A model of the geomagnetic field and its secular variation for epoch 2000 estimated from Ørsted data
A model of the geomagnetic field and its secular variation for epoch 2000 estimated from Ørsted data
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根据 Ørsted 数据估计的 2000 年地磁场及其长期变化模型
DOI：
10.1046/j.1365-246x.2002.01657.x
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发表时间：
2002
影响因子：
2.8
通讯作者：
N. Olsen
中科院分区：
文献类型：
--
作者：
N. Olsen
总结
Orsted和CHAMP等卫星提供的高精度地磁测量开启了地磁场研究的新时代。然而，为了充分利用数据准确性的提高，有必要改进从卫星数据推导出实地模型的通常方法。
本文介绍了推导的球谐模型的主要领域（度/阶29）和长期的变化（度/阶13）使用Orsted数据跨越2年以上（1999年3月至2001年9月），并采用新的建模方法，正确的统计处理的数据误差，并考虑外部场的贡献。磁层的贡献建模度/订单2;纬向条款每年和半年的周期性变化，与度n= 1的条款调制的磁层环电流的强度，同时测量的全球分布的地磁观测站。此外，观测资料被用来约束长期变化。
该模型估计使用迭代加权最小二乘法与Huber权重占非高斯数据误差分布。对于标量强度和垂直于磁场的一个矢量分量，在非极纬度实现的均方根失配为3 nT;在估计模型时，第三个矢量分量（由于姿态噪声，均方根失配为6.4 nT）被降权。将模型预测与CHAMP卫星的实际标量磁场观测结果进行比较，得出非极纬度和极纬度的均方根失配分别为3.4 nT和5.4 nT。
Summary
The availability of high-precision geomagnetic measurements from satellites such as Orsted and CHAMP opens a new era in geomagnetic field research. However, in order to take full advantage of the improved data accuracy it is necessary to refine the usual way of deriving field models from satellite data.
This paper describes the derivation of a spherical harmonic model of the main field (up to degree/order 29) and of the secular variation (up to degree/order 13) using Orsted data spanning more than 2 yr (1999 March–2001 September) and applying new modelling approaches for a correct statistical treatment of the data errors and for considering external field contributions. Magnetospheric contributions are modelled up to degree/order two; the zonal terms vary with annual and semi-annual periodicity, and terms with degree n= 1 are modulated with the strength of the magnetospheric ring current as measured simultaneously by globally distributed geomagnetic observatories. In addition, the observatory data are used to constrain secular variation.
The model is estimated using an iteratively reweighted least-squares method with Huber weights to account for the non-Gaussian data error distribution. The rms misfit achieved at non-polar latitudes is 3 nT for the scalar intensity and for one of the vector components perpendicular to the magnetic field; the third vector component (rms misfit of 6.4 nT owing to attitude noise) is downweighted when estimating the model. Comparing model predictions with actual scalar magnetic field observations from the CHAMP satellite yields an rms misfit of 3.4 nT at non-polar latitudes and 5.4 nT at polar latitudes.