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MODIS BRDF/Albedo Products from Snow-Covered Land

MODIS BRDF/Albedo Products from Snow-Covered Land. Production Crystal Schaaf , Alan Strahler, Xiaowen Li Department of Geography, Boston University Shunlin Liang Department of Geography, University of Maryland Feng Gao, Eric Moody NASA/GSFC Validation Julienne Stroeve

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MODIS BRDF/Albedo Products from Snow-Covered Land

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  1. MODIS BRDF/Albedo Products from Snow-Covered Land Production Crystal Schaaf, Alan Strahler, Xiaowen Li Department of Geography, Boston University Shunlin Liang Department of Geography, University of Maryland Feng Gao, Eric Moody NASA/GSFC Validation Julienne Stroeve National Snow and Ice Data Center (NSIDC), University of Colorado Anne Nolin Department of Geosciences, Oregon State University Jason Box Department of Geography, Ohio State University

  2. MODIS BRDF/Albedo Applications • Global mapping of surface albedo measures • Parameterize global climate and biogeochemical models • Initializing numerical weather prediction and mesoscale models • Quantifying the surface background for cloud studies • “Correction” of observations for directional effects • Nadir BRDF-Adjusted Reflectance (NBAR) standardizes reflectance to a specific view and illumination geometry—noon sun, nadir view • Characterization of surface scattering behavior • Non-Lambertian surface BRDF effects • Quantifying the surface anisotropy

  3. MODIS BRDF/Albedo Operational Product (MOD43) • MODIS BRDF/Albedo Product uses: • MODIS surface reflectances (MOD09) • Daily, gridded, cloud-cleared, atmospherically-corrected • MODIS channels 1-7 • Ross-Thick/Li-Sparse semiempirical BRDF model • MODIS BRDF/Albedo Product provides: • Surface anisotropy, (BRDF), albedo, nadir surface reflectance • Global land surfaces, 16-day periods • MODIS channels 1-7 plus 3 broadbands. • 1km gridded spatial resolution in 10º sinusoidal tiles • 500m products available for V005 reprocessing (summer 2005) • 0.05 deg Climate Modeling Grid (CMG) global geographic lat/lon • Gao, F., C. Schaaf, A. Strahler, A. Roesch, W. Lucht, R. Dickinson, The MODIS BRDF/Albedo Climate Modeling Grid Products and the Variability of Albedo for Major Global Vegetation Types, in press, J. Geophys. Res., 2004.

  4. MODIS BRDF/Albedo Operational Product (MOD43) • Snow or Snow Free Retrieval • Majority situation over 16-day period • New N2B conversion coefficients implemented for “pure”snow • Modtran simulations – S. Liang • Implemented in V004 reprocessing • NDVI<0 and NDSI>0.7 (Klein and Stroeve, 2002)

  5. MODIS BRDF/Albedo Algorithm • Full model inversions are used when sufficient high quality observations are available to adequately sample the BRDF. • Otherwise, lower quality magnitude inversions are performed which couple a priori knowledge of the surface anisotropy with any high quality MODIS observations that are available for a location. • Extensive Quality Assurance Flags are supplied indicating quality of the product, processing method used, and whether a snow or snow-free albedo was retrieved. • Blue-sky albedos • Can be computed as an interpolation between black-sky and white-sky albedos as a function of diffuse skylight.

  6. White-Sky Spectral Albedo 7 - 22 April, 2002 NIR (0.1-0.4)Red (0.0-0.16)Blue (0.0-0.18) No Data

  7. CMG Broadband White-Sky Albedo (0.3-5.0mm)January 2001 No Data

  8. CMG Broadband White-Sky Albedo (0.3-5.0mm)June 2001 No Data

  9. NBAR January 1-16, 2001 (2001001) April 7-22, 2001 (2001097) July 12-27, 2001 (2001193) October 16-31, 2001 (2001289)

  10. Spatially Complete Snow-Free MODIS Albedo Product • New initiative with the MODIS Atmosphere Group- Eric Moody • Fill values, poorest quality results, and seasonally snow covered results are replaced with temporal estimations and spatial interpolation. • 1 arc minute geographic lat/lon • http://modis-atmos.gsfc.nasa.gov/ALBEDO/index.html 0.0 0.8 Moody, E. G., M. D. King, S. Platnik, C. B. Schaaf, F. Gao, Spatially Complete Surface Albedo Datasets: Value-Added Products Derived from Terra MODIS Land Products, in press, IEEE, Trans Geosci. Remote Sens., 2004.

  11. Albedo/BRDF References Wang, Z., X. Zeng, M. Barlage, R. E. Dickinson, F. Gao, and C. Schaaf, Using MODIS BRDF and Albedo Data to Evaluate Global Model Land Surface Albedo, J. Hydrometeor., 5, 3-14, 2004. Zhou, L.et al., Comparison of seasonal and spatial variations of albedos from Moderate-Resolution Imaging Spectroradiometer (MODIS) and Common Land Model. J. Geophys. Res., 108, D15, 4488, doi:10.1029/2002JD003326, 2003. Gao et al., Detecting vegetation structure using a kernel-based BRDF model. Remote Sens. Environ., 86(2), 198-205, 2003. Oleson et al., Assessment of global climate model land surface albedo using MODIS data, Geophys. Res. Letters, 30(8), 1443, doi:10.1029/2002GL016749, 2003. Jin et al., Consistency of MODIS surface BRDF/Albedo retrievals: 1. Algorithm performance, J. Geophys. Res., 108(D5), 4158, doi:10.1029/2002JD002803, 2003. Jin et al., Consistency of MODIS surface BRDF/Albedo retrievals: 2. Validation, J. Geophys. Res., 108(D5), 4159, doi:10.1029/2002JD002804, 2003. Schaaf et al., First Operational BRDF, Albedo and Nadir Reflectance Products from MODIS, Remote Sens. Environ., 83, 135-148, 2002. Liang et al., Validating MODIS Land Surface Reflectance and Albedo Products: Methods and Preliminary Results, Remote Sens. Environ., 83, 149-162, 2002. Jin et al., Improving MODIS Surface BRDF/Albedo Retrieval with MISR Multi-angle Observations, IEEE Trans. Geosci. Remote Sens., 40, 1593-1604, 2002. Jin et al., How does snow impact the albedo of vegetated land surfaces as analyzed with MODIS data?, Geophys. Res. Let., 29, 10.1029/2001GL014132, 2002. Tsvetsinskaya et al., Relating MODIS derived surface albedo to soils andlandforms over Northern Africa and the Arabian Peninsula, Geophys. Res. Let., 29, 10.1029/2001GL014096, 2002. Gao et al., Bidirectional NDVI and Atmospherically Resistant BRDF Inversion for Vegetation Canopy, IEEE Trans. Geosci. Remote Sens., 40, 1269-1278, 2002. MODIS BRDF/Albedo User Guide (http://geography.bu.edu/brdf/userguide/index.html)

  12. Spectral Snow Albedo Statistics Derived From Terra MODIS land products • Multi-year hemispherical spectral snow albedo • Statistics provide “average” snow conditions • Binned by: • IGBP ecosystem class • NISE wet/dry snow type • Potential uses: • Stand-alone lookup table • In tandem with snow-free spatially complete albedo maps • Provides dynamically tailored surface maps • Currently processed MOD43B3 2001-2002 data • Plans to process all MOD43B3/MCD43B3 data

  13. Spectral Variability by IGBP Ecosystem Class and NISE Snow Type (wet/dry) • Forest statistics computed from 2001-2002 MOD43B3 data

  14. Overlaying the Snow Albedo Statistics onto the Snow-Free Spatially Complete Albedo Snow-Free Spatially Complete ProductJanuary 2002, 0.86µm Using NISE Snow Extent and Type to Overlay the Snow Albedo Statistics

  15. Combined Aqua + Terra Processing • BRDF specification requires multiple observations to capture anisotropy across viewing/illumination geometry • Combining observations from Aqua and Terra • Increase high-quality inversions • Best fit BRDF model retrieved directly from observations • Fewer lower-quality retrievals using the back-up algorithm • Back-up method relies on a priori designation of BRDF • Combined Aqua+Terra V004 completed by Jan 05

  16. CMG Broadband Black-sky Albedo (0.3-5.0mm) Terra (April 2004) Terra + Aqua

  17. CMG Broadband Black-sky Albedo (0.3-5.0mm)Terra (April 2004) Terra + Aqua Green: high quality Red: poorer quality

  18. Aqua + Terra (April 2004)

  19. Fort Peck, Montana

  20. Boulder, CO

  21. Validation Efforts • Baseline Surface Radiation Network (BSRN) Sites • http://bsrn.ethz.ch/ • SURFRAD (US BSRN sites) • http://www.srrb.noaa.gov/surfrad/index.html • Collaborator Field Sites • EOS core sites • http://landval.gsfc.nasa.gov/MODIS/coresite_gen.php • ORNL DAAC MODIS ascii subsets • flux, core, BSRN and validation sites • http://www.modis.ornl.gov/modis/index.cfm • Greenland Climate Network (GC-Net) Automatic Weather Stations (AWS) - • Stroeve, J., J. E. Box, F. Gao, S. Liang, A. Nolin, C. Schaaf, Accuracy Assessment of the MODIS 16-day Albedo Product for Snow: Comparisons with Greenland in situ Measurements , in presss Remote Sens. Environ., 2004

  22. Validation with Greenland insitu Measurements • Description of the Greenland GC-Net AWS Albedo Measurements • Upward and downward shortwave radiation fluxes are measured at several AWS distributed widely in latitude and elevation using pairs LI-COR 200SZ photoelectric diode pyranometers (0.4 m – 1.1 m). • A correction to the LI-COR albedo are made to convert them from a narrowband albedo (e.g. 0.4 m – 1.1 m) to a broadband (0.285 m – 2.8 m) albedo. • Comparisons with precision pyranometers suggest a residual uncertainty with an RMSE of 0.035 (absolute albedo).

  23. MODIS Albedo Vs Greenland In Situ Albedo Comparison between MOD43 16-day albedo and 16-day in situ albedo for both black sky (triangles) and white sky (squares) albedo for 15 Greenland AWS stations. MODIS albedo from both the “main” (closed symbols) and “backup” (open symbols) algorithm results are shown.

  24. Tracking Seasonal Variability(Ablation Region) Albedo Variability in 2002 at JAR2 (bare ice zone)

  25. Tracking Seasonal Variability(Accumulation Region) Albedo Variability in 2002 at Summit (dry snow zone)

  26. Statistical Differences between Greenland In Situ and MOD43 Albedo • Mean difference between MOD43 albedo and in situ albedo is 0.02 (RMSE=0.06). Using only the ‘main’ algorithm retrieval drops the RMSE to 0.04. • Many ‘backup’ algorithm retrievals occur when the sun is low in the sky. • About half of the of available satellite observations during the sunlit season are obtained under conditions where the solar zenith angle exceeds 70º. • At several of the more northern stations, mean differences increase to about 0.07. • Conclude that there is general agreement between MODIS and in situ observations for albedo < 0.7, while near the upper limit, a -0.05 MODIS albedo bias is evident from the scatter of the 16-site composite.

  27. MODIS Albedo/BRDF Products from Snow-Covered Land MODIS BRDF/Albedo User Guide http://geography.bu.edu/brdf/userguide/index.html April 7-22, 2001 (2001097) NIR (0.1-0.4)Red (0.0-0.16)Green (0.0-0.18)

  28. Albedo/BRDF References Roesch, A., C. Schaaf and F. Gao, Use of Moderate-Resolution Imaging Spectroradiometer bidirectional reflectance distribution function products to enhance simulated surface albedos, J. Geophys. Res., 109, D12, doi: 10.1029/2004JD004552, 2004. Roujean, J.-L., C. B. Schaaf, and W. Lucht, Fundamentals of bi-directional reflectance and BRDF modeling, in: Reflective Properties of Vegetation and Soil, editors: M. von Schoenmark, B. Geiger, H.P. Roeser, Wissenshaft und Technik Verlag, Berlin, Germany, 352pp., 105-120, 2004. Tian, Y., R. E. Dickinson, L. Zhou, R. B. Myneni, M. Friedl, C. B. Schaaf, M. Carroll, and F. Gao, Land boundary conditions from MODIS data and consequences for the albedo of a climate model, Geophys. Res. Let., 31, doi:10.1029/2003GL019104, 2004. Wang, Z., X. Zeng, M. Barlage, R. E. Dickinson, F. Gao, and C. Schaaf, Using MODIS BRDF and Albedo Data to Evaluate Global Model Land Surface Albedo, J. Hydrometeor., 5, 3-14, 2004. Zhou, L.et al., Comparison of seasonal and spatial variations of albedos from Moderate-Resolution Imaging Spectroradiometer (MODIS) and Common Land Model. J. Geophys. Res., 108, D15, 4488, doi:10.1029/2002JD003326, 2003. Gao et al., Detecting vegetation structure using a kernel-based BRDF model. Remote Sens. Environ., 86(2), 198-205, 2003. Oleson et al., Assessment of global climate model land surface albedo using MODIS data, Geophys. Res. Letters, 30(8), 1443, doi:10.1029/2002GL016749, 2003. Jin et al., Consistency of MODIS surface BRDF/Albedo retrievals: 1. Algorithm performance, J. Geophys. Res., 108(D5), 4158, doi:10.1029/2002JD002803, 2003. Jin et al., Consistency of MODIS surface BRDF/Albedo retrievals: 2. Validation, J. Geophys. Res., 108(D5), 4159, doi:10.1029/2002JD002804, 2003. Schaaf et al., First Operational BRDF, Albedo and Nadir Reflectance Products from MODIS, Remote Sens. Environ., 83, 135-148, 2002. Liang et al., Validating MODIS Land Surface Reflectance and Albedo Products: Methods and Preliminary Results, Remote Sens. Environ., 83, 149-162, 2002. Jin et al., Improving MODIS Surface BRDF/Albedo Retrieval with MISR Multi-angle Observations, IEEE Trans. Geosci. Remote Sens., 40, 1593-1604, 2002. Jin et al., How does snow impact the albedo of vegetated land surfaces as analyzed with MODIS data?, Geophys. Res. Let., 29, 10.1029/2001GL014132, 2002. Tsvetsinskaya et al., Relating MODIS derived surface albedo to soils andlandforms over Northern Africa and the Arabian Peninsula, Geophys. Res. Let., 29, 10.1029/2001GL014096, 2002. Gao et al., Bidirectional NDVI and Atmospherically Resistant BRDF Inversion for Vegetation Canopy, IEEE Trans. Geosci. Remote Sens., 40, 1269-1278, 2002. MODIS BRDF/Albedo User Guide (http://geography.bu.edu/brdf/userguide/index.html)

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