Impact of Soil Magnetic Properties on Moisture Content Prediction Using TDR

摘要

It is generally assumed that soil relative magnetic permeability is one for the prediction of soil moisture content using time domain reflectrometry (TDR) technique. However, the presence of iron and iron-bearing minerals may result in significant losses due to ferromagnetic relaxation processes. As the magnetic permeability is a multiplier in the electromagnetic wave propagation equation, ignoring it can result in significant errors of estimating travel time, propagation velocity, and dielectric permittivity of the soil medium. Attributing the velocity, attenuation, and frequency dependence to electrical properties alone will also result in incorrect estimation of soil moisture content when magnetic properties are different from free space. Therefore, this study is aimed at evaluating the extent of soil magnetic properties variations. The results are discussed in view of their impact on the prediction of soil moisture. The results demonstrated that ignoring soil magnetic effect due to iron and iron-bearing minerals causes significant errors in calculating wave propagation parameters. Calculated errors are 21.88, 3.38, 3.16, and 3.42 % for propagation constant, wave velocity, wavelength, and intrinsic impedance, respectively. This in turn highlights the importance of including the magnetic effect of the soil in the wave propagation calculations applied in the TDR data analysis methodologies. In addition, the calculated apparent dielectric constant is less than the actual one by 7.172 % leading to reduction in the predicted moisture content by about 3.64 % in soils using TDR techniques. However, since soil moisture content is a fundamental property in predicting the pollutant migration in soils, then predicted pollutant migration front will be underestimated.