土地沙化是北京市最主要的生态环境问题之一, 是制约其城市发展的重要因素, 研究北京土地沙化的动态变化趋势及成因对保障北京市的生态安全和改善其环境质量有重要意义。利用2007年4月SPOT5卫星的多光谱和全色影像, 结合植被覆盖度, 土壤类型和土地利用类型这3种辅助数据, 进行沙化信息提取。根据所提取的信息, 分析北京山前平原区土地沙化现状和动态变化特征, 并结合气象、水文等多元信息资料的统计分析数据对其沙化成因进行探讨。研究结果表明:在各种自然和人为因素的影响下, 研究区的沙化土地主要分布在永定河、潮白河、温榆河3条河流沿岸, 康庄、南口地区以及怀柔、密云大沙河地区;沙地类型主要是固定沙地,以轻度和中度沙化为主;2007年与1999年、2004年北京沙化土地数据相比, 沙化土地总面积呈减少趋势, 表明北京市防沙治沙工作卓有成效, 前景乐观, 但局部依然存在边治理边破坏的现象, 防沙治沙工作依然任重而道远。

Land desertification, which is also the key factor restricting the development of Beijing, has become one of the mostserious ecological enviro nmental problems in the capital.As a result, it is urgent to study the transformation trends and formation causes of the land desertification for guaranteeing the ecological security and improving the ecological environment quality in Beijing.SPOT5 data (including panchromatic and multibands) of Beijing area in April 2007 were acqui red.The land desertification in the piedmont plain of Beijing was recognized and ex tracted with three ty pes of data (vegetation coverage, soil type and land use) from above remote sensing data.According to the ex tracted information, the desert ification status and dynamic characteristics were analyzed and evaluated with the support of RS technology.Then the formation causes of desertification were discussed combined with multiple statistical data such as meteorological information, hy drological information and soon.The resultshows that with the double effect s of nature and human beings, Yongding River, Chaobai River, Dasha River, Kangzhuang, Nankou and thei r surrounding areas are the principal distributing areas of the desertification land in Beijing.They are all f ixed sand areas that mainly contain mild and moderate desertificatio n.By comparing the result data of the land desertification among the years of 1999, 2004 and 2007, it is found that the total area of the desertification land has the trend of decrease.The area of the desertification land in each county in the suburb is reduced except Yanqing.It proves that the action of preventing and controlling the land desertification has obtained prominent effect.However, the phenomenon of destroying at the same time of improving st ill exists in some areas.Combating the land desertification still has a lo ng way to go.