AERONET/ MISR/ MODIS retrieval

1
Simultaneous Retrievals of aerosol and surface
from a combination of AERONET- MODIS-MISR-POLDER
data
Algorithm Oleg Dubovik1,
Alexander Sinyuk1, MODIS Yoram
Kaufman1 Eric Vermote2
Jean-Claude
Roger2 MISR John Martonchik3,
Ralph Kahn3,
Dave Diner3, POLDER
Francois-Marie Breon4, AERONET Brent Holben1,
Ilya Slutsker1
1- NASA/GSFC, Greenbelt, MD, USA 2 - UMD,
Greenbelt, MD, USA 3 - NASA/JPL, CA, USA 4 -
CEA/DSM/LSCE, France
2
Retrieval of surface needs atmospheric correction
for aerosol effect
Retrieval of aerosol relies on assumption of
surface reflectance
Idea Less assumptions are needed in simultaneous
retrieval of aerosol and surface from combination
of up- and down - looking observations
3
Retrieval using combinations of up-looking
Ground-based and down-looking satellite observati
ons
Retrieved
Aerosol Properties - size distribution - real
ref. ind. - imag. ref. ind (AERONET sky channels)

• Surface Parameters
• BRDF (MISR, POLDER)
• Albedo (MODIS)

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AERONET- MISR - POLDER - MODIS data

• AERONET Ground-based Sun-sky radiometer
• - t(l) 0.02 at
• 6 channels 0.34, 0.38, 0.44, 0.67, 0.87, 1.02,
  1.65 mm
• I(l,Q) 0.05 at
• 4 channels 0.38, 0.44, 0.67, 0.87, 1.02, 1.65 mm
• 3 scattering angles 70
• P(l,Q) 0.02 at 0.87
• MISR
• Reflectance at
• 4 channels 0.45, 0.55, 0.67, 0.87 mm
• 9 viewing angles 70.5o, 60o, 45.6o,
  26.1o, 0o
• MODIS
• Reflectance at
• 7 channels 0.47, 0.55, 0.66, 0.87,1.2, 1.6, 2.1

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Retrieval scheme
MISR, POLDER MODIS

• Forward model
• - Detailed aerosol (same as in AERONET)
• Multiple scattering accounts for BRDF
• BRDF modeled using parameterized model
• (Rahman-Pinty-Verstraete, 1993)

Numerical inversion -Accounting for
noise -Solving Ill-posed problem - Setting a
priori constraints
Observations
aerosol particle sizes, complex refractive
index, parameters of BRDF (or Lambertian albedo)
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Inversion

• Statistically Optimized Minimization -
• Multi-term LSM Fitting (Dubovik and King 2000
  Dubovik 2004)

weighting
Lagrange parameters

• Measurements
• i1 - optical thickness
• i2 - AERONET radiances
• i3 - stellite radiances
• their covariances
• (should depend on l and Q)
• -lognormal error distributions

a priori restrictions on norms of derivatives
of i4 -size distr. variability i5 -n spectral
variability i6 -k spectral variability i7 -
surface reflectance spectral
variability
consistency Indicator
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Questions Issues

• Retrieved aerosol properties
• are there any improvements compare to
• conventional AERONET retrieval

• Retrieved surface properties
• reliable?
• are there any limitations?
• what is the difference with conventional
• atmospheric correction?

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Simultaneous fitting
August 9, 2003 t(0.44) 0.3
AERONET
MODIS
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Simultaneous fitting
Summer, 2003 MONGU
MISR-MODIS
August 9, 2003 t(0.44) 0.3
MISR
MODIS
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Comparisons of Surface Retrievals (with improved
vertical profile)
Surface Albedo
Surface BRDF
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Effect of Aerosol Vertical Distribution on the
Surface Retrievals
Assumed Profiles
12
Surface Effect on Retrievals of the Refractive
Index (low aerosol loading)
POLDER June 24, 2003 t(0.44) 0.26 , SZA470
MISR August 9, 2003 t(0.44) 0.3, SZA400
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Surface Effect on the Retrievals of the Size
Distribution (low aerosol loading)
MISR August 9, 2003 t(0.44) 0.3, SZA400
POLDER June 24, 2003 t(0.44) 0.26 , SZA470
14
Surface Effect on the Retrievals at High Aerosol
Loading
POLDER August 18, 2003 t(0.44) 0.63, SZA350
15
Surface Effect on the Retrievals of Single
Scattering Albedo
POLDER August 18, 2003 t(0.44) 0.63, SZA350
MISR August 9, 2003 t(0.44) 0.3, SZA400
16
Effect of Particle Non-Sphericity on the
Retrievals
June, 2003 Solar Village, Saudi Arabia
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Surface Effect on the Retrievals of Single
Scattering Albedo
(Almucantar inversion with corrected surface)
POLDER September 27, 2003 t(0.44) 0.24 ,
SZA700
POLDER June 7, 2003 t(0.44) 0.67 , SZA700
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Retrievals for Islands or Costal sites
Cape Verde (Island)
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• Results
• Simultaneous inversion of satellite and
• AERONET data has been developed
• Surface BRDF and Albedo can be retrieved
  simultaneously with aerosol (low and moderate t,)
• Improved retrievals of aerosol
• - refractive index and size (low t over
  vegetation)
• - wo(l) and size (over bright surface )
• The approach is very useful for sites with
  complex surface structure (Islands, costal)
• Plans
• Completing analysis
• Making operational retrievals

20
Comparisons of MISR and POLDER geometries
Mongu, August 7,9 ,10, 2003
21
Almucantar and principle plane retrievals Size
Distribution
POLDER September 27, 2003 t(0.44) 0.24 , PP
SZA340 ALM SZA700
POLDER June 7, 2003 t(0.44) 0.67 , PP
SZA230 ALM SZA700