基于TerraSAR-X/TanDEM-X干涉DEM的森林冠层高度估测

Forest Canopy Height Estimation from TerraSAR-X/TanDEM-X InSAR DEM

森林树高的大面积估测一直是森林资源调查和林业遥感所面临的技术难题。以云南省勐腊县森林资源为研究对象,将DEM差分法与TerraSAR-X/TanDEM-X全极化干涉数据、地形图相结合,用TerraSAR-X/TanDEM-X数据干涉生成各极化通道带有森林冠层高度的DSM,从地形图上提取地表高度DTM;对2个高度模型进行水平位置匹配,并提出用参考面将DSM与DTM转换为相对高度模型RDSM和RDTM,以消除高程基准差异;最后对RDSM和RDTM进行差分运算,估测出研究区各极化通道下的森林冠层高度分布。采用森林资源二类调查数据,对各极化通道的冠层估测高进行了合理性验证。研究表明:DTM的高程基准面低于DSM,平坦农地适合作为参考面提取相对高度模型。在小班尺度上与森林资源二类调查数据的对比显示:各极化通道的冠层估测高与小班林分高均呈显著的中等正相关,冠层高度估测值大小合理,人工林的估测结果略优于天然林;人工林与天然林的冠层估测结果均在主要坡度分布区间内与小班林分高的相关性高;各极化通道的估测结果整体上没有明显差异。从总体上来看,基于地形图和TerraSAR-X/TanDEM-X数据,利用DEM差分法来大面积估测森林冠层高度是一种有效可行的途径,为辅助森林资源调查工作提供了新思路。

Estimating forest height in large region are challenging forest investigation and forest remote sensing. This paper investigated the possibility of estimating forest canopy height from TerraSAR-X/TanDEM-X polarimetric and interferometric data and topographic map in the forest of Mengla in Yunnan, China. The TerraSAR-X/TanDEM-X data was interfered to produce four polarimetric digital surface model （ DSM ） , which contained forest canopy height. Meanwhile, the digital terrain model （ DTM） was extracted from the topographic map. After horizon-tally co-registering DTM with each polarimetric DSM, the relative height models were separately computed from DTM and each polarimetric DSM as RDSM and RDTM by referring to the same flat non-forest plot. Then forest can-opy height was estimated from the difference between RDTM and each polarimetric RDSM, and it finally produced four forest canopy height estimations. Forest inventory height was used to validate the reasonability of these estimated canopy heights. The result showed that the elevation datum of DTM was lower than that of DSM, and a flat agriculture plot could be used as the reference surface to extract RDSM and RDTM. Comparison to the forest inventory record showed that, on the plot scale, there were some significant positive correlation between the estimated canopy heights and the inventory height, and the estimated height value was reasonable. It was also found that the estimation on planted forest was a bit better than on natural forest. The correlation between the estimated canopy height and the inventory record was higher on the certain slope surface where natural forest and planted forest were mainly distributed. And there was no significant difference among the estimated heights from the four polarization channels. The result suggests that DEM difference between RDSM from TerraSAR-X/ TanDEM-X data and RDTM from topographic map could provide an effective tool to measure forest canopy height in large areas.