Abstract
Abstract. A substantial interpretation of electromagnetic induction (EMI) measurements requires quantifying optimal model parameters and uncertainty of a nonlinear inverse problem. For this purpose, an adaptive Bayesian Markov chain Monte Carlo (MCMC) algorithm is used to assess multi-orientation and multi-offset EMI measurements in an agriculture field with non-saline and saline soil. In MCMC the posterior distribution is computed using Bayes' rule. The electromagnetic forward model based on the full solution of Maxwell's equations was used to simulate the apparent electrical conductivity measured with the configurations of EMI instrument, the CMD Mini-Explorer. Uncertainty in the parameters for the three-layered earth model are investigated by using synthetic data. Our results show that in the scenario of non-saline soil, the parameters of layer thickness as compared to layers electrical conductivity are not very informative and are therefore difficult to resolve. Application of the proposed MCMC-based inversion to field measurements in a drip irrigation system demonstrates that the parameters of the model can be well estimated for the saline soil as compared to the non-saline soil, and provides useful insight about parameter uncertainty for the assessment of the model outputs.
Highlights
Electromagnetic induction (EMI) with low frequency is a powerful tool to map the hydrological processes in the vadose zone due to the sensitivity to water content and soil salinity (Robinson et al, 2009)
Ten pits were dug along the same transect and in each pit the bulk electrical conductivity σb profile was measured at 15 locations within a depth range of 0.05–1.5 m via 5TE capacitance sensors (Decagon Devices, Pullman, USA)
Ten pits were dug along the same transect and in each pit the vertical σb profile was measured at 15 locations within a depth range of 0.05–1.5 m via 5TE capacitance sensors (Decagon Devices, Pullman, USA). 5TE and EMI measurements were carried out on the same day 8 h after the drip irrigation system was stopped, so that the soil moisture concentration below the drippers is avoided, and enough time is given for the reduction of soil moisture impact due to root water uptake, evaporation and infiltration (Jadoon et al, 2015)
Summary
Electromagnetic induction (EMI) with low frequency is a powerful tool to map the hydrological processes in the vadose zone due to the sensitivity to water content and soil salinity (Robinson et al, 2009). The EMI instrument is used to measure soil apparent electrical conductivity (ECa), providing distribution of averaged electrical conductivity over a particular depth range. The depth of investigation of ECa depends on the coil spacing, the coil orientation, and the frequency of the energizing field. Mester et al (2011) reported that in the low induction number condition, the coil orientation, offset, and frequency have major, moderate and minor effects on the penetration depth, respectively. Salinity, and texture cannot be directly observed with EMI measurements. In non-saline soils, cation exchange capacity, and soil moisture and texture are factors responsible for ECa variations (Rhoades et al, 1976; Sudduth et al, 2003), whereas
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