The research of vegetation coverage classification using NDVI data in China

The Normalized Difference Vegetation Index (NDVI) is very important index, which often is a measure of the amount and vigor of vegetation at the surface. In general, the magnitude of NDVI is related to the level of photosynthetic activity in the observed vegetation. There have been quite a lot of successful examples in using this index to classify vegetation and to forecast the amount of crops in China. We used 12 monthly NOAA AVHRR NDVI data pretreated necessarily of the year 1999 to establish the standard deviation matrix of every ground surface element all over China, and then estimated the comparability between every two elements. But because of some deficiency when it is used to demonstrate the difference of NDVI changes within only a part of time, two factors should be considered, which include a factor for controlling range changes and a factor for controlling the direction of time changes. To establish the first factor is to distinguish the surface elements which have similar standard deviation but have different NDVI range changes in different range of time. To establish the second factor is to distinguish the change direction of all the NDVI of different elements. The standard deviation and the factors form a set, which helped us to analyze the conformation and difference of changes between elements, and finally we gained the classified result. And referring to Chinese vegetation and zoology distribution maps, we discussed every class in our result carefully.