Electrical resistivity tomography# 2D ERT modeling and inversion 2D ERT modeling and inversion ERT field data with topography ERT field data with topography 2D FEM modelling on two-layer example 2D FEM modelling on two-layer example Geoelectrics in 2.5D Geoelectrics in 2.5D Four-point sensitivities Four-point sensitivities 2D crosshole ERT inversion 2D crosshole ERT inversion 3D surface ERT inversion 3D surface ERT inversion 3D crosshole ERT inversion 3D crosshole ERT inversion 3D modeling in a closed geometry 3D modeling in a closed geometry