An advanced process for evaluating a linear dielectric constant–bulk electrical conductivity model using a capacitance sensor in field conditions

The Hilhorst model was used to convert bulk electrical conductivity (sigma(b)) to pore water electrical conductivity (sigma(p)) under laboratory conditions by using the linear relationship between the soil dielectric constant (epsilon(b)) and sigma(b). In the present study, applying the linear relationship epsilon(b)-sigma(b) to data obtained from field capacitance sensors resulted in strong positive autocorrelations between the residuals of that regression. We were able to derive an accurate offset of the relationship epsilon(b)-sigma(b) and to estimate the evolution of sigma(p) over time by including a stochastic component to the linear model, rearranging it to a time-varying dynamic linear model (DLM), and using Kalman filtering and smoothing. The offset proved to vary for each depth in the same soil profile. A reason for this might be the changes in soil temperature along the soil profile.