the University of Oklahoma Spectral Polarimetry for Identifying and Separating Mixed Biological Scatterers Svetlana Bachmann1,2, Dusan Zrnic2, 1 Cooperative Institute for Mesoscale Meteorological Studies, The University of Oklahoma; 2 NOAA/OAR National Severe Storm Laboratory, Norman, OK Case – KOUN (Norman, OK) - 09/07/2004 11pm CDT (04Z) – Clear Air with Mixed Biological Scatterers Summary A B Signal Processing Example – radial at azimuth 180 Spectral densities of polarimetric variables (Spectral Polarimetry) We examine Doppler spectra and show that separation of birds from insects is possible if the antenna is pointing in (or near) the direction of wind. Further, spectral densities of dual polarization variables contain discernible signatures that allow discrimination between birds and insects and lead to the measurement of winds aloft. Spectral fields DC removed from I and Q Ground Clutter removed Notch and Interpolate spectral coefficients corresponding to near-zero velocity Pulse Pair velocity estimator Ranges 30 - 70 km, Azimuths 0 - 360 Polarimetric variables are computed for each Doppler velocity (spectral density) using H- and V-channel spectral coefficients. Spectral densities are plotted for all range locations in a radial. H PH, dB Velocity, m s–1 Velocity, m s–1 PH Example - radial at azimuth 180 V Zdr |hv| dp Range, km Zdr Velocity, m s–1 Altitudes Flight velocity Flight direction Polarimetric values (Zrnic and Ryzhkov, 1998) below 3 km, mainly under 900 m 8 – 22 m s–1 Favorable winds –1 dB < Zdr < 3 dB dp > 100° several hundred meters 1 m s–1 or less (small insects, spiders, etc.) Passive wind tracers Zdr < 10 dB dp < 40° Facts Migrating Birds Wind-carried Insects Velocity, m s–1 Velocity, m s–1 Zdr, dB Range, km PPI at 0.5 elevation Continuous & Sporadic Bands above the noise power are evident in spectral fields for each radial of the PPI |hv| H channel Reflectivity Velocity, m s–1 Velocity, m s–1 |hv| 100 80 60 40 20 Velocity, m s–1 Insects Birds Range, km 20 15 10 5 -5 <-10 Z, dB dp Velocity, m s–1 Velocity, m s–1 dp,  Azimuth, deg Average spectral densities from 30 to 70 km range for each radial of PPI Polarimetric variables computed from selected spectral coefficients Migrating and wandering birds are not passive wind tracers and they contaminate wind velocity estimates. Wind-carried insects are useful scatterers that provide echoes needed for wind profiling. Zdr, (dB) VAD from spectral density of Zdr v, m s–1 30 20 10 -10 -20 -30 100 80 60 40 H channel Velocity Radar set up 30 km 70 km H channel Velocity Elevation Scan (PPI) – 360 radials at 0.5 elevation angle |hv| -35 100 80 60 40 20 Radial – two polarization channels 468 range locations Ra = 117 km v, m s–1 30 20 10 -10 -20 -30 Velocity, m s–1 H Range, km Noise V Ground Clutter Contaminated Good Separation 35 N S W E NE SE SW NW Range location – two time series of I & Q samples Recovered 128 I & Q samples H channel va = 35 m s–1 Azimuth Wind Velocity Insects Birds Histograms of polarimetric variables azimuth 180, ranges 20 – 70 km 128 I & Q samples V channel Zdr, dB vmax ~ 30 m s–1 Conclusions vmax ~14 m s–1 |hv| Polarimetric variables computed from contiguous sections of Doppler spectra allow almost perfect discrimination of birds and insects. Wind data contaminated by migrating birds can be recovered: by computing the mean Doppler velocity from selected spectral coefficients: window positioning - from block analysis of spectra or from polarimetric variables; window span - depends on number of spectral coefficients, needed accuracy of the estimator, and azimuth angle. by reconstructing VAD of wind from spectral densities of polarimetric variables. Range Horizontal Vertical For a range location Spectrum H and Spectrum V dp, deg Adaptive Window of selected spectral coefficients in Spectrum H A Range location Polarimetric Variables Zdr, |hv|, dp computed from contiguous sections of spectral coefficients discriminate Insects and Birds Dual Polarization Doppler Radar B