1. MODIS Reflectance Anisotropy and Albedo (Collection V005)
Crystal Schaaf, Alan Strahler, Jicheng Liu
Department of Geography and Environment,
Center for Remote Sensing,
Boston University

2. MODIS: System Characteristics
EOS-Terra Platform
Sun-synchronous, near-polar, km, 98.21° inclination
10:30 AM local solar equatorial crossing time (descending node
Launched December 18, 1999
EOS-Aqua Platform
Sun-synchronous, near-polar, 705.3km, 98.21° inclination
1:30 PM local solar equatorial crossing time (ascending node)
Launched May 4, 2002

3. MODIS Surface Reflectance (MOD09)
The MODIS surface reflectance product is an estimate of the surface spectral reflectance for each band as it would have been measured at ground level if there were no atmospheric scattering and absorption.
Bands (in nm):
Daily Browse
Mostly Cloudy!
Home page: 3

4. MODIS Anisotropy and Albedo
Inputs
Cloud-free, atmospherically-corrected, spectral surface reflectances from Aqua and Terra (MOD09/MYD09 BRFs) to sample the surface anisotropy over a 16 day period
Output
High quality full inversions provide well-sampled, best-fit anisotropy models of global land surfaces
Ross Thick Li Sparse Reciprocal semi-empirical model captures volumetric and geometric-optical scattering
Lower quality back-up algorithm performs magnitude inversions by coupling available reflectances with an a priori BRDF database

5. MODIS Anisotropy and Albedo

6. Semi-Empirical BRDF Model
Rλ (θi, Φi; θr, Φr) = fiso + fvolkvol + fgeokgeo
(Roujean et al., 1992)
Isotropic
Volumetric
Geometric
kvol, kgeo are kernels of view and illumination geometry
fiso, fvol, fgeo are spectrally dependent weights

7. Kernel model derivation
Kernel Models
Kernel model derivation
To derive a kernel model, we simplify and manipulate a complete physical model until it reaches the form
where k is a function only of view and illumination geometry (and fixed physical parameters)
c1 and c2 are constants containing variable physical parameters

8. Volume Scattering: Ross-Thick Kernel
Kernel formula
where  is the phase angle between illumination and view positions in the hemisphere
Constants
where s is leaf reflectance; s is the surface reflectance; LAI is the leaf area index; B is the average of secants of possible view and illumination angles (≈1.5)

9. Geometric-Optical Modeling: Viewing sunlit versus shadowed surfaces
Hotspot: When the viewer and sun have the same angles so only illuminated surfaces are visible

10. Geometric Optical Modeling: Li Kernels
Assumptions
Shadows are perfectly black
Sunlit surfaces, whether object or background, are equally bright
Some geometric approximations for the overlap of view and illumination shadows
Crown shape choices
Li-Sparse: low sphere, b/r=1, h/b=2
Li-Dense: tall, thin spheroid, b/r=2.5, h/b=2
Li-dense b r b r h
Li-sparse h

11. Geometric-Optical Modeling: Li-Sparse Kernel
Kernel model
where
Constants
where C is the brightness of sunlit surface; and  is the count density of spheroids

12. MODIS Anisotropy and Albedo Products
BRDF Model parameters
RossThickLiSparseR model parameters
Use parameters directly in simple polynomial to estimate albedo or reflectance quantities
BRDF shape factors capture some measure of structure
Nadir BRDF-Adjusted Reflectance (NBAR)
View angle corrected surface reflectances
Operational MODIS land cover classification and phenology
Albedo quantities
Bihemispherical reflectance under isotropic illumination (BHRiso)
White-sky albedo (wholly diffuse)
Directional-hemispherical reflectance (DHR) at local solar noon
Black-sky albedo (direct)
Intrinsic albedos can be combined as a function of diffuse skylight (optical depth) to obtain instantaneous actual albedos

13. MODIS Anisotropy and Albedo Product
Product Output
Spectral (Collections 004 and 005)
7 shortwave bands and three broad bands
Spatial
Sinusoidal 10deg2 tiles
500m (005)
1km (004, 005)
Climate Modeling Grid (CMG)
0.05deg in global lat/lon (004, 005)
30arcsec in global lat/lon (005)
Temporal
Every 16 days (004)
Every 8 days based on the last 16 days (005)

14. MODIS BRDF/Albedo Applications
Global characterization of surface scattering behavior
Non-Lambertian surface BRDF effects
Quantifying the surface anisotropy -- structure
“Correction” of observations for directional effects
Nadir BRDF-Adjusted Reflectance (NBAR) standardizes reflectance to specific view and illumination geometry—noon sun, nadir view – used operationally for MODIS LC and phenology
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

15. Multi-angle Indications of Vegetation Structure
MODIS BRDF Shape Factors
MISR RPV Classification
M. Hill, Univ. North Dakota

16. NIR (0.10-0.45) Red (0.0-0.1) Green (0.0-0.15)
NBAR
NIR ( ) Red ( ) Green ( )
Differences between MODIS surface reflectances from adjoining swaths and MODIS NBAR (Great Lakes/NY, 6 Sep 2000).

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

18. Temporal Signal

19. MODIS Land Cover Product —IGBP
MODIS data Nov 00–Oct 01
~2300 sites globally
Friedl, M. A., D. K. McIver, J. C. F. Hodges, X. Zhang, D. Muchoney, A. H. Strahler, C. E. Woodcock, S. Gopal, A. Schnieder, A. Cooper, A. Baccini, F. Gao, and C. Schaaf, Global land cover from MODIS: Algorithms and early results, Remote Sens. Environ., 83, , 2002.

20. Initial Efforts to Distinguish Crop Types
Credit W. Boykin-Morris

21. Second Most-Likely Class Classification Confidence Map
50%
100%

22. MODIS Vegetation Phenology: (Zhang et al. 2003, RSE; Zhang et al
MODIS Vegetation Phenology: (Zhang et al. 2003, RSE; Zhang et al GCB; Zhang et al. 2004, GRL; Zhang et al., 2006, JGR)
Quantifies Intra-annual Variation (phenology)
Greenup, maturity, senescence, dormancy
Use logistic functions fit to time trajectories of NBAR-EVI and use extreme points of the change rate of curvature to calculate phenology transition dates

23. (e.g., Northern Hemisphere Green Wave)
Global Results -2001
(e.g., Northern Hemisphere Green Wave)
V004 MCD12Q2 available
Credit: X. Zhang, M. Friedl, Bin Tan

24. MODIS Phenology
Harvard Forest

25.
V m White-Sky Albedo
500m km

26. 1 km albedo – RGB composite
Albedo of Sahara
1 km albedo – RGB composite
Tsvetsinskaya et al., Relating MODIS derived surface albedo to soils andlandforms over Northern
Africa and the Arabian Peninsula, Geophys. Res. Let., 29, /2001GL014096, 2002.

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

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

29. Collection V005 Emphasis on Validation/Intercomparison
BSRN/Surfrad calibrated albedometers
CERES/ARM Validation Experiment (CAVE)
EOS core sites (200x 200km)
ORNL subsets (7x7 km to 200X200 km)
Field Campaigns: SAFARI, ARM CLASIC
CLASIC - Cloud and LAnd Surface Interaction Campaign
Southern Great Plains, June 2007
Additional towers (radiation and flux), MAS, CAR

30. Oak Ridge National Lab Subsets

31. Boulder, CO

32. Fort Peck, Montana

33. MODIS Anisotropy and Albedo Validation
ARM SGP EF
ARM CLASIC – Cloud and LAnd Surface Interaction Campaign June 2007

34. MODIS Anisotropy and Albedo Validation
2003
Liu et al., GRL in review

35. CEOS/WGCV/LPV (Land Product Validation) Surface Radiation Subgroup
Workshops
October 2002 Boston
April 2005 Vienna
Product Intercomparison/Validation
Roujean et al., (POLDER/SEVIRI/MODIS)
Pinty et al., (MISR/MODIS/Meteosat)
Rutan et al., (MODIS/CERES)
Spring 2008 (Gabriela Schaepman-Strub has offered to host – venue TBD)
Website (supported by NASA)

36. MODIS/CERES Intercomparison
Continental
Deserts
Dave Rutan et al., 2007 ARM Meeting

37. MODIS Albedo for Modeling Applications
Produce CMG products and gap-filled (snow-free) products for model evaluations and parameterizations
NCAR CLM (Dickinson, Zeng, Oleson, Lawrence)
ECMWF (Morcrette)
ETH ECHAM (Roesch)
NCEP Noah (Mitchell)
GMAO LSM (Koster, Bounoua/Moody/King)
GISS (Y.-C. Zhang)
Establish long term data sets by linking MODIS with historical meterological satellites (AVHRR)
LTDR effort (Eric Vermote)

38. CMG Broadband Black-sky Albedo (0.3-5.0mm)
Use multiple MODIS sensors to increase the directional sampling of the surface and thus increase high quality anisotropy and albedo retrievals Te rra Terra + Aqua
Green: high quality Red: poorer quality

39. Spatially Complete White-Sky Albedo (LSN) January 1-16, 2002
Annual data sets and 5 year mean
Snow-free
0.8
0.6
Surface Albedo (0.86 µm)
0.4
0.2
0.0
Snow-covered
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 Transactions on Geoscience and Remote Sensing, Vol. 43, , 2005.

40. Gap-Filled Anisotropy Products
True color WSA based on gap-filled BRDF Model Parameters September
Q. Zhang et al., in preparation

41. MODIS Land Products: Data and Imagery
Collection 4 (V004) reprocessed MODIS Land Products (March 2000 to 2006).
Collection 5 (V005) reprocessing started (2000-mid 2002 complete – 2007 on).
LAADS (Collection V005 only)
EDC DAAC EDG (entire data set is available) and Data Pool (limited extent)
ORNL DAAC MODIS subsets over vegetation field sites
Gap-filled (V004) Terra Albedo (snow-free)
Gap-filled (V004) Terra Aqua BRDF model parameters
Global Browse Imagery

42. MODIS Land Products: Descriptions
MODIS BRDF/Albedo Product
Product description and userguide
MODLAND
MODLAND QA
Single most useful site with links to QA Known Issues, Product Definitions (Users Guides and Specs), Global Browse, etc.
MODLAND Validation

43. Albedo/BRDF References
Salomon, J., C. B. Schaaf, A. H. Strahler, F. Gao, Y. Jin, Validation of the MODIS Bidirectional Reflectance Distribution Function and Albedo Retrievals Using Combined Observations from the Aqua and Terra Platforms, IEEE Trans. Geosci. Remote Sens. Vol. 44, 2006.
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, doi: /2004JD
Moody, E. G., M. D. King, S., Platnick, C. B. Schaaf, and F. Gao, 2005: Spatially complete global spectral surface albedos: Value-added datasets derived from Terra MODIS land products. IEEE Trans. Geosci. Remote Sens., 43,
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, doi: /j.rse , 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: /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, doi: /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: /2002JD003326, 2003.
Gao et al., Detecting vegetation structure using a kernel-based BRDF model. Remote Sens. Environ., 86(2), , 2003.
Oleson et al., Assessment of global climate model land surface albedo using MODIS data, Geophys. Res. Letters, 30(8), 1443, doi: /2002GL016749, 2003.
Jin et al., Consistency of MODIS surface BRDF/Albedo retrievals: 1. Algorithm performance, J. Geophys. Res., 108(D5), 4158, doi: /2002JD002803, 2003.
Jin et al., Consistency of MODIS surface BRDF/Albedo retrievals: 2.Validation, J.Geophys. Res., 108, 4159, doi: /2002JD002804, 2003.
Schaaf et al., First Operational BRDF, Albedo and Nadir Reflectance Products from MODIS, Remote Sens. Environ., 83, , 2002.
Liang et al., Validating MODIS Land Surface Reflectance and Albedo Products: Methods and Preliminary Results, Remote Sens. Environ., 83, , 2002.
Jin et al., Improving MODIS Surface BRDF/Albedo Retrieval with MISR Multi-angle Observations, IEEE Trans. Geosci. Remote Sens., 40, , 2002.
Jin et al., How does snow impact the albedo of vegetated land surfaces as analyzed with MODIS data?, Geophys. Res. Let., 29, /2001GL014132, 2002.
Tsvetsinskaya et al., Relating MODIS derived surface albedo to soils andlandforms over Northern Africa and the Arabian Peninsula, Geophys. Res. Let., 29, /2001GL014096, 2002.
MODIS BRDF/Albedo User Guide (