The Dynamic Monitoring Of Vegetation In The Area Of Beijing And Tianjin Sandstorm Source Control Project Based On MODIS NDVI

Vegetation cover change is an important area of remote sensing, environmental science, meteorology, and many other disciplines to concern to, which is not only an important aspect for remote sensing to deal with, but also base of climate change analysis, carbon cycle of surface area and many other researches. This paper choices Beijing and Tianjin sandstorm source control area as a research area, with MODIS-NDVI images of time series(2000,2004,2008) as main data source, to systematically study vegetation cover change and driving mechanism.Five different kinds of vegetation indices studies have shown that, Normalized Difference Vegetation Index (NDVI) is the strongest to detect low vegetation cover and Global Environment Index (GEMI) is the best to eliminate the effect of soil background influence. Considering the characteristics of vegetation and spectrum of vegetation-soil interaction, NDVI is first vegetation index to measure vegetation change in study area, followed by GEMI.Through regression analysis between NDVI and natural factor, the reason that results in uneven spatial pattern of vegetation in study area is mainly rainfall. In the northwestern arid and semi-arid vegetation, the lowest vegetation level, in particular, likely causes desertification. Regression equation between vegetation cover and independent variables, that is, rainfall,10°accumulated temperature, aridity, DEM, longitude, temperature, latitude is as follows:vegetation cover=0.917 (rainfall)-0.026(10°accumulated temperature)+0.22 (aridity)+0.286 (DEM)+0.221 (longitude)+0.037 (temperature)From 2000 to 2008, in general, vegetation coverage of Beijing and Tianjin sandstorm source control area showed growth. Despite different vegetation cover changed frequently, in the mean tine, treatment and destruction existed, generally desertification degree reduced, vegetation transfered from low grade to high-grade, and vegetation has clearly risen. By comparing results of 4 partitions, In addition to increasing in farming-pastoral desertification control zone, low vegetation had different levels of reduction in other three partitions. Northern arid grassland desertification control area is main distribution area of low vegetation cover, and there were a large number of low vegetation cover in sand, which, transferred fast from low vegetation to high vegetation..Yanshan hill water source protection area was the best area of vegetation cover. Through analysis of landscape pattern indices, in entire study area, number of patch, landscape diversity and evenness index reduced, while aggregation index increased. Proportion of mosaic gradually moved from evenness to non-uniform and difference of proportion of landscape element widened further. Low vegetation cover shifted toward high vegetation, so high-cover vegetation increased gradually.Through a variety of driving force to promote vegetation change, from the point of long time-scale, natural and man-made factors are driving vegetation cover and landscape change. In the short time scale, natural factor has relative stability and human activities are undoubtedly the most important driver of landscape and vegetation cover change. Especially in Beijing and Tianjin sandstorm source control area, all kinds of forestry projects are more important compared to other factors.