A multiple parameter extraction and electromagnetic coupling correction technique for time domain induced polarisation full waveform data

摘要

The time domain induced polarisation (TDIP) method is characterised by a simple explanation and operational approach, and is used widely to prospect for various metal sulfide deposits. However, the existing TDIP method is parameterised with fewer interpretive output attributes than the frequency domain induced polarisation (FDIP) method, and there has been far less emphasis on electromagnetic (EM) coupling in the TDIP method. A new and simple method has been devised for the extraction of multiple parameters and the suppression of EM-coupling responses in full waveform TDIP data. The essence of this approach is the transformation of the TDIP rectangular wave into the fundamental wave and a series of odd harmonics using a discrete Fourier transform. By using real and imaginary components of the fundamental and odd harmonics, we can calculate various FDIP parameters, including the per cent frequency effect (PFE) and the phase. The decoupled PFE coefficients and decoupled phases can then be used to remove the EM-coupling response. This new method has been applied to a data set collected near a poly-metallic mine in the Tibetan Plateau. A comparison between the TDIP and FDIP methods with central gradient arrays was performed. The results indicate that the TDIP apparent chargeability results are affected greatly by the EM-coupling response. The PFEs and phases extracted from the TDIP full waveform data are in good agreement with those obtained from the FDIP data. Moreover, the locations of the high decoupled PFE coefficients and the large negative decoupled phases are consistent with the locations of known ore veins. This method can provide additional parameters for the subsurface media, improve the practical application effect and enrich the functionality of TDIP methods.