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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 VNP43C1 Climate Modeling Grid (CMG) BRDF/Albedo Model Parameters Product at 0.05 degrees spatial resolution supplies the weighting parameters associated with the RossThickLiSparseReciprocal BRDF model that best describes the anisotropy of each pixel. These three parameters (fiso , fvol , fgeo) are provided for each of the VIIRS spectral M bands, the three broad bands (0.3-0.7µm, 0.7-5.0µm, and 0.3-5.0µm), and the Day Night Band (DNB), at a 0.05 degree spatial resolution in global files in a geographic (lat/long) projection. These model parameters are based on the underlying 30arcsecond model parameters. Note that along coastlines, this means that the 30arcsecond 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 VNP43C1 CMG BRDF/Albedo Model Parameters Product also provides mandatory quality information. The quality and inversion status of the majority of the underlying 30arcsecond pixels is provided as well as the percentage of the underlying pixels that were present or were snow covered. Therefore, caution should be used when assessing these products for highest quality.  

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 VNP43C4 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 VNP43C3). 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:

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

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

Science Data Sets

The product includes four Science Data Sets (SDS) for each pixel in the tile. These SDSs are BRDF_Albedo_Parameter1, BRDF_Albedo_Parameter2, and BRDF_Albedo_Parameter3 representing the three model parameters fiso, fvol, fgeo for the RossThickLiSparseReciprocal BRDF model (each for the M bands (M1–M5, M7–M8 and M10–M11), the three broad bands, and the DNB), and BRDF_Albedo_Quality. They are provided in global files in a geographic (lat/long) projection (3600 rows X 7200 columns (X 10 bands)).

Note that the AS 5000 VIIRS VNP43 products are retrieved daily and represent the best BRDF possible based on 16 days’ worth of inputs with the day of interest (the center day of the retrieval period) emphasized.

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. 

References: 

1. 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.
2. 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.