Playing with my brand new EM38-4 in the park, finding old building foundations
With apologies for the colour scheme (I'm so sorry if you're colour blind!). This is the lower layer of a two layer 1D inversion model, interpolated. Was playing with maximizing the contrast to try to find the foundation of the Richardson Mansion that existed on this property prior to it being bulldozed in the 70s and donated to the City of Winnipeg to become Munson Park. I'm pretty sure I captured it in the red square in the middle.
Short form: it is a soil conductivity meter - it measures variations in electrical conductivity.
Long form, and assuming you have a little physics background. There are two coils in the device, one transmitter and one receiver. You pass an oscillating electrical signal through the first coil and it creates a magnetic field that is oscillating all around the device. This oscillating magnetic field causes electrons in the ground to oscillate back and forth, but how much they oscillate will depend on how electrically conductive the material is. These oscillating electrons in the ground will themselves create a (much smaller) secondary magnetic field, which can be detected on the receiver coil on the instrument. So you basically walk with this thing and make a map of electrical conductivity variations in the subsurface.
System costs about $40k. Very useful for finding archeological things, buried debris, mapping contaminated water (salty water is more electrically conductive, for example), for gravel exploration, fertilizer distribution mapping in agriculture, soil moisture content, and sometimes for utility detection (if the utility is conductive).
The reason I ask is that my wife and I are scientists (I'm remote sensing, she's a biogeochemist), and we've collaborated on a number of projects where we have to do very involved field sampling, digging or drilling of cores, etc.. and the time it takes to get that data just massively limits what we can do or say.
So I'm interested in all things remote sensing when it comes to sub-surface. We're interested in anything that can speed up/ scale/ increase the density of the data we work with.