Articles | Volume 21, issue 1
Hydrol. Earth Syst. Sci., 21, 495–513, 2017
Hydrol. Earth Syst. Sci., 21, 495–513, 2017

Research article 26 Jan 2017

Research article | 26 Jan 2017

Repeated electromagnetic induction measurements for mapping soil moisture at the field scale: validation with data from a wireless soil moisture monitoring network

Edoardo Martini1, Ulrike Werban1, Steffen Zacharias1, Marco Pohle1, Peter Dietrich1,2, and Ute Wollschläger3 Edoardo Martini et al.
  • 1Dept. Monitoring and Exploration Technologies, UFZ – Helmholtz Centre for Environmental Research, Permoserstraße 15, 04318 Leipzig, Germany
  • 2Centre for Applied Geoscience, University of Tübingen, Hölderlinstraße 12, 72074 Tübingen, Germany
  • 3Dept. Soil Physics, UFZ – Helmholtz Centre for Environmental Research, Theodor-Lieser-Straße 4, 06120 Halle (Saale), Germany

Abstract. Electromagnetic induction (EMI) measurements are widely used for soil mapping, as they allow fast and relatively low-cost surveys of soil apparent electrical conductivity (ECa). Although the use of non-invasive EMI for imaging spatial soil properties is very attractive, the dependence of ECa on several factors challenges any interpretation with respect to individual soil properties or states such as soil moisture (θ). The major aim of this study was to further investigate the potential of repeated EMI measurements to map θ, with particular focus on the temporal variability of the spatial patterns of ECa and θ. To this end, we compared repeated EMI measurements with high-resolution θ data from a wireless soil moisture and soil temperature monitoring network for an extensively managed hillslope area for which soil properties and θ dynamics are known. For the investigated site, (i) ECa showed small temporal variations whereas θ varied from very dry to almost saturation, (ii) temporal changes of the spatial pattern of ECa differed from those of the spatial pattern of θ, and (iii) the ECa–θ relationship varied with time. Results suggest that (i) depending upon site characteristics, stable soil properties can be the major control of ECa measured with EMI, and (ii) for soils with low clay content, the influence of θ on ECa may be confounded by changes of the electrical conductivity of the soil solution. Further, this study discusses the complex interplay between factors controlling ECa and θ, and the use of EMI-based ECa data with respect to hydrological applications.

Short summary
With a process-based interpretation of electromagnetic induction measurements, we discussed the potential and limitations of such a method for soil moisture mapping. Results will help clarify the complex and time-varying effect of stable soil properties and dynamic state variables on the physical parameters measured, with implications for future studies. We highlighted the importance of time-series data and the need for a multidisciplinary approach for proper interpretation.