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Change in Land Coverage in Northwest China During the Past Decade Monitored by NOAA-CHAIN

MA Ming-guo+1, JIAO Yuan-mei+{1, 2}, CHENG Guo-dong+1 (1. State Key Laboratory of Frozen Soil Engineering, CAREERI, CAS, Lanzhou Gansu 730000, China; 2. Yunnan Normal University, Tourism and Geographic Science Institute, Kunming Yunnan 650092, China)  
During the past ten years, the land coverage has changed a lot in Northwest China. Using the Land Coverage Dynamic Monitoring System NOAACHAIN, the NOAAAVHRR image data of Northwest China in August 1990 and 1999 is pre-processed. In this article the detail processes of atmosphere correction and geo-correction, and the calculation of system parameters are described. Through the statistics of vegetation index NDVI, the change in land coverage is obtained between these two periods. The results showed that the NDVI decreases in the whole Northwest China, and the vegetation degeneration is serious. The July NDVI peak difference is {-0.1439} with a decreasing area of 1^77 10 6 km 2 and an increasing area of 0^46 10 6 km 2. The August NDVI peak difference is {-0.1528} with a decreasing area of 2^01 10 6 km 2 and an increasing area of 0^402 10 6 km 2. The most serious degradation areas are distributed in the agri-herd interleaving areas in eastern Qinghai Province, the Tianshan Mountains and the lower reaches of the Tarim River in Xinjiang Region. And the more serious degradation areas are distributed in the Qaidam Basin in Qinghai Province, the Junggar Basin and southern Tarim Basin in Xinjiang Region, the northern Shaanxi Province, and the Minqin County and Qingyang Prefecture in Gansu Province. At the same time, the NDVI increases in some areas, such as, the Ili River Basin in northern Xinjiang Province, southern Qinghai Province, Lanzhou City of Gansu Province and the Qinling Mountains. NOAACHAIN is a pre-processing system of NOAAAVHRR data. As the result of the pre-processing, the NDVI can efficiently show the change in land coverage in Northwest China. Also the system exhibits a rather perfect stability. The key steps for NOAACHAIN are the confirmation and calculation of the parameters for atmosphere correction and the number of the GCPs for geo-correction.
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