EGM2008地球重力模型数据在中国大陆地区的精度分析

On the accuracy of EGM2008 earth gravitational model in Chinese Mainland

本文介绍了5′×5′的EGM2008地球重力模型及其在全球的精度评价.按照地形变化规律,将中国大陆大致分为7个区域,在10km网度上,将EGM2008地球重力模型数据与中国地面实测空间重力网格数据进行了对比.由于数据源的问题,中国大陆的模型数据精度普遍低于北美和欧洲.二种数据在地形平坦的东部地区差别较小,向西随着地形复杂程度的增加,二种数据之间的标准差从小于10mGal增大到50多mGal.畸变点分析表明精度极低的网格点均分布在地形起伏大的地区.总体而言,5′×5′的EGM2008地球重力模型数据在中国大陆将近80%的面积上的精度可达10mGal之内,可用于小比例尺重力编图和构造研究.在地形起伏较大的中国西部以青藏高原为例进一步比较了EGM2008重力模型和重力测点数据,结果表明在重力点分布稀疏不均匀的地区,平面网格数据难以准确表达重力场信息.由于缺少地面重力数据控制,EGM2008重力模型数据在中国西部精度较低,但模型数据依然在很大程度上提高了空间重力异常信息的丰富程度.将中国区域重力调查成果数据应用于地球模型的构建是一项有意义的工作.

The paper introduces the data sources and calculation method for building 5 X 5 minute grid EGM2008 Earth Gravitational Model and its global accuracy evaluation by US National Geospatial Intelligence Agency （NGA） and the third party scientists. The surface gravity data points or grid data were used for comparison with EGM2008 Earth Gravitational Model data. The previous study showed that the model data had good match with the terrestrial free air gravity data in most of NGA＇s non-proprietary data area such as north America, western Europe or Australia, while the accuracy of the model data is relatively lower in proprietary data area such as Chinese mainland. The different source of the data used for composing EGM2008 is the main reason= synthetic data are filled in contract areas like China＇s main land where surface gravity data cannot be used, while surface gravity data are used in other areas. The paper divides Chinese mainland into seven regions according to the variation regularity of the topography, and compares EGM2008 Earth Gravitational Model data and the ground measured free air gravity grid data in 10X 10 km grid in each region. The difference of the two datasets is generally small in the eastern plain region and Sichuan basin, the standard variation is 8. 91 and 8. 95 reGal respectively. From east to the west, as the terrains and landforms become more complex, the standard variation of the difference between the two dataset increases from less than 10 reGal to more than 50 regal. Distortional point analysis shows that the low fidelity data grids locate in the rough areas. On the whole, the 5 X 5 minute grid EGM2008 Earth Gravity Model can reach 10 mGal precision in almost 80~ area of Chinese mainland. The EGM2008 Earth Gravitational Gravity data can be used for small scale gravity mapping and tectonic geology research in these regions. The distribution of surface gravity measuring points also has great impact on the comparison result in the rough area. We choose the Qinghai-Tibet Plateau as a typical region with irregularly and sparsely distributed terrestrial gravity data to do further analysis. The result shows that in the rough area in western China, the grids of those surface gravity data could not precisely express the gravity effect caused by the land mass. Even though the accuracy of the EGM2008 data grids is relatively low, it can considerably rich the information of the free air gravity field. Since the deep source component in gravity field could not be recovered completely due to the lack of terrestrial survey data, the EGM2008 model data in these regions should be treated carefully when doing geological analysis. A more delicate Earth Gravitational Model could be built if Chinese regional gravity survey data are contributed.