1. MODIS/Meteosat/MISR Surface Albedo Comparison Exercise B. Pinty (1), M. Taberner (1), S. Liang (2), Y. Govaerts (3), J.V. Martonchik (4), Lattanzio (5), C. Barker Schaaf (6), M. M. Verstraete (1), R. E. Dickinson (7), N. Gobron (1), and J-L. Widlowski (1) (1) Institute for Environment and Sustainability of EC-JRC, Ispra (VA) Italy (2) University of Maryland, College Park, USA (3) EUMETSAT, Darmstadt, Germany (4) Jet Propulsion Laboratory, Caltech, Pasadena, USA (5) Makalumedia gmbh, Darmstadt, Germany (6) Boston University, Boston, USA (7) SEAC, Georgia Institute of Technology, Atlanta, USA 2nd CEOS/WGCV/LPV Workshop on Albedo Products, Vienna, April 27-28, 2005

2. Various types of Surface albedo (1) BHR : Bi-Hemispherical Reflectance is the ratio between the upward and the downward radiant fluxes, that is, accounting for the downwelling diffuse intensities from the sky. Depends on both surface and ambient atmospheric radiative properties and …the Sun angle. All quantities can be defined monochromatic or broadband

3. Various types of Surface albedo (2) DHR: Directional Hemispherical Reflectance is the ratio between the upward flux and the downward collimated flux coming thus from one single direction (Black sky). Depends on surface radiative properties and …the Sun angle. All quantities can be defined monochromatic or broadband BHR iso : If the downwelling diffuse intensities from the sky is assumed fully isotropic then the BHR is equal to the integral of the DHR over all incoming directions (White sky). Depends on surface radiative properties only.

4. Surface albedo products from space agencies MODIS delivers DHRs (Black sky) and BHR iso (White sky) MISR delivers DHRs and BHRs as flux ratios but under ambient conditions and for the Sun illumination conditions at time of observations EUMETSAT delivers DHRs for a fixed Sun angle and all information needed to reconstruct the DHRs and BHRiso and all information needed to reconstruct the DHRs at any other Sun angle as well as the BHRiso to reconstruct the BHRs may require some investments or some level of assumption The albedo products may also differ wrt the spectral bands of integration they refer to.

5. Parameterization of the surface- atmosphere radiative coupling Assuming that the field of downwelling diffuse intensity reaching the surface is PERFECTLY isotropic yields a convenient parameterization for the BLUE SKY ALBEDO Surface level Sun angle Atmospheric optical depth (type of atmosphere) Surface BRF (amplitude and shape) ratio of direct to total downward flux ratio of diffuse to total downward flux with Pinty et al., JAS, 2005

6. Surface albedo comparison Perform a comparison between MODIS-Meteosat- MISR surface albedo products : a user perspective. Compare similar physical quantities, e,g., BHRs, BHR iso, DHRs. Based on year 2001 products: latest public version available. For two large geographical regions : Africa- Southern Europe and North-East Europe.

7. Comparison of Surface BHR iso products from MODIS/Meteosat/MODIS Select the same period of time and identical geographical regions Achieve the needed transformations (e.g., BHRs, spectral conversions) to ensure comparison of physical quantities having same meaning Identify the product values showing appropriate QA

8. Albedo comparison for an ‘Ideal’ Band (0.4-1.1μm)

9. Govaerts, pers. Com

11. Spectral Correction for the Meteosat large band effects

12. Spectral conversion to the ‘Ideal’ Band (0.4-1.1μm) MeteosatMISR

14. January 2001

15. MISR low & MODIS high MISR high & MODIS low

16. January 2001

17. Histogram of BHR iso differences

18. (MISR-MODIS) Albedo

19. June 2001 January 2001 Using Shunlin’s conversion factors Using Yves’s conversion factors

20. January 2001

21. Mean BHR values over common area with valid values from one of the two other sensors

22. Ratio of the mean values

23. Primary Eigenvectors

24. Correlation between pairs of samples

25. Results for year 2001 Shortwave domain (0.3-3.0 μm) Africa –Southern Europe

26. Primary Eigenvectors

27. October 2001

28. Results for year 2001 Visible domain (0.3-0.7 μm)

30. Results for year 2001 Near-infrared domain (0.7-3.0 μm)

32. Results for year 2001 Shortwave domain (0.3-3.0 μm) Northern –Eastern Europe

35. Full inversion Magnitude inversion Backup solution

36. Mean BHR values over common area with valid values from one of the two other sensors Full inversion

39. Primary Eigenvectors Full inversion

40. Northern –Eastern Europe Hexadecad 6: End of March 2001

43. Issues and caveats An error was recently identified in the MISR processing code: BHRs tend to be biased high by about 2 to 3% on average (season & latitude dependent). The nominal spectral conversion formulae (from Liang and Govaerts) agree well. MODIS BHRs are off when estimated from the backup algorithm.

44. Africa –Southern Europe

45. Magnitude inversion January 2001 June 2001

46. Northern – Eastern Europe

47. Magnitude inversion January 2001 June 2001

48. Conclusions and Perspectives Albedo (BHR iso ) comparison reveals very good agreement between MODIS- MISR-Meteosat (high QA) products. Extend the comparison exercise globally. Repeat the exercise for DHRs.