Fig. 1. Schematic of the M-layer model. Rx and Tx represent the receiver and transmitter coil of the noninvasive electromagnetic ground conductivity meter; t is the thickness of the soil layer; is the apparent electrical conductivity; ₀ is the apparent electrical conductivity of free space; µ is the magnetic permeability; µ₀ is the magnetic permeability of free space; h = height; and M is the number of layers including the semi-infinite layer at the bottom.