Daily snow albedo is calculated using various inputs such as the MODIS surface reflectance product (MOD09), Bidirectional Reflectance Distribution Function (BRDF), land cover product and a Digital Elevation Model (DEM) (Klein and Stroeve, 2002). Models of the BRDF of snow are created using the discrete-ordinate radiative transfer (DISORT) model of Stamnes et al. (1988) to correct for anisotropic scattering effects over non-forested surfaces. A narrowband or spectral albedo is calculated for each of the shortwave MODIS bands, then combined into a spectrally-integrated broadband albedo. Snow is treated as an anisotropic surface except in forests where it is treated as an isotropic surface.
There are important limitations to the MOD10A1 daily snow albedo product. For example, it is difficult to perform an atmospheric correction over a bright surface such as snow. In addition, utilizing the appropriate per-pixel BRDFs can be problematic, and correction for anisotropic scattering must be included. Also, narrow to broadband conversion specific for snow on different surfaces must be calculated and this can be difficult. In consideration of these limitations, we are exploring an enhancement to the daily snow albedo product algorithm by coupling the periodic per-pixel snow albedo (MCD43) with the daily surface reflectances. Use of the newly-reprocessed Version 005 data along with improved cloud discrimination will contribute to the improvement of the daily product. Some preliminary validation of the new daily snow albedo product is provided.
References
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