1. BSRN Validation for GEWEX/ISCCP R. T. Pinker Department of Meteorology University of Maryland College Park, MD CEOS/WGCV Land Product Validation Workshop on Albedo April 27-28, 2005 EGU 2005 Vienna

2. Highlights  What is available on global scale from GEWEX  Scale issues-same satellites, different spatial gridding  Scale issues-different satellites  Evaluation of products Discussion in context of : CEOS/WGCV Land Product Workshop Boston, 23-24 October, 2002

3. Error budgets oScaling may be much larger source of error than calibration or narrow to broadband transformation. What to measure-albedo; reflectance; spectral intervals oThe scientific community has primary interest in the total albedo. Therefore, it is recommended that priority should be given to measurements of this parameter. oThere is also interest in spectral albedo, both broadband and narrow band. oBroadband intervals of interest are the visible and NIR for which instrumentation of acceptable quality is available. oHigh spectral resolution albedo or BRDF are also of interest in building spectral libraries and for evaluating narrow band albedo from satellites.

4. Global distribution of surface SW radiation at 0.5 degree, Jan 1992 Both downward and upward fluxes are computed, allowing derivation of albedo What we do

5. Approach to Derive SW o Start with spectral reference albedo models as boundary conditions o Compute surface upwelling and down- welling fluxes:  Clear conditions  All conditions Compute spectrally for:  diffuse  total Albedo: ratio of upwelling to down -welling flux

6. Narrow to broad band transformations-updates To derive angularly and seasonally dependent relationships between narrowband reflectance and broadband albedo, under clear sky conditions, as observed from the several different satellites. The simulations will utilize surface types based on the University of Maryland land cover classifications. Extensive model simulations with MODTRAN 3.7 10 solar zenith angle bins 16 gaussian points in zenith and 8 in zenith direction to obtain the spectral flux 20 climatological profiles for temperature, water vapor and ozone in 4 seasons Newly developed spectral surface albedo models Objective Narrow to broadband transformations are based on:

7. Evergreen Needle leaf Forest0.74 0.39 0.14 ASTER Evergreen Broadleaf Forest 0.83 0.46 0.18 ASTER Deciduous Needle leaf Forest0.74 0.39 0.14 ASTER Deciduous Broadleaf Forest 0.83 0.46 0.18 ASTER Mixed Forest0.79 0.42 0.16 ASTER Woodlands0.35 0.25 0.09 ASTER/Bowker Wooded Grasslands0.36 0.32 0.12 ASTER/Bowker Closed Bushland/Shrubland0.37 0.36 0.13 ASTER/Bowker Open Shrubland0.19 0.22 0.07 ASTER/Bowker Grassland0.07 0.19 0.03 ASTER Cropland0.54 0.51 0.20 ASTER/Bowker Barren0.55 1.35 1.13 ASTER/Bowker Urban ASTER Updated Surface Spectral Reflectance Models Compatible with Current Global Land Cover Classifications Scaling Factors for the surface types according to UMD land cover classification Ch1Ch2Ch2 Scaling Scaling Scaling Source Surface typefactor factor factor (0.3-0.5) (1.3-2)(2-4) Channel 2 Channel 1

8. What albedo products are available:* At global scale  ISCCP D1 UMD GEWEX/SRB, 2.5 deg, 1983-2001 (There are other estimates based on ISCCP D1, such as: LaRC GEWEX/SRB; ISCCP D1-FD)  MODIS 1 deg, UMD SRB model, about 3 years At continental scale ISCCP DX based estimates, 0.5 deg; 1990-2001 At regional scale  GOES based estimates at 0.5 degree for the US; 1996-current  Improved above product for 1996-2000 at 0.5 and 1/8 deg resolution  GOES based estimates at 0.5 deg, Amazon basin for 1998-2000. * This is not a comprehensive review of everything available

9. Examples of low resolution albedo products

10. .20.19.18.17.16.15.14.13.12.11.10.09.08.07.06.05.04.20.19.18.17.16.15.14.13.12.11.10.09.08.07.06.05.04 Based on GOES pixel level data; available for 1998-2000

11. Manaus: Reserva Ducke Fezenda Dimona Ji-Parana: Reserva Jaru Fazenda Nossa Senhora da Apparacida Maraba: Reserva Vale do Rio Doce Fazenda Boa Sorte Forest Pasture Annual mean Variability among sites Seasonal variability ForestObs0.1330.122-0.147Weak, higher in dry, lower in wet season GOES0.0880.079-0.104Very weak DX0.1130.103-0.129Lower in Jun/Jul/Aug PastureObs0.1760.169-0.193Stronger, Lower in dry season GOES0.0900.075-0.100Very weak DX0.1160.102-0.127Lower in Jun/Jul/Aug Analysis based on Berbet, M. et al. (2003); observations made in 1990-1993 (Culf et al., 1996). The observation uncertainty of the order of 0.006 (Wright et al. 1996). GOES and DX estimates are available from 1998/03 – 2001/02, and from 1998/07 – 2001/02, respectively. Both observed and satellite derived albedo are generally lower in dry and higher in wet months. Satellite driven albedo show smaller difference between the vegetation cover, and weak seasonal variability.

12. Based on GOES pixel level 1/2 deg 1/8 th deg

13. GOES 1/8th ISCCP DX, 0.5 deg

14. Albedo based on MODIS using ratio of surface fluxes The surface parameters used to calculate spectral surface albedo needed in the inference scheme for SRB were taken from the MODIS Bidirectional Reflectance Distribution Function (BRDF) and Albedo Product (MOD43B) at the 0.25° resolution (Lucht et al., 2000; Schaaf et al., 2002). The three weighting parameters associated with the RossThickLiSparseReciprocal BRDF model that best describes the anisotropy of each pixel are provided for each of the MODIS spectral bands as well as for the three broad bands (0.3-0.7 µm, 0.7-5.0 µm, and 0.3-5.0 µm). For two broad bands (0.3-0.7 µm, 0.7-5.0 µm), these parameters were used with simple polynomials to estimate the white sky albedo and the black sky albedo for the monthly mean solar zenith angle.

15. Auxiliary information for driving SRB model: Level-3 MODIS Atmosphere Monthly Global Product at 1° x 1° resolution, processed with the latest collection 4 algorithms for: Cloud_Fraction_Total, Cloud_Optical_Thickness_Combined,Optical_Depth_ Land_And_Ocean aerosol, Total_Ozone, and Atmospheric_Water_Vapor Missing aerosol optical depths over arid areas were filled from the MODIS-GOCART integrated monthly aerosol optical depth data, School of Earth and Atmosphere Sciences, Georgia Institute of Technology. Missing cloud optical thickness values were replaced by interpolated values.

16. One degree spatial resolution

17. From MODIS, V004 product

18. MODIS swath data at highest resolution

19. Evaluation of GOES surface albedos against SURFRAD stations during summer and winter, Fort Pack, MT (0.5 degree)

20. Evaluation os GOES surface albedo against SURFRAD stations during summer and winter Goodwin Creek, MS (0.5 degree)

21. Comparison between derived broadband albedo for different satellites Comparison between the derived broadband surface albedo and broadband surface observations - The methodology will be tested with ground observations at the semi-arid USDA-ARS Walnut Gulch Experimental Watershed in Arizona. The surface observations started in July 1999 and continue up to now. Total short-wave, infrared and PAR upward and downward fluxes are measured at 5 minute intervals. Comparison between the derived broadband albedo from GOES and broadband albedo observed from a satellite with broad band sensor – Evaluation

22. Semi-Arid region: Walnut Gulch, AZ

23. Ongoing observations in sub-Sahel Need for ground truth on surface albedo

24. No information on savannah type vegetation

26. Summary o Global products of spectral and total surface albedos are available o As yet, not fully evaluated o Usefulness of ground observations for evaluation of low resolution products not obvious-preferably, consistency among satellites important o Ground observations of albedo important, but should not be expected to match the satellite based albedos o Documentation of the annual cycle for different surface types important for benchmarking