Extracting Precaution Line Of The Oasis-Desert Transition Belt Based On "3S" Techniques

The oasis, which constitutes the arid area, sustains the lives and development of the local people , and forms a contradictory with the desert. The two eco-systems can invert each other in some conditions. The ecotone between oasis and desert is the most prominent area to these activities. It records the most sensitive and intact information on the transition belt. It' s significant to further the study on the environmental evolvement and forming mechanism, and this helps to open out its ecological essential, protect and develop the oasis. Located in the cross belt which converges northeaster and northwester, Yutian Oasis is threatened by the flowing sand, and has the bad natural conditions. To make it the key study area will be useful to protect and develop the eco-system in the western China. Yutian County is also one of the 20 poorest counties in China. To study this area can help the local government take some effective measurements and work out the detailed plan. All those will make the local people rich as early as possible.The paper has made detailed observation by the existing apparatus and the field observation stations. Based on the image and the vector database of the Yutian Oasis, the study has obtained the precise coordinates of investigation points by GPS technique, and overlapped them with the images. After classifying the images with the maximum likelihood supervised classification method, we import the result into CIS software, and analyze the Yutian Oasis changes about land cover' s quantity, quality and spatial position from 1976 to 2001. By contrast to the data of the past years' fieldwork, we have analyzed the environmental changes and the desertification degree of the study area in the past 25 years, and extracted the precaution line of the oasis' s environmental evolvement.On the base of the changes of natural, social and economic environment, the study validates the precaution line' s functions: locating the fragile area and indicating the eco-system' s changes. This is the newest application in the arid area study of the western China, also the paper' s innovation and emphasis. We can acquire the visual comprehension about the whole or local trend of the study area' s changes through analyzing the precaution line, and make it possible to forecast the future development of Yutian Oasis. Using the precaution lines of different periods, the end of the paper has analyzed the most possible development trend of Yutian Oasis-Desert transition belt in next 5 or 10 years, and given the constructive advices to local eco-system protection, social or economic project. The study result will be relevant to the evolvement, management, and sustainable development of the other oases in the arid area of the western China.