A Study Of The Geomorphologic Forms Classification Based On Relief

Relief is the largest relative elevation of unit area,which can reflect the relief of land surface;it's a quantitative index to describe geomorphologic forms.Relief has wide applications which include land-use evaluation,the sensitivity evaluation of soil erosion, evaluation of the ecological environment,environment assessment of habitat suitability, geomorphologic mapping,evaluation of the geological environment,etc.Use different scale relief will affect the basic conclusions of relevant studies.Relief can be used as an important reference factor of geomorphologic forms classification.In this paper,based on the 1:250 000 DEM data of Beijng-Tianjin-Hebei region,use the neighborhood analysis,obtain multi-scale relief through the Focal function,divide geomorphology of the area into five levels by relief:plains,hills,small relief mountain, medium relief mountain and large relief mountain,analyses the scale-dependent features of relief.Through significant changes in elevation models,it determines the optimum statistical unit.According to geomorphologic characteristics of the area for studying,it establishes the geomorphologic classification criteria by relief of optimum statistical unit and altitude,and draw geomorphologic classification map of Beijng-Tianjin-Hebei region.The research shows that the Focal function is significantly better than Block function in improving accuracy of relief calculation.The factor of square or circular can be used to calculate the reliefs in Focal function.Count the area ratio of geomorphic type in every scale, we can conclude that there is an obvious characteristic of scale-dependent on the relief. Among them,the area ratio of plains reduces gradually with the increasing of the scale,at 63×63 or R=31,the area ratio of plains tended to be stable,respectively reached 39.49%and 40.64%;the area ratio of hills first increase and then decrease,at 5×5 or R=3,the area ratio of hills reached maximum,respectively reached 37.51%and 37.36%;the area ratio of small relief mountains first increase and then decrease,at 29×29 or R=17,the area ratio of hills reached maximum,respectively reached 29.25%and 29.23%;the area ratio of medium relief mountain occurred from 11×11 or R=6,the area ratio increase gradually with the increasing of the scale,at 63×63 or R=31,respectively reached 22.91%and 19.72%;the area ratio of large relief mountain occurred from 15×15 or R=9,the area ratio increase gradually with the increasing of the scale,at 63×63 or R=31,respectively reached 1.97%and 1.26%.This shows that the main terrain of Beijing-Tianjin-Hebei region is almost the plains,hills,small relief mountains and medium relief mountains.In accordance with the integrity of the mountain and the universality of region,use significant change in elevation model,find that the optimum statistical unit at square neighborhood is 31×31,with an area of 9.61km~2;at circular neighborhood,the optimum statistical unit is R=16,with an area of 8.55km~2.Refer previous criteria for geomorphologic classification,combine with the actual topography of the study area,use the relief of optimum statistical unit and DEM,divided the study area into plains,basin,hills,low mountain,middle mountain,high mountain and plateau.It compiles two maps of Beijing-Tianjin-Hebei geomorphic classification,counts the areas of all types of landform.At the map of geomorphological type divided by the relief of square neighborhood optimum statistical unit,the area of plains were 12.47%less than actual area,the area of mountains were 7.54%more than actual area,the area of plateau were 5.94% less than actual area;at the map of geomorphological type divided by the relief of circular neighborhood optimum statistical unit,the area of plains were 9.19%less than actual area,the area of mountains were 6.18%more than actual area,the area of plateau were 5.1%less than actual area.Comparative analysis show that the selection of the filter shape will affect the calculation results of relief,the use of circular filter is superior to a square filter in the calculation model of relief.