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摘要:
从误差传播定律和全微分理论出发,在综合考虑重力测点和地形DEM水平位置误差和高程误差的基础上,提出了一种基于DEM数据客观、有效的重力中区地形改正精度评价方法。通过理论模型研究,认为重力地形改正值及其误差与地改半径呈正相关关系,随着地改半径的增大地改值及其误差增速变小;在地形改正区域较远时,高程误差比水平位置误差对地形改正误差的贡献大,但在地改区域较近时水平位置误差的影响不可忽视,地形改正的均方误差由高程误差和水平位置误差的影响共同组成;DEM分辨率对地形改正误差影响较大,特别是相对近区应选取精度和分辨率更高的DEM。秦岭地区实际资料计算证明,利用本方法评价的地形改正精度与现行规范要求相近,克服了以往地形改正精度虚高的假象;1∶1万DEM数据能完全满足1∶5万重力调查中区地形改正的要求,基本能满足1∶1万~1∶2.5万重力调查的需求;若使用1∶5万地形DEM进行1∶5万重力调查中区地形改正时,起始半径应大于300 m。
Abstract:Starting from the law of error propagation and total differential theory, on the basis of comprehensively considering the horizontal position error and elevation error of gravity measurement points and terrain DEM, an objective and effective method for evaluating the accuracy of terrain correction in mid-gravity region based on DEM data has proposed.Through theoretical model research, it is believed that the gravity terrain correction value and its error have a positive correlation with the terrain correction radius,with the increase of the ground modification radius, the ground modification value and its error growth rate become smaller; the elevation error has a greater contribution to the terrain correction error than the horizontal position error, and the mean square error of the terrain correction is mainly composed of the elevation error; the DEM resolution has a great influence on the terrain correction error, especially the DEM with higher precision and resolution should be selected in the relatively near area.The calculation of the actual data in the Qinling Mountains proves that the terrain correction accuracy evaluated by this method is similar to the requirements of the current specification, which overcomes the false high accuracy of terrain correction in the past; the 1∶10,000 DEM data can fully meet the requirements of terrain correction in the middle area of the 1∶50,000 gravity survey, and can basically meet the needs of the 1∶10,000 ~ 1∶25,000 gravity survey; if a 1∶50,000 terrain DEM is used to correct the terrain in the middle area of the 1∶50,000 gravity survey, the starting radius should be greater than 300 meters.
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表 1 数字高程模型(DEM)精度指标
Table 1. Digital elevation model (DEM) accuracy metrics
比例尺 格网
尺寸(m)平面位置
中误差(m)地貌
类型高程中误差(m) 一级 二级 三级 1∶ 5000 2.5 2.5 平地 0.5 0.7 1.0 丘陵地 1.2 1.7 2.5 3.75 山地 2.5 3.3 5.0 高山地 4.0 6.0 8.0 1∶ 10000 5 5.0 平地 0.5 0.7 1.0 丘陵地 1.2 1.7 2.5 7.5 山地 2.5 3.3 5.0 高山地 5.0 6.7 10.0 1∶ 25000 10 12.5 平地 1.5 2.0 3.0 丘陵地 2.5 3.5 5.0 18.75 山地 4.0 5.5 8.0 高山地 7.0 9.5 14.0 1∶ 50000 25 25.0 平地 3 4 6 丘陵地 5 7 10 37.5 山地 8 11 16 高山地 14 19 28 1∶ 100000 50 50.0 平地 6 8 12 丘陵地 10 14 20 75.0 山地 16 22 32 高山地 28 38 54 表 2 用实测高程点对DEM高程精度的评价统计表
Table 2. Statistical table for evaluating DEM elevation accuracy with measured elevation points
工作地区 实测
点数(个)DEM
比例尺实测高程和DEM高程之差( m) 最小值 最大值 平均值 中误差 陕西
凤县某地2347 1∶1万 −7.299 6.882 −0.221 2.847 1∶5万 −28.916 18.055 −5.404 9.565 陕西
山阳县
某地1986 1∶1万 −8.234 4.748 −1.721 2.607 1∶5万 −32.516 46.905 7.459 16.030 表 3 陕西凤县某地1∶5万DEM计算地改误差 统计表(10−5 m/s2)
Table 3. Statistical table of 1∶50,000 DEM Terrain correction errors in a place in Fengxian County, Shaanxi Province (10−5 m/s2)
计算范围(m) 最小值 最大值 平均值 均方误差 20~2 000 0.0037 1.0160 0.1959 0.2175 50~2 000 0.0028 0.6143 0.0966 0.1051 100~2 000 0.0025 0.4399 0.0517 0.0559 200~2 000 0.0018 0.3082 0.0238 0.0260 300~2 000 0.0016 0.2540 0.0145 0.0162 500~2 000 0.0015 0.1840 0.0063 0.0076 -
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