Polarization diversity Polarization diversity at McGill Radar Observatoryat McGill Radar Observatory
• Dual Polarization on the S-band Radar.
Polarization Diversity: the concept
WE IMPLEMENTED A
TRANSMISSION AT 45 DEGREES:
EQUAL POWER IN. EV and EH
E
EH
EV
AND A SIMULTANEOUS, BUT SEPARATE, RECEPTION OF THE VERTICAL AND HORIZONTAL COMPONENTS OF THE ELECTRIC VECTOR.
Because of the drops’ deformation the medium is
anisotropic for EM propagation and scattering. Thus,the vertical and the horizontal components of the electric vector,EV and EH, are scattered differently and propagate at different speeds.
What information do we obtain from polarization diversity at 450 transmission and simultaneous reception of ZH and
ZV?
ZDR
DP
HV
• Equivalent reflectivity.Ze
• Ratio of to . Measures the average deformation (axis ratio) of targets.
ZH ZV
• Correlation between and . Measures the variability of shapes and orientations of the targets.
ZH ZV
MEASURABLES
• Phase difference between EH and EV . Measures the total path-integrated “mass x deformation”.(the radial derivative of , KDP, is often displayed)DP
eZ
DP
DRZ
HV
Polarimetric measurements at 2.7 PPI
Bright band not evidentin Ze is well seen in ZDR
and ρHV
Convective shower ofsimilar Ze as the BBappears different in ZDR
and ρHV
Polarimetric Measurements of BIRDS
1) Vr shows lower birds moving NE-SW while higher birds travel NW-SE.
2) ZDR is generally high and partly dependent on azimuth
3) φDP strongly dependent onazimuth (depending on whether the bird is viewedlengthwise or head-tail.
4)ρHV: Unexplained
Connection between R and polarimetric measurables
ZDR and KDP are monotonic functions of R
Errors due to DSD variability: reliable 5-yr DSDs
Estimated R
Tru
e R
Several sources of errors in rain estimation:Several sources of errors in rain estimation:Polarimetric radar Polarimetric radar
Drop deformation ?
Measurement noise in KDP, ZDR
DSD variability: Zh,
v, KDP, ZDR R
Methods of deriving R-(Zh,v,KDP,ZDR) relationships
Propagation of the DSD variability and measurement noise into R
DSD variability from 5-year data
Assumed radar noise:
σZh = 0.3 dB
σZDR = 0.17 dB
σKDP = 0.11deg/km
IDENTIFICATION OF ARTIFACTS, etc. (0.9º PPI through FLOYD)
GROUND CLUTTER(identifiedBy zero Dopplervelocity)
VrZeBut zeroDopplervelocity isalso foundin precipitation.
BEFORE DUAL POLARIZATION
HVDP
AFTER
GROUND CLUTTER
More likelybirds takingadvantage of the good winds.
Partial beam blockingby a nearby building
Is it allrain?
HV
2.72.700 PPI in PPI instratiformstratiformprecipitationprecipitation
Target ID
Z Zdr
Z Vr
Z
Vr
Z (= 0.5 deg) ZDR (= 0.5 deg)
KDP (= 0.5 degTarget ID(= 0.5 deg)
Light rainMod.rain
Rain/hail
Hail
Zoom on the Zoom on the strong cellstrong cell(0.5° PPI)(0.5° PPI)
Dry snow
graupel
Rain/Hail Wet snow
Z ZDR
KDPTarget ID
Vertical section through the strong cellVertical section through the strong cell
R Z(mm/h) (dB)
r =120km (h =2.6km)
80(1.7)
120
ZDR
(dB)
Vr
120
80
mesocyclone
HAILSTORM IN THE OTTAWA REGION (24/5/00)HAILSTORM IN THE OTTAWA REGION (24/5/00)
KDP
(deg/km)
Hi Z, low ZDR,low KDP:
HAIL !
Target IDTarget ID
r =120km(h =2.6km)
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