FDTD simulation of GPR with a realistic multi-pole debye description of lossy and dispersive media

Simulation of electromagnetic wave propagation in lossy and dispersive media requires a realistic description of the electrical and dielectric media parameters. We measured the complex dielectric permittivity of fine sand and silty clay in the GPR frequency range using the coaxial transmission line technique. We inverted the data with single- and multi-pole Debye models and a constant dc conductivity term. FDTD simulations were carried out on the basis of the different Debye pole media descriptions and compared to simulations with constant electromagnetic parameters. We show that for soils with a fine-grained texture, the frequency-dependence of the real part of the dielectric permittivity cannot be neglected. Therefore a multi-pole Debye description of the medium must be used for simulations: one Debye pole describing the relaxation of free water in the lower GHz region and two poles describing the bound water and interfacial relaxations in the upper MHz region.