The Snow Covered Area product is based on a Normalized Difference Snow Index(NDSI), which is similar to NDVI, but exploits different bands in the equation (Equation 3),namely Green (Band 4) and Short Wavelength Near-infrared (SWNIR, Band 6).

It isimportant to note that the Band 6 sensor on MODIS Aqua malfunctioned shortly after launch,so Snow Covered Area from the Aqua sensor is calculated using Bands 3 and 7.

This mayintroduce errors in identifying snow in vegetated areas, as the use of Band 7 results in falsesnow detection. For this reason the MODIS Terra product has been provided for the CAFF-system.