Magnetic resonance sounding
MRS is also known as NMR (nuclear magnetic resonance) and is a geophysical method that uses the magnetic spin moment of water to directly measure how much water is in the subsurface and how easily it moves in the subsoil.
By applying an electric field that is targeted to excite the water molecules from their current orientation along the earths magnetic field and then measuring the decay signal from these molecules as they again orientate themselves to the earths magnetic field it is possible to detect the water directly.
Making MRS measurements can be useful whenever information about water content in the subsurface is desired. Some examples of applications are:
Finding the best site for making a drinking water well
Mapping groundwater and groundwater flow
Determing optimal filter depth before making a drilling
Mapping geological layers that can not be resolved with other geophysical methods. Mapping weakness zones in mountains.
Many other application are possible, whenever information about the water is needed directly or it is used as an indicator to disolve other geological information.
The MRS method is sensitive to cultural electromagnetic noise and for this reason it is not possible to make these measurements everywhere, but where they can be made they are highly useful.