Standardizing Terminology and Description of Satellite-Derived Land Surface Albedo Products

1. Standardizing Terminology and Description of Satellite-Derived Land Surface Albedo Products Gabriela Schaepman-StrubEuropean Space Agency (ESA) External FellowF. Berendse, M. Schaepman, B. van den Hurk, B. Holtslag Landflux Workshop, Toulouse, May 28-31, 2007

2. Albedo? photospheric albedo true albedo planetary albedo nearinfrared albedo plane albedo visible albedo surface albedo ground albedo blue-sky albedo cloud albedo white-sky albedo bright-sky albedo dust albedo single scattering albedo apparant albedo simple albedo spherical albedo multispectral albedo “Primarily, the chief trouble in straightening out the matter of albedo has arisen from the fact that the term itself is used in different senses by different writers and sometimes by the same writer.” Louis Bell, 1917 broadband albedo radar albedo black-sky albedo geometric albedo object albedo planetary albedo spectral albedo lunar albedo all-sky albedo leaf albedo inherent albedo global albedo

3. Definitions Applicable to Land Surface Albedo ‘Albedo is defined as the ratio of reflected solar shortwave radiation from a surface to that incident upon it.’ Strugnell and Lucht (2001), J. Climate 14(7), 1360–1376 ‘Albedo at some level z of a geophysical system is defined as the ratio between the upward flux density or irradiance exiting that particular level and the downward flux density impinging on that same level z.’ Pinty et al. (2005), J. Atm. Sci. 62, 2580-2591 Ei Lr

4. Current Angular Sampling Concepts • Instantaneous multi-angular viewing (# vz) e.g., MISR (9 cams), Chris (tilting) • Daily composites (# sz)e.g., Meteosat, flight campaigns • Multiple-day composites (#sz, vz)e.g., MODIS (16 days)

5. Albedo - Geometrical-Optical Considerations DHR‘black-sky albedo’intrinsic property BHR‘blue-sky albedo’ambient illum. cond. Satellite observations Schaepman-Strub et al., RSE (2006). Nicodemus et al. (1977)NASA technical note - standardization (in prep.)

6. Physical Description of Reflectance Quantities

7. Reflectance Terminology – Numerical Implications MISR - Howland

8. DHR versus Solar Zenith Angle and BHR(iso) of Snow BHRiso BHRiso DHR = BHR = BHRiso~50-57° SZ BHR Schaepman-Strub et al., RSE (2006)

9. fi fr Ei qi qr Lr From Satellite Observations to Land Surface Albedo Products

10. Standardizing the Description of Satellite Albedo Products • Objective • Standardized list for operational albedo products describing observations, processing, a priori information, etc. • Importance • Provide relevant product information to user (e.g., ATBD’s often do not contain all information, are long, not updated). • Increase knowledge on albedo products (e.g., intercomparison studies, applications (comparison with flux tower measurements)). • Facilitate the selection of adequate albedo product for applications.

11. Towards a Standardized Product Description

12. Towards a Standardized Product Description cont. Schaepman-Strub et al., in prep.

13. Albedo Changes in the Arctic River Lowlands • Determine seasonal variation and longterm albedo change in the Northeastern Siberian Arctic Tundra and their feedback on vegetation development and permafrost degradation. • Main factors contributing to albedo variation • Snow cover (including microscale dynamics) • Variation in soil moisture • Thawing lakes dynamics • Changes in the phenological cycle • Vegetation development (e.g., shrub encroachment)

14. Albedo in Northeastern Siberia – from Potential Changes towards Predictions Changes per decade in summer atmospheric heating (latent plus sensible heat flux) in Alaskan tundra. Chapin et al., Science 310, 2005

15. Effect of Structural Complexity on Land-Surface Energy Exchange Thompson et al., JVS (15), 2004

16. Flux Tower Site Chokurdah (NE Siberia) Courtesy: K. v. Huisteden, Free University of Amsterdam

17. Selected Area of Interest

18. First Analysis 2000– MODIS Product Quality Flags Full inversion Magnitude inv.

19. First Results – MODIS Black-Sky Albedo (DHR) - 2000 MODIS DHR (red) MODIS DHR (green) Snow height [cm] MODIS DHR (NIR) MODIS DHR (broadband)

20. Arctic Land Surface Albedo in IPY (endorsed only) • Trischenko, Fernandes, CCRS (PI) ‘Surface Albedo Feedback and Energy Budget in the Arctic (SAFE-Arctic)’ - restriction to the Western arctic • Oerbaek (PI), Norwegian Polar Institute‘Network for ARCtic Climate and Biological DIVersity Studies’8 selected sites (Europe, Ca, USA, Russia) • Williams (PI), Univ. of Edinburgh‘Arctic Biosphere-Atmosphere Coupling across multiple Scales’ (Sweden, Finland)

21. Developments and Challenges • Intercomparison of albedo products of different sensors • Spatially continuous fields (multiple-sensor approach?) • Long-term continuity • Identification of adequate spectral resolution of albedo in e.g., climate models and corresponding implementation -> CEOS/LPV albedo workshop planned in 2008 -> Vegetation development (e.g., shrub encroachment) is a transitional effect - satellite-derived albedo is a more adequate description than albedo assignment based on discrete land cover classes.

22. From Prediction to Mitigation Strategies….

23. Time for Discussion!

24. MODIS DHR versus BHRiso