Journal cover Journal topic
Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/hess-2017-288
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
30 May 2017
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Hydrology and Earth System Sciences (HESS).
Calibrating electromagnetic induction conductivities with time-domain reflectometry measurements
Giovanna Dragonetti1, Alessandro Comegna2, Ali Ajeel2, Gian Piero Deidda3, Nicola Lamaddalena1, Giuseppe Rodriguez4, Giulio Vignoli3,5, and Antonio Coppola2 1Mediterranean Agronomic Institute (MAIB) – Land & Water Department, Valenzano (Bari), Italy
2University of Basilicata, School of Agricultural, Forestry and Environmental Sciences – Hydraulics and Hydrology Division, Potenza, Italy
3Dipartimento di Ingegneria Civile, Ambientale e Architettura, Università di Cagliari, Cagliari, Italy
4Dipartimento di Mate matica e Informatica, Università di Cagliari, Cagliari, Italy
5Groundwater and Quaternary Geology Mapping Department, Geological Survey of Denmark and Greenland, Aarhus, Denmark
Abstract. This paper deals with the issue of monitoring the horizontal and vertical distribution of bulk electrical conductivity, σb, in the soil root zone by using Electromagnetic Induction (EMI) sensors under different water and salinity conditions. In order to deduce the actual distribution of depth-specific σb from EMI depth-weighted apparent electrical conductivity (ECa) measurements, we inverted the signal by using a regularized 1D inversion procedure designed to manage nonlinear multiple EMI-depth responses. The inversion technique is based on the coupling of the damped Gauss-Newton method with truncated generalized singular value decomposition (TGSVD). The ill-posedness of the EMI data inversion is addressed by using a sharp stabilizer term in the objective function. This specific stabilizer promotes the reconstruction of blocky targets, thereby contributing to enhance the spatial resolution of the EMI reconstruction. Time-Domain Reflectometry (TDR) data are used as ground-truth data for calibration of the inversion results. An experimental field was divided into four transects 30 m long and 2.8 m wide, cultivated with green bean and irrigated with water at two different salinity levels and using two different irrigation volumes, to induce different salinity and water contents within the soil profile. For each transect, 26 regularly spaced monitoring sites (1 m apart) were selected for soil measurements using a Geonics EM-38 and a Tektronix Reflectometer. Despite the original discrepancies in the EMI and TDR data, we found a significantly high correlation of the means and standard deviations of the two data series, especially after filtering the TDR data. Based on these findings, the paper introduces a novel methodology to calibrate EMI-based electrical conductivity via TDR direct measurements by simply using the statistics of the two data series.

Citation: Dragonetti, G., Comegna, A., Ajeel, A., Deidda, G. P., Lamaddalena, N., Rodriguez, G., Vignoli, G., and Coppola, A.: Calibrating electromagnetic induction conductivities with time-domain reflectometry measurements, Hydrol. Earth Syst. Sci. Discuss., https://doi.org/10.5194/hess-2017-288, in review, 2017.
Giovanna Dragonetti et al.
Giovanna Dragonetti et al.
Giovanna Dragonetti et al.

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Short summary
The paper aims to infer the bulk electrical conductivity distribution in the root zone from EMI readings. TDR measurements were used as ground-truth data to evaluate the goodness of the estimations by EMI inversion. The approach is based on the mean and standard deviation of the EMI and TDR series. It looks for the physical reasons for the differences between EMI- and TDR-based electrical conductivity and provides a correction of the bias based on the statistical sources of the discrepancies.
The paper aims to infer the bulk electrical conductivity distribution in the root zone from EMI...
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