Mitigation of installation-related effects for small-scale borehole-to-surface ERT

Small-scale resistivity inhomogeneities can result from the local distribution of water and nutrient uptake plants. Measuring small-scale Electrical Resistivity Tomography (ERT) in field comes with a set particularities, especially when including borehole electrodes for better resolution depth. We apply borehole-to-surface ERT over palaeochannel. Combining surface detailed profiles along measurement line allows delineation finer layering within coarser lithology. Our setup includes electrode tool 20 ring electrodes, electrically coupled to ground via conductive mud. Two main points are addressed this publication: (1) In field, we by filling cavities around soil mud, i.e., need account unknown inversion. If not incorporated, mud has considerable influence on resistivities close tool, but also region electrodes. Consequently, alongside 3D inversion scheme representing Complete Electrode Model (CEM), include as separate uncoupled region. model geometry layer do allow an rest model. (2) Due small distances overall nature array, depth installation must be known accurately However, it is easy measure required accuracy, due roughness, e.g., weathered loose at or vegetation. investigate tilted optimise angle before inverting resistivities. An accurate knowledge positions crucial reliable precise result. The establish coordinate system surface, φ describing direction top view. sensitive plane (in-plane) defined x-z cutting through = 0° 180°. A tilting vertical described θ. manifests increased misfit between data both sides use difference angle. true found searching minimum objective function, goodness model, while assuming different depths each see functionwhich attributed correct range, shown synthetic study. Through our optimisations, determine θ, accuracy 2° 3° few centimetres, depending partially subsurface resistivities, optimisation works mainly predominantly horizontally layered soils. directions out (out-of-plane) projected onto plane, since out-of-plane tilt negligible data. After optimisation,