f Application of combined resistivity and IP multielectrode-measurements for envrionmental investigation

In common IP surveys normally unpolarizeable elektrodes are used to overcome polarisation effects near the electrodes. Moreover, rather high primary currents are necessary as the potential differences due to the IP effect are normally much smaller compared to the voltages observed in common DC – surveys. Using a multielectrode equipment it is not possible to use unpolarizeable electrodes as current injection is done with the same node as the measurements of potential differences. Moreover the use of multicore cable for current injection as well as for potential measurements limits the strength of the primary current. Under favourable conditions the maximum current due to our experience was 1.6 A with the SYSCAL multielectrode system. In addition, the time necessary for both types of measurements is much higher than for resistivity surveys only. On the other hand multielectrode surveys produce much more data along a profile in less time compared to conventional IP procedures allowing a better determined 2d inversion of the data. The above mentioned limitations raise the question if significant measurements of the IP effect are possible at all using a multielectrode equipment and how a two-dimensional combined inversion can be performed properly. A case study demonstrates that in some cases also a multielectrode equipment using steel stakes can produce high quality IP data. Further, sometimes only the combination of IP and Resistivity measurements can solve environmental problems and make correct interpretation of geoelectric data possible. In our surveys we used a STING multielectrode equipment with 100 electrodes for the resistivity survey and the SYSCAL system with a booster for combined measurements of IP and resistivity. Conventional steel stakes were used as electrodes.