Methodology:

Crustal susceptibility distribution is inferred from magnetic inversion of airborne magnetic data. The inversion is carried out with the academic software JIF3D (https://sourceforge.net/projects/jif3d/) developed by Max Moorkamp.

The susceptibility inversion model is discretised into meshes with equal horizontal cell sizes of 250m. The vertical cell size is 100m at the surface. The vertical cell size increases with depth by a factor 1.1 for each cell. Increasing vertical cell size with depth is introduced to account for decreasing resolution with increasing distance to the source in potential field applications.

Additionally, a padding area of 20% around the study area is added to avoid edge effects. The resulting inversion mesh contains 324 cells east-west direction, 276 cells in north-south direction and 38 cells in the z direction (32.7 km below sea level). To constrain the model geometry, the bedrock topography and Curie Point depths are used as model boundaries.

All cells are set to a starting value of 0 SI and are iteratively updated during the magnetic inversion process.

Data format is NetCDF4. Each physical parameter has his own NetCDF file.

* Input_mag.nc contains the input magnetic field. The variables in NetCDF file are projection_x_coordinate (polar stereographic), projection_y_coordinate (polar stereographic), projection_z_coordinate (station height in meter), crs (map projection information), magnetic_field (magnetic field in nT), dT (Error in nT)

* Inv_mag.nc contains the inverted magnetic field. The variables in NetCDF file are projection_x_coordinate (polar stereographic), projection_y_coordinate (polar stereographic), projection_z_coordinate (station height in meter), crs (map projection information), inverted_magnetic_field (magnetic field in nT), dT (Error in nT)

* inv_susceptibility.nc contains the inverted crustal susceptibility distribution. The variables in NetCDF file are projection_x_coordinate (polar stereographic), x_cell_bnds (cell boundaries in x direction in polar stereographic coordinates), x_origin (model origin in x direction polar stereographic), projection_y_coordinate (polar stereographic), y_cell_bnds (cell boundaries in y direction in polar stereographic coordinates), y_origin (model origin in y direction polar stereographic), projection_z_coordinate (Model depth in meter), z_cell_bnds (cell boundaries in z direction in m), z_origin (model origin in depth in meter), crs (map projection information), susceptibility (Crustal susceptibility distribution in SI).

Data collection:

The data preparation and the inversion set up is performed in python (version 3.10.11). The inversion itself is carried out in the JIF3D software using a Linux terminal (JIF3D is a software developed by Max Moorkamp available under a GNU General Public License (v3) via subversion at https://svn.code.sf.net/p/jif3d/jif3dsvn/trunk/jif3D )

Data quality:

The RMS error between observed and inverted magnetic field is 0.97 nT. The end members of the residual between observed and inverted values are + 551 nT, and -130nT with a standard deviation of 12 nT.