The Good, the Bad, and the Ugly: Airborne EM and the Regolith

EM signals may be highly influenced by the regolith in weathered terrain, to the point of obscuring geologic targets at deeper levels. In time-domain data, this influence can extend from the earliest measurement times into the mid-range time gates. The degree of interference by the regolith varies according to the terrain, and is mostly influenced by the longevity and variability of weathering. Examples from different parts of Africa illustrate the extent to which long-lived regolith dominates the signal of airborne EM surveys.