GeoForschungsZentrum anomaly magnetic map (GAMMA): A candidate model for the world digital magnetic anomaly map

The World Digital Magnetic Anomaly Map (WDMAM) is an ongoing effort toward the mapping of worldwide available aeromagnetic data. It is led by a task force of the International Association for Geomagnetism and Aeronomy (IAGA) and aims at distributing a global map in printed and digital forms. In this paper, we describe in detail our candidate model which has to be evaluated by the IAGA task force together with five other candidate maps. After discussing the quality of the available data, we show a simple but effective method applied to successfully process, reduce, and merge together individual compilations. The near-surface data are corrected using global field models and further refined with two-dimensional polynomial corrections. After the upward continuation to 5 km altitude, data are resampled to a 3 minute grid and merged together. We then calculate a spherical harmonic model up to degree 199 and analyze the magnetic spectrum of the global map. This helps us to confirm that wavelengths larger than 400 km are spurious at a global scale in aeromagnetic compilations. Therefore we substitute them using a satellite-based lithospheric field model (MF5) to degree 100. Finally, our proposed candidate map for WDMAM is presented. Copyright 2007 by the American Geophysical Union.