9:30 AM - 9:45 AM
[SEM14-03] Analyses on dispersion characteristics of complex resistivities from time-domain as well as spectral induced polarization data
★Invited Papers
Keywords:Time domain induced polarization, Spectral induced polarization, Complex resistivity, Dispersion characteristics
Dispersion characteristics of complex resistivity (CR) of subsurface have become to be important in induced polarization (IP) survey methods, which had usually targeted to image chargeability anomalies in the past. The characteristics appear in the form of decay curves of overvoltage in time-domain (TD) IP data, while dispersion curves of amplitudes and phases of CR in spectral IP (SIP). TD IP and SIP methods are theoretically equivalent via the Fourier transform even though measured TD IP and SIP data may differ due to noise and measurable acquisition ranges. Extracting Cole-Cole parameters from overvoltage decays of TD IP is considered unfeasible in old studies due to the limited band ranges of old instruments. However, recent advancements in instruments have significantly increased accuracy and sampling rates in measurement (~ several kHz) to make spectral analysis become possible not only in frequency domain (FD) but also in TD. Accordingly, interests of comparative studies between TD IP and SIP methods have increased recently.
In this study, we performed comparative analyses on dispersion characteristics of CR from TD IP and SIP data. Even though the most direct way of the comparison between TD IP and SIP data can be performed through Fourier transforms considering full-time source waveform of TD IP, measuring and processing full-time waveform data are difficult and time consuming. Thus, we used time a domain Cole-Cole model, which illustrates decay curves of over-voltage of TD IP. Firstly, synthetic TD IP and SIP responses for numerical models were interpreted using developed in-house inversion algorithms and comparatively analyzed. Further, TD IP and SIP data measured in laboratory experiments were digitized and used in order to estimate and compare SIP parameters after analyzing the characteristics of spectral dispersion of CR in the TD IP as well as SIP data. Finally, we compared inversion results from TD IP and SIP data obtained along the same survey line with the identical electrode spacing in a non-aqueous phase liquid (NAPL) contaminated site.
IP anomaly of NAPL was properly located from not only inversion of TD IP data but also SIP data using the in-house algorithms, and the characteristics of spectral dispersion of CR were properly analyzed for both data sets. This study is supported by SEM project (No.2018002440005) and the KETEP (No. 20194010201920).
In this study, we performed comparative analyses on dispersion characteristics of CR from TD IP and SIP data. Even though the most direct way of the comparison between TD IP and SIP data can be performed through Fourier transforms considering full-time source waveform of TD IP, measuring and processing full-time waveform data are difficult and time consuming. Thus, we used time a domain Cole-Cole model, which illustrates decay curves of over-voltage of TD IP. Firstly, synthetic TD IP and SIP responses for numerical models were interpreted using developed in-house inversion algorithms and comparatively analyzed. Further, TD IP and SIP data measured in laboratory experiments were digitized and used in order to estimate and compare SIP parameters after analyzing the characteristics of spectral dispersion of CR in the TD IP as well as SIP data. Finally, we compared inversion results from TD IP and SIP data obtained along the same survey line with the identical electrode spacing in a non-aqueous phase liquid (NAPL) contaminated site.
IP anomaly of NAPL was properly located from not only inversion of TD IP data but also SIP data using the in-house algorithms, and the characteristics of spectral dispersion of CR were properly analyzed for both data sets. This study is supported by SEM project (No.2018002440005) and the KETEP (No. 20194010201920).