Resolving Fine -Scale Hydrological Features In Electrical Resistivity Tomography Images

The resolution of electrical resistivity tomography surveys is limited by the data quantity, data<br>quality, and the survey configuration (electrode count, spacing, borehole separation). Inevitably, we are<br>forced to interpret data from regions containing substantial variability at a scale much finer than the<br>resolution of the method. To understand the effects of these fine-scale structures on interpretation, data<br>were created by converting hydrological parameters from high-resolution flow simulations to electrical<br>conductivity. The data were then forward modeled using fine, high-resolution meshes and inverted using<br>the same coarse meshes that were used for normal inversion of field data. The modeling simulated<br>earlier experiments from the Sandia-Tech Vadose Zone Facility. In those experiments, geophysical<br>imaging techniques were employed to monitor the unsaturated flow of potable water and transport of a<br>salt tracer through fluvial sediments.<br>Comparing images to the original hydrological models shows that the images are smoother and<br>much of the fine detail is lost but major features such as the center of a zone of infiltrating water are<br>correctly represented. However, comparing images of synthetic data with images from previous field<br>studies shows that the hydrological models themselves poorly represent the original field conditions.<br>The synthetic models show narrower zones of infiltration with much higher saturation than the field<br>case.