Standard inversion methods for inverting aeromagnetic anomalies into magnetic susceptibility contrast in the crust are based on the assumption that the core field is constant over the region considered. This assumption, however, does not hold over regions of a few thousand kilometer extent. An inversion technique is developed which takes into account the variations in the core field, both in direction and in intensity. It can also take into account the surface topography of a magnetic layer within the lithosphere. The technique is applied to a scalar magnetic anomaly map of eastern Europe and the Middle East, derived from the magnetometer satellite (MAGSAT) data. The magnetic susceptibility contrast map thus obtained delineates the major tectonic features of the region. Small-scale Precambrian shields are characterized by high magnetic susceptibility. The Alpine-Himalayan belt has a distinct magnetic signature. The collision zones are low-susceptibility regions, whereas the continental plates within the belt have high magnetic susceptibility. The well-known iron formation of Kursk is delineated by a strong magnetic susceptibility high.
The magnetometer satellite has measured the Earth's magnetic field at two distinct local times, dawn and dusk, and provided two independent magnetic anomaly maps. The scalar magnetic anomaly map is based on the common features of the two maps. A covariance technique is developed which selects these common features on the basis of the correlation spectra of the two maps.