Uses electromagnetic radiation to detect subsurface features. Operates generally with frequencies between 10-1000 MHz. Depth of penetration vary between less than a meter to a hundred meters. Depth of penetration is related to the type of material and not the precision of the instrument.
Velocity is dependent on the electrical conductivity and dielectric constant.
Velocity increases with an increase in porosity. It decreases with addition of water in material. Fractures in rocks have a limited effect on propagation of electromagnetic energy. Reducing the frequency too low, may cause the waves to diffuse. The change in wavelength effects the frequency of the wave.