Classification of Oasis Desertification Land Based on SPOT High Spatial Resolution Imagery: A Case Study of the Turpan Oasis, Xinjiang
基于SPOT高分辨率遥感数据的绿洲荒漠化土地分类方法——以吐鲁番绿洲为例

Oasis is the major portion with relatively high productivity and hosts a lot of lives in arid areas. It takes up only 4% of the area but sustains 95% of the population and above 90% of social wealth in Xinjiang, China, which is a typical arid area in the world. Oasis is the citadel to explore in desert and mountainous areas, and therefore plays a fundamental role in the development of society and economy in Xinjiang. The Turpan Basin is a typical oasis-desert interlaced area in eastern Xinjiang, and an important part of the ecologically and environmentally fragile zone of northwestern Oasis in China. Desertification is the most serious environmental problem in the Turpan Basin. It is important to accurately and rapidly monitor desertification. Satellite remote sensing has become a commonly used technique in desertification monitoring. High resolution remote sensing imagery, SPOT data, was used in this study. First, a classification system which is able to reflect desertification types and characteristics was built in terms of land use/cover characteristics. A series of atmospheric and geometric corrections and imagery enhancement were performed on the SPOT imagery before using it. There were 10 characteristic bands derived from the SPOT data, such as NDVI K-L, and NDMI. Inter-class separability was applied to choose the optimum combination of bands. Based on spectrum and spatial characteristics of different features, combined with supervised classification results, a decision tree was built to derive land use/cover information, in particular the desertification distribution. Results showed that wind erosion desertification and salinization were the major desertification types in the study area. Moderate wind erosion desertification was distributed on the edge and the periphery of oasis, accounting for 64.05% of the total area. Salinization land, mild and serious wind erosion desertification were distributed within the oasis, accounting for 6.6, 7.58 and 2.23% of the total area, respectively. The salinization degree of Turpan was higher than that of tuokexun, whereas wind erosion desertification degree was contrary to the former. The decision tree classification method made full use of spectral and spatial information of land features, and seems capable of discriminating land features.