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Geophysical Support
Electromagnetics
Electromagnetic
methods measure changes in the electrical conductivity of the subsurface. The two factors
that are most likely to cause a change in conductivity are variations in water content,
and the presence of metallic objects. Variations in water content reflect porosity
and fluid saturation that can be related to variations in water table and the type
of rocks and soils in the subsurface. Electromagnetic measurements provide some overlapping
information with magnetic mapping, and also provide information on the conductivity
variations in the subsurface. However, it is not always possible to determine the type
of source from electromagnetic measurements alone, and magnetic measurements may be
used to isolate the metallic objects from the conductivity variations caused by non-metallic
objects.