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)