A framework for simulation and inversion in electromagnetics

Abstract

Simulations and inversions of electromagnetic geophysical data are paramount for discerning meaningful information about the subsurface from these data. Depending on the nature of the source electromagnetic experiments may be classified as time-domain or frequency-domain. Multiple heterogeneous and sometimes anisotropic physical properties, including electrical conductivity and magnetic permeability, may need be considered in a simulation. Depending on what one wants to accomplish in an inversion, the parameters which one inverts for may be a voxel-based description of the earth or some parametric representation that must be mapped onto a simulation mesh. Each of these permutations of the electromagnetic problem has implications in a numerical implementation of the forward simulation as well as in the computation of the sensitivities, which are required when considering gradient-based inversions. This paper proposes a framework for organizing and implementing electromagnetic simulations and gradient-based inversions in a modular, extensible fashion. We take an object-oriented approach for defining and organizing each of the necessary elements in an electromagnetic simulation, including: the physical properties, sources, formulation of the discrete problem to be solved, the resulting fields and fluxes, and receivers used to sample to the electromagnetic responses. A corresponding implementation is provided as part of the open source simulation and parameter estimation project SimPEG (http://simpeg.xyz). The application of the framework is demonstrated through two synthetic examples and one field example

EMagPy: Open-source standalone software for processing, forward modeling and inversion of electromagnetic induction data

“…(Auken et al, 2015), or EM4Soil (Monteiro Santos, 2004). In addition, several open source software codes exist, such as the Matlab-based open-source GUI for EMI data, FEMIC (Elwaseif et al, 2017), or the Python-based open-source codes SimPEG (Heagy et al, 2017) and pyGIMLI (Rücker et al 2017). Open-source software has several benefits over commercial software, for instance it has better reproducibility, it is free and allows the user to interrogate the source code and, where necessary, adapt and customize for their own application.…”

Exploring the Model Space of Airborne Electromagnetic Data to Delineate Large‐Scale Structure and Heterogeneity Within an Aquifer System

“…To find an inversion model, , which fit the observed AEM data and favored prior knowledge in the regularization function, , we used SimPEG, a Python‐based open‐source geophysics software package (Cockett et al., 2015; Heagy et al., 2017) to minimize the following objective function, : …”

3D electromagnetic modelling and inversion: a case for open source

“…SimPEG is an open-source framework and set of tools for simulation and gradient-based parameter estimation in geophysics. It includes finite volume simulations and inversion routines for a variety of geophysical applications including potential fields, vadose zone flow, DC resistivity, induced polarization, self-potential and electromagnetics (Cockett et al, 2015;Kang and Oldenburg, 2016;Heagy et al, 2017;Miller et al, 2017;Cockett et al, 2018;Miller et al, 2018;Witter et al, 2018). Simulations may be performed on several different mesh types, including cylindrically symmetric meshes, 3D tensor meshes and OcTree meshes.…”