Influence of trenches and soil water detection instruments on EM38-MK2 sensor readings

Abstract

Electromagnetic induction (EMI) sensors, such as the EM38-MK2, measure soil apparent electrical conductivity (EC_a). The EC_a values are then calibrated with soil water content, often determined by metal-containing instruments. Such instruments and soil trenches may interfere with EC_a measurements. This study established whether multi-sensor capacitance probes (small copper rings), neutron water meter access tubes (galvanized steel) and soil trenches interfere with EC_a measurements by EM38-MK2 sensors. The EM38-MK2 sensor was moved towards and away from the potential interfering obstruction in a horizontal or vertical mode without re-zeroing the device. The soil trenches had no significant influence on the measurement of EC_a. On the other hand, both the capacitance probes and the access tubes influenced the EC_a measurement of the EM38-MK2 sensor when it was operated closer than 1 m from the two devices. Measurements of EC_a were either less stable (only in the vertical mode) or lower. However, the magnitude of reduction in EC_a was so small that it would likely not have any practical influence. Nevertheless, in field surveys with the EM38-MK2 sensor, a distance of at least 1 m should be kept from either the capacitance probes or galvanized-steel access tubes to avoid interferences. When encountering such devices during field surveys, it should be safe to continue measurements without additional re-zeroing of the sensor.