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Aerosol and Surface Retrieval from a Combination of Up-looking and Down-looking Observations. Oleg Dubovik 1,2 , Charles Gatebe 1,2 , Alexander Sinyuk 1,2 , Eric Vermote 1,2 , Michael King 2 and Brent Holben 2 1- University of Maryland, 2- Goddard Space Flight Center, NASA. - PowerPoint PPT Presentation
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Oleg DubovikOleg Dubovik1,21,2, Charles Gatebe, Charles Gatebe1,21,2, Alexander Sinyuk, Alexander Sinyuk1,21,2, , Eric VermoteEric Vermote1,21,2, Michael King, Michael King22 and Brent Holben and Brent Holben22
1- University of Maryland,
2- Goddard Space Flight Center, NASA
IGARSS 2003, Toulouse, France, July 21-25, 2003IGARSS 2003, Toulouse, France, July 21-25, 2003
Aerosol and Surface Retrieval from a Combination of Up-looking and Down-looking Observations
Aerosol and Surface Retrieval from a Combination of Up-looking and Down-looking Observations
Outlines of presentation:Outlines of presentation:
An idea of the retrieval using a An idea of the retrieval using a combination of up- and down- looking combination of up- and down- looking observationsobservations;;
Retrieval method and algorithm using Retrieval method and algorithm using data combination data combination
Applications to the combined Applications to the combined measurements by CAR and AERONETmeasurements by CAR and AERONET
during SAFARI - 2000during SAFARI - 2000
CONCLUSIONSCONCLUSIONS
IGARSS 2003, Toulouse, France, July 21-25, 2003IGARSS 2003, Toulouse, France, July 21-25, 2003
Retrieval of surface needs atmospheric correction for aerosol effect
Retrieval of aerosol relies on assumption of surface reflectance
Idea: No assumptions are needed in simultaneous retrieval of aerosol and surface from combination of up- and down - looking observations
Retrieval using combinations of up- and down-looking observations
Retrieved:
Aerosol above plane:- size distribution- real ref. ind.- imag. ref. ind
Aerosol below plane:- size distribution- real ref. ind.- imag. ref. ind
Surface Parameters:- albedo, etc.
- Single scattering: aerosol particles - homogeneous spheres
Particle Size Distribution:0.05 m ≤ r(22 bins) ≤ 15 m
Complex Refractive Index at = 0.34 - 1.27 m
0.01
0.02
0.04
0.05
0.07
0.1 1 10 (Radius )m
- Multiple scattering: Nakajima-Nakajima DisOrds with Lambertian or green vegetation
surface Model (Gobron et al., 1997)
Specifications of Forward Model
0.00
0.01
0.10
Wavelength ( )m0.44 0.67 0.87 1.02
Imarinary Part Imaginary Part
1.35
1.40
1.45
1.50
1.55
1.60
Wavelength ( )m0.44 0.67 0.87 1.02
Real Part
- Atmospheric Model: 2 aerosol layers
observationsobservations fitting of observations byfitting of observations byforward modelforward model
forward model of forward model of the observationsthe observations:
- For each aerosol layer- For each aerosol layer : : particle sizes, ref. index,particle sizes, ref. index, etc.etc.
- Parameters of surface- Parameters of surface
Retrieval scheme:Retrieval scheme:
Inversion Procedure
Measurements accuracy:
AERONET, AATS-14) ± 0.02 I() AERONET± 5% I() CAR± 10%
Inversion strategy: statistically optimized fitting (Dubovik and King, 2000)
εsky2
εi2 fi
∗−fi x( )( )2
λ,θ( )i
∑ +εsky
2
εa2 fj
a −fj x( )( )2
j∑ → (Ntotal-Nx)ˆ ε sky
2
measurements a priori
Lagrange parameter
consistencyindicator
weighting
SAFARI 2000 Southern Africa Region August- September, 2000
Combined Observations (September 6):
Up-looking :
Aircraft: CAR, AATS-14 photometers Ground: AERONET photometers
Down-looking :
Aircraft: CAR
CAR - Cloud Absorption Radiometer
8 spectral channels: 0.34, 0.38, 0.47, 0.68, 0.87, 1.03, 1.19, 1.27 m
Measures radiation transmitted* and reflected:
0° ≤ Obs. Zenith ≤ 180°0° ≤ Obs. Azimuth ≤ 360°
* Stray light problems for
scattering angles ≤ 10°
Flown by CV-580 aircraftat ~ 700 m above ground
Univ. of Washington CV-580
Up-looking Sunphotometer data:
AATS-14 - NASA Ames Tracking 14- channel AATS-14 - NASA Ames Tracking 14- channel Sun-photometerSun-photometer ( ( = = 0.35, 0.38, 0.45, 0.50, 0.53,0.35, 0.38, 0.45, 0.50, 0.53,
0.60, 0.68, 0.78, 0.87, 0.94, 1.02, 1.24, 1.56, 2.14)0.60, 0.68, 0.78, 0.87, 0.94, 1.02, 1.24, 1.56, 2.14) : :
± 0.02 ± 0.02 usedused 8 8 values (some interpolated for CAR values (some interpolated for CAR ): ):
0.34, 0.38, 0.47, 0.68, 0.87, 1.03, 1.20, 1.270.34, 0.38, 0.47, 0.68, 0.87, 1.03, 1.20, 1.27 mm
AERONET Ground-based Sun-sky radiometer:AERONET Ground-based Sun-sky radiometer:
± 0.02 at± 0.02 at
6 channels6 channels: 0.34, 0.38, 0.44, 0.67, 0.87, 1.02 : 0.34, 0.38, 0.44, 0.67, 0.87, 1.02 mm
± 0.05% at± 0.05% at4 channels4 channels: 0.44, 0.67, 0.87, 1.02 : 0.44, 0.67, 0.87, 1.02 mm
3° ≤ scattering angles ≤ ~70°
Optical thickness on September 6
AERONETAERONETdaily variationsdaily variations
0
0.5
1
1.5
2
2.5
5:00 7:00 9:00 11:00 13:00 15:00
Mongu/Zambia, September 6, 2000
1.02 m0.87 m0.67 m0.44 m0.38 m0.34 m
Optical Thickness
Time of DayCAR
AERONETalmucantar
AATS-14 AATS-14 versus AERONETAERONET
0
0.5
1
1.5
2
0.2 0.4 0.6 0.8 1 1.2
AERONET (ground-based)
AATS-14 (airborne)
"AERONET - AATS-14"
Optical Thickness
Wavelengths ( )m
α = 1.82
α=1.74α=2.12
Aerosol retrieved from combinedCAR - AERONET - AATS-14 obs.
0.4
0.5
0.6
0.7
0.8
0.9
0.4 0.6 0.8 1.0 1.2
Single Scattering Albedo
Below PlaneAbove PlaneAERONET
Single Scattering Albedo
Wavelength ( )m
1.3
1.35
1.4
1.45
1.5
1.55
1.6
1.65
0.4 0.6 0.8 1 1.2
Real Part of Ref. Index
BelowAboveAERONET
Real Part of the Ref. Index
Wavelengths ( )m
0
0.05
0.1
0.15
0.2
0.1 1.0 10
Volume Size Distribution
Below PlaneAbove PlaneBelow + AboveAERONET
dV/dlnR (
m3 /m
2 )
(Radius )m
Surface reflectance retrieved from combined CAR-AERONET-AATS observations
0
0.1
0.2
0.3
0.4
0.5
0.6
0.2 0.4 0.6 0.8 1 1.2 1.4
Lambertian Surface Albedo
CAR + AERONET inversion
CAR (Gatebe et al., 2000)
MODIS (Sept. 2 , Sept. 10)
Albedo
Wavelengths ( )m
Mongu, September 6, 2000
LambertianLambertian approximationMongu, Zambia
Surface reflectance retrieved from combined CAR-AERONET-AATS observations
Vegetation BRDF Model:Gobron et al. [1997]:
Spectral properties: - leaf reflectance; - leaf transmittance; - soil albedo (Lambertian);
Spectral properties: - height of the canopy (~0.4 - 0.9 m);
- leaf area index (~0.26 - 0.32); - equivalent diameter of a single leaf (~ 6-9 cm)
Vegetation model of surface reflectance
Mongu, Zambia
0
0.1
0.2
0.3
0.4
-80 -60 -40 -20 0 20 40 60 80
Retrieved BRDF(vegetation model)
1.27 m1.22 m1.03 m0.87 m0.67 m0.47 m0.34 m
Reflectance
( )Angles degree
Comparison of model retrieved BRDFwith corrected direct BRDF
Gatebe et al. 2003
0
0.1
0.2
0.3
0.4
0.5
-50 0 50
Vegetation model BRDF (lines)
6S corrected BRDF (points)
1.22 m0.87 m0.67 m0.47 m0.34 m
( )Angle degree
Reflectance
BRDF constrains model:- positive and smooth;- PP symmetrical
Conclusions:Conclusions:
Retrieval of both aerosol and surface from combined Retrieval of both aerosol and surface from combined up- and down-looking observations has been up- and down-looking observations has been
developeddeveloped;;
Applications to the combined measurements by CAR, Applications to the combined measurements by CAR, ATSS-14 and AERONET resulted to the aerosol and ATSS-14 and AERONET resulted to the aerosol and surface consistent with all used observationssurface consistent with all used observations
Issues to address in follow-on studies:Issues to address in follow-on studies: - clarifying use of BRDF models (different types, - clarifying use of BRDF models (different types, optimum parameterization, sensitivity, etc);optimum parameterization, sensitivity, etc); - testing with more real data;- testing with more real data; - designing “closure” experiment for the algorithm - designing “closure” experiment for the algorithm
IGARSS 2003, Toulouse, France, July 21-25, 2003IGARSS 2003, Toulouse, France, July 21-25, 2003
