Validation of MODIS Snow Covered Days by the Combined Using of MODIS Aqua and Terra Snow Cover Products and In-Situ Observations All over China

New snow cover products are produced by combination of Aqua and Terra MODIS snow cover products from 2001.Then MODIS snow-covered days are produced by this new snow cover products through two standards.Through comparison of these two different snow-covered days all over China,it is found that among the three major snow cover centers,snow cover is more stable in Xinjiang Region than that in the other two regions,including the Tibetan Plateau and Northeast China-Inner Mongolia Region.The MODIS snow cover days are validated and calibrated by using 595 in-situ observations of snow cover days all over China after 2001.The outcome indicates that the unstable and stable snow-covered areas reach to 490.6 104 km2 and 334.4×104 km2,respectively.The stable snow-covered area in the Tibetan Plateau,Xinjiang Region and Northeast China-Inner Mongolia Region is about 153.7×104 km2,56.8×104 km2 and 117.9×104 km2,respectively.