Comparison of measuring strategies for frequency-and time-domain induced polarization

Spectral induced polarization (SIP) is an increasingly interesting technique for field investigations since it can provide valuable information on the properties of the subsurface deposits or groundwater units. Field measurements can be carried out in the frequency domain (FD) or in the time domain (TD) but should lead to the same spectral subsurface description. IP measurements are superimposed by other phenomena like cable crosstalk, capacitive coupling and induction effects, hindering IP data analysis. There is a number of ways to avoid these distortions, like separating current and potential cables.We applied TDIP and FDIP on two test sites using a ABEM Terrameter LS2 and a Radic SIP256C instrument. We used different layouts and measuring schemes (multi-gradient vs. dipole-dipole forward and backward) or waveforms (50 vs. 100% duty cycle) and compared the results. The comparison between forward and reverse arrays enables to assess reciprocity as a measure of data quality. On the test site in Sweden with good coupling and strong IP effects, there is an excellent reciprocity agreement for the dipole-dipole array, but the 50% and 100% data differ from each other. Separated cables cannot improve the data quality further, also for multi-gradient data. In contrast, the FDIP data show also a good quality but some discrepancies which origin is not fully clear. After inversion, we obtain similar subsurface models of Cole-Cole behaviour with a comparable frequency range.The test site in Germany is totally different: The electrode coupling in dry sand was very bad and the IP effects are weak. Consequently the ratio of coupling and IP effects is much bigger. Here, we can see a clear improvement by using separated cables. Processing requires far more effort. Furthermore, the subsurface does not follow a Cole-Cole model but shows rather a constant phase angle. Hence, the spectral content of the data is limited, even though the spectral content is again comparable