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

MODIS: System Characteristics EOS-Terra Platform Sun-synchronous, near-polar, 705.3 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

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): 1 620-670 2 841-876 3 459-479 545-565 1230-1250 Daily Browse 6 1628-1652 Mostly Cloudy! 7 2105-2155 Home page: http://modis-sr.ltdri.org/html/surfref.htm 3

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

MODIS Anisotropy and Albedo

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

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

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)

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

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

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

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

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)

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

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

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

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

Temporal Signal

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, 287-302, 2002.

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

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

MODIS Vegetation Phenology: (Zhang et al. 2003, RSE; Zhang et al MODIS Vegetation Phenology: (Zhang et al. 2003, RSE; Zhang et al. 2004 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

(e.g., Northern Hemisphere Green Wave) Global Results -2001 (e.g., Northern Hemisphere Green Wave) 2001-2004 V004 MCD12Q2 available Credit: X. Zhang, M. Friedl, Bin Tan

MODIS Phenology Harvard Forest

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

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, 10.1029/2001GL014096, 2002.

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

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

Collection V005 Emphasis on Validation/Intercomparison BSRN/Surfrad calibrated albedometers http://www.gewex.org/bsrn.html http://bsrn.ethz.ch/ CERES/ARM Validation Experiment (CAVE) http://www-cave.larc.nasa.gov/cave/cave2.0/SfcObs.html EOS core sites (200x 200km) http://landval.gsfc.nasa.gov/ ORNL subsets (7x7 km to 200X200 km) http://www.modis.ornl.gov/modis/index.cfm Field Campaigns: SAFARI, ARM CLASIC CLASIC - Cloud and LAnd Surface Interaction Campaign Southern Great Plains, 10-30 June 2007 Additional towers (radiation and flux), MAS, CAR http://www.ars.usda.gov/Research/docs.htm?docid=15299

Oak Ridge National Lab Subsets http://www.modis.ornl.gov/modis/index.cfm

Boulder, CO

Fort Peck, Montana

MODIS Anisotropy and Albedo Validation ARM SGP EF-15 2003 ARM CLASIC – Cloud and LAnd Surface Interaction Campaign 10-30 June 2007

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

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) http://lpvs.gsfc.nasa.gov

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

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) http://ltdr.nascom.nasa.gov/ltdr/ltdr.html

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

Spatially Complete White-Sky Albedo (LSN) January 1-16, 2002 Annual data sets and 5 year mean 2000-2004 Snow-free 0.8 0.6 Surface Albedo (0.86 µm) 0.4 0.2 0.0 Snow-covered http://modis-atmos.gsfc.nasa.gov/ALBEDO/index.html 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, 144-158, 2005.

Gap-Filled Anisotropy Products True color WSA based on gap-filled BRDF Model Parameters September 2001-2005 http://www-modis.bu.edu/brdf_albedo/gapfill5years.html Q. Zhang et al., in preparation

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) http://ladsweb.nascom.nasa.gov:8300/index.html EDC DAAC EDG (entire data set is available) and Data Pool (limited extent) http://edcimswww.cr.usgs.gov/pub/imswelcome/ http://lpdaac.usgs.gov/datapool/datapool.asp ORNL DAAC MODIS subsets over vegetation field sites http://www.modis.ornl.gov/modis/index.cfm Gap-filled (V004) Terra Albedo (snow-free) http://modis-atmos.gsfc.nasa.gov/ALBEDO/index.html Gap-filled (V004) Terra Aqua BRDF model parameters http://www-modis.bu.edu/brdf_albedo/gapfill5years.html Global Browse Imagery http://landweb.nascom.nasa.gov/cgi-bin/browse/browse.cgi

MODIS Land Products: Descriptions MODIS BRDF/Albedo Product Product description and userguide http://www-modis.bu.edu/brdf/ http://www-modis.bu.edu/brdf/userguide/index.html MODLAND http://modis-land.gsfc.nasa.gov/ MODLAND QA Single most useful site with links to QA Known Issues, Product Definitions (Users Guides and Specs), Global Browse, etc. http://landweb.nascom.nasa.gov/cgi-bin/QA_WWW/newPage.cgi MODLAND Validation http://landval.gsfc.nasa.gov/

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:10.1029/2004JD005190. 2005. 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, 144-158. 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:10.1016/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, 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, 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. MODIS BRDF/Albedo User Guide (http://www-modis.bu.edu/brdf/userguide/index.html)