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Pseudosection plots of raw DC resistivity or IP data


 

When profiling, voltages are usually measured at several positions for every current source location. Measurements at wider separations between the potential pair and the transmitter pair provide information about deeper structures. The conventional method of plotting such results is the pseudosection, so called because it is not a true geological cross-section. Values of apparent resistivity are plotted on the graph as shown in figures below. The vertical axis represents separation distance, NOT depth. When all values are plotted, the result is contoured. Interpretation is tricky and requires some experience.


Figure 1. Plotting dipole-dipole data. The current source electrode pair (I) and the voltage measuring electrode par (V) are spaced a metres apart (2m in this case). spacing between the current pair and the voltage pair varies, and is n×a metres (n is an integer). This figure shows 4 voltage measurements for one current source location.


profiling concepts

Figure 2. Animation illustrating the process of gathering and plotting data as a pseudosection. The survey involved a dipole-dipole array with a = 2 m, and n = 4. For each measurement, notice the positions of current electrodes (left pair) and potential electrodes (right pair).  Vertical axis of the plotted data is NOT depth, it is n value, from 1 to 4 in this case. 

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