EA-ERT: a new ensemble approach to convert time-lapse ERT data to soil water content

TL;DR

EA-ERT is an innovative ensemble method that improves the conversion of time-lapse ERT data into soil water content estimates, enhancing robustness and uncertainty evaluation in subsurface hydrological studies.

Contribution

The paper introduces EA-ERT, a novel ensemble approach that integrates multiple ERT inversions with in-situ data to estimate soil water content and its uncertainty.

Findings

Good fit with in-situ measurements

Identified high-uncertainty areas

Robust, automatable conversion method

Abstract

Electrical Resistivity Tomography (ERT) is increasingly used to study subsurface hydrological processes. It shows promising potential for estimating soil water content, a key but challenging property to quantify. However, converting the resistivity signal into water content is complex. This encourages developing approaches to increase the robustness of estimates while facilitating the evaluation of uncertainties. In this paper, we propose an innovative method, called the Ensemble Approach ERT (EA-ERT), to build an ensemble model of electrical resistivity calibrated from field data and then to convert it into a spatial distribution of water content. This approach combines time-lapse ERT data with point-based in-situ soil water content measurements. It enables i) circumventing inversion parameter choice by evaluating the performance of a large number of models, ii) estimating uncertainty in the final model by calculating the coefficient of variation among the models composing the ensemble, and iii) converting electrical resistivity models to water content. The method was tested at two dissimilar field sites in southern France. For each site, an ensemble model, built from multiple inversions, was selected and converted into soil water content. The calculated values showed a good fit, with small differences compared to in-situ measurements. Areas of high uncertainty were identified, providing complementary information to the more classical indicators from the inversion code. EA-ERT provides a robust and automatable method to convert ERT data to related parameters, contributing to improved monitoring and understanding processes in the subsurface.