AEROSOL over CLOUD - IUP

POLARIZATION &
ANISOTROPY of
REFLECTANCES for
ATMOSPHERIC
SCIENCES coupled with
OBSERVATIONS from a
LIDAR
PARASOL
• LOA/CNRS/Lille
• LATMOS/CNRS/Paris 6
• LMD/CNRS/Paris 6
• LSCE/CNRS/CEA/Paris
Collaborations:MODIS/CALIPSO/NASA
CNES/Toulouse (Level 1)
CGTD/CNRS/CNES/U. Lille (Level 2, 3, 4)

Directional
Measurements
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Wide FOV CCD Camera with 1600 km swath width
•+/- 43 degrees cross track - +/- 51degrees along track
Spectral
Measurements
9 spectral bands: 443-1020nm
3 are polarized (490, 670, 865 nm)
• Spatial resolution : 6.2 km x 5.3 km
• No onboard calibration system - Inflight vicarious calibration :
–2-3% absolute calibration accuracy
–1% spectral calibration accuracy
–1% polarization calibration accuracy

Over Ocean,the POLDER instrument carries enough
informations to discriminate between three different
modes of particles:
• fine mode (pollution or biomass burning),
• spherical coarse mode (maritime),
• non-spherical coarse mode (dust) (when
geometrical conditions are suitable).
Over land, the POLDER instrument uses the polarized
radiances for getting:
• fine mode (pollution or biomass burning),
• the corresponding angström exponent.

One single NS model = Volten et al.
R = ρ 670 /ρ 865 ; DLm = quality of the fit.
The fraction of AOD due to major natural and anthropogenic
components : fine mode, and a coarse mode with a combination of
hydrated spherical particles and of non spherical particles (dust).
Upper: Total radiances
Lower: Polarized radiances
Dots: measurements
Lines: retrieval
Herman et al., 2004

Why polarization is useful for aerosol remote sensing over land:
L
sol
p
• is low compared to atmospheric contribution
• is spectrally independent
• is more uniform
• can be roughly estimated from surface classification
Maximum variation of the surface
polarization from Beijing to
Xianghe ~ 2.0×10 -3 at 110°-120° After atmospheric corrections from AERONET
Fan et al., 2007
Deuzé et al., 2001

Clear atmosphere (AOT=0.03) : reflectance
at TOA is close to the surface values
Clear atmosphere (AOT=0.08) : the reflectance
at TOA is again close to the surface values
AEROSOL
Hazy atmosphere : large aerosol contribution,
1.0×10 -2 at 110°-120° for AOT=0.31
Hazy atmosphere : aerosol contribution < 10 -3 for
AOT =0.7
Illustration for
Biomass Burning
Aerosols
Limitation for some
aerosol types:
Illustration for
Desert Aerosols
Deuzé et al., 2001

LEVEL 3
Total Fine Mode
Non-Spherical Coarse: « Dust » Spherical Coarse: « maritime »
PARASOL Optical thicknesses over Ocean Sept 2005

Years
2005/6
2006/7
2007/8
2008/9
season
AOD (accumulation mode)
MAM JJA SON DJF

Benefits from Polarization:
•Determination of the refractive index (real part),
•The absorption (in the blue) and the altitude
•Aerosols above a cloud deck
New scheme that can work over land

Refractive index of the aerosols
within the accumulation mode
Spectral effect
for the size
determination,
here:
R = L 670/L 865
Spectral ratio
2,2
2
1,8
1,6
1,4
1,2
R 133
R 145
R 160
P 133
P 145
P 160
0,8
0,6
0,4
0,2
1
-0,2
0,02 0,04 0,06 0,08 0,1 0,12 0,14 0,16 0,18
Mean radius
1
0
Polarization ratio
around 110° at 670nm
Refractive Index
Polarization ratio
Log-normal size distributions
reff=0.07-0.13-0.17-0.22μm
m=1.35-1.45-1.60

Refractive index of the large spherical mode:
radiances
Polarized
radiances
Based on the location of the rainbow
observed in polarized light
Polarized phase function q( Θ)
0,2
0,1
-0,1
-0,2
0
Coarse mode
Spherical particles
rmoy=0.75 μm-sigma=0.70
λ=865 nm
q 0.75mu 1.33
q 0.75mu 1.37
q 0.75mu 1.40
q 0.75mu 1.45
q 0.75mu 1.50
80 100 120 140 160 180
Scattering angle Θ
(145°/155°) the refractive index
is estimated to be 1.35±0.02
Exact Reff value is not crucial

490nm
POLARIZED RADIANCE
0,0360
0,0340
0,0320
0,0300
0,0280
0,0260
0,0240
0,0220
0,0200
ω 0 = 0.860, 0.880, 0.902, 0.925, 0.947, 0.974
reff = 0.2µm
Molecular
Absorption
Scattering angle: 102°
0,02 0,04 0,06 0,08 0,10 0,12 0,14
no surface
Z=0.5km
Z=1.5km
Z=2.5km
Z=3.5km
Z=4.5km
Z=5.5km
Z=6.5km
Z=7.5km
Z=8.5km
Z=9.5km
Z=10.5km
AOD(490nm)=0.5
m'=0.020
m'=0.015
m'=0.025
m'=0.010
m'=0.030
m'=0.005
RADIANCE
Z=1.5km
AOD(490nm)=1.0
Z=3.5km
Z=5.5km
Aerosol Properties
are extrapolated in
the blue
Z km
4.0
3.0
Altitude:
over land
and ocean
3.5

June 2006 - December 2008
Comparison with CALIOP over land

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AEROSOL over CLOUD
*LIDAR Alt from 5km Cloud Layer product
Case study: Aug. 18 2006
CALIOP
PARASOL
MODIS

865nm
Detection (and quantification) of aerosol layers above cloud
Waquet et al., 2009
Inversion: Lidar/Parasol/Modis
AOT
Lidar PATH

f j * - PARASOL data:
Angular measurements (~15 angles) of
- Intensity (λ = 0.49; 0.67; 0.87; 1.02 μm)
- Polarization (λ = 0.49; 0.67; 0.87 μm)
A Priori Constraints limiting derivatives (e.g. Dubovik 2004) of
- for aerosols (e.g. in AERONET, Dubovik and King 2000) :
- aerosol size distribution variability over size range;
- spectral variability of complex refractive index;
- for surface (e.g. in AERONET/satellite retrievals, Sinuyk et al. 2007) :
- spectral variability of BRF/ PBRF parameters.
New inversion scheme
Both bi-directional intensity and polarization reflectance and aerosols are retrieved simultaneously
Single - Pixel Retrieval:
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*
f j
∗
0j = F ⎧
⎪ ⎛
j
⎨ ⎜
⎩ ⎪ ⎝
a j - Parameters to be retrieved:
-Aerosol propetries:
- size distribution; - real refractive index- altitude
- imaginary refractive index; - particle shape
-Surface properties (over land):
- BRF parameters; -BPRF parameters
D j
⎞
⎟
⎠
a j +
Δ j m
a
Δ j
Multi-term LSM Multi-Pixel Solution:
Multi-Pixel a priori constraints (e.g.Dubovik et al. 2008):
- limited spatial variability of each aerosol /surface parameter
- limited temporal variability of each aerosol /surface
parameter
NOTE: degree of variability constraints (smoothnes) can be
different and adequately chosen for each parameter
Dubovik et al., 2009

B
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Retrieved parameters:
Refractive index (réel): 1.53-1.55
Non-spherical fraction: 97%
Aerosol layer altitude (width 1.5 km): 0.4 km (Jan 1); 0.5 km (Jan 3)
0.7 km (Jan 5); 1.2km (Jan 6)
Aerosol Optical Thickness
Preliminary results from PARASOL over a bright surface ( Banizoumbou, Niger)
PARASOL: 4 PIXELS
North 13 0 30 ’’, East 2 0 36 ’’; North 13 0 30 ’’, East 2 0 43 ’’
North 13 0 36 ’’, East 2 0 36 ’’. North 13 0 36 ’’, East 2 0 43 ’’
5
4
3
2
1
Aerosol Optical Thickness over BANIZOUMBOU
(January 1-6, 2007)
0.44 AERONET
0.67 AERONET
0.87 AERONET
1.02 AERONET
0.44 PARASOL
0.67 PARASOL
0.87 PARASOL
1.02 PARASOL
0
1 2 3 4 5 6 7
Days: 1- 6 of January, 2007
Single Scattering Albedo
1
0.95
0.9
0.85
Absorption of Aerosol over BANIZOUMBU
(January 1-6, 2007)
0.8
Jan 1, AERONET
Jan 3, AERONET
Jan 5, AERONET
Jan 6, AERONET
0.75
Jan 1, PARASOL
Jan 3, PARASOL
Jan 5, PARASOL
0.7
Jan 6, PARASOL
0.4 0.5 0.6 0.7 0.8 0.9 1 1.1
Wavelengths, μm
Surface Albedo
0.7
0.6
0.5
0.4
0.3
0.2
0.1
January 3, 2007
January 6, 2007
Surface albedo over BANIZOUMBU
(January 1-6, 2007)
MODIS
PARASOL
0
0 0.5 1 1.5 2 2.5
Wavelengths, μm

PARASOL data are available: New instrument
Level 1 data :http://parasol-polder.cnes.fr/
PARASOL aerosol and cloud products are available on line at
http://www.icare.univ-lille1.fr/
PARASOL is slowly leaving the A-Train
New instrument: Extension to MIR channels (1.6 and
2.1µm) and to UV (0.36µm)

The debate : How good (or
bad) are the present aerosol
products over ocean?

AOD P =a x AOD M + b (0.25°x0.25° resolution; 52 months)

Red dots: AERONET oceanic sites
4206 Coincident measurements: 03/2005-06/2008

Backup slides

AOT of PARASOL/POLDER-2
AOT of PARASOL
VALIDATION: land
AOT of AERONET Fine Mode (r≤0.3µm)
Ångström Exponent of PARASOL
Ångström Exponent of PARASOL
Ångström Exponent of AERONET Fine Mode
AOT of AERONET Fine Mode (r≤0.3µm) Ångström Exponent of AERONET Fine Mode

Total AOT 670 nm
Fine Mode AOT 550nm
GSFC [Anthropogenic] Hamburg
Parasol MODIS
MODIS give very good results for total AOT.
Parasol and MODIS fine mode AOT are excellent
Parasol MODIS
Bréon et al. 2009/GEOMON
AOD COMPARISON BETWEEN MODIS or PARASOL with AERONET

Fine Mode AOT 550nm
Total AOT 670 nm
Mongu [Biomass Burning]
Parasol MODIS
Bréon et al. 2009/GEOMON
MODIS gives
good results
for total AOT.
Parasol fine
mode AOT is
excellent -
MODIS is not
as good
AOD COMPARISON BETWEEN MODIS or PARASOL with AERONET

AEROSOL over CLOUD - Detection
Difference in Cloud Top Pressure retrieval from O2 and Rayleigh Scattering.
04 2005 08 2005