MODIS Online Nadir BRDF-Adjusted Reflectance (NBAR) Products

The Bi-directional Reflectance Distribution Function (BRDF) models the anisotropic scattering effects of surfaces under different illumination and observation conditions. In simple terms, BRDF describes mathematically the changes in reflectance that we observe when an illuminated target is viewed from different angles. BRDF enables prediction of surface reflectance as a function of solar and viewing geometry. The BRDF is wavelength dependent and is determined by the structural and optical properties of the surface. These properties include shadowing, multiple scattering, transmission, reflection, and absorption and emission by surface elements.

The high temporal frequency and large area coverage of MODIS make it well suited to determine the land surface BRDF properties from multi-date observations that are useful for time series analyses which need to account for observations that have different sensor/solar geometries. The BRDF parameters derived from the BRDF fitting can be inverted to predict what reflectance should be in a given sensor/solar geometry. This allows prediction of reflectance for nadir observations at a mean solar zenith angle over the 16 days period to generate Nadir BRDF adjusted reflectance (NBAR) products.

MODIS NBAR products are operationally produced from 16 days of registered, multi-band, atmospherically corrected surface reflectance data from the MODIS instrument aboard the Terra and Aqua satellite at a 500m spatial resolution. Geoscience Australia use Direct Broadcast MOD43 package from Boston University to generate NBAR composite products. In addition to the NBAR composite products, the BRDF parameters for each band, the ancillary and band quality information are also provided for customer download.

Description Format Processing Projection
NBAR Band 1~7 GEOTIFF SeaDAS - MOD09 - MOD43 - MRT Equirectangular
BRDF parameters Band 1~7 GEOTIFF SeaDAS - MOD09 - MOD43 - MRT Equirectangular
BRDF Ancillary Band 1~7 GEOTIFF SeaDAS - MOD09 - MOD43 - MRT Equirectangular
BRDF Band 1~7 quality GEOTIFF SeaDAS - MOD09 - MOD43 - MRT Equirectangular

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