Methods for field measurement of electrical parameters of soil as functions of frequency

Abstract

In this article, the application of four-electrode and two-electrode arrays to measure electrical parameters of soil as functions of frequency is investigated and its feasibility is evaluated by simulations and measurements. First, the experimental arrays are simulated using finite element method to solve a rigorous electromagnetic problem. New geometric factors are presented, which yield correct estimates of resistivity and permittivity even for reduced spacing. Formulas are proposed for calculating the geometric factors. Then, a series of case studies is carried out considering different soil representations, geometric parameters and excitation frequencies. It was found that increasing excitation frequency and distance between electrodes decreases accuracy. However, resistivity and permittivity of soil can be determined for frequencies up to 2 MHz when using reduced spacing. For the four-electrode array, a discrepancy of less than 3% between estimate and reference is obtained when using distance between electrodes less than 0.5 m. Next, measurements using four and two electrode methods were performed, and it was found that the four-electrode method is the most suitable for measuring soil parameters, given that it was the one that provided consistent results. An analytical equation was also proposed to represent the electrical parameters measured for this case.