基于LiDAR的青藏高原山坡小流域地形提取方法

Terrain Extraction of Small Hillside Watershed on Qinghai-Tibet Plateau Based on LiDAR

数字高程模型(DEM)的精度和分辨率影响着地形分析的结果,这种影响在高原、高山地带尤为明显。以拉萨河夺底沟小流域一处山坡为研究对象,选取典型剖面对比3种DEM数据对实际地形的还原效果。分析表明:SRTM和ASTER GDEM地形数据在青藏高原高山区存在高估山谷谷底高程、漏失地形要素的现象,使用LiDAR技术获取的DEM则可以准确反映实际地形。针对8种分辨率(1,2,5,10,15,20,25,30 m)的LiDAR DEM,使用局部方差均值分析坡度、平面曲率、剖面曲率等地形属性,发现低分辨率DEM在高山地区会遗失大量地形信息,造成地形平坦化和山坡微地形改变。为避免高山地区地形特征失真,给出了坡度和曲率研究适用的最小分辨率阈值:在坡度研究中使用的DEM分辨率应<5 m,曲率研究的最优分辨率为1 m。研究表明在青藏高原高山区,使用LiDAR技术提取高分辨率DEM具有远大的应用前景。

The accuracy and resolution of the Digital Elevation Model(DEM)affect the results of terrain analysis,and such effect is particularly evident in plateau and high mountains.With a hillside slope in the Duodigou watershed which is a sub-basin of the Lhasa River Basin as study object,we examined the abilities of three types of DEM data in reflecting the real terrain of typical profiles.As the analysis shows,in the high mountains of the Qinghai-Tibet Plateau,the SRTM and ASTER GDEM data have overestimated the elevation of the bottom of the valley and lost terrain features,while the DEM obtained using LiDAR(Light Detection And Ranging)technology can accurately reflect the actual terrain.We elaborated the terrain features,inclusive of slope gradient,plane curvatures and profile curvatures,of LiDAR DEMs of eight resolutions(1 m,2 m,5 m,10 m,15 m,20 m,25 m,30 m)by means of local variance.We found that DEMs of low resolutions have lost much topographical information in high mountains,causing attenuations of the terrain and changes in the microtopography of hillsides.In order to avoid the distortion in high mountain areas,we further gave the minimum resolution for studies of slopes or curvatures.The resolution of DEMs used in slope studies should be higher than 5 m,and the optimal resolution for curvature studies is 1 m.The study has shown that the use of LiDAR technology to extract high-resolution DEMs has a promising application prospect in high mountains of the Qinghai-Tibet Plateau.