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Wave Polarization,Polarimetric SAR, and

Polarimetric Scattering Models

Yisok Oh

Dept. of Radio Engineering, Hong-Ik University

다음은 PACRIM Training Course (Workshop)의 강의 Note 중에서

1.1 Wave Properties 만을 발췌한 것으로 ,전파의 성질을 이해하는데 도움이 될 것입니다 .

Seoul National University, February 16-19, 2000

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Contents

1. Wave Polarization1.1 Wave Properties1.2 Polarization Synthesis

2. Polarimetric Radar System2.1 A Scatterometer System2.2 NASA/JPL POLSAR System

3. Polarimetric Scattering Models3.1 Surface Scattering3.2 Volume Scattering

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1.1 Wave Properties

-. What is the “Field”?-. Waves : Electromagnetic Waves by Maxwell-. Planewave Propagation in free space-. Polarization : Basic concepts-. Microwave Generation : DC to AC-. Microwave Guidance by Waveguides/ Trans. lines-. Microwave Radiation by Antennas-. EM Wave Reflection from infinite planes-. Microwave Scattering from

-. Point Targets-. Distributed Targets

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Electromagnetic Fields

Fields: Spatial distribution of a physical quantity.

Static Fields

No time-variation

Separation of Electric Field andMagnetic Field

Electromagnetic Fields

Time-varying Fields

Dynamic Fields

Co-existence ofElectric and Magnetic fields

: DC : AC

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Electrostatic FieldsE : Electric Field(showing flux lines)

Assuming infinite plates, mVd

VE /

V

Conducting Plates

E d

+

-

Direction of E : From + charges to - charges

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Magnetostatic Fields

IEEE Emblem

I : Current

H : Magnetic Field(showing flux line)

voltage

current

Electric Fields

Magnetic Fields

Assuming an infinite current line, mAI

H /2

I

H

Direction of H : Right-hand rule, RIH ˆˆˆ

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Dynamic (Time-Varying) Fields

c SS

c S

sdt

DsdJldH

t

DJH

sdt

BldE

t

BE

ElectromotiveForce(Voltage Source)

ConductionCurrent

DisplacementCurrent

Maxwell’s Equations

Time-varyingElectric Field

E(r,t)

Time-varyingMagnetic Field

H(r,t)

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WavesConsider Water wave in a pond.

Cut water surface at once(t=t0) with Kwan-Woo’s Sword ( 청룡언월도 ) and look

X(Spatial Displacement)

Wave Height

Log the height ofFishing Buoy (x=x0)as a time function

t(Time)

Wave Height

Even though the wave comes toward me, the water doesn’t !

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Electromagnetic (EM) Waves

xkztEtrE ˆcos),( 00 An Example of an EM wave:

Magnitude(source,distance,etc.)

SinusoidalWave

TimeVariation

Z-directedpropagation

Vector(Polarization)

T

2

2

k

Time

TxE

z, distancexE

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Phase Velocity

0 kzt = constantSame Phase

Assume these circles are surfing boards.

Phase velocity = velocity of the equi-phase point

kt

k

constt

t

zvp

0

Poynting Vector: trHtrEtrS ,,,

: Real Power Flow (Magnitude and Direction)

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Time-Harmonic Fields

Time-harmonic Assumption: tje Time variation

xeErE jkz ˆ)( 0

yeE

rH jkz ˆ)( 0

HjE (Maxwell Equation)

vacuumin

377

zyx ˆˆˆ z : wave prop. direction

(Phasor form)

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Planewave Propagation

x

y

z

Hy

Ex

zHE ˆ

xeErE jkz ˆ)( 0

Planewave: wavefront is plane

Spherical wave near an antenna

Approximate Planewave

in the Far-zone

22D

R

Z-directed propagatingLinear polarized (x-direction)Wave

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Polarization: shape of the locus of the E vector tip at a given point in space as a function of time.

jkzjyx eeyaxazE ˆˆ

,0

Polarization

Linear

Circular

Elliptical

2,

yx aa

Other Cases

Conditions Examples

xeEzE jkz ˆ)( 0

jkzeyjxzE ˆˆ

jkzeyjxzE ˆ2ˆ

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Exercise (determination of polarization)

jkzeyxzE ˆˆ2Find polarization of the wave,

Find instantaneous electric field:

Plot electric field:

Determinepolarization

kztyx

tjzEtzE

cosˆˆ2

expRe,

tyxtE cosˆˆ2,0

2

1

Ex

Ey

0t

t

Linear pol. with 21tan 1

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Polarization Ellipse

sin2sin2tan

cos2tan2tan

Lin. Pol.

0

0

Circular Pol.090

045

= Rotation Angle

= Ellipticity Angle

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Various Polarization States

Left Circular pol.

Wave direction Thumb

Electric Field Other fingers of left hand

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Microwave Generation

Oscillators

Tubes Solid State

KlystronTWTMagnetron

Gunn Diode MESFETHEMT, etc.

High Power

Light, Cheap

D.C. Power

Microwave(A.C.)

Instability

Resonator

Amplifying

A MESFETOscillator:

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Microwave Guidance

Two Conductors

Single Conductor

No Conductor

(Transverse ElectroMagnetic)

Waveguides

Coaxial CableTwo-wireMicrostrip

Rectangular,CircularWaveguides

DielectricWaveguide

TEM wave TE, TM waves(Optical fibers)

EH

directionA Coaxial Cable :

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Microwave RadiationDipole Antenna :

Transmission Line

(Wave guider)

Radiator(Discontinuity)

* Current : temporal Variation of charges

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Antennas

WireAntenna

ApertureAntenna

ReflectorAntenna

PrintedAntenna

Microstrip AntennaCoaxial Cable

ElectricField Lines

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EM Wave ReflectioniE

iH x

z

Perpendicular PolarizationElectric field is perpendicular

to the incidence plane

iE

iH

x

z

Parallel PolarizationElectric field is parallel to the incidence plane

Horizontal PolarizationElectric field is horizontal to Earth surface

Vertical PolarizationMagnetic field is horizontal to Earth surface

Infiniteplane

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Microwave Scattering

Radar System

Radar System

PointTarget

DistributedTarget

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2

4 R

GGPP rttr

0

3

200

4

ill

rttr A

GGPP

dsR

ggA

areaillum

rtill

.4 ,

,where

: Radar Cross Section 2m0: Scattering Coefficient