Open-source direct current resistivity software development for groundwater applications

Abstract:

The open-source software development we present was motivated by our Geoscientists Without Borders (GWB) Project, which builds capability for the community in Myanmar to acquire and interpret direct current (DC) resistivity data to find groundwater resources. To facilitate this capability, we improved the DC portion of the existing open-source geophysical software module, SimPEG-DC. Our main goal was to generate 1D and 2D inversion software that local engineers and students could readily run within a reasonable amount of time (less than 5 minutes) using their own computers. Four main improvements made within the SimPEG-DC package were made: (a) the development of the 1D layered-earth solution, (b) the implementation of Quadtree and Octree meshes, and (c) a novel projection methodology which reduces any electrode configuration to unique pole-pole source-receiver pairs within a DC survey for forward modelling and sensitivity calculations. To increase the accessibility of the improved SimPEG-DC package for the community in Myanmar, we developed 8 “apps” using Jupyter Notebooks that can be used to promote understanding of the fundamental physics of the DC method as well as to invert various types of field DC data from 1D vertical soundings to 2D arrays. To highlight the impact of our improvements, we applied 1D, 2D, and 3D inversions to field DC data sets obtained at Kawpiphtaw Village in Mon State, Myanmar, and interpreted hydrostratigraphy of the region. Through rapid development using feedback between a local team and the open-source SimPEG community, both the 2D and 3D codes' runtime and memory usage were reduced by at least a factor of 10, compared to the previous implementation. This allowed local users to run both 2D and 3D inversions within several minutes. The developed apps, which are publicly accessible through our github repository: https://github.com/simpeg-research/gwb-dc-inversions, have been actively used by the local Myanmar community to interpret the field DC data sets acquired in 23 local villages to find productive aquifers.