MODIS BRDF/Albedo CMG Product (MOD43C) User's Guide
MOD43C3 CMG NBAR Product
The MOD43C3 Climate Modeling Grid (CMG) Nadir BRDF-Adjusted
Reflectance (NBAR) Product (MODIS/Terra Nadir BRDF-Adjusted
Reflectance 16-Day L3 Global 0.05Deg CMG) is computed for each of
the MODIS spectral bands (1-7) at the mean solar zenith angle of
each 16 day period. The data are provided in global files in a
geographic (lat/lon) projection. Since the view angle effects
have been removed from the directional reflectances, this results
in a stable and consistent reflectance product.These NBAR values
are based on spatial averages of the
underlying 1-km NBAR data. 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 albedo quantities
themselves, the MOD43C3 CMG NBAR 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.
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 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.
While the full MOD43C3
specification should be
consulted for the most current description,
the
product includes thwo Science Data Sets (SDS) for each cmg-pixel in
the
tile. These SDSs are Nadir_Reflectance (NBAR) at the mean solar zenith angle of
the 16 day period for 7 spectral bands and Nadir_Reflectance_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 7 bands)).
The Nadir_Reflectance (NBAR) SDS is specified as:
Data Field Name: INT16 ("YDim", "XDim",
"Num_Land_Bands"")
Description: Nadir BRDF-adjusted reflectance (NBAR) at mean solar zenith angle
for bands 1-7
Data conversions:
file data=(NBAR / scale_factor) + add_offset
NBAR=(file data - add_offset)*scale_factor
The Nadir_Reflectance_Quality SDS is specified as:
Data Field Name: UINT32 Nadir_Reflectance_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
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 (NBAR) SDS they include:
| Name: | Type: | Value: |
| long_name | HDF-STRING |
"Global_Nadir_Reflectance" |
| units | HDF-STRING | "reflectance, 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 |
And for the Nadir_Reflectance_Quality SDS, they include:
| Name: | Type: | Value: |
| long_name | HDF-STRING | "Aggregated_Nadir_Reflectance_Quality" |
| units | HDF-STRING | "concatenated flags" |
| valid_range | HDF-uint32 | 0, 4294967294 |
| _FillValue | HDF-uint32 | 4294967295 |
In addition to the albedo and quality information (SDSs and Local
Attributes) that is provided at a per-cmg-pixel level, each Level 3 MOD43C3 CMG NBAR 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 MOD43C3 specification for the complete listing).
|
