Three Step Depth Focussed Inversion as a Tool to Resolve Small Resistivity Contrasts by ERT

In more recent times Electrical Resistivity Tomography (ERT) has become a valuable tool for many<br>environmental research themes. Within these topics the resistivity contrasts of the different layers and<br>zones are of importance, i.e. sand, clay, water salinity and preferential infiltration pathways are quite<br>small. Inclusions with such small resistivity contrasts to the surrounding are difficult to resolve by ERT<br>inversion and typically the following problems occur: 1.) the true resistivity contrasts are underestimated<br>2.) the size of the anomalous zone is overestimated 4.) fake anomalies arise beside and between the true<br>anomalous zones. 4.) surface heterogeneities infer fake anomalies into the subsurface.