地形调节植被指数及其在森林动态监测中的应用

A topography-adjusted vegetation index(TAVI) and its application in dynamic forest monitoring

森林一般分布在复杂地形山区,消除地形影响成为提高森林遥感监测精度必须解决的基本问题之一。本文提出一种无需DEM数据支持、仅依据光学遥感影像近红外波段与红光波段数据就能有效消除山区地形影响的地形调节植被指数(TAVI)。以1998年与2008年两期LandsatTM影像为实证研究数据,进行TAVI抗地形影响性能验证并采用TAVI进行研究区森林覆盖变化监测。通过TAVI与太阳入射角余弦值回归分析和与NDVI比较分析表明,TAVI与太阳入射角余弦值一元线性回归方程斜率在-0.04～0.04之间,相关系数在-0.08～0.08之间,明显优于NDVI,其消除地形影响的效果显著。利用TAVI反演得到的复杂地形山区森林覆盖信息呈面状空间分布,没有出现受地形控制的纹理形态。监测结果表明,研究区1998—2008年森林资源总体呈持续增长趋势。

Forests are usually distributed on rugged mountains,therefore the elimination of topographic effects becomes one of the essential issues to improve monitoring accuracy of forest cover by remote sensing.Here we introduced a novel topography-adjusted vegetation index（TAVI） which is capable of removing topographic effects in rugged terrain based only on infrared and red wavebands data from optical remote sensing images,without support of digital elevation model（DEM） data.The Landsat TM images acquired in 1998 and 2008 respectively were utilized in case study to validate the TAVI performance and monitor the changes of forest cover with TAVI.From the regression analysis between TAVI and the solar incidence cosine and contrast analysis between TAVI and normalized difference vegetation index（NDVI） in the study area,it was discovered that TAVI can resist the topographic effects remarkably and was much better than NDVI in that the slope of linear regression equation of TAVI and the solar incidence cosine was only between ±0.04,and also their correlation coefficient was just between ±0.08.The forest cover images in rugged areas computed from TAVI displayed a planar spatial distribution instead of texture pattern resulting from topography.The dynamic monitoring results turn out that forests in the research area grow in a generally sustainable way during 1998-2008.