GREENMAG - Magnetic anomaly map of Greenland

Greenland Magnetic Compilation (GREENMAG) ==================================== The development of this new magnetic compilation from Greenland (GREENMAG) was initiated by the working group of Satellite- and Aerogeophysics at the Christian-Albrechts-University (CAU) in Kiel, Germany, and GEUS as part of the ESA project GOCE+Greenland in 2021. The here presented magnetic anomaly map covers whole Greenland including the Inland Ice and the adjacent shelf regions. It is built out of all accessible modern regional aeromagnetic surveys from Greenland but also uses older datasets without GPS positioning in areas where modern data are lacking. Magnetic data are currently taken from the surveys of the projects AEROMAG, AEM, GICAS, EASTMAR, ICEBRIDGE, GAP91/92, AWI93-96, LOMGRAV, NOO-73, several projects from the German Federal Institute for Geosciences and Natural Resource (BGR), Geological Survey of Canada (GSC) and Alfred Wegener Institute (AWI) and from offshore datasets acquired by the TGS-NOPEC TGS GEOPHYSICAL COMPANY. Since long wavelength components in aeromagnetic data are often considered as unreliable, they are replaced by the ones from the LCS-1 satellite model (Gaussian coefficients with degrees n = 13 – 133). The magnetic anomaly map is generated by a methodology that combines equivalent source modelling and a spherical harmonic expansion. The datapoints at their actual measuring locations are used as data input and magnetic dipoles are employed as equivalent sources that are arranged in three uniform grids with different source spacing and depths (coarsest spacing: 10 x 10 km; finest spacing: 0.7 x 0.7 km). The presented magnetic anomaly map is simulated from the dipole responses at a constant height of 2000 m asl and with a grid spacing of 400 x 400 m. Regularizations in the inversion for the different equivalent source grids are chosen such that the resulting resolution is flexible and adapted to the largely varying magnetic data coverage in Greenland. Data Download ============ Downloadable data include (1) the GREENMAG magnetic anomaly map as ArcView Binary Raster Grids (files *.flt, *.hdr) and in a column based ASCII-table (files *.XYZ) and (2) a table with the locations of used data points. The magnetic anomaly maps are provided as two versions. One is simulated from all three equivalent source grids, but the other is simulated only from the coarse and medium equivalent source grids.

格陵兰磁数据汇编（GREENMAG）
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本格陵兰磁数据汇编（GREENMAG）由德国基尔克里斯蒂安-阿尔布雷希茨大学（Christian-Albrechts-University, CAU）卫星与航空地球物理工作组，以及丹麦地质调查局（Geological Survey of Denmark and Greenland, GEUS）于2021年作为欧洲空间局（ESA）GOCE+格陵兰项目的组成部分启动研发。

本次发布的磁异常图覆盖整个格陵兰区域，包括内陆冰盖及邻近陆架区域。该数据集整合了格陵兰地区所有可获取的现代区域航空磁测数据，同时在现代数据匮乏的区域采用了无GPS定位的老旧数据集。

当前所用的磁数据源自以下项目与机构的勘测成果：AEROMAG、AEM、GICAS、EASTMAR、ICEBRIDGE、GAP91/92、AWI93-96、LOMGRAV、NOO-73，以及德国联邦地球科学与自然资源研究所（BGR）、加拿大地质调查局（Geological Survey of Canada, GSC）、阿尔弗雷德·魏格纳研究所（Alfred Wegener Institute, AWI）的多项相关项目，另有TGS-NOPEC地球物理公司（TGS GEOPHYSICAL COMPANY）获取的近海数据集。

由于航空磁测数据中的长波分量通常可靠性较低，因此采用LCS-1卫星模型的对应分量（阶数n=13至133的高斯系数）进行替换。

本磁异常图采用等效源建模与球谐展开相结合的方法生成：以实测点位的原始数据作为输入，以磁偶极子作为等效源，将其排布为三组不同间距与深度的均匀网格（最粗间距：10×10 km；最精细间距：0.7×0.7 km）。本次发布的磁异常图基于海拔2000米的恒定高度处的偶极子响应模拟得到，输出网格间距为400×400 m。针对不同等效源网格的反演正则化参数经过优选，使得最终成果的分辨率具备灵活性，可适配格陵兰地区差异显著的磁数据覆盖情况。

数据下载
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可下载的数据包括：（1）GREENMAG磁异常图，格式为ArcView二进制栅格网格（文件后缀为*.flt、*.hdr）以及基于列的ASCII表格（文件后缀为*.XYZ）；（2）所用数据点的位置表。磁异常图提供两个版本：其一由全部三组等效源网格模拟生成，其二仅由粗、中分辨率等效源网格模拟生成。