wenbo sun, bruce wielicki, david young, and constantine lukashin 1.introduction 2.objective 3.effect...

Wenbo Sun, Bruce Wielicki, David Young, and Constantine Lukashin

1. Introduction

2. Objective

3. Effect of anisotropic air molecules on radiation polarization

4. Depolarization of linearly polarized light by aerosols

5. Height of GSLC site on laser depolarization at TOA

6. Conclusion

Depolarization of polarized light by atmospheric molecules and aerosols


CLARREO Science Definition Team Meeting, Hampton, VA, April 10-12, 2012

E1E10

E10 E1

E2

21

22

1

2

||

||

E

E

I

IDePol

0DePol

For single scattering, if particle shape is symmetric to the incidence direction, the scattered light is not depolarized; but multiple scattering can cause depolarization for any particle shapes.

The depolarization of the linearly polarized light by atmospheric components will incur uncertainty in the calibration of space-borne sensors for polarization with ground to space laser calibration (GSLC) system.

Polarized light is depolarized by atmospheric components

Introduction

1. In this study, we firstly examine the effect of molecular anisotropy on the polarization of Earth-atmosphere solar radiation.

2. We also calculated the depolarization of light by small sphere aggregates and irregular Gaussian-shaped particles, to reveal the effect of aerosols on the depolarization of linearly polarized light.

3. By doing these, we aim to achieve an accurate modeling of polarized radiation for CLARREO PDM and GSLC applications.

Objective

cos2

3000

0cos2

300

00)cos1(4

3sin4

3

00sin4

3)cos1(

4

3

)(

22

22

P

2

)1(2

For randomly oriented anisotropic molecule Rayleigh scattering (Hansen and Travis 1974)

Effect of anisotropic air molecules on radiation polarization

cos2

3000

0cos2

300

00)cos1(4

3sin

4

3

00sin4

3)1()cos1(

4

3

)(

'

22

22

P

For isotropic molecule Rayleigh scattering (Chandraskhar 1950)

1

21'

03.0For air

How does the air molecule depolarization affect the polarization of upward radiation?


WL = 490 nm SZA = 21.72 deg

90 75 60 45 30 15 00.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

SZA = 21.72o

WL = 490 nmPristine SkyOcean Surface Wind = 7.5 m/s

anisotropic molecule

D

OP

VZA (deg)

RAZ = 0o

isotropic molecule

0 15 30 45 60 75 900.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

RAZ = 180o

VZA (deg)

DO

P

90 75 60 45 30 15 00.08

0.12

0.16

0.2

0.24

0.28RAZ = 0o

VZA (deg)

Refl

ecta

nce

0 15 30 45 60 75 900.08

0.12

0.16

0.2

0.24

0.28

RAZ = 180o

Refl

ecta

nce

VZA (deg)


WL = 490 nm SZA = 41.58 deg

90 75 60 45 30 15 00.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

SZA = 41.58o



DO

P

VZA (deg)

RAZ = 0o

isotropic molecule

0 15 30 45 60 75 900.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

RAZ = 180o

VZA (deg)

DO

P

90 75 60 45 30 15 00.06

0.12

0.18

0.24

0.3

0.36

0.42RAZ = 0o

VZA (deg)

Refle

ctance

0 15 30 45 60 75 900.06

0.12

0.18

0.24

0.3

0.36

0.42

RAZ = 180o

Refl

ecta

nce

VZA (deg)


90 75 60 45 30 15 00.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

SZA = 21.72o



DO

P

VZA (deg)

RAZ = 0o

isotropic molecule

0 15 30 45 60 75 900.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

RAZ = 180o

VZA (deg)

DO

P

90 75 60 45 30 15 00.06

0.08

0.1

0.12

0.14

0.16

0.18RAZ = 0o

VZA (deg)

Refl

ecta

nce

0 15 30 45 60 75 900.06

0.08

0.1

0.12

0.14

0.16

0.18

RAZ = 180o

Refl

ecta

nce

VZA (deg)

WL = 532 nm SZA = 21.72 deg

Wenbo Sun, Bruce Wielicki, David Young, and Constantine Lukashin90 75 60 45 30 15 00.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

SZA = 41.58o



DO

P

VZA (deg)

RAZ = 0o

isotropic molecule

0 15 30 45 60 75 900.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

RAZ = 180o

VZA (deg)

DO

P

90 75 60 45 30 15 0

0.05

0.1

0.15

0.2

0.25

0.3RAZ = 0o

VZA (deg)

Refle

ctance

0 15 30 45 60 75 90

0.05

0.1

0.15

0.2

0.25

0.3

RAZ = 180o

Refl

ecta

nce

VZA (deg)

WL = 532 nm SZA = 41.58 deg


Comparison of Pristine-sky DOP and reflectance at 490 nm and 532 nm, SZA = 21.72 deg

90 75 60 45 30 15 00.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

SZA = 21.72o

Pristine SkyOcean Surface Wind = 7.5 m/s

WL = 532 nm

DO

P

VZA (deg)

RAZ = 0o

WL = 490 nm

0 15 30 45 60 75 900.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

RAZ = 180o

VZA (deg)

DO

P

90 75 60 45 30 15 00.06

0.12

0.18

0.24

0.3RAZ = 0o

VZA (deg)

Refl

ecta

nce

0 15 30 45 60 75 900.06

0.12

0.18

0.24

0.3

RAZ = 180o

Refl

ecta

nce

VZA (deg)


Comparison of Pristine-sky DOP and reflectance at 490 nm and 532 nm, SZA = 41.58 deg

90 75 60 45 30 15 00.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

SZA = 41.58o

Pristine SkyOcean Surface Wind = 7.5 m/s

WL = 532 nm

D

OP

VZA (deg)

RAZ = 0o

WL = 490 nm

0 15 30 45 60 75 900.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

RAZ = 180o

VZA (deg)

DO

P

90 75 60 45 30 15 00.04

0.08

0.12

0.16

0.2

0.24

0.28

0.320.360.4

RAZ = 0o

VZA (deg)

Refl

ecta

nce

0 15 30 45 60 75 900.04

0.08

0.12

0.16

0.2

0.24

0.28

0.320.360.4

RAZ = 180o

Refl

ecta

nce

VZA (deg)

CALIPSO-measured depolarization ratios of different aerosols

Depolarization of linearly polarized light by aerosols

0

0

0

0

44434241

34333231

24232221

14131211

24

V

U

Q

I

PPPP

PPPP

PPPP

PPPP

R

V

U

Q

I

s

0

0

00

00

00

00

4

0

00

0

4443

4333

2212

1211

2

Q

I

PP

PP

PP

PP

R

Q

I

s

)(4 0120112

QPIPR

I s

)(4 0220122

QPIPR

Q s

)(4 01120111221 IPIPR

III s

)(4 01220112221 IPIPR

IIQ s

0122121121 )2(8

IPPPR

I s

01221122 )(8

IPPR

I s

221211

2211

1

2

2 PPP

PP

I

I

002 I 010 II 010 IQ

We define I1 and I2 as parallel and perpendicular intensity of scattered light;

I01 and I02 as parallel and perpendicular intensity of incident light, respectively.

For linearly polarized incidence, in a proper coordinate system, we can have

For any light scattered by any particles

For linearly polarized light scattered by randomly oriented particles

Depolarization ratio for linearly polarized incidence is

Note: This is only for scattered light. For total field, we must add the transmitted light.

Calculation of the depolarization of linearly polarized light by aerosol particles

In this study, depolarization ratios of 3 particle habits are calculated. Refractive index of smoke aerosol (1.53+0.001i) is used.

.

UPML

UPML

UP

ML

UP

ML

Inner surfacefor wave source

Incident + scattered field

Scattered field only

Scattered field only

Incidence

t

H

E 0

t

E

H 0

The FDTD is a direct numerical solutionof the source-free Maxwell’s equationsdiscretized both spatially and temporarily

Phase matrix elements of irregular aerosols are calculated by the 3D UPML FDTD light scattering model

Comparison of phase matrix elements from Mie theory and the FDTD

Validation of the light scattering model

0 20 40 60 80 100 120 140 160 1800.01

0.1

1

10

100

0.01

0.1

1

10

100

x = 0.25

x = 0.5

Aggregate of 2 spheresof size parameter x

Dep

olar

izat

ion

Rat

io a

t 532

nm

(%

)

Scattering Angle (deg)

0 20 40 60 80 100 120 140 160 1800.01

0.1

1

10

100

0.01

0.1

1

10

100

x = 0.25

x = 0.5

Depo

larizt

ion R

atio

at 5

32 n

m (%

)Scattering Angle (deg)

Aggregate of 4 spheresof size parameter x

Randomly Oriented

Randomly Oriented

Depolarization ratio at 532 nm as function of scattering angle for sphere aggregates of smoke particles

Depolarization ratios of irregular aerosols have common featuresDepolarization ratios of irregular aerosols have common features

Depolarization ratio at 532 nm as function of scattering angle for Gaussian-shaped aerosol particles

0 20 40 60 80 100 120 140 160 1800.01

0.1

1

10

100

0.01

0.1

1

10

100

0 20 40 60 80 100 120 140 160 1800.01

0.1

1

10

100

0.01

0.1

1

10

100

Phase matrix elements of Gaussian particlesPhase matrix elements of Gaussian particles

Why do depolarization ratios of irregular aerosols have common features?Why do depolarization ratios of irregular aerosols have common features?

221211

2211

1

2

2 PPP

PP

I

I

Height of GSLC site on laser depolarization at TOA

0 10 20 30 40 50 60 70 80 900.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Site Altitude = 3 km

VZA (deg)

DO

P

Site Altitude = 0 km

0 10 20 30 40 50 60 70 80 900.01

0.1

1

Nor

mal

ized

For

war

d-S

catte

red

Rad

ianc

e x

VZA (deg)

532 nm DOP and normalized forward-scattered radiance at TOA for GSLC site at 0 km and 3 km altitude (AOT = 0.1 below 3 km only)

3 km

AOT = 0.1

AOT = 0.0

Received = Direct + Forward-Scattered

Conclusion

1.Aerosol is the primary component of clear atmosphere to depolarize light. Air molecules are secondary issue.

2.Randomly oriented small irregular particles have some common depolarization properties as functions of scattering angle and size parameter.

3.Depolarization ratio of scattered light in the forward-scattering direction is very small, generally smaller than ~0.3% for aerosols.

4.Lager particles result in smaller forward-scattering depolarization ratio but larger backscattering depolarization ratio.

5.Over mountain > 3km, linearly polarized laser beam is little depolarized by the atmosphere. The laser intensity is also little affected by the atmosphere.

wenbo sun, bruce wielicki, david young, and constantine lukashin 1.introduction 2.objective 3.effect...

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