基于高分7号卫星DEM的坡度坡长计算精度评价

Evaluation of the Accuracy of Extraction of Slope and Length Based on DEM of GF-7 Satellite

[目的]坡度和坡长作为重要的地形因子,其计算的准确性直接影响坡面土壤侵蚀模型的评价精度。高分7号卫星的高精度高程测量能力在地形因子的准确提取上具有较大潜力,期望能将其利用到坡度和坡长提取之中,实现对地形的准确表达。这需要对利用高分7号卫星DEM提取坡度坡长的结果进行精度评价。[方法]利用地形因子(LS)计算工具,对陕西省吴堡县4个小流域高分7号卫星、1∶10000地形图、激光雷达影像生成的DEM进行坡度、坡长的提取。采用相关系数(r)、相对偏差和绝对偏差作为评价指标,评价高分7号提取地形因子的精度。[结果]与激光雷达和1∶10000地形图的坡度和坡长相比,高分7号提取的流域平均坡度偏低7.50%~9.02%,坡长偏大1.83%~19.35%,但坡长和坡度分级的面积比例并不存在显著差异;高分7号提取的坡度结果偏差(16.46%~44.26%)明显小于坡长的偏差(75.25%~140.87%);高分7号所提取的坡度坡长在沟间地上的相对偏差(坡度15.48%~56.63%,坡长50.02%~130.79%)明显低于沟谷地(坡度21.28%~63.61%,坡长93.01%~192.51%)。[结论]利用高分7号DEM提取坡度坡长时,对于获取坡长坡度面积分级和对指定点的坡度提取时是可行的,而对于指定点的坡长提取时则结果不够可靠,在研究流域中坡长坡度的空间分布上具有较大优势,而提取具体某一位置处的坡长坡度时的优势则不明显。

[Objective]Slope and slope length are essential topographic factors,and their calculation accuracy directly affects the evaluation accuracy of slope soil erosion model.The high-precision elevation measurement capability of Gaofen-7 satellite has great potential in the accurate extraction of terrain factors,and it is expected that it can be used in the extraction of slope and slope length to achieve accurate expression of terrain.It is necessary to evaluate the accuracy of the results of slope length extraction using the DEM of Gaofen-7 satellite.[Methods]The slope and slope length of DEM generated by Gaofen-7 satellite,1∶10000 topographic map and LiDAR images in 4 small basins in Wubu County,Shaanxi Province were extracted by using the terrain factor(LS)calculation tool.Correlation coefficient(r),relative deviation(RE)and absolute deviation were used as evaluation indexes to evaluate the accuracy of extraction of topographic factors by Gaofen-7.[Results]Compared with the slope and slope length of LiDAR and 1∶10000 topographic map,the average slope extracted by GF-7 was 7.50%~9.02%lower,and the slope length was 1.83%~19.35%larger.However,the area distributions of slope length and slope derived from the three data sources had no significant difference.Comparing the results of slope and slope length,the discrepancy in[JP2]slope(RE:16.46%~44.26%)derived from different sources is significantly lower than that(RE:75.25%~140.87%)was slope length.The discrepancy between different sources was enhanced in gully areas(RE of slope 15.48%~56.63%,slope length:50.02%~130.79%),while being decreased in inter-gully areas(RE of slope 21.28%~63.61%,RE of slope length 93.01%~192.51%).[JP][Conclusion]It was feasible to obtain areal grading characters of slope or slope length and slope of specified locations using DEMs generated from Gaofen-7 satellite,while the results of slope length for specified locations were less reliable.In conclusion,the Gaofen-7 satellite had a great advantage in describing the spatial distribution of slope length and slope at the watershed scale,while being less capable of capturing slope length and slope at a specific site.