干旱区生态环境知识资源中心

Because of the capability of remote sensing to acquire synoptic coverage and repetitive data acquisition it has become a widely used technique for monitoring the effects of human activity on terrestrial ecosystems. This paper presents the spatial extent, magnitude and temporal behavior of land desertification around Holinguole caused by city expansion. The selected test area, Huoliguole City, is a typical grassland city in China that is located in the northeast of China. A time-series of Landsat TM images covering a period of 20 years (1987-2006) were used. The data sets were geometrically and radiometrically pre-processed in a rigorous fashion, followed by a linear spectral mixture unmixing model to extract feature images of vegetation and sandy soil. The biomass images were derived using a polynomial regression model based on the ground-based observations of the amount of grass and a vegetation index based on satellite remote sensing. By combing the vegetation fraction images, the sandy soil fraction images, biomass images, and PC (principal components) images, the grassland desertification information around the built-up area of the city was extracted based on BP (Back-Propagation) neural network algorithm. The results of our studies indicate significant expansion of the city over the last 20 years, and a similar trend was also observed in the temporal magnitude behavior of severe grassland desertification away from the city.