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Development and Validation of a Low-cost DC Resistivity Meter for Humanitarian Geophysics Applications

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 electronics 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 DC resistivity meter design and develop an optional modular Raspberry Pi data-logging system to improve the unit's functionality, usability and to ensure data integrity. Numerical modeling and physical testing demonstrates that the system is more robust than previously published low-cost designs and works in a more diverse range of geological scenarios - especially conductive environments. Our instrument was tested in a Geoscientists Without Borders (GWB) project jointly run between researchers from Colorado School of Mines (CSM) and Universit矤'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 cost 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.