UMass Boston

The MCD43A1 BRDF/Albedo Model Parameters Product (MODIS/Terra BRDF/Albedo Model_1 Daily L3 Global 500m SIN Grid) supplies the weighting parameters associated with the RossThickLiSparseReciprocal BRDF model that best describes the anisotropy of each pixel. These three parameters (fiso , fvol , fgeo) are provided for each of the MODIS spectral bands as well as for three broad bands (0.3-0.7µm, 0.7-5.0µm, and 0.3-5.0µm). These parameters can be used in a forward version of the model to reconstruct the surface anisotropic effects and thus correct directional reflectances to a common view geometry (this is the procedure that is used to produce MCD43A4 Nadir BRDF-Adjusted Reflectances - NBAR) or to compute the integrated black-sky (at some solar zenith angle) and white-sky albedos (as are done for MCD43A3). Alternately, the parameters can be used with a simple polynomial to easily estimate the black-sky albedo with good accuracy for any desired solar zenith angle.

The polynomial is as follows:

The appropriate constants are:

Similarly, the white-sky albedo can be computed by using the equation:

and the estimates of the white-sky kernel integrals are:

Science Data Sets

While the full MCD43A1 specification should be consulted for the most current description, the product includes four Science Data Sets (SDS) for each pixel in the tile. These SDSs are BRDF_Albedo_Parameters (three model parameters representing fiso, fvol, fgeo for the RossThickLiSparseReciprocal BRDF model that are computed for bands 1-7 and three broad bands), and BRDF_Albedo_Band_Mandatory_Quality* (containing 1 byte of quality flags).

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.

Mandatory QA values for Collection 6:

          0 = processed, good quality (full BRDF inversions)

          1 = processed, see other QA (magnitude BRDF inversions)

Mandatory QA values for Collection 6.1:

0 = processed, good quality (full BRDF inversions)

1 = processed, see other QA (magnitude BRDF inversions)

2 = processed, good quality (full BRDF inversions, only Band 6 is fill value due to non-functional or noisy detectors)

3 = processed, see other QA (magnitude BRDF inversions, only Band 6 is fill value due to non-functional or noisy detectors)

4 = processed, good quality (full BRDF inversions, only Band 5 is fill value due to non-functional or noisy detectors)

5 = processed, see other QA (magnitude BRDF inversions, only Band 5 is fill value due to non-functional or noisy detectors)

6 = processed, good quality (full BRDF inversions, both Band5 and Band 6 are fill value due to non-functional or noisy detectors)

7 = processed, see other QA (magnitude BRDF inversions, both Band 5 and Band 6 are fill value due to non-functional or noisy

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 BRDF_Albedo_Parameters SDS they include:

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 MCD43A1 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 MCD43A1 specification for the complete listing).