Polarimetric Weather Radar Remote Sensing Martin Hagen Institut für Physik der Atmosphäre, DLR OberpfaffenhofenMartin Hagen
Institut für Physik der Atmosphäre, DLR Oberpfaffenhofen
Institut für Physik der Atmosphäre 2Martin Hagen, WFMN09, Chemnitz, 25 - 27 Nov. 2009
State of the Art of Weather Radar
Doppler and dual-polarization Cancellation of ground
clutter Correction of attenuation
of precipitation
Institut für Physik der Atmosphäre 4Martin Hagen, WFMN09, Chemnitz, 25 - 27 Nov. 2009
Weather Radar
Wetterdienst.
Meteorologists require more:
how much rainfall? what kind of hydrometeors? how will the weather be in 10 .. 90 minutes?
Reflectivity in dBZ 7 19 28 37 46 55
Institut für Physik der Atmosphäre 5Martin Hagen, WFMN09, Chemnitz, 25 - 27 Nov. 2009
Radar Principle
Radar: Radio Detection and Ranging
A weather radar measures the power (and phase) of a transmitted electro-magnetic wave packet reflected by a particle:
Radar equation for volume targets:
Particles smaller than the wave length: (C-Band
= 5 cm, D < 5 mm) Rayleigh-scatter
r
Pt
Pr
Radar constant
D K = 6 i4
unit: dBZ
Quantification Identification
Institut für Physik der Atmosphäre 6Martin Hagen, WFMN09, Chemnitz, 25 - 27 Nov. 2009
Radar Reflectivity Factor
Institut für Physik der Atmosphäre 7Martin Hagen, WFMN09, Chemnitz, 25 - 27 Nov. 2009
Cloud and precipitation particles have different shapes, phase, size and falling behaviour
scattering properties Polarization
displaces Doppler shift of waves
Polarization and Doppler
Microphysics and Dynamics
Institut für Physik der Atmosphäre 8Martin Hagen, WFMN09, Chemnitz, 25 - 27 Nov. 2009
1960 1985 1995 2002 Doppler Radar
Doppler Radar
1976 1986 1990 2004 polarimetric Radar
polarimetric Radar
polarimetric Radar
Polarization and Doppler Radar Development
Institut für Physik der Atmosphäre 9Martin Hagen, WFMN09, Chemnitz, 25 - 27 Nov. 2009
Weather Radars in Europe (2005)
(almost) all are Dopplerized rapidly increasing number of polarimetric radars
Institut für Physik der Atmosphäre 10Martin Hagen, WFMN09, Chemnitz, 25 - 27 Nov. 2009
Polarization Doppler Radar POLDIRAD
1986 installed as the first fully polarimetric weather radar in Europe. Operations normally for research, not for operational service
www.pa.op.dlr.de/poldirad
Rosenheim / Miesbach
/ Bad Tölz
Doppler Velocity
Diff. Reflectivity
Depolar. Ratio
Different. Phase
Institut für Physik der Atmosphäre 11Martin Hagen, WFMN09, Chemnitz, 25 - 27 Nov. 2009
Doppler
-
observer
example sound: v = ±20 m/s, f0
= 5 kHz, c = 300 m/s
=> f = 5 ±
= 5 GHz, c = 3×108
m/s
f = f0f = f0 (1 + v/c) f = f0 (1 - v/c)
Institut für Physik der Atmosphäre 12Martin Hagen, WFMN09, Chemnitz, 25 - 27 Nov. 2009
Interpretation of the Doppler Velocity
blue/green
towards
from
radar
Institut für Physik der Atmosphäre 13Martin Hagen, WFMN09, Chemnitz, 25 - 27 Nov. 2009
Uniform Wind Technique
wind constant within segment.

vv v +
u = v
Institut für Physik der Atmosphäre 14Martin Hagen, WFMN09, Chemnitz, 25 - 27 Nov. 2009
Dual- Doppler Radar Observations
resolution 3-D wind fields are required
Combination of Doppler observations from different directions using more than one radar
Hohen- peißen- berg
Ober- pfaffen-
hofen37 km
Institut für Physik der Atmosphäre 15Martin Hagen, WFMN09, Chemnitz, 25 - 27 Nov. 2009
Doppler-velocity measured by the individual radars
Dual-Doppler Analyse HohenpeißenbergOberpfaffenhofen
(flow relative to storm motion) West - East from Oberpfaffenhofen (km)
So ut
h - N
or th
fr om
O be
rp fa
ffe nh
of en
(k m
-15 -70 -65 -60 -55 -50 -45 -40 -35 -30
Institut für Physik der Atmosphäre 16Martin Hagen, WFMN09, Chemnitz, 25 - 27 Nov. 2009
Doppler Wind Field using dual-Doppler and Uniform Wind
Institut für Physik der Atmosphäre 17Martin Hagen, WFMN09, Chemnitz, 25 - 27 Nov. 2009
Bistatic Doppler Radar
operating with
a magnetron
Institut für Physik der Atmosphäre 18Martin Hagen, WFMN09, Chemnitz, 25 - 27 Nov. 2009
Bistatic Doppler Radar
2002 1557 UTC Elevation 5.4°
Institut für Physik der Atmosphäre 19Martin Hagen, WFMN09, Chemnitz, 25 - 27 Nov. 2009
Polarimetric Radar Observations
Rain Graupel Hail
linear circular elliptic
•
alternating H and V transmit (pulse to pulse), simultaneous H and V receive
Institut für Physik der Atmosphäre 20Martin Hagen, WFMN09, Chemnitz, 25 - 27 Nov. 2009
Polarimetric Radar Observations
Rain Graupel Hail
linear circular elliptic
ZHH ZVVZ ZHH ZVH
Correlation coefficient between H and V: ρHV Differential propagation phase between H and V: DP
Institut für Physik der Atmosphäre 21Martin Hagen, WFMN09, Chemnitz, 25 - 27 Nov. 2009
Falling raindrops (app. 2 –
Observations in a vertical pointing wind channel
(Univ. Mainz), 5 mm drop.
Deq = 2.6 mm 3.4 mm 5.8 mm
Deq = 7.4 mm 8.0 mm
Example: shape of falling raindrops
b aa
b
Institut für Physik der Atmosphäre 22Martin Hagen, WFMN09, Chemnitz, 25 - 27 Nov. 2009
Rain rate and radar reflectivity
Empirical relation between rain rate R and reflectivity z
z in mm-6
bz a = R
N (D
N (D
R=13.6 mm/h R=13.6 mm/h
Institut für Physik der Atmosphäre 23Martin Hagen, WFMN09, Chemnitz, 25 - 27 Nov. 2009
Rain rate and polarimetric radar measurements
Additional information about raindrop size distribution by differential reflectivity:
sensitive to large drops.
N (D
N (D
cb ZDRz a = R
7000 1-minute drop size
Oberpfaffenhofen, 1996
Small errors in polarimetric quantities can give large errors in rain rate estimation.
Institut für Physik der Atmosphäre 24Martin Hagen, WFMN09, Chemnitz, 25 - 27 Nov. 2009
Classification of hydrometeors
Z
LDR
ZDR
Institut für Physik der Atmosphäre 25Martin Hagen, WFMN09, Chemnitz, 25 - 27 Nov. 2009
Thunderstorm line observation 12 Aug. 2004
Institut für Physik der Atmosphäre 26Martin Hagen, WFMN09, Chemnitz, 25 - 27 Nov. 2009
Hydrometeor classification 12 Aug. 2004
Institut für Physik der Atmosphäre 28Martin Hagen, WFMN09, Chemnitz, 25 - 27 Nov. 2009
Classification by Vivekanandan
et al. (1999)
Additional parameters like correlation coefficient ρHV (0) and specific differential phase KDP . Decision tree becomes difficult to define „Fuzzi Logic“ will be used to
identify the most probable particle class.
Institut für Physik der Atmosphäre 29Martin Hagen, WFMN09, Chemnitz, 25 - 27 Nov. 2009
Reflectivity
Classification
Institut für Physik der Atmosphäre 30Martin Hagen, WFMN09, Chemnitz, 25 - 27 Nov. 2009
Attenuation and Propagation degrades Classification
Attenuation can’t be recognized easily (C-Band)
Frequently observed are negative ZDR values behind reflectivity cores negative ZDR is not expected in rain
reflectivity ZH 20070815 1820
differential reflectivity ZDR
40 km 40 km 47 km
Institut für Physik der Atmosphäre 31Martin Hagen, WFMN09, Chemnitz, 25 - 27 Nov. 2009
Attenuation: Vertical Cross-Section (RHI)
strong attenuation at 3 –
4 km height (below melting layer), high Z and LDR indicate presence of hail. hail spike (flare echo) ???? must be wet melting hail with shedding water shell. unknown particle properties
no correction possible
differential reflectivity ZDR differential phase phiDP
Institut für Physik der Atmosphäre 32Martin Hagen, WFMN09, Chemnitz, 25 - 27 Nov. 2009
Quality index field for polarimetric radar products
Quality control settings for use of polarimetric data for rain rate estimation.Reflectivity
bad good
Institut für Physik der Atmosphäre 33Martin Hagen, WFMN09, Chemnitz, 25 - 27 Nov. 2009
From Research to Application
Further presentations: ground clutter
(Jens Reimann) hydrometeor classification
(Tobias Otto)
Institut für Physik der Atmosphäre 34Martin Hagen, WFMN09, Chemnitz, 25 - 27 Nov. 2009
Polarimetric Weather Radar Remote SensingMartin HagenInstitut für Physik der Atmosphäre, DLR Oberpfaffenhofen
State of the Art of Weather Radar
Weather Radar
Radar Principle
Polarization Doppler Radar POLDIRAD
Uniform Wind Technique
Bistatic Doppler Radar
Bistatic Doppler Radar
Polarimetric Radar Observations
Polarimetric Radar Observations
Rain rate and polarimetric radar measurements
Classification of hydrometeors
Hydrometeor classification 12 Aug. 2004
Classification by Vivekanandan et al. (1999)
Foliennummer 29
Attenuation: Vertical Cross-Section (RHI)
From Research to Application