Compare Geonics EM31 and EM38
Both measure apparent conductivity per meter as well as the inphase
ratio of secondary to primary magnetic field in parts per thousand. Their measurement resolution is +/-0.1% of full scale, making their ability to discern targets about the same. Their components and operating controls look fairly similar. Essentially, the EM31 and EM38 work on the same principles and measure the same factors.
So what is the difference between the EM31 and EM38?
Application. The EM31 and EM38 are used for different applications because of the difference in intercoil spacing, which affects the effective depth of exploration. The EM31 has a coil spacing of 3.7 meters that allows it to reach depths of approximately 6 meters in the vertical dipole mode and approximately 3 meters in the horizontal dipole mode. These depths make the EM31 great for mapping soil materials, groundwater contaminants, buried metal, or any other subsurface feature that affects ground conductivity as well as environmental or engineering site exploration.
The EM38, on the other hand, has a much smaller intercoil spacing of either 1 meter or 0.5 meter. This means its depth of exploration ranges from about 1.5 meter to 0.375 meters, depending on coil selection and dipole mode. The shallow nature of the EM38 makes it suitable for applications in agriculture, archaeology, and general soil sciences. EM38s are particularly popular for determining the apparent clay content, salinity, and moisture in soils. By mapping very near surface apparent conductivities, farmers can plant crops in better places relative to their crop’s need for moisture and other factors, pipeline or facility operators can map variations in soils for cathodic protection or surface spills, archaeologist can search for buried foundations, and everyone can look for metal buried just beneath the surface and too deep for a metal detector to locate. Geonics EM-31 and EM-38 are some of the most versatile near surface geophysical instruments made.