A spherical harmonic model of the lithospheric magnetic field of Mars
A spherical harmonic model of the lithospheric magnetic field of Mars
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DOI：
10.1002/2013je004555
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发表时间：
2014-06-01
影响因子：
4.8
通讯作者：
Grott, M.
中科院分区：
文献类型：
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作者：
Morschhauser, A.;Lesur, V.;Grott, M.
我们提出了一个火星岩石圈磁场的模型，它是基于火星全球勘测轨道卫星数据和表示的扩展的球谐函数（SH）的程度和顺序110。为了获得可靠的、分辨率良好的火星岩石圈磁场模型，采用了几种技术：使用修正的Huber范数来适当处理数据异常值，根据对数据的先验分析对映射相位轨道数据进行加权，并通过外部和内部场的联合反演来处理静态外部场。此外，导致不切实际的强异常的数据中的时间变化被认为是噪声，并通过另外最小化在表面高度处的垂直向下的内部场分量的水平梯度的测量来处理。在这里，我们使用迭代重新加权最小二乘算法来接近绝对测量（L1范数），允许更好地表示强局部磁异常相比，传统的最小二乘测量（L2范数）。由此产生的模型再现了火星岩石圈场的所有已知特征，并显示了丰富的细节。它的特点是噪音低，向下继续到地面时坚固耐用。我们展示了这些属性如何有助于通过调查与撞击和火山有关的磁特征来提高对火星过去和现在磁场的认识。此外，我们提出了一些以前未描述的孤立异常，它可以用来确定古磁极位置和磁化强度。
We present a model of the lithospheric magnetic field of Mars which is based on Mars Global Surveyor orbiting satellite data and represented by an expansion of spherical harmonic (SH) functions up to degree and order 110. Several techniques were applied in order to obtain a reliable and well-resolved model of the Martian lithospheric magnetic field: A modified Huber-Norm was used to properly treat data outliers, the mapping phase orbit data was weighted based on an a priori analysis of the data, and static external fields were treated by a joint inversion of external and internal fields. Further, temporal variabilities in the data which lead to unrealistically strong anomalies were considered as noise and handled by additionally minimizing a measure of the horizontal gradient of the vertically down internal field component at surface altitude. Here we use an iteratively reweighted least squares algorithm to approach an absolute measure (L1 norm), allowing for a better representation of strong localized magnetic anomalies as compared to the conventional least squares measure (L2 norm). The resulting model reproduces all known characteristics of the Martian lithospheric field and shows a rich level of detail. It is characterized by a low level of noise and robust when downward continued to the surface. We show how these properties can help to improve the knowledge of the Martian past and present magnetic field by investigating magnetic signatures associated with impacts and volcanoes. Additionally, we present some previously undescribed isolated anomalies, which can be used to determine paleopole positions and magnetization strengths.