV 88D Zdr = S only PV PH

  10. WSR88-D Block Diagram Power Measurement I&Q (H) H Receiver Test plane Coupler S NEXRAD Switching Network only PH, PV TX V Receiver I&Q (V) S only PV, PH, Measure:

  11. Transmit Power Measurement S only PV, PH, Measure: S only only PH, PV PV S PH only PV M= N= S PH Because the electrical paths are identical, all uncertainties cancel for these two ratios!

  12. Zdr Cal. For NEXRAD 88D Zdr = S S only PV PH only PH PV 88D Zdr, cal= 88D Zdr MN = Zdr

  13. Sun Measurements • Scan the sun passively • Scan parameters • 7 deg. By 3 deg. Box • 1 deg./ sec • 0.1 deg. elevation steps • Sun power at about -100 dBm; Spol sensitivity -113 dBm • Grid data (we used data from 3 consecutive box scans) • Integrate data over about 1 to 1.25 degree width 17

  14. Sun Measurements On 8 August 10 consecutive box sun scans made The calculated S1S2 numbers are (linear scale) 0.7760 0.7789 0.7854 0.7773 0.7843 0.7713 0.7795 0.7745 0.7812 0.7767 The mean is 0.7885 with a standard deviation of 0.0041. The fractional standard deviation is 0.023dB The 2 sigma uncertainty of 0.7885 is: -1.032 +/- 0.007 dB mean uncertainty Caveat: Neglects Type B errors! 18

  15. Solar Scan Data V-H power H V Some Zdr bias in sharp reflectivity gradients

  16. Crosspolar Power Measurements Similar analysis can be done for crosspolar power measurements: • Scan rate of 12 deg/sec • 14 PPI scans, 64 point intergration -0.312 -0.335 -0.326 -0.341 -0.347 -0.357 -0.347 -0.263 -0.276 -0.304 -0.337 -0.319 -0.343 -0.319 (dB) The mean is -.323 dB and the fractional standard deviation is .026 dB The mean of the numbers above, however, has a two standard deviation fractional uncertainty of 0.014 dB. (The uncertainty figure of 0.014dB is for only the Type A errors. It does not include any possible Type B errors, e.g., errors that may be the result of the data processing or other unknown sources) 21

  17. Measuring Cross-polar Power Ratio • Can alternate between H and V transmit PPI scans • Close time proximity • Indexed beams • Can point radar at a line of clutter targets and alternate H and V transmit • Average a lot of data • Watch for saturation 20

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

  19. Thank Youfor Your AttentionQuestions? hubbert@ucar.edu 23

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