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The MCD43A4 Nadir BRDF-Adjusted Reflectance (NBAR) Product (MODIS/Terra Nadir BRDF-Adjusted Reflectance Daily L3 Global 500m SIN Grid) is computed for each of the MODIS spectral bands (1-7) at local solar noon of the day of interest. Since the view angle effects will have been removed from the directional reflectances, this will result in a more stable and consistent product. NBAR values are being directly used as the primary input to the advanced technique classifiers used in the production of the global MODIS Land Cover Product MCD12Q1 [1]. The user community has been taking advantage of the NBAR data for those situations where composited surface reflectances were traditionally used.

Note: Reprocessed (V006 and higher) MODIS BRDF/Albedo products from Day 2000065 (5 March 2000 to present) have been assigned a "Validated (Stage 3) Status".

References Cited

1. Friedl, M. A., D. Muchoney, D. McIver, F. Gao, J. F. C. Hodges and A. H. Strahler, Characterization of North American land cover from NOAA-AVHRR data using the EOS MODIS land cover classification algorithm, Geophys. Res. Let., 27, 977, 2000.

2. Schaaf, C. B., F. Gao, A. H. Strahler, W. Lucht, X. Li, T. Tsang, N. C. Strugnell, X. Zhang, Y. Jin, J.-P. Muller, P. Lewis, M. Barnsley, P. Hobson, M. Disney, G. Roberts, M. Dunderdale, C. Doll, R. d'Entremont, B. Hu, S. Liang, and J. L. Privette, First Operational BRDF, Albedo and Nadir Reflectance Products from MODIS, Remote Sens. Environ., 83, 135-148, 2002.

3. Lucht, W., C.B. Schaaf, and A.H. Strahler. An Algorithm for the retrieval of albedo from space using semiempirical BRDF models, IEEE Trans. Geosci. Remote Sens., 38, 977-998, 2000.

4. Lucht, W., Expected retrieval accuracies of bidirectional reflectance and albedo from EOS-MODIS and MISR angular sampling, J. Geophys. Res., 103, 8763-8778, 1998.

5. Lucht, W., and P. Lewis. Theoretical noise sensitivity of BRDF and albedo retrieval from the EOS-MODIS and MISR sensors with respect to angular sampling, Int. J. Remote Sensing, 21, 81-98, 2000.

Science Data Sets

While the full MCD43A4 specification should be consulted for the most current description, the product includes two Science Data Sets (SDS) for each pixel in the tile. These SDSs are Nadir_Reflectance (computed for bands 1-7 at the local solar noon zenith angle of the day of interest) and BRDF_Albedo_Band_Mandatory_Quality SDS  (containing 1 byte of quality flags) and is defined in the specification.

The Nadir_Reflectance SDS is specified as:

•  Data Field Name: INT16 Nadir_Reflectance ("YDim", "XDim", "Num_Land_Bands")

•  Description: Nadir BRDF-adjusted reflectance (NBAR) at mean szn of the period

•  Data conversions:

              file data=(Nadir_Reflectance / scale_factor) + add_offset
              Nadir_Reflectance=(file data - add_offset)*scale_factor

And for the BRDF_Albedo_Band_Mandatory_Quality SDS see specification (V006 and V006.1)

Note that the V006 and V006.1 MODIS MCD43 products are retrieved daily and represent the best BRDF possible based on 16 days’ worth of inputs with the day of interest emphasized.  Unlike the earlier reprocessed versions (where the date of the product signifies the first day of the retrieval period), and the Direct Broadcast version (where the date signifies the last day of the retrieval period), the date associated with each daily V006 and V006.1 retrieval is the center of the moving 16 day input window. This change is in response to user requests.

Local Attributes

In addition to the actual SDS data values produced at each pixel in a tile, each SDS is associated with a number of standard Local Attributes that apply to the data. For the Nadir_Reflectance SDS they include:

And for the BRDF_Albedo_Band_Mandatory_Quality SDS see specification (V006 and V006.1)

Global Attributes (Metadata)

In addition to the albedo and quality information (SDSs and Local Attributes) that is provided at a per-pixel level, each tile of the Level 3 MCD43A4 Parameters Product also includes three types of Global Attributes or Metadata which summarize the tile. These are Core, Archive, and Structural Metadata. Of particular interest to the user community are the Core Metadata QAFlags of SCIENCEQUALITYFLAG and SCIENCEQUALITYFLAGEXPLANATION and some of the Additional Attributes which identify the tile number or which summarize the quality of the product over that entire tile (see the full MCD43A4 specification (V006 and V006.1) for the complete listing).