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

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Depolarization of polarized light by atmospheric molecules and aerosols Wenbo Sun, Bruce Wielicki, David Young, and Constantine Lukashin Wenbo Sun, Bruce Wielicki ... – PowerPoint PPT presentation

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


1
Depolarization of polarized light by atmospheric
molecules and aerosols  

 
Wenbo Sun, Bruce Wielicki, David Young, and
Constantine Lukashin
Wenbo Sun, Bruce Wielicki, David Young, and
Constantine Lukashin
  • Introduction
  • Objective
  • Effect of anisotropic air molecules on radiation
    polarization
  • Depolarization of linearly polarized light by
    aerosols
  • Height of GSLC site on laser depolarization at
    TOA
  • Conclusion

CLARREO Science Definition Team Meeting, Hampton,
VA, April 10-12, 2012
2
Introduction  
 
Polarized light is depolarized by atmospheric
components
E10
E1
E10
E1
E2
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.
3
Objective  
 
  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.

4
Effect of anisotropic air molecules on radiation
polarization  
 
For isotropic molecule Rayleigh scattering
(Chandraskhar 1950)
For randomly oriented anisotropic molecule
Rayleigh scattering (Hansen and Travis 1974)
For air
How does the air molecule depolarization affect
the polarization of upward radiation?
5
WL 490 nm SZA 21.72 deg  

 
Wenbo Sun, Bruce Wielicki, David Young, and
Constantine Lukashin
6
WL 490 nm SZA 41.58 deg  

 
Wenbo Sun, Bruce Wielicki, David Young, and
Constantine Lukashin
7
WL 532 nm SZA 21.72 deg  

 
Wenbo Sun, Bruce Wielicki, David Young, and
Constantine Lukashin
8
WL 532 nm SZA 41.58 deg  

 
Wenbo Sun, Bruce Wielicki, David Young, and
Constantine Lukashin
9
Comparison of Pristine-sky DOP and reflectance at
490 nm and 532 nm, SZA 21.72 deg  

 
Wenbo Sun, Bruce Wielicki, David Young, and
Constantine Lukashin
10
Comparison of Pristine-sky DOP and reflectance at
490 nm and 532 nm, SZA 41.58 deg  

 
Wenbo Sun, Bruce Wielicki, David Young, and
Constantine Lukashin
11
Depolarization of linearly polarized light by
aerosols
CALIPSO-measured depolarization ratios of
different aerosols
12
For any light scattered by any particles
Calculation of the depolarization of linearly
polarized light by aerosol particles
For linearly polarized light scattered by
randomly oriented particles
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
Depolarization ratio for linearly polarized
incidence is
In this study, depolarization ratios of 3
particle habits are calculated. Refractive index
of smoke aerosol (1.530.001i) is used.
Note This is only for scattered light. For total
field, we must add the transmitted light.
13
Phase matrix elements of irregular aerosols are
calculated by the 3D UPML FDTD light scattering
model
The FDTD is a direct numerical solution of the
source-free Maxwells equations discretized both
spatially and temporarily
UPML
Scattered field only
Incident scattered field
UPML
UPML
.
Incidence
Inner surface for wave source
Scattered field only
UPML
14
Validation of the light scattering model
Comparison of phase matrix elements from Mie
theory and the FDTD
15
Depolarization ratios of irregular aerosols have
common features
Randomly Oriented
Randomly Oriented
Depolarization ratio at 532 nm as function of
scattering angle for sphere aggregates of smoke
particles
16
Depolarization ratio at 532 nm as function of
scattering angle for Gaussian-shaped aerosol
particles
17
Why do depolarization ratios of irregular
aerosols have common features?
Phase matrix elements of Gaussian particles
18
Height of GSLC site on laser depolarization at TOA
Received Direct Forward-Scattered
AOT 0.0
AOT 0.1
3 km
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)
19
Conclusion
  • Aerosol is the primary component of clear
    atmosphere to depolarize light. Air molecules are
    secondary issue.
  • Randomly oriented small irregular particles have
    some common depolarization properties as
    functions of scattering angle and size parameter.
  • Depolarization ratio of scattered light in the
    forward-scattering direction is very small,
    generally smaller than 0.3 for aerosols.
  • Lager particles result in smaller
    forward-scattering depolarization ratio but
    larger backscattering depolarization ratio.
  • Over mountain gt 3km, linearly polarized laser
    beam is little depolarized by the atmosphere. The
    laser intensity is also little affected by the
    atmosphere.
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