Magnetic anomaly map of the world: merging satellite, airborne, marine and ground-based magnetic data sets

We report here a simple but practical method to combine systematically the magnetic surveys of disparate specifications from marine, ground, aeromagnetic and satellite platforms that aims to be helpful in the framework of the world digital magnetic anomaly map project. Because the satellite coverage and data quality is more uniform than near-surface surveys, it is adopted as the base map for wavelengths larger than 400 km and up to spherical harmonic degree inclusive of 16 (∼ 2500 km). After checking that satellite models and large aeromagnetic wavelengths are not consistent, we filter out wavelengths longer than 400 km in aeromagnetic compilations. Existing regional grids and, when available, individual surveys, are merged to give a more uniform spatial variation of the magnetic anomalies. The effects of merging the grids are examined by plotting profiles and difference maps of the overlapping regions. A preliminary global map is obtained after combining the magnetic anomaly map with the downward continued CHAMP satellite derived magnetic anomaly map. Forthcoming availability of new datasets, as well as improvements in the procedure, will help to produce increasingly reliable maps.