In-situ broadband soil measurements: Dielectric and magnetic properties

This paper presents an in-situ method for measuring both electric and magnetic properties of Hawaiian volcanic soil for GPR applications in a broad frequency range from 50 MHz to 1GHz. For the in-situ probe, we combined two monopole antennas with parasitic elements into one piece to achieve reflection (S₁₁) and transmission (S₂₁) measurements simultaneously. Finally, the in-situ probe has a shape of a multi-conductor TEM transmission line, which consists of five conducting rods, two ground plates and two coaxial feed connectors. In a typical measurement the in-situ probe is connected to a two ports vector network analyzer and system calibration is then performed to characterize the sample free device. The calibration is based on measurements of the S-parameters for sample free and sample loaded devices. A unique post processing algorithm has been developed to extract accurate constitutive parameters (ε* μ*) from the scattering parameters (S₁₁, S₂₁) of the soil probe, which will be discussed in this paper. The prototype in-situ soil probe and post processing algorithm were also tested by both numerical simulation and actual soils in volcanic red soil. The simulation results showed around 1 % of error over the operational frequencies between 100 MHz and 800 MHz. Actual measurement results conducted by the in-situ probe and developed algorithms were in very good agreement with those obtained by a laboratory method. Simulation and actual measurement data will be presented in this paper.