AATSR atmospheric correction

Transcription

1 AATSR atmospheric correction Objective: Retrieval of aerosol opacity and bidirectional reflectance over land surface Talk structure Science background and objectives Dual-angle method Validation and satellite intercomparisons Conclusions and open issues Peter North, Will Grey and Sietse Los

2 Aerosol scattering

3 Land surface products Requirements for atmospheric correction Albedo fapar LAI Vegetation fractional cover Time series analysis See North, P.R.J., RSE 2002

4 Land surface angular effects

5 Dual-angle aerosol/reflectance retrieval North et al., 1999, IEEE Trans. Geosci. Remote Sens.

6 Model inversion Dual-angle fit to coupled atmosphere/surface radiative transfer model Minimum error of fit corresponds to most probable AOT North,P.R.J. et al., IEEE TGARS 1998, North, P.R.J., JGR 2002; Grey, W.M.F. et al. 2005

7 Longitude 56 o N 108 o W 107 o W 106 o W 105 o W 104 o W 103 o W 55 o N ATSR-2 TOA 55 o N 54 o N Latitude Latitude 54 o N 53 o N 53 o N 52 o N University of Wales Swansea CEH Wallingford 109 o W 108 o W 107 o W 106 o W 105 o W Longitude North,P.R.J. JGR 2002 North, P.R.J., JGR 2002

8 Longitude 56 o N 108 o W 107 o W 106 o W 105 o W 104 o W 103 o W 55 o N ATSR-2 Corrected 55 o N 54 o N Latitude Latitude 54 o N 53 o N 53 o N 52 o N University of Wales Swansea CEH Wallingford 109 o W 108 o W 107 o W 106 o W 105 o W Longitude North,P.R.J. JGR 2002 North, P.R.J., JGR 2002

9 56 o N Longitude 108 o W 107 o W 106 o W 105 o W 104 o W 103 o W 55 o N Latitude 55 o N 54 o N 54 o N 53 o N Latitude 53 o N 52 o N University of Wales Swansea CEH Wallingford 109 o W 108 o W 107 o W 106 o W 105 o W Longitude North,P.R.J. JGR 2002 North, P.R.J., JGR 2002

10 Atmospheric correction University of Wales Swansea CEH Wallingford CEH Monks Wood University of Durham North, P.R.J., MetOffice JGR 2002

11 Lille AERONET site nadir 1630nm (NIR) nadir 870nm (NIR) forward 555nm (Green)

12 Top-of-atmosphere reflectance Aerosol Surfaceoptical reflectance depth AOD Channels Forward view 555nm (Visible) Nadir View 870nm (NIR) Nadir View 1630nm (SWIR) University of Wales Swansea CEH Wallingford CEH Monks Wood University of Durham MetOffice

13 Ouagadougou, Birkina Faso AERONET Site Channels Forward view 555nm (Visible) Nadir View 870nm (NIR) Nadir View 1630nm (SWIR)

14 Time series of Aerosol Optical Depth at Ouagadougou

15 Solar Village, Saudi Arabia AERONET Site Channels Forward view 555nm (Visible) Nadir View 870nm (NIR) Nadir View 1630nm (SWIR) Mean reflectance is 0.37 at 670nm

16 AERONET versus AATSR Aerosol Optical Depth Grey,W.M.F., North,P.R.J. et al., submitted IEEE TGARS 2005

17 AATSR vs MODIS surface reflectance AATSR 659 vs MODIS 647nm AATSR 870 vs MODIS 885nm

18 Aerosol optical depth of the Sahel and Southern Sahara during March 2003 MODIS MISR Grey,W.M.F., North,P.R.J. et al., submitted IEEE TGARS 2005

19 July 1995 August 1995 Aerosol optical depth at 550nm over N. Africa and Europe

20 Discussion Globally applicable method for ATSR-2 / AATSR aerosol and surface reflectance retrieval Retrieval over bright surfaces Intercomparison (MISR, MODIS, TOMS) Further work Surface biophysical parameters Improved cloud clearing aerosol models

21 Acknowledgements This work was carried out within NERCs CLASSIC programme. We are also grateful to following organisations: NEODC for supplying the ATSR-2 data, ESA for supplying the AATSR data, AERONET investigators for the sun-photometer data and, NASA for the TOMS, MISR and MODIS aerosol products, and MODIS BRDF dataset.

22 ATSR-2 at 550nm TOMS at 380nm Aerosol optical depth over parts of Africa and Europe for Dec 96 University of Wales Swansea CEH Wallingford

23 Aerosol Optical Depth at 550nm over Africa and Europe for the first two weeks in October 2004 University of Wales Swansea CEH Wallingford

24 Modeled BRDF Spruce Solar zenith: 45 degrees NIR: wavelength 870nm RED: wavelength 670nm

25 Spectral invariance of BRDF University of Wales Swansea CEH Wallingford CEH Monks Wood North, P.R.J. University et al, of IEEE Durham TGARS 37(1), MetOffice 1999

26 Model fit to BRDF ( ( ) r( λ,ω)= ( 1 D λ )P Ω w λ + γ w λ 1 g D λ + g 1 D λ BRDF model separating single & multiple scattering R 2 =0.99 University of Wales Swansea CEH Wallingford CEH Monks Wood North, P.R.J. University et al, of IEEE Durham TGARS 37(1), MetOffice 1999

27 FLIGHT 3D Model European beech Coniferous forest

28 Example: parameter estimation Relation between NDVI and f APAR by Monte Carlo simulation of 162,000 measurements. Corresponding S/N is 4.49 University of Wales Swansea CEH Wallingford CEH Monks Wood University North P.R.J., of Durham RSE 80, , MetOffice 2002.

29 Dual-angle AATSR Top-of-atmosphere reflectance Channels Nadir view 555nm (Visible) Nadir View 870nm (Near Infrared) Nadir View 1630nm (Shortwave Infrared) University of Wales Swansea CEH Wallingford Channels Forward view 555nm (Visible) Nadir View 870nm (Near Infrared) Nadir View 1630nm (Shortwave Infrared) CEH Monks Wood University of Durham MetOffice