How to judge IP data during induced polarization survey?
I.P. surveys have traditionally been used in the mineral exploration industry, particularly for metal sulfides, where heavy electrical generators producing high currents of the order of 10 Amperes are used. The apparent I.P. values from such surveys are usually less than 100 msec. (or mV/V).
One recent development is the addition of I.P. capability to battery based systems used in engineering and environmental surveys where currents of 1 Ampere or less are normally used. An accompanying phenomenon is the observation of I.P. values of over 1000 msec. (or less than -1000 msec.) in some data sets. Such values are almost certainly caused by noise due to a very weak IP signal.
To check whether such high I.P. values are real, first check the apparent resistivity pseudosection. If it shows unusually high and low values that vary in an erratic manner, the data is noisy. If the apparent resistivity values are noisy, then the apparent I.P. values are almost certainly unreliable. Next check the apparent I.P. pseudosection. If the apparent I.P. values show an erratic pattern (frequently with anomalous values lined up diagonally with an apex at a doubtful electrode), then the I.P. values are too noisy to be interpretable. There has been some recent work on improving the reliability of I.P. measurements made with the multi-electrode type of systems.