EM31 CMD (Conductivity Mapping)
Technical Explanation
EM31 / CMD surveys use a ground-based electromagnetic instrument to measure soil conductivity without contact. The EM31 tool (on a long boom) can penetrate ~6 m deep, mapping variations in subsurface conductivity that often indicate buried structures, voids, or contamination. It’s excellent for quickly surveying large areas for anomalies.
Main requirements
Required for broad-area geophysical mapping of the shallow subsurface (e.g. locating old foundations, mine shafts, contamination plumes). Needs relatively open terrain to carry the instrument and absence of extensive surface metal (which can interfere). Provides rapid coverage where higher detail point surveys may later be focused.