Mapping depth-to-clay using fitted multiple depth response curves of a proximal EMI sensor

• Published in: Geoderma Vol. 162; no. 1; pp. 151 - 158
• Main Authors: Saey, Timothy, Van Meirvenne, Marc, De Smedt, Philippe, Cockx, Liesbet, Meerschman, Eef, Islam, Mohammad Monirul, Meeuws, Fun
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 15.04.2011; Elsevier
• Subjects: Agronomy. Soil science and plant productions; Arrays; Belgium; Biological and medical sciences; Coefficients; Coiling; Deposition; Depth inversion; Depth modelling; Depth response functions; DUALEM-21S; Earth sciences; Earth, ocean, space; Electromagnetic induction; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; Geophysics: general, magnetic, electric and thermic methods and properties; Imaging; Internal geophysics; Loess; Mathematical models; Maxwell's equations; Paleolandscape; Soil map; Soils; Surficial geology; Belgium; Europe; Western Europe; Electromagnetic induction; Depth modelling; Paleolandscape; DUALEM-21S; Depth response functions; Soil map; Depth inversion; Weichselian; loess; two-layer models; variograms; measurement sensor; Modeling; clay; electromagnetic induction; instruments; Cenozoic; soils; electrical resistivity; clastic rocks; models; Quaternary; Tertiary; cartography; sedimentary rocks; upper Pleistocene; depth; prediction; soils maps; Phanerozoic; electrical conductivity; Pleistocene
• ISSN: 0016-7061; 1872-6259
• DOI: 10.1016/j.geoderma.2011.01.015

As an alternative for the depth response approximations based on the theoretical Maxwell's equations, a procedure was proposed to fit depth response curves for different coil configurations. A 39 ha study area was selected in the Belgian loess belt, where loess material was situated on a Tertiary substrate. A survey with the DUALEM-21S electromagnetic induction instrument was carried out to map the depth-to-clay ( z clay). The depth response curves were fitted both for the vertical and perpendicular coil configurations using 85 depth observations of z clay. The resulting depth response curves R( z clay) were: R p, s ( z clay ) = 0 .8135 ⋅ e -1 .4131 ⋅ z clay s for the perpendicular coil configuration (with s as the intercoil spacing) and R v, s ( z clay ) = 0 .9802 ⋅ e -0 .8102 ⋅ z clay s for the vertical coil configuration. A set of 4 equations based on the developed depth response functions was used to model z clay at each of the 209 400 measurement points. These z clay predictions were validated using geo-electrical imaging. With two multi-electrode resistivity arrays, z clay was 1D-inverted at 95 locations along two transects, assuming a two-layered soil system. A coefficient of determination of 0.95, with a root mean-squared estimation error of 0.22 m, was found between the predicted and 1D-inverted depths. This procedure allowed the accurate 3D-reconstruction of the paleolandscape before the deposition of the loess. Flow lines were modelled on this paleosurface, revealing past or subsurface stream patterns not visible on the present relief. ► A procedure was proposed to fit depth response curves for different coil configurations. ► A survey with the DUALEM-21S electromagnetic induction instrument was carried out to map the depth-to-clay. ► The depth-to-clay predictions were validated using geo-electrical imaging. ► This procedure allowed the accurate 3D-reconstruction of the paleolandscape.