MODIS BRDF/Albedo Products from Terra and Aqua

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MODIS BRDF/Albedo Products from Terra and Aqua

• Jonathan Salomon
• Crystal Schaaf, Alan Strahler, Jicheng Liu, Ziti
  Jiao, Yanmin Shuai,
• John Hodges, Xiaowen Li, Feng Gao
• Department of Geography
• Boston University
• (schaaf_at_bu.edu)

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MODIS BRDF/Albedo Algorithm

• BRDF modellinear combination of a constant
  (fiso) and two weighted (fvol, fgeo)
  trigonometric functions (kvol, kgeo) derived
  from physical models of volumetric and
  geometric-optical surface scattering.
• Full model inversions are used when sufficient
  high quality atmospherically-corrected cloud-free
  observations are available over a 16-day period
  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.
• Retrieved BRDF models are used to derive
  intrinsic measures of albedo (fully diffuse or
  white-sky albedo and direct beam or black-sky
  albedo).

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MODIS BRDF/Albedo Standard Products

• Collection 4 (V004) reprocessed MODIS Land
  Products (March 2000 to present).
• BRDF Model Parameters
• MODIS bands 1-7 plus three broadbands
• Albedos
• white-sky and black-sky (at local solar noon)
• Nadir BRDF-Adjusted Reflectances (NBAR)
• MODIS bands 1-7
• Extensive Quality Assurance Flags
• 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.

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NBAR
January 1-16, 2001 (2001001) April 7-22, 2001
(2001097)
July 12-27, 2001 (2001193) October 16-31, 2001
(2001289)
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Spectral Albedo of Sahara
1 km albedo RGB true color composite
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CMG Broadband White-Sky Albedo (0.3-5.0mm)January
2001
No Data
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CMG Broadband White-Sky Albedo (0.3-5.0mm)June
2001
No Data
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Combined Aqua Terra Processing

• BRDF specification requires multiple observations
  to capture anisotropy across viewing/illumination
  geometry
• Combining observations from Aqua and Terra
• Increased 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 V004 AquaTerra MCD43 Products available
  
• (May 2002 to present)

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CMG Broadband Black-sky Albedo (0.3-5.0mm) Terra
(April 2004) Terra Aqua
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CMG Broadband Black-sky Albedo (0.3-5.0mm) Terra
(April 2004) Terra Aqua
Green high quality Red poorer quality
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Aqua Terra (April 2004)
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MODIS BRDF/Albedo Standard Products

• V005 Level2G/Level3 Standard Land Products
  (MCD43B)
• Single combined AquaTerra product (Terra alone
  prior to May 2002)
• Sinusoidal equal-area projection - HDF-EOS
• Tiles - 1200x1200 pixels for the 1-km products
• Tiles 2400x2400 pixels for the 500-m products
• Revised format and QA (snow and mandatory
  separate bytes)
• V005 Climate Modeling Grid Products (CMG)
  (MCD43C)
• Geographic (lat/lon) projectionm HDF-EOS
• Global - coarse resolution - 0.05degree (3 arc
  min or 5km)
• Include snow free version
• Revised format and QA

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V005 500m White-Sky Albedo
2001193
500m 1km
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Validation Sites

• Validated Stage-1
• Product accuracy has been estimated using a small
  number of independent measurements obtained from
  selected locations and time periods and
  ground-truth/field program effort.
• Baseline Surface Radiation Network (BSRN)
• http//bsrn.ethz.ch/
• SURFRAD Network (US BSRN sites)
• http//www.srrb.noaa.gov/surfrad/index.html
• EOS core validation sites (200x200 pixels
  subsets)
• http//modis-land.gsfc.nasa.gov/val/coresite_gen.a
  sp
• 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 ,
  doi10.1016/j.rse.2004.09.001, Remote Sens.
  Environ., 2004.
• MODIS 7x7 pixel subsets in ascii at ORNL
• 276 sites (BSRN stations, EOS core sites, Flux
  sites and LTER sites)
• http//www.modis.ornl.gov/modis/index.cfm

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MODIS Subsets
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Boulder, CO V004, 2003
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ARM SGP Central Site V004, 2003
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Fort Peck, Montana V004, 2003
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Desert Rock, NV V004, 2003
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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.
Stroeve, J., J. 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., Remote Sens.
Environ., 94, 46-60, 2005.
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Albedo/BRDF References

• Gao, F., C. Schaaf, A. Strahler, A. Roesch, W.
  Lucht, and R. Dickinson, The MODIS BRDF/Albedo
  Climate Modeling Grid Products and the
  Variability of Albedo for Major Global Vegetation
  Types, J. Geophys. Res., 110, D01104,
  doi10.1029/2004JD005190. 2005.
• Moody, E. G., M. D. King, S., Platnick, C. B.
  Schaaf, and F. Gao, Spatially complete global
  spectral surface albedos Value-added datasets
  derived from Terra MODIS land products. IEEE
  Trans. Geosci. Remote Sens., 43, 144-158, 2005.
• Stroeve, J., J. 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., Remote Sens.
  Environ., 94, 46-60, doi10.1016/j.rse.2004.09.001
  , 2005.
• 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.
• 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, doi10.1029/2003GL019104,
  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, doi10.1029/2002JD003326, 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, doi10.1029/2002GL01674
  9, 2003.
• Jin et al., Consistency of MODIS surface
  BRDF/Albedo retrievals 1. Algorithm performance,
  J. Geophys. Res., 108(D5), 4158,
  doi10.1029/2002JD002803, 2003.
• Jin et al., Consistency of MODIS surface
  BRDF/Albedo retrievals 2.Validation, J.Geophys.
  Res., 108, 4159, doi10.1029/2002JD002804, 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, 10.1029/2001GL01413
  2, 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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Validation with Greenland in situ 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).