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地表真实面积很难直接测量和计算,一般利用投影面积代替地表面积。在地形起伏较小的平原地区,地表真实面积和投影面积相差不大,但在地形起伏复杂的山区,两者差异较为明显,为计算地形起伏复杂的横断山区地表面积,选取西藏自治区昌都县作为研究区,推导了地表粗糙度的地学意义,基于地表粗糙度地学意义计算地表真实面积并定量分析了地表真实面积与垂直投影面积之间的差异。实验结果表明:相同土地覆被下,DEM分辨率越高,地表真实面积与垂直面积差异越大;草地、灌木林地、有林地、疏林地和难利用地的地表真实面积与其垂直投影面积差异较大,分别占垂直投影面积的11.275%、13.447%、16.586%、13.644%和17.282%,对于地形起伏复杂的山区而言,地表真实面积与垂直投影面积之间的差异不容忽视;坡度越大,地表真实面积与垂直投影面积之间的差异越明显,当坡度>75°时,差异迅速增大。基于地表粗糙度地学意义可快速获取地表真实面积,若建立典型地区地表粗糙度数据库,可为该地区土地利用变化、森林资源调查和作物面积估产等提供更加科学有效的数据。
The real surface area is difficult to measure and calculate directly. Generally, the projected area is used instead of the surface area. In plain areas with small topography, the difference between the true surface area and the projected area is not obvious. However, in mountainous areas with undulating topography, the difference between the two is obvious. For the purpose of calculating the undulating surface area of the Hengduan Mountains, In the study area, the geology significance of the surface roughness was deduced. The real surface area of the earth surface was calculated based on the geological significance of surface roughness and the difference between the real surface area and the vertical projection area was quantitatively analyzed. The experimental results show that under the same land cover, the higher the DEM resolution is, the greater the difference between the real area and the vertical area of the surface is. The difference between the true surface area of the grassland, the shrub land, the forest land, the sparse forest land and the hard-to-use land and its vertical projection area Respectively, accounting for 11.275%, 13.447%, 16.586%, 13.644% and 17.282% of the vertical projection area, respectively. For the mountainous area with undulating topography, the difference between the true surface area and the vertical projection area can not be ignored; the greater the slope, The difference between the true surface area and the vertical projection area is more obvious. When the slope is greater than 75 °, the difference rapidly increases. Based on the geographical significance of surface roughness, the real surface area can be quickly obtained. If a typical regional surface roughness database is established, it can provide more scientific and effective data for land use change, forest resources survey and crop area estimation in this area.