Research On The Method Of Extracting Vegetation Cover Change Based On "3S" Technology In Arid Area

The response to terrene ecosystem is the important part of the current research on global change. Moreover, studying the relationship between vegetation cover and environment evolvement is the most complex and vivacious field. Vegetation plays an important role not only in bio-chemical cycling, but also in water cycling. Vegetation regulates material and energy exchange inside or outside of plant according to the situation of water and gas etc, so it can be seen that vegetation cover and its change is mainly related with environmental change of regional ecosystem。It is very significant for evaluation of ecologic environment and sustainable development of the local agriculture and stock rising to precisely and rapidly monitor the change of vegetation cover of Oasis in arid or semi-arid on large area. Comparing to traditional community research methods, remote sensing technology has undoubted superiority for monitoring vegetation cover in large area. Remote sensing technology has widely been adopted in research field of monitoring vegetation cover change in the past years. This paper systematically studies and reviews the past concerns and research with land cover\use change using remote sensing technology, introduced the basic theory, main methods (vegetation index) and involved research progress for remote sensing application of vegetation study. Taking the Yutian Oasis as an example, we used multitemporal and the same seasonal pattern TM images to study vegetation changes in different years,. First, we obtained an SAVI(Soil Adjusted Vegetation lndex), which is extremely related with terrene vegetation. Then, we extended the SAVI a scale based on 0-255. Finally, we made color components of SAVI data. The research shows that the aspects of color composition maps of multitemporal NDVI data of the Yutian Oasis can give us a clear view of vegetation change in area, for instance , the black or gray parts on the image stand for water, desert and gravel desert. the red and fuchsine parts are degradation vegetation area. The white or hoar parts are the main body of Oasis. The green or cyan parts are in edge of Oasis and Keliya river valley, because SAVI is from low to high, and coverage is also from low to high in three images. Then we obtained the area and geographical locatin of vegetation cover change in every class with the support of PCI and Arc/info. With the study results, we chose thirty investigation swatches (1km×1km) to investigate and analyze carefully the natural or artificial factors in the cause of change . In general, the vegetation cover of the large area in the Yutian Oasis is very good, and the Oasis is relatively in the stable situation. However, the ecological environment in parts of this Oasis is not allowed us to hold a optimistic attitude. These parts are located near the ecotone between oasis and desert. They can be called the protection belt or barrier for the Oasis. We must take them seriously. The research can transform remote sensed images from frequency to space and provide us with changing trend and intensity. We can further analyze the cause of these changes, based on study results and artificial and natural factors. This research can also be easily applied to other land cover change and provide direct and fast evidence for environmental management.