Monitoring of Land Cover Changes in Northwest China During the Past Decade using AVHRR data

摘要

For the months July and August, 144 AVHRR images were pre-processed for 1990, 1992, 1994, 1996 and 1999 with a NOAA pre-processing chain (NOAA-CHAIN). A differencing method was applied to estimate the change of the NDVI between different years. The trend lines for six typical region's NDVI average values in each year were subsequently analyzed. The vegetation condition of most of the regions in the Northwest of China is poor. From 1990 to 1999, most regions have negative NDVI difference values. Concomittantly, locally, some regions show positive NDVI differences, indicating that the vegetation conditions in the regions where an increase occurs, more or less improve. The most largely increasing region with regards to vegetation growth conditions mainly include the North and West of the Xingjiang Province, e.g., the Aertai Mountains, Tacheng, Kelamayi, north of Shihezi, the region between Shihezi and Kuerle, Yining, Akesu, Lanzhou and Dingxi of the Gansu Province. The trend lines of the first three typical regions show an upward path while those of the last three regions a downward one. Comparing the slopes of the six trend lines, it is indicated that the decrease in NDVI range is larger than the NDVI increase for the Northwest of China.