# Presentation: 506904

## MODIS BRDF/Albedo Product:Evaluation, Validation, and Applications

- Development Team
- Crystal B. SCHAAF, Alan H. STRAHLER, Feng GAO, Yufang JIN
- Collaborators
- Wolfgang LUCHT, Xiaowen LI, Xiaoyang ZHANG,  Elena TSVETSINSKAYA,
- Jan-Peter MULLER, Michael BARNSLEY, Philip LEWIS, Gareth ROBERTS,
- Christopher DOLL, Shunlin LIANG, David ROY, and Jeffrey PRIVETTE
*Center for Remote Sensing, Boston University, 725 Commonwealth Avenue, Boston, MA 02215, USA *
*Tel.  +617-358-0503, Fax +617-353-3200, e-mail:schaaf@bu.edu.*
*Potsdam-Institut f**ü**r Klimafolgenforschung, Postfach 601203, D-14412 Potsdam, Germany*
*Research Center for Remote Sensing, Beijing Normal University,  Beijing, China*
*Depart. of Geomatic Engineering, University College London, Gower St., London, WCIE 6BT, UK*
*Department of Geography, University College London, Gower St., London, WCIE 6BT, UK*
*Department of Geography, University of Wales Swansea, Singleton Park, Swansea, SA2 8PP, UK*
*Department of Geography, University of Maryland, College Park, MD 20742, USA*
*NASA/Goddard Space Flight Center, Code 923, Greenbelt, MD 20771, USA*

## Product Overview

- The MODIS BRDF/Albedo Product uses multidate, multispectral, cloud-cleared, atmospherically-corrected MODIS surface reflectances and the Ross-Thick/Li-Sparse semiempirical BRDF model to provide global measures of albedo, nadir surface reflectance and surface reflectance anisotropy every 16 days at a 1km gridded spatial resolution.*  *
- BRDF model parameters describe the surface anisotropy. Albedo and surface reflectance can then be computed at any desired view and illumination geometry.
- Bihemispherical albedo (white-sky) and directional hemispherical albedo (black-sky) at local solar noon are computed.  Actual albedos can be estimated by interpolating the diffuse and direct beam albedos as a function of diffuse skylight.
- Nadir BRDF-adjusted Reflectances (NBAR) at mean overpass solar zenith angle.  Surface reflectances corrected to a common nadir viewing geometry

## CMG Broadband White-Sky Albedo (0.3-5.0mm)1 - 16 January, 2002

- 0.0	           0.2                0.4

- No Data

## CMG Broadband White-Sky Albedo (0.3-5.0mm)18 February - 5 March, 2002

- 0.0	           0.2                0.4

- No Data

## CMG Broadband White-Sky Albedo (0.3-5.0mm)7 - 22 April, 2002

- 0.0	           0.2                0.4

- No Data

## White Sky Albedo 7 - 22 April, 2002

- No Data

- NIR (0.1-0.4) Red (0.0-0.16) Blue (0.0-0.18)

## Nadir BRDF-Adjusted Reflectance (NBAR)7 - 22 April, 2002

- No Data

- NIR (0.1-0.4) Red (0.0-0.16) Green (0.0-0.18)

## NBAR from Land Cover Training Sites in the Southern US

- NBAR represent the primary input to MOD12Q1 MODIS Land Cover Product

## MOD43B Quality Assurance Flags

- MOD43B 1km ISG products contain two 32 bit-packed words:
- First Word (Band Independent): Mandatory QA, Period,		Land/Water, Sensor, **Snow/NoSnow**, Solar Zenith Angle
- Second Word (Band Dependent):BRDF retrieved with the  		highest quality Full Inversion (0-7) or the lower quality 		Magnitude Inversion  (8-10)
- For Example: Between 60oN - 60 oS for September, 2001
- 47% of all land pixels were retrieved with a full inversion
- 45% with a magnitude inversion (a priori BRDF shape)
- 8% were not retrieved due to an absence of quality obs.

## MOD43B Quality Assurance Flags

** ****Good                            Moderate                 Poor      Bad**

** ****Full Inversion Quality   Magnitude Inversion Quality **

- Southwestern North America

- West Africa—Sahel

## Full vs. Magnitude Inversions, Baja Tile

- Dates:
- 193–208: Clear, full inversion pixels
- 209–224: Many cloudy dates, magnitude inversion pixels
- 225–240: Clear, full inversion pixels

## Terra-only NBARJune/July, 2002

## Terra+Aqua NBARJune/July 2002

## Terra-only Quality Flags 

- Red: High quality
- Cyan:Low quality

## Terra + Aqua Quality Flags

- Red: High quality
- Cyan:Low quality

## Terra and Aqua NIR White Sky Albedo Comparison

## MOD43B MODIS BRDF/ALBEDO PRODUCT VALIDATION

- SURFRAD/ARM Comparisons -- Y. Jin (BU)
- BARC Field Campaigns -- S. Liang (UMD)
- SAVE/SAFARI Field Campaigns -- J. Privette (GSFC)
- 						 G. Roberts (UCL)
- Barton Bendish Field Campaigns -- M. Barnsley (UWales, Swansea)
- 						 P. Lewis (UCL)
- China Field Campaigns -- X. Li  (BU & Beijing Normal U.)

## Surface Radiation Budget Network (SURFRAD)US participation in BSRN

- Six instrumented sites continuously measuring solar radiation (including PAR, direct and diffuse).
- Data packaged and distributed as half hour values by the CERES/ARM Validation Experiment (CAVE) for 2001.

## MODIS, SURFRAD, and CERES Comparisons

## MODIS vs SURFRAD Growing Season Results (2001)

## Current Product Status

- The Team evaluation has focused on the temporal stability and consistency of the products, on the variability by land cover and on the MOD43B Quality Assurance Flags.
- MODIS-Aqua directional reflectances will be added to MODIS-Terra values to increase sampling and improve quality of retrieved BRDFs.
- Reprocessed 1km MOD43B BRDF/Albedo products are available from November 2000 onward (in ISG in 10o tiles).  Products were upgraded to a Validated Level-1 status as of 6/11/02.
- The MOD43C CMG 1/4 degree products are also available from July 2001 onward (in a geographic Lat/Lon projection in global files).
- Schaaf et al., First Operational BRDF, Albedo and Nadir Reflectance Product from MODIS, in press, Remote Sensing Environ., 2002

## Research Efforts Utilizing MODIS Albedo/BRDF CMG Products

- Collaborative Efforts Underway:
- Community Climate Systems Model (CCSM):    (Dickinson/Bonan/Zeng/Yang/Houser)
- Albedo variation in arid lands
- Albedo variation of snow-covered vegetation
- European Center - Hamburg (ECHAM4): (Knorr/Kinne/Wild/Roesch)
- Albedo parameterization
- Lund-Potsdam-Jena (LPJ): (Lucht)
- Phenology/Albedo variations

## Desert AlbedoTrue-color White-sky Spectral Albedo from MODIS

- Desert albedos are clearly nonuniform, with implications for global climate modeling *(Tsvetsinskaya et al., GRL, 2002; Nature, N&V, 2002).*

## Snow versus Non-snow Albedos 40–50°N Nov 00–Jan 01

- Temporal consistency and magnitude of spectral albedos compare well with published results.
- Narrow to broadband conversion over pure snow backgrounds result in low broadband values.
-  Collaborative effort to adress this is underway (Stroeve, Liang, Nolin, Gao, Klein).

- Jin et al., How does Snow Impact the Albedo of Vegetated Land Surfaces as Analyzed with MODIS Data?, GRL, 2002.

## Utilization of MODIS BRDF/Albedo Standard Products 

- Additional Validation Sites
- GSFC, UNH
- BSRN
- MODIS Processing
- MODIS Cloud Products (King/Moody/Baum)
- MODIS Land Cover, LST (Wan)
- MODIS Surface Reflectance - vis, NIR, MIR (Vermote)
- Burn Scar (Roy)
- Community Outreach
- Workshops

## MODIS Workshop on Surface Radiation Budget Variables and Snow and Ice Products,  21-23 October, 2002, Boston University

**CEOS/WGCV Land Product Validation Workshop on Albedo**
**23-24 October, 2002, Boston University**

**Goals:** Foster communication between the field measurement community and the producers and users of satellite derived albedo data sets.  Identify challenges and discuss ways to move forward.
- Contact Crystal Schaaf (schaaf@bu.edu), Jeff Privette (jeff.privette@gsfc.nasa.gov)

**Goals:** Introduce users to the characteristics and applications of the MODIS land radiation products: Surface Reflectance, LST, BRDF/Albedo, Snow albedo, Snow/Ice extent
- Agenda and details posted at http://geography.bu.edu/brdf/
- Contact Alan Strahler (alan@bu.edu), Crystal Schaaf (schaaf@bu.edu)

## MOD43B MODIS BRDF/Albedo Product Summary 

- Evaluations indicate that the MOD43B algorithms have performed well throughout 2000, 2001 and into 2002.
- Reprocessed Terra albedo measures appear temporally stable and consistent.
- Indications are that the QA flags are appropriate--- (users must consult flags to determine whether snow or non-snow albedos).
-  Initial validations and comparisons over sites in the US are encouraging with errors of less than 10% in the growing season.
- Based on these analyses, MOD43B products have been upgraded to a status of “Validated (level 1)” .
- Further increases in quality are expected with the addition of Aqua surface reflectances.

## MOD43B MODIS BRDF/ALBEDO PRODUCT

- Reprocessed (V003) Standard Products (starting with the 16 day period beginning on Day 2000305 -- 31 October 2000) are available from EDC at http://edcdaac.usgs.gov/main.html
- Global CMG Products on a 1/4 degree resolution Geographical Grid (starting with Day 2001193 in July, 2001) are also available from EDC at http://edcdaac.usgs.gov/main.html
- Users Guide is available at http://geography.bu.edu/brdf/userguide/index.html
- Browse images (based on 5km resolution products) can be viewed at
- http://modland.nascom.nasa.gov/browse/