Fully polarimetric analysis of weather radar signatures [Elektronische Ressource] = Vollpolarimetrische Analyse von Wetterradar-Signaturen / von Michele Galletti

Gall_Mi

Informations

• Publié par: technische_universitat_chemnitz
• Publié le: 01 janvier 2009
• Nombre de lectures: 60
• Langue: English
• Poids de l'ouvrage: 3 Mo

Extrait

Fully Polarimetric Analysis of Weather Radar
Signatures

Vollpolarimetrische Analyse von Wetterradar-
Signaturen



Dissertation

zur Erlangung des akademischen Grades




Dr.-Ing.




vorgelegt

der Fakultaet fuer Elektrotechnik und Informationstechnik

der Technischen Universitaet Chemnitz




von Dipl. Phys. Michele Galletti

geboren am 13-11-1978 in Bologna




Chemnitz, den 26 Januar 2009

Fully Polarimetric Analysis of Weather
Radar Signatures

Vollpolarimetrische Analyse von
Wetterradar-Signaturen



Dissertation

zur Erlangung des akademischen Grades




Dr.-Ing.




vorgelegt

der Fakultaet fuer Elektrotechnik und Informationstechnik

der Technischen Universitaet Chemnitz




von Dipl. Phys. Michele Galletti

geboren am 13-11-1978 in Bologna




Chemnitz, den 26 Januar 2009
i
ABSTRACT

The present doctoral thesis deals with radar polarimetry, namely with the investigation of
properties of polarimetric variables potentially useful in radar meteorology.
For use with dual-polarization radars, the degree of polarization is analyzed. This variable
is available to planned operational radars. The degree of polarization is dependent on
transmit polarization state and, consequently, it is dependent on the radar system
operating mode. The primary operating mode of operational radars consists in
simultaneous transmission and simultaneous receive of both horizontal and vertical
components. The secondary operating mode consists of horizontal transmission and
simultaneous receive. Both degrees of polarization are investigated in this thesis.
Also, as operational systems are being updated to dual-polarization, research should start
investigating the capabilities of fully polarimetric weather radar systems. Among the
numerous variables available from this operating mode, the target entropy was chosen for
investigation, also because of its close relation to the degree of polarization.




ZUSAMMENFASSUNG


Diese (Doktor)arbeit beschäftigt sich mit Radar-Polarimetrie, insbesondere mit der
Untersuchung der Eigenschaften von polarimetrischen Variablen, die potenziellen Nutzen
für die Radar-Meteorologie haben.
Für den Einsatz in Dual-Polarisations-Radargeräten wird der Polarisationsgrad analysiert.
Diese Variable wird in künftigen operationellen Radargeräten verfügbar sein. Der
Polarisationsgrad hängt vom transmittierten Polarisationszustand und in weiterer Folge
auch vom Betriebsmodus des Radargeräts ab. Der Hauptbetriebsmodus von
operationellen Radargeräten sendet und empfängt gleichzeitig sowohl die horizontale als
auch die vertikale Komponente. Der sekundäre Betriebsmodus sendet und
empfängt simultan die horizontal polarisierte Komponente. In dieser Arbeit werden
beide Polarisationsgrade untersucht.
Da operationelle Systeme derzeit auf den Dual-Polarisationsmodus aufgerüstet werden,
sollte künftig die Anwendungsmöglichkeiten von vollpolarimetrischen
Wetterradarsystemen untersucht werden. Aus allen Variablen, die in diesem
Betriebsmodus zur Verfügung stehen, wurde die Entropie (des gemessen Objektes)
ausgewählt und wegen seiner engen Beziehung zum Polarisationsgrad näher untersucht.






ii CONTENTS



1. Introduction 1

1.1 Dual-polarization operational weather radars 3
1.2 Fully polarimetric weather radars 5


2. Fundamentals of Radar Polarimetry 8

2.1 Wave Polarimetry: Jones vector 9
2.2 Wave Polarimetry: Wave Covariance matrix 11
2.3 Target Polarimetry: Scattering matrix 13
2.4 Target Polarimetry: Kennaugh matrix 15
2.5 Target Polarimetry: Covariance (coherency) 19
2.6 Target Decomposition Theorems 22
2.7 Problems in theoretical polarimetry 25
2.8 Spinorial Concepts 28


3. Polarimetric Weather Radar 36

3.1 Poldirad Architecture 38
3.2 Construction of the Instantaneous Scattering Matrix (ISM) 43
3.3 Weather Radar Variables 47
3.3.1 Fully polarimetric measurements at horizontal/vertical polarization 47
3.3.2 LDR mode 50
3.3.3 Z mode 51 DR
3.3.4 Weather radar variables at circular polarization basis 52
3.4 Weather radar variables: phenomenology 54
3.4.1 Copolar Correlation Coefficient 57
3.4.2 Linear Depolarization Ratio 59


4. Theoretical Results 61

4.1 Overview 61
4.2 The Depolarization Response: Theory 64
4.3 The Depolarizati: Applications 70
4.3.1 Anisotropic weather targets 70
4.3.2 Isotropic weather targets 73
4.4 Propagation effects 75
4.4.1 Degree of polarization-propagation effects 75
4.4.2 Entropy – propagation effects 76
iii
5. Experimental Results 79


5.1 Overview 79
5.2 Case study 1: Convective event 79
5.3 Case study 2: Convective event 85
5.3.1 Observation of rain 85
5.3.2 Observation of isotropic weather targets (frozen hydrometeors) 91
5.4 Case study 3: Stratiform event 93


6. Conclusions (Thesen) 98







iv List of Symbols

ALD Alignment Direction
B Huynen Generator of target structure 0
CDR circular depolarization ratio
CP canting parameter
δco backscatter differential phase
H target entropy
H wave entropy w
KDP Specific Differential phase
LDR linear depolarization ratio (transmit polarization not specified)
LDR linear depolarization ratio at horizontal polarization transmit H
LDR linear depolarization ratio at vertical polarization transmit V
ORTT Orientation parameter
ρ copolar correlation coefficient hv
copolar correlation coefficient measured at hybrid mode
ρ cross-polar correlation coefficient at horizontal polarization transmit xh
ρ cross-polar correlation coefficient at vertical polarization transmit xv
p degree of polarization at horizontal polarization transmit H
p degree of polarization at vertical polarization transmit V
p degree of polarization at right-hand circular polarization transmit RHC
p degree of polarization at left-hand circular polarization transmit LHC
p degree of polarization at circular transmit (with no further specification) C
p degree of polarization at +45° linear polarization transmit +45
p degree of polarization at -45° linear polarization transmit -45
p degree of polarization at slant linear transmit (with no further specification) 45
Rx receive
Tx transmit
Z Differential Reflectivity DR
Z Reflectivity at horizontal polarization transmit H
Z Reflectivity at vertical polarization transmit V
v List of Acronyms


ADC Analog-to-Digital Converter
AME Antenna Mounted Electronics
CW Continuous Wave
DARR Delft Atmospheric Research Radar
DC Direct Current
DFT Digital Fourier Transform
DLR Deutsches Zentrum fuer Luft- und Raumfahrt (German Aerospace Center)
DLR-IPA DLR-Institut fuer Physik der Atmosphaere
DLR-HR DLR-Institut fuer Hochfrequenztechnik und Radarsysteme
DLR-HR-RK DLR-HR-Radarkonzepte Abteilung
DSP Digital Signal Processor
EEC Enterprise Electronics Corporation
IF Intermediate Frequency
ISM Instantaneous Scattering Matrix
OMT Ortho-Mode Transducer
POLDIRAD Polarization Diversity Radar
PPI Plane Position Indicator
PRF Pulse Repetition Frequency
PRI Pulse Repetition Interval
RF Radio Frequency
RHI Range Height Indicator
SAR Synthetic Aperture Radar
STC Sensitivity Time Control
WCM Wave Covariance Matrix







vi

List of Figures



Fig. 1.1 Pulsing scheme for hybrid mode 3
Fig. 1.2 Pulsing scheme for horizontal Tx, simultaneous Rx mode 3
Fig. 1.3 Pulsing scheme for single pol. receive, alternate transmission 4
Fig. 1.4 Pulsing scheme for fully polarimetric systems (I) 6
Fig. 1.5 Pulsing scheme for fully polarimetric systems (II) 6

Fig. 2.1 Degree of Polarization vs. Wave Entropy 13

Fig. 3.1 Institute for Atmospheric Physics 36
Fig. 3.2 Poldirad parabolic reflector 40
Fig. 3.3 Poldirad Boom 40
Fig. 3.4 RF enclosure 41
Fig. 3.5 Poldirad from behind 41
Fig. 3.6 IF enclosure 42
Fig. 3.7 Magnetron 42
Fig. 3.8 Alternating pulsing scheme 44
Fig. 3.9 Copolar correlation coefficient, experimental plot 57
Fig. 3.10 Copolar correfficient, theoretical plot 58

Fig. 4.1 Depolarization response plots: examples 67
Fig. 4.2 Simulation for a Marshall-Palmer drop size distribution 71
Fig. 4.3 Depolarization response plots: weather targets 73
Fig. 4.4 Simulation for isotropic weather targets 74

Fig. 5.1 Case study 1, convective event, RHIs 80
Fig. 5.2 Case study 1, convective event, rayplots 8