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Aerosol and Surface Retrieval from a Combination of Uplooking and Downlooking Observations

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... the combined measurements by CAR and AERONET. during SAFARI - 2000 ... t(l) 0.02 used 8 values (some interpolated for CAR l) ... CAR - AERONET - AATS-14 obs. ... – PowerPoint PPT presentation

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Title: Aerosol and Surface Retrieval from a Combination of Uplooking and Downlooking Observations


1
Aerosol and Surface Retrieval from a Combination
of Up-looking and Down-looking Observations
Oleg Dubovik1,2, Charles Gatebe1,2, Alexander
Sinyuk1,2, Eric Vermote1,2, Michael King2 and
Brent Holben2 1- University of Maryland,
2- Goddard Space Flight Center, NASA
IGARSS 2003, Toulouse, France, July 21-25, 2003
2
  • Outlines of presentation
  • An idea of the retrieval using a combination of
    up- and down- looking observations
  • Retrieval method and algorithm using data
    combination
  • Applications to the combined measurements by CAR
    and AERONET
  • during SAFARI - 2000
  • CONCLUSIONS

IGARSS 2003, Toulouse, France, July 21-25, 2003
3
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
4
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.
5
Specifications of Forward Model
- Single scattering aerosol particles -
homogeneous spheres
- Atmospheric Model 2 aerosol layers
Complex Refractive Index at l 0.34 - 1.27 mm
Particle Size Distribution 0.05 mm r(22 bins)
15 mm









  • Multiple scattering Nakajima-Nakajima DisOrds
    with Lambertian or green vegetation
  • surface Model (Gobron et
    al., 1997)

6
Retrieval scheme
forward model of the observations
observations
fitting of observations by forward model
- For each aerosol layer particle sizes, ref.
index, etc. - Parameters of surface
7
Inversion Procedure
Measurements accuracy t(l) (AERONET,
AATS-14) 0.02 I(l,Q) (AERONET) 5 I(l,Q)
(CAR) 10
Inversion strategy statistically
optimized fitting
(Dubovik and
King, 2000)
weighting
Lagrange parameter
consistency indicator
a priori
measurements
8
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
9
CAR - Cloud Absorption Radiometer
Univ. of Washington CV-580
Flown by CV-580 aircraft at 700 m above ground
8 spectral channels 0.34, 0.38, 0.47, 0.68,
0.87, 1.03, 1.19, 1.27 mm
Measures radiation transmitted and
reflected 0 Obs. Zenith 180 0 Obs.
Azimuth 360
Stray light problems for scattering angles
10
10
Up-looking Sunphotometer data
  • AATS-14 - NASA Ames Tracking 14- channel
  • Sun-photometer (l 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)
  • - t(l) 0.02 used 8 values (some interpolated
    for CAR l)
  • 0.34, 0.38, 0.47, 0.68, 0.87, 1.03, 1.20, 1.27
    mm
  • 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
    mm
  • I(l,Q) 0.05 at
  • 4 channels 0.44, 0.67, 0.87, 1.02 mm
  • 3 scattering angles 70

11
Optical thickness t(l) on September 6
  • AERONET
  • daily variations

AATS-14 versus AERONET
12
Aerosol retrieved from combined CAR - AERONET -
AATS-14 obs.
13
Surface reflectance retrieved from combined
CAR-AERONET-AATS observations
Lambertian approximation
Mongu, September 6, 2000
Mongu, Zambia
14
Surface reflectance retrieved from combined
CAR-AERONET-AATS observations
Vegetation model of surface reflectance
Mongu, Zambia
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)
15
Comparison of model retrieved BRDF with corrected
direct BRDF
BRDF constrains model - positive and smooth -
PP symmetrical
Gatebe et al. 2003
16
  • Conclusions
  • Retrieval of both aerosol and surface from
    combined up- and down-looking observations has
    been developed
  • Applications to the combined measurements by CAR,
    ATSS-14 and AERONET resulted to the aerosol and
    surface consistent with all used observations
  • Issues to address in follow-on studies
  • - clarifying use of BRDF models (different
    types,
  • optimum parameterization, sensitivity,
    etc)
  • - testing with more real data
  • - designing closure experiment for the
    algorithm

IGARSS 2003, Toulouse, France, July 21-25, 2003
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