EMI surveys can be used to produce more detailed, spatially accurate soil maps EMI is a technique to measure the total salts or electrical conductivity of a soil. The instrument we use is an EM-38 attached to an ATV and linked with a data logger and GPS to allow for mapping of the conductivity readings. The unit is about 1 meter long with a sending coil at one end and a receiving coil at the other. The transmitting coil induces a magnetic field that varies in intensity based on soil properties. The receiving coil measures the primary and secondary induced currents in the soil and relates the two to soil conductivity.
To learn more about EMI, please see the article.