Discrete Role In Slope Scale Effect And Smoothing Effect

Taking Xiannangou Catchment and the JingBian Area; represent two different terrain types of Loess Plateau in northern Shannxi as examples, the research established different resolution DEMs based on1:10000,1:50000and1:250000topographic digital maps using different methods. We analyzed the influence of DEM resolution on the derived slope and slope length, and then explored what scale effect contains and how it works. And then multi-resolution DEMs of the two areas were established based on1:10000topographic digital map. On the basis of the established DEMs, the changing regularity of scale effect’s different components with DEM resolution reduction was investigated. In the end, we discussed the relationship of scale effect to terrain type. The main contents and conclusions are as follows:(1) The influence of DEM resolution on topological characteristics and the mechanism of action. With the reduction of DEM resolution, the derived slope becomes gentler and slope length becomes longer. The effect of resolution on topological characteristics such as slope and slope length equals to the effects of the generalization (terrain-smoothing) and sampling (terrain-discretization) on them. In the process of the DEM resolution changing from high to low, the slope reduction is mainly caused by generalization effect not by sampling effect, but the increase of slope length can be more attributed to sampling effect and generalization effect attributes less.(2) The influence of different data process methods. DEMs in the four experimental groups were established by different data process methods. The result indicates that DEMs with the same resolution and cellsize in all groups are similar, and the changing regularity of topological characteristics with DEM resolution reduction among the different resolution DEMs is the same, but the DEMs established by interpolation based on large scale topographic map are more systematically changed.(3) The changing regularity of scale effect’s different components with DEM resolution reduction. With the decrease of resolution, mean slope tends to be lower following logarithmic function, and decrement of slope is becoming lager, but the rate of decrease becomes lower. The influences of total resolution effect, terrain-smoothing effect and terrain-discretization effect on slope reduction increase as the resolution becomes larger, but the rate of slope reduction caused by these effects is becoming smaller. The slope reduction is more attributed to terrain-smoothing than terrain-discretization, and the rate of terrain-smoothing to total resolution becomes lager and larger. The influence degree of DEM resolution on slope reduction increases when the resolution changes from0to200m, then the influence slows down, and up to a steady level. So,200m resolution is set as the threshold of slope reduction. The average of slope length tends to be longer with the decrease of DEM resolution. Terrain-smoothing has less effect on slope length and the magnitude of its effect grows a little with the resolution reduction.(4) The generalization effect of DEM resolution on slope and slope length is more pronounced on areas with relatively steep terrain, and in contrast, the sampling effect of DEM resolution on the two topographic characteristics is more apparent on areas of relatively flat terrain.