| Desertification is one of the most serious ecological and environmental problems in the world. It directly influences regional economic development and social stability. Understanding the distribution and development trend of desertification provides us important scientific basis for desertification control and rehabilitation, in which desertification index system is a key indicator of the level of desertification dynamic change.Based on investigation of current research and previous efforts on desertification and guided by the design principle, this dissertation proposes a desertification index system suitable for large-scale desertification monitoring using remote sensing techniques. First, five desertification indices were retrieved from NOAA and MODIS satellite data. Then, the desertification status and the dynamic changes from 1995 to 2001 in central Asia and China were analyzed. In addition, we delineated the annual boundary between vegetated and non-vegetated areas and assessed the desertification status in arid and semiarid region of central Asia and China based on the NOAA-AVHRR NDVI time-series dataset from 1982 to 2000.Main research results and initiatives in this thesis include as following:1. An integrated desertification indexes are proposed and the construction of a desertification monitoring index system using remote sensing techniques is recommended.According to the desertification index design principle and the research aim of this dissertation, we selected five desertification indexes (MSAVI, FVC, Albedo, LST and TVDI) suitable for large-scale desertification monitoring using remote sensing technique. After applying different index and index combinations on desertification monitoring and its precision evaluation in test area, the result shows that the precision of index combination of MSAVI, FVC, Albedo, LST and TVDI is superior than others. In term of the desertification climate types, the potential extent of desertification in China and central Asia was respectively divided into four categories: dry sub-humid area, semi-arid area, arid area, high and cold area. Different desertification index system was built for each area.2. Selection of a suitable method on remote sensing retrieval of desertification indexes andthe spatial distribution of desertification was analyzed in study area.Based on analysis and comparison of current retrieval algorithms, we utilized a suitable algorithm on large scale to retrieve five desertification indexes with ten-day NOAA AVHRR data set in 1995 and 16-day MODIS data set in 2001, and built the database of desertification monitoring indexes in China and central Asia. At the same time, we analyzed the spatial distribution characteristic of the indexes in China and central Asia.3. An optimal classifier for desertification monitoring was determined and desertification status and dynamic change analysis in China were evaluated and analyzed.In test area Kerqin desert, by assessing the classification accuracies of three types of classifiers(unsupervised classifier, maximum likelihood classifier and decision tree classifier), we select decision tree classifier for desertification monitoring. Supported by desertification index system and the database of desertification indexes, utilizing the cumulated MSAVI values, averaged albedo, averaged land surface temperature and averaged TVDI in growing season, and the annual maximum fraction of vegetation cover in China, the desertification status in 1995 and 2001 was classified by decision tree classifier, and analysis of desertification changes from 1995 to 2001 was also completed in study area. The result shows that there is a trend of development as a whole accompanied with occasionally local improvement in desertificated areas in China, the desertification extension is faster than rehabilitating.4. Evaluation of desertification status and desertification dynamic monitoring in central Asia. Central Asia has great influence on the ecological environment of China, especially in thear...
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