Calculation method for the topographic index in TOPMODEL
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摘要: 地形指数ln(α/tanβ)是一些以物理概念为基础的水文模型的重要参数。TOPMODEL是以计算ln(α/tanβ)指数及其分布为基础的。对于栅格DEM,α为上坡区域通过单位等高线长汇集到单元网格内的面积,反映径流在流域中任一点的累积趋势,tanβ为单元网格的坡角,反映重力使径流顺坡移动的趋势。目前普遍使用的计算该地形指数的方法为多流向法。方法中计算α和tanβ用的均是与流出单元网格流向垂直的等高线长。另外计算下坡单元网格累积汇流面积时没有考虑欲计算ln(α/tanβ)值的单元网格的面积。这些是不合理的。计算α值应该用与流入单元网格流向垂直的等高线长,据此提出了改进后的ln(α/tanβ)的计算方法。方法中计算下坡单元累积汇流面积时包括了欲计算ln(α/tanβ)的单元网格的面积。分析了两种方法计算结果间的差值。
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关键词:
- 地形指数ln(α/tanβ) /
- 计算方法 /
- TOPMODEL /
- 等高线长 /
- 累积汇流面积
Abstract: The topographic index, ln(α/tanβ), is an important parameter of many physically based hydrological models.The TOPMODEL is based on the calculation of ln(α/tanβ) index and its distribution.In terms of a digital elevation model (DEM), α is the cumulative upslope area draining through per contour length to a pixel, which reflects the tendency of water to accumulate at any point in the catchment, tanβ is the local slope angle of the cell, which reflects the tendency for gravitational forces to move that water downslide.The calculation method for ln (α/tanβ) index widely used is the multiple flow direction algorithm developed by Quinn et al (1991).It follows that, in the algorithm, the contour length normal to the direction of flow flowing out the current cell is used to determine both α and tanβ, and that the calculated total cumulative contributing area of downslide grid cell does not include the area of the current cell.These are unreasonable.It is found that the contour length used to determine α should be that normal to the direction of flow entering into the current cell, rather than that flow out the current cell.The improved algorithm calculating the ln(α/tanβ) index is presented, in which the area of the current cell is included in the calculated total cumulative contributing area of downslide grid cell.The different between the results of the two algorithms is described. -
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