GECO: a global gravity model by locally combining GOCE data and EGM2008
GECO: a global gravity model by locally combining GOCE data and EGM2008
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DOI：
10.1007/s11200-015-1114-4
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发表时间：
2016-04-01
影响因子：
0.9
通讯作者：
Sampietro, Daniele
中科院分区：
文献类型：
--
作者：
Gilardoni, Maddalena;Reguzzoni, Mirko;Sampietro, Daniele
EGM 2008模型是目前对全球重力场最高分辨率的描述之一。它提供了两个不完全一致的误差信息来源：球谐系数方差和误差方差地理图，例如大地水准面起伏。在目前的工作中，来自GOCE卫星的全球模型的重力场信息被用来提高EGM 2008模型在低到中频率的精度，特别是在EGM 2008计算时没有数据的地区。关键问题是建立两个模型的误差协方差矩阵，以实现最优最小二乘组合：GOCE球谐系数的全误差协方差矩阵由逐阶块对角矩阵近似，而对于EGM 2008，逐点误差方差取自提供的大地水准面误差图，误差空间相关性取自系数方差。由于计算的原因，组合直接在局部区域的规则网格上的大地水准面值方面执行。对世界各地的重叠区域重复组合，然后进行谐波分析，得到新的组合模型。它被称为GECO，并扩展到EGM 2008的最大程度。与其他最近的组合模型，如EIGEN-6C 4，并在南极洲的新的重力数据集的基础上的本地大地水准面进行比较，以评估其质量。主要结论是，所提出的组合，加权不同的输入贡献不仅在全球的基础上，而且根据一些本地的错误信息，可以执行甚至比其他更复杂的组合在输入的全球错误描述是不够可靠的地区。
The EGM2008 model is nowadays one of the description of the global gravitational field at the highest resolution. It is delivered with two, not fully consistent, sources of information on its error: spherical harmonic coefficient variances and a geographical map of error variances, e.g. in terms of geoid undulation. In the present work, the gravity field information derived from a GOCE satellite-only global model is used to improve the accuracy of EGM2008 model in the low to medium frequencies, especially in areas where no data were available at the time of EGM2008 computation. The key issue is to set up the error covariance matrices of the two models for an optimal least-squares combination: the full error covariance matrix of GOCE spherical harmonic coefficients is approximated by an order-wise block-diagonal matrix, while for EGM2008, the point wise error variances are taken from the provided geoid error map and the error spatial correlations from the coefficient variances. Due to computational reasons the combination is directly performed in terms of geoid values over a regular grid on local areas. Repeating the combination for overlapping areas all over the world and then performing a harmonic analysis, a new combined model is obtained. It is called GECO and extends up to the EGM2008 maximum degree. Comparisons with other recent combined models, such as EIGEN-6C4, and a local geoid based on new gravity datasets in Antarctica are performed to evaluate its quality. The main conclusion is that the proposed combination, weighting the different input contributions not only on a global basis but also according to some local error information, can perform even better than other more sophisticated combinations in areas where the input global error description is not reliable enough.