Magnetometry

Abstract

Magnetometry is a near-surface geophysical method that measures small changes in the earth’s magnetic field, which are a product of differences in the retained magnetism of materials within the upper few meters of the ground. Objects made of iron, or any other highly magnetic material will produce distinct readings of positive (and sometimes positive and negative dipole) readings when plotted in maps. More subtle buried units such as ditches or other features that accumulated organic material over time will be displayed as low value positive anomalies. Built features or disturbed units that are composed of materials lower in magnetic susceptibility than the surrounding ground will be displayed as negative magnetic anomalies. This method can be used to quickly map the extent of these buried features over large areas of otherwise invisible past landscapes, but have little ability to map the depth of those materials. When magnetic readings can be extracted from a broad aerial data coverage, and then compared to the GPR reflection profiles, the units visible with GPR can be interpreted with respect to their composition, at least regarding their magnetic properties. When an understanding of the magnetic properties of buried materials can be understood in this way, the origin of features visible in magnetic maps can be more accurately interpreted.