Development and validation of a low-cost direct current resistivity meter for humanitarian geophysics applications

Abstract

Insufficient access to safe drinking water is one of the most challenging global humanitarian issues. The development of low-cost microcontrollers and the widespread availability of cheap electronic components raise the possibility of developing and using low-cost geophysical instrumentation with open-source designs and software solutions to circumvent geophysical instrumentation capital cost issues. To these ends, we alter an existing low-cost direct current (DC) resistivity meter design and develop an optional modular Raspberry Pi data-logging system to improve the unit’s functionality and usability and to ensure data integrity. Numerical modeling and physical testing demonstrate that the system is more robust than previously published low-cost designs and works in a more diverse range of geologic scenarios — especially conductive environments. Our instrument was tested in a Geoscientists Without Borders project jointly run between researchers from Colorado School of Mines (CSM) and Université d’Abomey-Calavi (UAC), Cotonou, Benin. A key project component involved CSM and UAC students constructing and validating two low-cost DC resistivity meters and then using these instruments for fieldwork aimed at better characterizing and monitoring the health of a local aquifer used as a groundwater source for communities in the Cotonou region. The low-cost instruments were successfully used alongside a commercial resistivity meter to acquire data for 2D inversion of aquifer hydrostratigraphy, indicating the presence of a clay-sand contact. The costs of the redesigned instrument and data logger, respectively, are $177 and $108 (in 2021 USD) with future cost reductions possible, which are fractions of the price of commercial resistivity meters.