Field-scale estimation of soil properties from spectral induced polarization tomography

Abstract

Estimates of soil properties such as Cation Exchange Capacity (CEC), water content, grain size characteristics, and permeability are important in geotechnical engineering, water resources, and agriculture. We develop a nonintrusive approach to estimate these properties in the field using spectral induced polarization (SIP) tomography. This geophysical method provides information about the frequency dependence of the complex electrical conductivity of porous media. Using 18 soil samples collected from a Bordeaux vineyard, we first conducted a laboratory study using SIP over the frequency range 10 mHz-45 kHz. The laboratory data were used to confirm the accuracy of a recently developed dynamic Stern layer petrophysical model. The results are consistent with published values from previous works using soils. A comparison was made by comparing the field complex conductivity spectra and the experimental data at two locations where core samples were obtained. The model was then used in concert with field data to image the spatial distribution of CEC, water content, permeability, and mean grain size along a vineyard transect. For clay and sandy textures found in the field, measured and estimated CEC agree rather well (from 6 to 40% discrepancy). Our approach provides an efficient way to estimate important soil properties in a non-invasive manner, in high resolution, and over field-relevant scales of the critical zone of the Earth.

Near‐surface geophysical imaging of a thermokarst pond in the discontinuous permafrost zone in Nunavik (Québec), Canada

“…However, the quality of the SIPT data above 25 Hz was low to apply the petrophysical models recently developed by 22,[39][40][41]64 and derive quantitative estimation of water content, permeability or cation exchange capacity. This highlights the need to adapt the method of filtering and 2D inversion of the data, especially to be able to accommodate induction effects and, doing so, keep a larger amount of data.…”

“…In this way, the in-phase component σ 0 reflects the contribution of the ionic conduction within the pore space or at the grain surface, while the imaginary part σ 0 0 reflects the polarization effect at the grain surface. 40…”

“…The method for the inversion of the SIPT data was adapted from the one of. 40 See this reference for a more detailed description. The real and imaginary parts of the complex conductivity were inverted separately as a function of frequency, using the software ResIPy.…”

“…However, due to the frozen conditions and the severe filtering strategy used for the SIPT data, no quantitative estimation of the subsurface hydrological properties could be done with the petrophysical relations proposed in the literature for unfrozen conditions. [39][40][41]64 In the future, the use of the mechanistic relations developed by 22 for frozen condition would be an interesting step forward.…”

“…This ability has been recently used to derive textural and hydrogeological information about the subsurface, using petrophysical relations developed on a fundamental basis. [39][40][41] We propose here to extend the scope of SIP tomography (SIPT) to permafrost terrains for delineating frozen areas and detecting fine-grained, frost-susceptible sediments. Indeed, the presence of ice within a porous medium induces several specific polarization mechanisms.…”