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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. 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.

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Aerosol and Surface Retrieval from a Combination of Up-looking and Down-looking Observations

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  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 needsatmospheric correction for aerosol effect Retrieval of aerosol reliesonassumption 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 2000Southern Africa Region August- September, 2000 Combined Observations (September 6): Up-looking: Aircraft: CAR, AATS-14 photometers Ground: AERONET photometers Down-looking : Aircraft: CAR

  9. Univ. of Washington CV-580 CAR - Cloud Absorption Radiometer 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, 1.27mm 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 used8 values (some interpolated for CAR l): 0.34, 0.38, 0.47, 0.68, 0.87, 1.03, 1.20, 1.27mm • 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 versusAERONET

  12. Aerosol retrieved from combinedCAR - 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 BRDFwith 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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