MODIS BRDF/Albedo Product (MOD43C) User's Guide

MOD43C2 CMG BRDF/Albedo Model Parameters Product

The MOD43C2 Climate Modeling Grid (CMG) BRDF/Albedo Model Parameters Product (MODIS/Terra BRDF/Albedo Parameters 16-Day L3 Global 0.05Deg CMG) supplies the weighting parameters associated with the RossThickLiSparseReciprocal BRDF model that best describes the anisotropy of each pixel. These three parameters ( f_iso, f_vol, f_geo) 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) at a 0.05 degree spatial resolution in global files in a geographic (lat/lon) projectionn. These model parameters are based on the underlying 1-km model parameters. Note that along coastlines, this means that the 1-km pixels that lie over shallow water will be averaged into the 0.05 degree CMG pixel. In addition to the spectral and broadband parameters themselves, the MOD43C2 CMG BRDF/Albedo Model Parameters Product also provides extensive quality information. The quality and inversion status of the majority of the underlying 1-km pixels is provided as well as the percentage of the underlying pixels that were present or were snow covered.

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 MOD43B4 Nadir BRDF-Adjusted Reflectances - NBAR) or to compute the integrated black-sky (at some solar zenith angle) and white-sky albedos (as is done for MOD43B3). 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 [1],[2]. The polynomial is as follows:

The appropriate constants are:

Term Isotropic (iso) RossThick (vol) LiSparseR (geo)

g₀ 1.0 -0.007574 -1.284909

g₁ 0.0 -0.070987 -0.166314

g₂ 0.0 0.307588 0.041840

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

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

Term Isotropic (iso) RossThick (vol) LiSparseR (geo)

White-sky
integral g 1.0 0.189184 -1.377622

Note: Reprocessed (V004) MODIS BRDF/Albedo products from Day 2000065 (5 March 2000) have been assigned a "Validated (Level 1) Status". Users are urged to use the band specific quality flags to isolate the highest quality full inversion results for their own science applications. MOD43B and MOD43C products will continue to be evaluated and validated by the MODIS Science Team and MODIS Validation Scientists.

References Cited

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.

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.

Science Data Sets

While the full MOD43C2 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_Parameter0, BRDF_Albedo_Parameter1, and BRDF_Albedo_Parameter2 representing the three model parameters fiso, fvol, fgeo for the RossThickLiSparseReciprocal BRDF model (each for bands 1-7 and three broad bands), and BRDF_Albedo_Quality (containing one 32-bit word of quality flags).They are provided in global files in a geographic (lat/lon) projection (3600 rows X 7200 columns (X 10 bands)).

The BRDF_Albedo_Parameters SDSes are specified as:

Data Field Name: INT16 BRDF_Albedo_Parameter0 ("YDim", "XDim", "Num_Land_Bands_Plus3")

Description: BRDF and albedo model parameter fiso for bands 1-7, and the vis, NIR and SW broadbands
Data conversions:
file data=(BRDF_Albedo_Parameter0 / scale_factor) + add_offset
BRDF_Albedo_Parameter0=(file data - add_offset)*scale_factor

Data Field Name: INT16 BRDF_Albedo_Parameter1 ("YDim", "XDim", "Num_Land_Bands_Plus3")

Description: BRDF and albedo model parameter fvol for bands 1-7, and the vis, NIR and SW broadbands
Data conversions:
file data=(BRDF_Albedo_Parameter1 / scale_factor) + add_offset
BRDF_Albedo_Parameter1=(file data - add_offset)*scale_factor

Data Field Name: INT16 BRDF_Albedo_Parameter2 ("YDim", "XDim", "Num_Land_Bands_Plus3")

Description: BRDF and albedo model parameter fgeo for bands 1-7, and the vis, NIR and SW broadbands
Data conversions:
file data=(BRDF_Albedo_Parameter2 / scale_factor) + add_offset
BRDF_Albedo_Parameter2=(file data - add_offset)*scale_factor

The BRDF_Albedo_Quality SDS is specified as:

Data Field Name: UINT32 BRDF_Albedo_Quality ("YDim","XDim")

Description: BRDF and albedo quality information

00-01 Mandatory QA
0 = Majority processed, good quality
1 = Majority processed, see other QA
2 = Majority not processed due to cloud effects
3 = Majority not processed due to other effects
02 Period used
0 = 16 days
1 = 32 days
03-05 AM/MISR/PM
0 = AM
1 = AM/PM
2 = AM/PM/MISR
3 = AM/MISR
4 = PM
5 = PM/MISR
6 = MISR
06-07 BRDF Quality
0 = Majority full inversion
1 = Majority magnitude inversion
2 = Majority Bus-in DB parameters
(not currently used)
3 = Majority Fill Value
08-15 Percent Inputs
0-100
(percent of the processed finer resolution data that contributed to this CMG pixel)
16-23 Percent Snow
0-100
24-27 Mean Szn of Obs
0 = 0-5 degrees
1 = 5-10 degrees
2 = 10-15 degrees
3 = 15-20 degrees
4 = 20-25 degrees
5 = 25-30 degrees
6 = 30-35 degrees
7 = 35-40 degrees
8 = 40-45 degrees
9 = 45-50 degrees
10 = 50-55 degrees
11 = 55-60 degrees
12 = 60-65 degrees
13 = 65-70 degrees
14 = 70-75 degrees
15 = 75-80 degrees
16 = 80-90 degrees
28-30 TBD
31 QAfill

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_Parameter* SDSes they include:

Name: Type: Value:

long_name HDF-STRING "BRDF_Isotropic_Weight
(or BRDF_Volumetric_Weight or BRDF_Geometric_Weight)"

units HDF-STRING "no units"

valid_range HDF-int16 0, 32766

_FillValue HDF-int16 32767

add_offset HDF-float64 0.0

add_offset_err HDF-float64 0.0

calibrated_nt HDF-int32 5

scale_factor HDF-float64 0.001

scale_factor_err HDF-float64 0.0

For the BRDF_Albedo_Quality SDS, they include:

Name: Type: Value:

long_name HDF-STRING "Aggregated_Albedo_Quality"

units HDF-STRING "concatenated flags"

valid_range HDF-uint32 0, 4294967294

_FillValue HDF-uint32 4294967295

Global Attributes (Metadata)

In addition to the parameter and quality information (SDSs and Local Attributes) that is provided at a per-CMG-pixel level, each Level 3 MOD43C2 BRDF/Albedo Parameters Product also includes three types of Global Attributes or Metadata which summarize the file. 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 AdditionalAttributes which summarize the quality of the product over that entire file (see the full MOD43C2 specification for the complete listing).