VNP43IA1 and VNP43MA1 BRDF/Albedo Model Parameters Product
VIIRS User Guide Collection 1
This Guide is a living document that describes the VIIRS BRDF and Albedo Products. The purpose of the document is to give the potential user an understanding of the VNP43 products and the current state of the data in those products.
Note: Users are urged to use the band specific quality flags to isolate the highest quality full inversion results for their own science applications.
The VNP43IA1 and VNP43MA1 BRDF Model Parameters Products supply the weighting parameters associated with the RossThickLiSparseReciprocal BRDF model that best describe the anisotropy of each pixel. VNP43IA1 provides information for the three VIIRS Imagery bands (I1, I2, and I3) at a 500m scale, and VNP43MA1 provides information for the nine Moderate bands (M1- M5, M7-M8, M10-M11) at a 1km scale , as well as the information for the three broad bands (0.3-0.7µm, 0.7-5.0µm, and 0.3-5.0µm). Thus note that IA1 refers not to just the I1 band but to the first of the 4 BRDF products (the BRDF model parameters) for all I bands. 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 the VNP43IA4 and VNP43MA4 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 VNP43IA3 and VNP43MA3). Alternately, these 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:
The product includes four types of Science Data Sets (SDS) for each pixel in the tile. These SDSs are the BRDF_Albedo_Parameters (three model parameters representing fiso, fvol, fgeo for the RossThickLiSparseReciprocal BRDF model that are computed for the spectral bands and three broadbands), and BRDF_Albedo_Band_Mandatory_Quality (containing 1 byte of quality flags).
Note that the Collection 1 VIIRS VNP43 products are retrieved daily and represent the best BRDF possible based on 16 days’ worth of inputs with the day of interest emphasized. The date associated with each daily retrieval is the center of the moving 16 day retrieval window.
For the File Specifications for VNP43IA1 and VNP43MA1, please visit: https://ladsweb.modaps.eosdis.nasa.gov/filespec/VIIRS/collection1
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.
Professor Crystal Schaaf’s Lab
University of Massachusetts Boston
100 Morrissey Blvd.