摘要
植被覆盖变化分析需要选择一组合适的变量来测量和描述其变化。卫星传感器,如美国陆地卫星TM,具有提供大范围植被覆盖信息的优势,使对陆地表面过程的监测变得便利。本文讨论利用卫星数据对瑞典耶姆特兰(Jmtland)县山区干燥石南群落进行变化检测。本研究分别用到了1984年、1994年陆地卫星5的TM数据和2000年陆地卫星7的ETM+数据。在对图像进行辐射归一化、几何纠正和地形纠正处理之后,我们比较了不同的变化检测方法。对"变化"和"无变化"两种变化类型的检测,NDVI图像差值方法的精度最高,总体精度达到94%(k=0.87)。NDVI回归分析方法可以提取更多的变化信息,可以检测到山区干燥石南群落中3种类别的植被变化。通过应用模糊集阈值技术,变化检测的总体精度从65%(k=0.45)提高到74%(k=0.59)。这些方法产生的变化结果可以显示脆弱的山区石南群落中植被变化区域的位置,并反映出不同的植被变化程度(植被覆盖减少程度:高、中和无)。1984～2000年间,该研究区域内共有17%的干燥和极端干燥石南植被发生了变化。平均起来,4%的被研究石南群落发生了较大程度的变化,也就是说,在该期间这些石南植被经历了"较大程度的植被覆盖减少"。研究结果显示:①"大幅度的植被减少"的区域中,研究区南部低的高山带(low alpine zone)植被覆盖减少程度最大;②主要的变化发生在1994～2000年期间。
Vegetation cover-change analysis requires selection of an appropriate set of variables for measuring and characterizing change.Satellite sensors like Landsat TM offer the advantages of wide spatial coverage while providing land-cover information. This facilitates the monitoring of surface processes.This study discusses change detection in mountainous dry-heath communities in Jmtland County,Sweden, using satellite data.Landsat-5 TM and Landsat-7 ETM+ data from 1984,1994 and 2000,respectively,were used.Different change detection methods were compared after the images had been radiometrically normalized,georeferenced and corrected for topographic effects.For detection of the classes change - no change the NDVI image differencing method was the most accurate with an overall accuracy of 94% (k = 0.87).Additional change information was extracted from an alternative method called NDVI regression analysis and vegetation change in 3 categories within mountainous dry-heath communities were detected.By applying a fuzzy set thresholding technique the overall accuracy was improved from of 65% (k = 0.45) to 74% (k = 0.59).The methods used generate a change product showing the location of changed areas in sensitive mountainous heath communities,and it also indicates the extent of the change (high,moderate and unchanged vegetation cover decrease).A total of 17% of the dry and extremely dry-heath vegetation within the study area has changed between 1984 and 2000.On average 4% of the studied heath communities have been classified as high change,i.e.have experienced 'high vegetation cover decrease' during the period.The results show that the low alpine zone of the southern part of the study area shows the highest amount of 'high vegetation cover decrease'.The results also show that the main change occurred between 1994 and 2000.
