以中分辨率成像光谱仪数据(Moderate resolution imaging spectroradiometer, MODIS)为基础计算泾河流域归一化差异植被指数(Normalized difference vegetation index, NDVI)在2001～2004年的时间序列值，分别采用相关系数r值和成对t检验的t值定量描述年内NDVI 曲线在年际间的协同性和差异性。以农田、森林、灌丛和草地4种土地利用类型NDVI曲线在年际间变化显著的面积百分比为参数，在2001～2004年间分为1、2和3年间隔共6个时间组，比较分析4种土地利用类型的NDVI曲线在6个时间组内的协同性和差异性，进 而探讨泾河流域植被年际变化及其与土地利用之间的关系。结果表明：4种土地利用类型NDVI波动对外界环境的响应在不同的时间间隔里表现一致，在2001～2003年和2001～2004 年间变化比较明显；在各个时间组内比较发现有较大面积的农田和草地NDVI协同性较差，尤其在 2001～2002年间，这可能与退耕还林还草政策的实施有关；4年来泾河流域内4种土地利用类型的NDVI值有增加趋势，植被状况趋于良好；NDVI年际间差异最明显的是草地，其次是农田和灌丛，森林的NDVI比较稳定。
Aims NDVI is extensively used as an important index in evaluating vegetation growth and dynamics, including inter-annual dynamics; however, research on the relationship between inter-annual vegetation dynamics and land use is largely lacking. This study was conducted in the Jinghe watershed to determine inter-annual NDVI dynamics in different land use types.
Methods MODIS data were used to calculate NDVI time serial values from 2001 to 2004. Correlation coefficient (r) and t-test were used to test the consistency in six temporal intervals including one-, two-and three-year scales of four land use types: cropland, forest, shrub and grassland. We calculated the percent area to quantify the spatial extent of significant inter- annual NDVI variation.
Important findings The four land use types had similarNDVI dynamics in all temporal scales. Differences were significant in 2001-2003 and 2001-2004. Cropland and grassland were generally less consistent than forest and shrub in six temporal intervals, especially in 2001-2002, which may be the result of the policy of returning farmland to forest and grassland. Annual NDVI tended to increase over time in the four land use types, suggesting vegetation in this area was gradually restored. Grassland had the greatest percent of area with significantly increasing NDVI, followed by cropland, shrub and forest.