Research Of The Scale Effect On Derived Slope From Dems

Slope is an important parameter for hydrology and soil erosion model, understanding changes of slope with the changing resolution is very important for improving the precision of hydrological simulation. In this study, taking Xiannangou watershed, representing the loess hilly geomorphology landscape, as the test area, a series of hydrologically corrected DEMs were generated using ANUDEM based on the 1:10,000 digital topographic map. Different resolution slope gradients were extracted within the ARC/INFO slope calculation methods. By applying terrain analysis and geostatistical methods, changes of DEM-derived slope with horizontal resolution and their spatial distribution were systematically investigated. The main conclusions are as follows:Research shows that with DEM resolution decreasing, slope at single point shows uncertainty. Slope at the edgeline decreases sharply, at borderline and streamline decrease slowly. slope at positive and negative terrain both decrease. Slope at negative terrain decrease faster than the positive terrain. low slope terrain increases at first and then decreases, middle slope terrain shows slight changes, and steep slope terrain decreases with logarithm greatly. With the decrease of DEM resolution, mean slope of the basin decreases with logarithm. With resolution reduction, ramp areas continue to increase while steep areas gradually decrease.With DEM resolution reduction, mean profile curvature of the watershed decreases with power function, profile curvature tend to concentrate at small values, topographic relief become smaller. The aspect frequency distribution with different resolutions both have"double peaks".Slope cumulative frequency distribution with resolution reduction, the peak continuously move to left. The peak of profile curvature frequency distribution also move to left with resolution reduction, it means profile curvature tend to concentrate at small values, topographic relief become smaller.It is showed from the semi-variance analysis that slope is strongly spatially dependent, the exponential model can describe the spatial variability of slope. With DEM resolution reducing, sill and nugget decrease, range increases. The variograms of profile curvature have the similar laws. Make an Analysis of high frequency information based on spatial frequency theory. The results show that the process of cartographic generalization played an effect that reducing peak and filling valley.