基于Landsat／TM和ETM＋的理塘草地沙化趋势及其驱动力分析

文章利用1989、1994、2000和2005年的4期Landsat／TM，ETM＋遥感影像，在几何校正、辐射定标、大气校正的基础上计算了归一化植被指数（NDVI），建立最小二乘法线性回归方程对多时相NDVI进行同化处理，基于二分模型提取植被覆盖度并转换成荒漠化指数（DI），对理塘县城附近约103．1km2范围的分类研究结果表明：（1）分为无沙化、轻度、中度、重度和严重沙化5级，其中2005年中度、重度和严重沙化面积分别为2．562km2、2．925km2和1．576km2；中度沙化比1989年减少9．69％，重度和严重沙化分别增多35．79％和161．8％；（2）2005年中度以上沙化面积比1989年增加1．470km2，增加了26．3％，年增加率为1．47％；（3）沙化面积呈前期小、中期大幅增加、后期增加减缓的总体趋势；（4）降水量和风速因子的变化趋势有利于缓解沙化，气温变化趋势没有反映出对沙化的促进作用。人类活动是造成沙化趋于恶化的主要因素；（5）沙化增加趋势与同类研究结果一致。

Analysis of Trend and Driving Force of Desertification in Litang Grassland Based on Landsat/TM and ETM+

Using the four remote sensing images of Landsat/TM and ETM ＋ in 1989, 1994, 2000 and 2005, the normalized difference vegetation index （NDVI） is calculated on the basis of the geometric correction, radiometric calibration and atmospheric correction. The multitemporal NDVI images are assimilated through setting up linear regression equation by least square method. Based on the binary model, the vegetation coverage is extracted from the NDVI and converted into the desertification index （DI）. According to the classifiable research in about 103. 1 km2 around the Litang county town, it shows that （ 1 ） the desertification areas can be classified into five levels, i. e , non-desertification, mild-desertification, mederate-desertification, and serious desertification. The area of moderate-desertification, severe-desertification and serious-desertification in 2005 were 2. 562, 2.925 and 1.576 kmz respectively; moderate-desertification decreased by 9. 69% than that in 1989, severe-desertification increased by 35.79%, serious-desertification increased by 161.8% ; （2） the area of moderate-desertification and above levels increased 1.470 km2 than that in I989 with increasing rate of 26. 3% and annual increased rate of I. 47% ; （3） the overall tendency of desertification area shows small increasing in the early stage, substantial increasing in the medium term and slow increasing in late stage; （4） the variation trends of precipitation and wind speed are in favor of retarding the desertification, while the changing trend of temperature does not reflect any promotion to the desertification. Actually human activity is the main factor to worsen the desertification; （5） the increasing trend of desertification is consistent with the results from similar studies.