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The Chinese Sun Hazemeter Network(CSHNET)provides the necessary ground-based observation to validate and assess the applicability of MODIS aerosol optical depth(AOD)products over different ecological and geographic regions in China for the first time.The validation results show that the comprehensive utilization ratio and applicability of MODIS products varied very much over different regions and seasons from August 2004 to July 2005.On the Tibetan Plateau,the comprehensive utilization ratio of MODIS data was low:MODIS products only accounted for 16% of the ground-based observation;on average,31% to 45% of MODIS products fell within the retrieval errors issued by NASA.A similar result was found in northern desert areas with the ratio of MODIS to observation ranging from 15% to 55%,with 7% to 39% of MODIS products within errors.In the remote northeast corner of China,low ratios of MODIS to observation were also found ranging from 14% to 46%,with 49% to 69% of MODIS within errors.The forested sites exhibited moderate ratios of MODIS to observation ranging from 46% to 65%,with 30% to 59% of MODIS within errors.This was similar to numbers observed at sites along eastern seashore of China and inland urban sites with the ratio of MODIS to observation between 63% to 75%,with 25% to 67% of MODIS within errors for sites along eastern seashore of China and 43% to 78%,with 35% to 75% of MODIS within errors for inland urban sites.The ratio of MODIS to observation over agricultural areas ranged from 61% to 89%;59%-88% of MODIS fell within the retrieval errors.At homogeneous and well vegetated areas,the comprehensive utilization ratio of MODIS products was over 80% and above 70% of MODIS products fell within the retrieval errors in growing Season.