A new magnetic anomaly map for Greenland based on a combination of equivalent source modeling and spherical harmonic expansion

Abstract. The Greenland Magnetic Map (GREENMAG) is a new compilation of magnetic anomaly data that covers the inland ice, ice-free coastal areas, and adjacent shelf regions of Greenland. GREENMAG is based on all accessible modern regional aeromagnetic surveys from Greenland and vintage datasets without GPS positioning in areas where modern data are lacking.

The magnetic anomaly map is generated by a combination of equivalent source (ES) modeling and spherical harmonic expansion. Hereby, the data points are used at their actual measurement location as input data for the inversion of the ES modeling. The equivalent sources are represented by magnetic dipoles that are arranged in three uniform grids with different source spacing and depths (coarsest spacing: 10 x 10 km; medium spacing: 2 x 2 km; finest spacing: 0.7 x 0.7 km). Regularization in the inversion for the different equivalent source grids are chosen such that the resulting resolution is adapted to the largely varying magnetic data coverage in Greenland. Since long wavelength components in aeromagnetic data are considered unreliable, they are replaced by the LCS-1 satellite model based on magnetic gradient measurements of the Swarm and CHAMP missions. For combination, the responses from the individual equivalent dipole sources are transferred to spherical harmonics and replaced for degree n=13-133 by the Gaussian coefficients of the LCS-1 model.

The final magnetic anomaly map is calculated from the combined model at a constant height of 2000 m.a.s.l. (WGS84) and with a grid spacing of 400 x 400 m.

The comparison between the GREENMAG and the earlier compilation from the Circum-Arctic Mapping Project (CAMP-M) highlights the enhanced level of detail now available across many regions of Greenland.