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There is a high demand for high detection accuracy and resolution with respect to anomalous bodies due to the increased development of underground spaces. This study focused on the weighted inversion of observed data from individual array type electrical resistivity tomography (ERT), and developed an improved method of applying a data weighing function to the geoelectrical inversion procedure. In this method, the weighting factor as an observed data weighting term was introduced into the objective function. For individual arrays, the sensitivity decreases with increasing electrode interval. Therefore, the Jacobian matrices were computed for the observed data of individual arrays to determine the value of the weighting factor, and the weighting factor was calculated automatically during inversion. In this work, 2D combined inversion of ERT data from four-electrode Alfa-type arrays is examined. The effectiveness of the weighted inversion method was demonstrated using various synthetic and real data examples. The results indicated that the inversion method based on observed data weighted function could improve the contribution of observed data with depth information to the objective function. It has been proven that the combined weighted inversion method could be a feasible tool for improving the accuracies of positioning and resolution while imaging deep anomalous bodies in the subsurface. [ABSTRACT FROM AUTHOR]

Metros are mass rapid-transit systems that have helped solve commuting problems for residents of metropolises throughout the world. However, adverse geological structures, leading to problem such as water inrush and mud gushing, pose a major threat to metro construction. Geophysical survey techniques provide quick and relatively inexpensive ways to detect adverse geological structures ahead of the tunnel face. Left line of the R3 metro tunnel in Qingdao, China will pass an aquifer sand layer under the Wolong River. To map the geological conditions below the river, we proposed a comprehensive prospecting method that would combine the merits of surface electrical resistivity imaging (S-ERT), seismic ahead prospecting, and tunnel-face and borehole electrical resistivity imaging (TBERI). The prospecting scheme was effectively revealed in a numerical model analysis, in which the stratum distribution was reconstructed using S-ERT. Field tests validated the synthetic results. The ahead prospecting scheme was able to reconstruct the distribution of an aquifer sand layer. Based on the results obtained, we believe that, the proposed scheme could play an important role in metro tunnel construction. [ABSTRACT FROM AUTHOR]