f Impedance Estimation from Magnetic Field Measurement

In the VLF method, the ratio between the vertical and the horizontal magnetic field (the tippet) are measured to detect localized changes in electrical conductivity contrasts. The measurements themselves do not give a direct estimation of electrical conductivity contrasts. The tipper is merely an indicator of the presence of a conductivity contrast by exhibiting a well-defined response across a contact and decaying on either side.