Dictionary:Electromagnetic sounding

An electromagnetic technique designed to determine variations in electrical conductivity with depth, usually assuming horizontal layering. Measurements are usually made at a number of frequencies (in frequency-domain sounding) or at several time intervals after a transient pulse (in time-domain or transient electromagnetic sounding) using a fixed source and receiver. Soundings can also be made at constant frequency by varying the spacing between source and receiver. See transient electromagnetic method and Spies and Frischknecht (1989) and compare electric sounding.