Minimisation of Electrode Polarisation Errors when Using Optimised or Generic Resistivity Imaging Arrays

Polarisation potentials are caused when metallic electrodes are used to transmit current in resistivity imaging surveys. If these electrodes are subsequently used to measure potential differences, the decaying polarisation potentials can be a source of significant error. In this paper we describe a general method to minimise the impact of polarisation errors by rearranging the resistivity measurements to maximise the time between any electrode injecting current and later measuring potential. This method does not rely on the existence of a natural ordering of the measurements and can therefore be used with arbitrary resistivity imaging arrays, specifically including those generated by automated optimisation schemes. The method uses a global minimisation algorithm ("simulated annealing") to attempt to avoid local minima without performing an exhaustive search of the configuration space. We determine the control parameters and permutation types for the method from the results of a series of numerical experiments on a randomly generated measurement sequence. We then demonstrate the efficacy of the method using real data measured with a permanently installed resistivity monitoring system on an active landslide. The results show that polarisation errors can be effectively eliminated when using optimised resistivity imaging arrays.