Development of the Aqua MODIS NDSI fractional snow cover algorithm and validation results

The principal purpose of this paper is to describe the development and validation of an algorithm to estimate the fraction of snow cover within a 500-m pixel of the Moderate Resolution Imaging Spectroradiometer (MODIS) operating on the Earth Observing System Aqua spacecraft. The performance of this algorithm and algorithms applicable to the MODIS on the Terra spacecraft are compared. Validation efforts show that both pixel-level, fractional snow cover relationships for the Terra and Aqua MODIS instruments work well as quantified by such measures as correlation coefficient (r) and root-mean-square error when compared to Landat-7 Enhanced Thematic Mapper ground-truth observations covering a substantial range of snow cover conditions. Over all the scenes used herein, the correlation coefficients were near 0.9 and the RMSE near 0.10. However, somewhat better performance was found for the Terra MODIS versus the Aqua MODIS over nearly concurrently observed scenes. Furthermore, it is clear that more improvements in fractional snow cover estimates within MODIS pixels should be pursued to better account for variability in slope and aspect, atmospheric effects, snow cover types, and land cover.