absorption from aeronet : accuracy, issues, improvementsthe averaged optical properties of various...
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ABSORPTION from AERONET : Accuracy, Issues, Improvements
O. DubovikO. Dubovik11, B. N. Holben, B. N. Holben11, T. F. Eck, T. F. Eck11, A. Smirnov, A. Smirnov11, , 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)
The averaged optical properties of The averaged optical properties of various aerosol types various aerosol types ((Dubovik Dubovik et al., 2002, JAS)et al., 2002, JAS)
+
_
flaming combustionRio Branco, Brazil
smoldering combustionQuebec fires, July 2002
ABSORPTION of SMOKE
Retrieved Properties of Saharan DustAngstrom < 0.75 Dubovik et al., 2002
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.1 1 10
Average Size Distributions
Persian GulfSaudi ArabiaCape Verde
Radius (µm)
dV/d
lnR
(µm
3 /µm
2 )
τ(0.44) = 0.7
0.75
0.85
0.95
0.40 0.60 0.80 1.0
Average Single Scattering Albedo
Persian Gulf (n = 1.55)Saudi Arabia (n = 1.56)Cape Verde (n = 1.48)
Sing
le S
catte
ring
Alb
edo
Wavelenths (micron)
AERONET Observations of Asian DustSingle Scattering Albedo
0.86
0.88
0.90
0.92
0.94
0.96
0.98
400 500 600 700 800 900 1000 1100
Beijing 2001 α = 0.38Yulin 2002 α = 0.13
Sing
le S
catte
ring
Alb
edo
Wavelength (nm)
Comparioson of Asian dust in different locations and different years
0.88
0.90
0.92
0.94
0.96
0.98
1.00
400 500 600 700 800 900 1000 1100
Comparison of Asian Dust Single Scattering Albedoversus Saharan and Saudi Arabian Dust
BeijingAnmyon, S. KoreaDunhuang, ChinaKanpur, IndiaCape VerdeSaudi Arabia - SVBahrain
Sing
le S
catt
erin
g A
lbed
o
Wavelength (nm)
Eck et al., submittedEck et al., submitted
Urban Pollution in Beijing
0.76
0.80
0.84
0.88
0.92
0.96
1.00
400 500 600 700 800 900 1000 1100
Comparison of Asian 'Urban' Single Scattering Albedoversus Other Urban/Industrial Sites
BeijingAnmyonKanpurGSFCParisMexico CityMaldives
Sing
le S
catt
erin
g A
lbed
o
Wavelength (nm)
0.00
0.05
0.10
0.15
0.20
0.1 1 10
Beijing, China 2001 & 2002 AOD>0.4Mean of 31 almucantars / AOD level
Spheroid Model Inversions Sky Error < 7%
0.460.570.680.851.151.411.872.59
dV/ d
(ln
r) [
µ m3 /µ
m2 ]
Radius (µm)
AOD 440 nm Angstrom Exp (440/870 nm) > 0.75α440-870
1.151.291.211.281.131.211.171.16
GSFC, Paris, Mexico City, Maldives data from Dubovik et al. [2002] Table 1.
Eck et al, acceptedEck et al, accepted
Accuracy ???
Retrieval accuracy and limitationsSensitivity tests byDubovik et al. 2000
Real Part Imaginary PartSSA
τ(0.44) ≤ 0.20.05
80-100%0.05-0.07
τ(0.44) ≥ 0.50.02550%0.03
Size Distribution:
0.00
20.00
40.00
60.00
80.00
0.1 1 10
τ(0.44) = 0.05τ(0.44) = 0.2τ(0.44) = 0.5τ(0.44) = 1.0
Err
ors
(%)
Radius (µm)
bias ∆τ = ± 0.01Effective
Random errors Nonsphericitybiases
0
0.05
0.1
0.15
0.1 1 10
aureolefull almucantar
dV/d
lnR
(µm
3/µ
m2 )
Radius (µm)
1.30
1.35
1.40
1.45
1.50
1.55
1.60
Wavelength (µm)0.44 0.67 0.87 1.02
Real Part
wide angularcoverage
0.50
0.60
0.70
0.80
0.90
1.00
440
670
870
1020
440
670
870
1020
440
670
870
1020
440
670
870
1020realretrievedtau+0.01tau-0.01tau+0.02tau-0.02sky*1.05sky*0.95angl+0.5angl-0.5angl+1angl-1ga+30%ga-30%ga+50%ga-50%
τ(440nm)=0.05 τ(440nm)=0.20 τ(440nm)=0.50 τ(440nm)=1.00
wavelength, nm
optical depth, sky radiance, angular pointing and ground albedoerror effects
∆τ bias influence at ∆ω0
∆τ bias:
˜ ω 0 =τscat
τext + ∆τ
0.7
0.75
0.8
0.85
0.9
0.95
0 0.2 0.4 0.6 0.8 1
ω0(real)
ω0(real)-0.03
τ+0.01
τ+0.02τ+0.03
ω0(re
triev
ed)
τ
Sky Radiance bias:
˜ ω 0 =τscat 1- ∆( )
τext
= ω0 1- ∆( )
1.20
1.30
1.40
1.50
1.60
1.70
1.80
440
670
870
1020
440
670
870
1020
440
670
870
1020
440
670
870
1020
440
670
870
1020realretrreal/fine real/coarseretrreal/finereal/coarseretrreal/finereal/coarsefull<75<40<30
homogeneous
external mixture 1
external mixture 2
internal mixture 1
internal mixture 2
n1=1.45 n2=1.45
n1=1.45 k1=0.0035 n2=1.53 k2=0.008
n1=1.65 k1=0.035 n2=1.33 k2=0.0005
core=0.038 µm
ratio-0.33
error effects of particle mixing for different angular ranges:full almucantar, up to 75, 40 or 30 degrees
wavelengths, nm
0.50
0.60
0.70
0.80
0.90
1.00
440
670
870
1020
440
670
870
1020
440
670
870
1020
440
670
870
1020
440
670
870
1020
realretrreal retrrealretrrealfull<75<40<30
homogeneous
external mixture 1
external mixture 2
internal mixture 1
internal mixture 2
n1=1.45 n2=1.45
n1=1.45 k1=0.0035 n2=1.53 k2=0.008
n1=1.65 k1=0.035 n2=1.33 k2=0.0005
core=0.038 µm
ratio-0.33
wavelength, nm
error effects of particles mixing for different angular range of sky radiances:full almucantar, up to 75, 40 or 30 degrees
Retrieval using combinations of up-looking Ground-based and down-looking satellite
observations
Retrieved:
Aerosol Properties:- size distribution- real ref. ind. - imag. ref. ind(AERONET sky channels)
Surface Parameters:-BRDF (MISR channels)-Albedo (MODIS IR channels)
Comparisons of Surface Retrievals (Albedo)
POLDER: September 27, 2003τ(0.44) ~ 0.24 , SZA=340
0
0.1
0.2
0.3
0.4
0.5
0.4 0.5 0.6 0.7 0.8 0.9 1 1.1
Solar Village,June 7,2003
spheroid model, retrievedsphere model, retrievedassumed
Surf
ace
Alb
edo
Wavelength (µm)
POLDER: June 7, 2003τ(0.44) ~ 0.67 , SZA=230
MISR: September 27, 2003τ(0.44) ~ 0.24 , SZA=310
0
0.1
0.2
0.3
0.4
0.5
0.4 0.5 0.6 0.7 0.8 0.9 1 1.1
spheroid model, POLDERsphere model, POLDERassumedspheroid model, MISRsphere model, MISR
Surf
ace
Alb
edo
Wavelength (µm)
Solar Village, September 27, 2003
Surface Effect on the Retrievals of Single Scattering Albedo
POLDER: September 27, 2003τ(0.44) ~ 0.24 , SZA=700
POLDER: June 7, 2003τ(0.44) ~ 0.67 , SZA=700
(Almucantar inversion with corrected surface)
0.6
0.65
0.7
0.75
0.8
0.85
0.9
0.95
1
0.4 0.5 0.6 0.7 0.8 0.9 1 1.1
Solar Village,June 7,2003
spheroid model, retrieved surface albedo spheroid modelsurface albedo assumedsphere model, retrieved surface albedo sphere modelsurface albedo assumed
Sing
le S
catte
ring
Alb
edo
Wavelength (µm)
0.6
0.65
0.7
0.75
0.8
0.85
0.9
0.95
1
0.4 0.5 0.6 0.7 0.8 0.9 1 1.1
Solar Village,September 27,2003
spheroid model, retrieved surface albedo spheroid modelsurface albedo assumedsphere model, retrieved surface albedo sphere modelsurface albedo assumed
Sing
le S
catte
ring
Alb
edo
Wavelength (µm)
Validation
Studies of:
- Haywood, et al. (2003,…
- Muller , et al. (2003, 2004)
- Reid, et al. (2003, 2004?)
- Mallet, et al. (2003, 2004,…)
- Osborne, S. R., J.M. Haywood, et al. (2004)
-- Shuster G., et al.
- P. Formenti, et al.
- S. Despiau, Mallet, et al
- M. Companelli, et al.
-….
Error estimates:Error estimates:
New strategy: Errors are to be provided in each single retrievals for all retrieved parameters
Important Error Factors:- Aerosol Loading - Scattering Angle Range - Number of Angles (homogeneity)- Number of spectral channels- Aerosol Typeetc.
Rigorous ERRORS estimates:Rigorous ERRORS estimates:General caseGeneral case: : large number of unknownslarge number of unknowns
andand redundant measurementsredundant measurements
U - matrix of partial derivatives in the vicinity of solution
∆ˆ x i( )2 ≈ ∆ˆ x irandom( )2
+ ∆ˆ x ibias( )2
∆ˆ x bias = UTC-1U( )−1UTC-1∆Ibias
ˆ x Above is valid:
- in linear approximation- for Normal Noise- no a priori constraints
C∆ˆ x random = UTC-1U( )−1
ERRORS estimates withERRORS estimates witha priori constraintsa priori constraints
C∆ ˆ x random = UTC-1U + U a
T Ca−1Ua( )-1
∆ˆ x bias = UTC-1U + U aT Ca
−1Ua( )−1UTC-1∆Ibias + U a
T Ca−1∆Ia
bias( )
ISSUES:- in linear approximation- for Normal Noise- strongly dependent on a priori constraints- very challenging in most interesting cases
Examples of error estimates
0
0.05
0.1
0.15
0.1 1 10
dV/d
lnR
(µm
3 /µm
2 )
Radius(µm)
GSFC, τ(0.44) = 0.7
1.25
1.3
1.35
1.4
1.45
0.4 0.6 0.8 1
GSFC, τ(0.44) = 0.7
Rea
l Par
t of R
efra
ctiv
e In
dex
Wavelength ( µm)
0.6
0.7
0.8
0.9
1
0.4 0.6 0.8 1
GSFC, τ(0.44) = 0.07
Sing
le S
catte
ring
Alb
edo
Wavelength ( µm)
0.8
0.9
1
0.4 0.6 0.8 1
GSFC, τ(0.44) = 0.7
Sing
le S
catte
ring
Alb
edo
Wavelength (µm)high loading
low loading
AERONET inversion developments
Forward model:- accounting for particle shape- using non-lambertian surface- modeling polarization
Retrieval flexibility:- additional spectral channels- different geometries
Inversion of combined data:- different geometries - combining with satellite- combining with aircraft
Output improvements:- detailed phase function- degree of polarization- flexible separation of modes- fluxes and forcing- details of fitting (biases and random)
Errors estimation:-for individual retrieval-for absorption optical thickness-for phase functions, etc.
Perspectives:- assuming bi-component aerosols- combining with polarimetric
satellite observations- retrieval of shape distribution
Fine and Coarse modes separations
RadianceRadiance
Beijing aerosol
0.1
1
10
100
0 45 90 135 180
totalfine modecoarse mode
Phas
e Fu
nctio
n
Particle Radius (micron)02:05:2003,09:27:51,PolarPP,Beijing,14
0
0.3
0.6
0.9
0 45 90 135 180
totalfine modecoarse mode
Line
ar P
olar
izat
ion
(-F12
/F11
)
Particle Radius (micron)02:05:2003,09:27:51,PolarPP,Beijing,14
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.1 1 10
dV/d
lnR
(µm
3 /µm
2 )
Particle Radius (micron)
Coarse
Fine
Coarse
02:05:2003,09:27:51,PolarPP,Beijing,14
Beijing Aerosol
Flexible separation betweenfine and coarse modes
(currently: ~0.6 µm)
0.45µm