ObjectiveSlope aspect is an important part of site factors and is very important for terrain analysis. Calculating slope aspect based on DEM is of great significance to natural habitat analysis and geo-ecological process simulation. Terrain is so complex in mountain area that the solar radiation of slope has large differences due to terrain shading. In this paper, the method of slope aspect extraction based on DEM and solar radiation has maintained the objectivity of slope aspect calculated from DEM in mountain area. At the same time, it can be consisted with the sunny and shady slope aspects. This lays the foundation for the study of mountain meteorology, soil distribution, site conditions and suitability analysis.

MethodBased on the digital terrain analysis, a solar radiation reference model in Beijing area was established to realize an extraction method of solar radiation equivalent slope aspect, in which the model of solar radiation analysis based on DEM was applied to explore the relationship between solar radiation and slope aspect, slope degree and altitude. The standard solar radiation was calculated based on the elevation, slope degree and slope aspect of the plots, a solar radiation equivalent slope aspect was inferred with slope aspect calculated from DEM and standard solar radiation.

Result2000 plots of the forest resource survey (FRS) in Beijing mountain area were selected as the test data. The slope aspect calculated from DEM with cell size 30, 60, 90, 120, 150 and 200 m was taken as the evaluation criterion. There were 1 398 plots of which the difference between solar radiation and standard solar radiation was less than 5%, which accounted for 69.9% of the whole plots. The slope aspect of these plots can be calculated from the 30 m DEM. Terrain shading had a larger impact on 602 plots. According to the calculation of solar radiation reference model, the solar radiation equivalent slope aspect of 583 plots was consistent with the evaluation criterion.

ConclusionThe consistency analysis with evaluation criterion showed that the consistency of the solar radiation equivalent slope aspect in the test data reached 99.05%, while the consistency of the FRS slope aspect in the test data was 72.05%. Therefore, the proposed method of solar radiation equivalent slope aspect can reflect the influence of terrain shading based on this method, the extraction of the aspect was scientific and practical, so that a new and more objective method for calculating aspect was provided for the research and production practice of the forest resource survey and site conditions.