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