Compensation Technique to Minimize Capacitive Cable Coupling Effects in Multi-channel IP Systems

The Spectral Induced Polarization (SIP) method measures the frequency-dependent electrical resistivity of rocks and sediments. Standard multi-channel instruments fail if ac signals of much more than a few Hertz and cable length of hundreds of meters are used. Capacitive couplings between the individual wires of the multi-core cable and between these wires and the soil are the main reasons for technical caused systematic errors. But reliable resistivities data for high frequencies are essential to characterize soils with short relaxation times. We have tested a new compensation technique, which eliminates effectively the effects of capacitive coupling between current cable and the earth (C-E coupling). This technique is based on an active shielding of the current cable. Hereby the useful frequency range could expand by more than one order to higher frequencies. Capacitive coupling between current and voltage cables (C-P coupling) also distorts resistivity data at high frequencies for configurations were these cables run close to each other (e.g. Wenner and reciprocal dipole-dipole). Separating these cables increase the data quality significant. But it also expands the amount of fieldwork. We found a technical solution that this additional expenditure occurs only in case of need. Furthermore no unconventional configurations are required.