MODIS BRDF/Albedo Product (MOD43B) User's Guide
MOD43B4 NBAR Product
The MOD43B4 Nadir BRDF-Adjusted Reflectance (NBAR) Product
(MODIS/Terra Nadir BRDF-Adjusted Reflectance 16-Day L3 Global 1km
SIN Grid) is computed for each of the MODIS spectral bands (1-7)
at the mean solar zenith angle of each 16 day period. 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 MOD12Q1 [1].
It is anticipated that the user community will be quick to take
advantage of the NBAR data for those situations where composited
surface reflectances may have been traditionally used.
In addition to the spectral NBAR values, the MOD43B4 NBAR Product
also provides extensive quality information. Band-averaged
quality information and band-independent data are stored in the
first 32-bit word, while band-specific quality information and
inversion status information are stored in the second 32-bit word
[2],[3],[4],[5].
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
- 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.
- 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.
- Lucht, W., Expected retrieval accuracies of
bidirectional reflectance and albedo from EOS-MODIS and
MISR angular sampling, J. Geophys. Res., 103, 8763-8778,
1998.
- 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.
While the full MOD43B4 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 mean solar
zenith angle of the 16 day period) and Nadir_Reflectance_Quality
(containing two 32-bit words of quality flags).
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
The Nadir_Reflectance_Quality SDS is specified as:
Data Field Name: UINT32 Nadir_Reflectance_Quality("YDim","XDim",
"Num_QC_Words")
Description: BRDF and albedo quality information
Num_QC_Words #1 holds band-averaged quality and inversion status
information and band-independent data
(bits 00-01 are the MODLAND mandatory QA)
00-01 Mandatory QA
0 = processed, good quality
1 = processed, see other QA
2 = not processed due to cloud effects
3 = not processed due to other effects
02-03 Period used
0 = 16 days
1 = 32 days
04-07 land/water
0 = Shallow ocean
1 = Land (Nothing else but land)
2 = Ocean coastlines and lake shores
3 = Shallow inland water
4 = Ephemeral water
5 = Deep inland water
6 = Moderate or continental ocean
7 = Deep ocean
08-10 AM/MISR/PM
0 = AM
1 = AM/PM
2 = AM/PM/MISR
3 = AM/MISR
4 = PM
5 = PM/MISR
6 = MISR
11-15 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
16-17 snow/no snow
0 = no Snow
1 = Snow present
18-30 TBD
31 QAfill
Num_QC_Words #2 holds band-specific quality and inversion status
information
00-03 Band1 Quality
0 = RMSE good, WoD(ref) good, WoD(WSA) good
1 = RMSE good, WoD(ref) good, WoD(WSA) moderate
2 = RMSE good, WoD(ref) moderate, WoD(WSA) good
3 = RMSE good, WoD(ref) moderate, WoD(WSA) moderate
4 = RMSE moderate, WoD(ref) good, WoD(WSA) good
5 = RMSE moderate, WoD(ref) good, WoD(WSA) moderate
6 = RMSE moderate, WoD(ref) moderate, WoD(WSA) good
7 = RMSE moderate, WoD(ref)moderate, WoD(WSA)moderate
8 = magnitude inversion (numobs >=7)
9 = magnitude inversion (numobs >3&<7)
10 = magnitude inversion (numobs <=3)
11 = Bus-in DB parameters (not currently used)
15 = Fill value
04-07 Band2 Quality (see explanation for band1)
08-11 Band3 Quality (see explanation for band1)
12-15 Band4 Quality (see explanation for band1)
16-19 Band5 Quality (see explanation for band1)
20-23 Band6 Quality (see explanation for band1)
24-27 Band7 Quality (see explanation for band1)
28-30 TBD
31 QAFill
(Note that while the RMSE indicates the fit of the full
inversion, the Weights of Determination (WoD) give some
indication of noise expected in the full retrieval and are
dependent on the angular sampling of the available surface
reflectances [4],[5],[6].)
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:
| Name: | Type: | Value: |
| long_name | HDF-STRING | "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 | 0.0001 |
| scale_factor_err | HDF-float64 | 0.0 |
And for the Nadir_Reflectance_Quality SDS, they include:
| Name: | Type: | Value: |
| long_name | HDF-STRING | "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-pixel level, each tile of the Level 3 MOD43B4 NBAR
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
AdditionalAttributes which identify the tile number or which
summarize the quality of the product over that entire tile (see
the full MOD43B4 specification
for the complete listing).
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