Space-borne Observations of Aerosols: new capabilities using multiangle polarization

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Space-borne Observations of Aerosols new
capabilities using multiangle polarization

• D. Tanré,
• the PARASOL team
• POLARIZATION ANISOTROPY of REFLECTANCES for
  ATMOSPHERIC SCIENCES coupled with OBSERVATIONS
  from a LIDAR

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Remote Sensing From satellite (using the solar
spectrum)
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• Improvements we can expect from polarization
• Better aerosol characterization polarization is
  more sensitive to some aerosol properties (like
  the refractive index)
• Easier estimate of the surface contribution over
  land

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Refractive index of the aerosols within the
accumulation mode
Polarization ratio around 110 at
670nm Refractive Index
Spectral effect for the size determination,
here
Log-normal size distributions reff0.07-0.13-0.17-
0.22mm m1.35-1.45-1.60
Herman et al., 2005
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Refractive index of the large spherical mode
Based on the location of the rainbow observed in
polarized light
radiances
Polarized radiances
(145/155) the refractive index is estimated to
be 1.350.02
Exact Reff value is not crucial
Herman et al., 2005
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Maritime aerosols Large mode is dominant (low
content)
Biomass burning aerosols Fine mode is dominant
(moderate content)
Examples of  good  aerosol inversion over ocean
(surface is well determined) measurements are
well fitted
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• Based on the spectral dependence, particles are
  large but
• No rainbow in polarization
•  Smooth  radiances in backscattered direction

Example of  bad  aerosol inversion over ocean
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Non-Spherical Aerosols in the Coarse mode
Scattering matrix of mineral aerosol particles
One Average model used for non spherical
particles. (H.Volten et al., J.G.R. 2001)
Herman et al., 2005
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Three modes over ocean fine, spherical coarse
and non-spherical coarse.
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The number of retrieved parameters depends upon
the geometrical conditions range of the
scattering angle is important
13 views of the same target
Lm total radiance Lpm polarised rad.
West
GLINT
East
d, dacc, racc, macc, a
d, dacc, racc, macc, mcoarse, a NSI
dns/(dcsdcns)
OVER OCEAN
d, dacc, a
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Total
Fine Mode
Non-Spherical Coarse  Dust 
Spherical Coarse  Maritime 
PARASOL Optical thicknesses over Ocean Sept
2005
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Why polarization is useful for aerosol remote
sensing over land
Rayleigh
Aerosols
Surface

• is low compared to atmospheric contribution
• is spectrally independent
• is more uniform
• can be roughly estimated from surface
  classification

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Fan et al., 2007
Maximum variation of the surface polarization
from Beijing to Xianghe 2.010-3 at 110-120
After atmospheric corrections from AERONET
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Deuzé et al., 2001
AEROSOL
Clear atmosphere (AOT0.03) the reflectance
at TOA is close to the surface values
Hazy atmosphere large aerosol contribution,
1.010-2 at 110-120 for AOT0.31
Illustration for Biomass Burning Aerosols
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Deuzé et al., 2001
Clear atmosphere (AOT0.08) the reflectance
at TOA is again close to the surface values
Hazy atmosphere aerosol contribution lt 10-3 for
AOT 0.7
Limitation for some aerosol types Illustration
for Desert Aerosols
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Aerosol size cut-off
Fan et al., 2007
Over Bejing
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Fan et al., 2007
78 coincident days
70 coincident days
(03/2005-05/2006)
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Spring 2005
Fine Mode
Winter 2007
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Mar.05 - Feb.06 PARA. MOD. 0.136 0.138 0.016 0.01
0 Mar.06 - Dec.06 PARA. MOD. 0.137 0.140 0.012
0.006

• Calibration procedures are different
• LUTs are different
• Spectral versus directional/polarization