DEM分辨率对地形因子提取精度的影响

Effects of DEM resolution on the accuracy of topographic factor derived from DEM

为揭示DEM分辨率对地形因子（LS）提取精度的影响,本研究将30 m分辨率DEM数据进行重采样,分别计算30、60、90、120、250、500和1 000 m 7个不同分辨率下我国黑土区、黄土区和红壤区的LS因子值,分析3个土壤类型区LS因子随着DEM分辨率变化的特点,并进一步研究LS因子与坡度和坡长的相关性及其空间分布情况。结果表明：黑土区LS因子值最小、黄土区次之,红壤区LS因子值最大;坡度因子比坡长因子对DEM分辨率的变化更为敏感,随着分辨率的降低,L因子值整体变化不大,有轻微先增大后减小趋势,S因子值和LS因子标准差均呈现降低态势;随着DEM分辨率降低,3个土壤类型区的LS因子值均逐渐减小,当分辨率由30 m下降到1 000 m时,LS因子值可降至原来的1/6~1/3;DEM分辨率为30 m时,LS与坡度的相关系数在0.78~0.86之间（P〈0.05）,与坡长的相关系数在0.34~0.46之间（P〈0.05）,随着DEM分辨率的降低,LS因子与坡长和坡度的相关系数均有明显的降低趋势。在应用土壤流失模型过程中,DEM分辨率对LS因子值的影响不可忽视,研究结果对于大中尺度研究中DEM分辨率选取和参数修正具有一定的参考和借鉴价值。

[Background]Topographic factor（ LS factor） including slope length（ L factor in variable λ）and slope gradient（ S factor in variable θ） is one essential parameter of Revised Universal Soil Loss Equation（ RUSLE）. LS factor is greatly influenced by Digital Elevation Model（ DEM） resolution.However,most researchers adopted only one specific DEM resolution,and the influences caused by DEM resolution were commonly ignored. The objective of this paper was to explore the impacts of DEM resolution on LS and provide certain experience for DEM resolution correction in a specific scale.[Methods]The black soil region,loess region,and red soil region were chosen as the study areas. Atfirst,we re-sampled the ASTER GDEM（ 30 m） to 6 other DEM resolutions,namely,60 m,90 m,120 m,250 m,500 m and 1 000 m using the platform of Arc GIS Desktop 10. 0. Then,the LS factor in these regions was calculated using Arc Macro Language（ AML） in the platform of Arc Info Workstation 9. x.Finally,quantitative relation between LS and DEM under different resolutions was explored for studying the effects of DEM resolution on the accuracy of LS. [Results] LS factor in black soil region was the minimum,and that in the red soil region was the maximum. The S factor was more sensitive to the variation of DEM resolution compared to the L factor. With the DEM resolution decreasing,the overall change trend of L factor was not very significant. Whilec S factor and the standard deviation of LS factor gradually decreased. When the grid size of the DEM increased,all LS factor decreased in all of the three soil regions with different magnitude. With the DEM resolution reduced from 30 m to 1 000 m,LS factor dropped to 1/6- 1/3 of that in the resolution of 30 m. When the DEM resolution was 30 m,the correlation coefficient between LS factor and slope degree,and that between LS factor and the slope length was 0. 78- 0. 86（ P 〈0. 05）,and 0. 34- 0. 46（ P 〈0. 05）,respectively. With the decreasing of the DEM resolution,correlation coefficient tended to be significantly lower. In terms of its spatial distribution,LS factor value tended to be much larger in the middle part of steep slopes comparing with the peak and foot of the mountain. When the DEM resolution was 1 000 m,LS factor value in more than 60% of the whole study area was at the lowest class. [Conclusions]The impact of DEM resolution on the LS factor is significant and it should not be ignored when using distributed soil loss model. We should take necessary measures to reduce the impact of DEM resolution on the LS factor,and the results of this paper may provide certain references for DEM resolution and correction parameter selection in large and medium scale.