Size distributions from AERONET : Accuracy, Issues, Improvements O. Dubovik O. Dubovik 1 1 , B. N. Holben , B. N. Holben 1 1 , A. Smirnov , A. Smirnov 1, 1, T. F. Eck T. F. Eck 1 1 , , T. Lapyonok T. Lapyonok 1 1 , A. Sinyuk , A. Sinyuk 1 1 , M. Sorokin , M. Sorokin 1 1 , D. Tanre , D. Tanre 2 2 , , P.Goloub P.Goloub 2 2 , I. Slutsker , I. Slutsker 1 1 and D. Giles and D. Giles 1 1 1- Goddard Space Flight Center, NASA (AERONET) 2- Université de Sci. et Tech. de Lille , France (PHOTON)
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Size distributions from AERONET : Accuracy, Issues ... · (Dubovik and King, JGR, 2000)and King, JGR, 2000. Single scattering: aerosol particles - homogeneous spheres Particle Size
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Size distributions from AERONET : Accuracy, Issues, Improvements
O. DubovikO. Dubovik11, B. N. Holben, B. N. Holben11, A. Smirnov, A. Smirnov1,1, T. F. EckT. F. Eck11, , T. LapyonokT. Lapyonok11, A. Sinyuk, A. Sinyuk11, M. Sorokin, M. Sorokin11, D. Tanre, D. Tanre2 2 , ,
P.GoloubP.Goloub22, I. Slutsker, I. Slutsker1 1 and D. Gilesand D. Giles11
1- Goddard Space Flight Center, NASA (AERONET)2- Université de Sci. et Tech. de Lille , France (PHOTON)
ObservationsObservationsNumerical inversion:Numerical inversion:-Accounting for noise-Solving Ill-posed problem- Setting a priori constraints
Forward model:Forward model:-Spectral and angular scattering by particles with different sizes, compositions and shapes- Accounting for multiple scattering in atmosphere
Complex Refractive Index at λ = 0.44; 0.67; 0.87; 1.02 µm
0.01
0.02
0.04
0.05
0.07
0.1 1 10
dV/d
lnR
(µm
3 /µm
2 )
Radius (µm)
Multiple scattering:scalar radiative transfer with Lambertianground reflectance solved by DisOrds (Nakajima-Tanaka or Stamnes et al.)
INPUTINPUT of Forward Model
0.00
0.01
0.10
Wavelength (µm)0.44 0.67 0.87 1.02
Imarinary PartImaginary Part
1.35
1.40
1.45
1.50
1.55
1.60
Wavelength (µm)0.44 0.67 0.87 1.02
Real Part
0.01
0.1
1
10
100
1000
0 20 40 60 80 100 120 140
Almucantar Fitting
Inte
nsity
Scattering Angle (degree)
Int(0.44) * 1000
Int(0.67) * 100
Int(0.87) * 10
Int(1.02)
0
0.1
0.2
0.3
0.4
0.5
0.40 0.60 0.80 1.0
Fitting of optical thicknessin retrievals
MeasurementsFitting
Opt
ical
thic
knes
s
Wavelenths (micron)
0
0.05
0.1
0.15
0.2
0.25
0. 1 10
Retireved size distribution
Radius (microns)
µm3 /µ
m2 )
1.35
1.40
1.45
1.50
1.55
1.60
Wavelength ( µm)0.44 0.67 0.87 1.02
Real Part
0.00
0.01
0.10
Wavelength ( µm)0.44 0.67 0.87 1.02
Imarinary PartImaginary Part
Fitting as a retrieval strategy
Accuracy ???
Theoretical limitations
Forward model:- particle shapes: spheres, spheroids (shape retrieval ?)- particles are homogeneous (bi-components ?)- horizontal homogeneous- vertically homogenous aerosol or assumed profile of extinction (?)- assumed surface albedo or assumed BRDF - assumed gaseous absorption
Inversion assumptions:- smoothness constraints on size distribution- smoothness constraints of spectral dependence of ref. Index- log-normal distribution of random errors
Perspectives:- assuming bi-component aerosols- retrieval of BRDF from combination of AERONET with satellite and aircraft observations- retrieval of shape distribution
((++) ) CAN BECAN BE retrievedretrieved ((--) ) CAN NOT BECAN NOT BE retrievedretrieved
Sensitivity to forward model limitationsSensitivity to forward model limitationsMixed aerosols (inhomogeneous spherical aerosols):Mixed aerosols (inhomogeneous spherical aerosols):
-- ExternallyExternally mixed (mixed (nn(l) and (l) and kk(l) different for fine and coarse modes)(l) different for fine and coarse modes)
-- InternallyInternally mixed (mixed (nn(l) and (l) and kk(l) different for core and shell) (l) different for core and shell) -- Biomass BurningBiomass Burning
Non-spherical aerosols:-- SpheroidsSpheroids ((prolateprolate, axis ratio 2) , axis ratio 2) -- Desert dustDesert dust