Effective electrical resistivity tomography surveys for environmental monitoring

The paper emphasizes the need for careful design of ERT surveys for reliable, high resolution imaging of subsurface processes. In this paper we discuss the use of the resolution radius matrix to compare the resolution achieved with different configurations of electrodes. The most critical factor in designing ERT surveys is the aspect ratio of the image plane. The aspect ratio is the length of the boreholes fitted with electrodes divided by the separation of the boreholes. With a large aspect ratios the resolution in the center of the image plane is about the same as the resolution near the boreholes. As the aspect ratio decreases the resolution drops in the center of the image plane but stays roughly the same near the edges. Data collected with ratios less than about 1.5:1 have an unacceptably low resolution in the center of the images. This problem can be partly offset by including surface electrodes as well as borehole electrodes. The resolution does appear to improve with increased numbers of electrodes. However, using large numbers of electrodes with large aspect ratios tends to produce only limited improvements in resolution while greatly increasing the data acquisition time.