Geomagnetic depth sounding by means of oceanographic and aeromagnetic surveys

The investigation of underground conductivity structures by means of geomagnetic data (i.e., geomagnetic depth sounding (GDS)) has been extensively carried out over land areas using three component recordings. However, the large amount of data collected for many years by airborne and/or shipborne magnetometry all over the world have generally been used to infer only static magnetic anomalies. The time-varying magnetic field has normally been subtracted as an unwanted nuisance. An immediate application of the land-based GDS techniques to airborne and shipborne surveys is not possible because normally these latter surveys measure only the total field intensity. Notwithstanding such a substantial limitation, we discuss three possible techniques for performing GDS analyses by means of aeromagnetic and oceanographic ship surveys. We conclude that GDS analyses can be perfornted at differing levels of sophistication which can be expected to provide important information on the location (at least) of principal conductivity anomalies associated with, e.g., ocean ridges, volcanic areas, and similar features.