High-Resolution Surveying With Small-Loop Frequency Domain Electromagnetic Systems: Efficient Survey Design and Adaptive Processing

The range of near-surface applications whereby the electrical and magnetic properties of the subsurface are investigated expands continually [1], and, particularly for terrestrial applications, increasingly higher spatial sampling densities are deployed [2]. Within the broad range of geophysical methods, small-loop frequency-domain electromagnetic (FDEM) instrumentation is often used to record variations of multiple EM properties simultaneously [3]-[7]. Such instruments typically incorporate at least one transmitter in combination with one or more receivers. The resulting transmitter-receiver pairs are commonly configured in either a horizontal coplanar (HCP), vertical coplanar (VCP), vertical coaxial (VCA), or perpendicular (PRP) orientation [8], [9]. A distinction can be made between symmetrical (e.g., HCP, VCP, and VCA) and asymmetrical (e.g., PRP) coil configurations [10], [11] in relation to survey heading. Although the former render an isotropic response unaffected by the acquisition direction, an asymmetrical configuration will produce different responses based on survey heading.

Automated summary

The range of near-surface applications investigating the electrical and magnetic properties of the subsurface is expanding, with increasing spatial sampling densities for terrestrial applications. Small-loop frequency-domain electromagnetic (FDEM) instruments are commonly used to record variations of multiple EM properties simultaneously, with different coil configurations producing isotropic or directional responses.