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If a pixel in MODIS bands 2 and 4 has an NDSI value greater than or equal to 0.4 and the reflectance in bands 2 and 4 is greater than 0.10 (as shown by the cross-hatched rectangle), it is mapped as snow.
A separate group of criteria tests is used to better detect snow in vegetated regions. If the value of NDSI and NDVI of a pixel falls in the region indicated by the left polygon, it is mapped as snow.