Electromagnetic Coupling in Frequency and Time‐domain Induced‐polarization Surveys Over a Multilayered Earth

Abstract

Electromagnetic coupling responses in frequency and time‐domain induced‐polarization measurements over a multilayered earth are evaluated. For collinear dipole‐dipole and pole‐dipole configurations over a dissipative layered subsurface, the percent frequency effects of electromagnetic coupling are seen to be as high as 60 percent for large [Formula: see text] values, where L is the length of the receiving dipole, [Formula: see text] is the conductivity of the top layer of the half‐space, and f is the higher frequency of excitation used. In both frequency and time‐domain analyses, the distinctive effects of layering compared to that of a homogeneous half‐space response are shown for different electrode configurations, layer geometry, and electrical parameters of the subsurface. The pole‐dipole configuration of electrodes, in general, exhibits higher coupling compared to the dipole‐dipole configuration. In time‐domain measurements, the late off‐time transient decays reflect almost entirely the normal polarizability of the layered subsurface, in that the coupling responses are significant only during the early off‐time of the transient. The mutual impedance between grounded dipoles of arbitrary length is computed by extension of the complete solution of the boundary‐value problem of a horizontal electric dipole situated over a multilayered half‐space. A number of nomograms are presented for various layered structures to eliminate the electromagnetic coupling response in the induced‐polarization measurements in order to obtain the true polarization effect of the subsurface.

Doubling the spectrum of time-domain induced polarization by harmonic de-noising, drift correction, spike removal, tapered gating and data uncertainty estimation

“…The duration of the EM effect depends on the electrode separation and the impedance of the subsurface (Zonge et al 2005). Other studies have suggested methods for handling/removing the EM coupling effects (Dey & Morrison 1973;Johnson 1984;Routh & Oldenburg 2001) but this is not within of the scope of this study.…”

Decoupling spectral induced polarisation data based on Cole-Cole parameters

“…A number of methods have been suggested (Dey and Morrison, 1973;Wynn and Zonge, 1975;Pelton et al, 1978;Song, 1984;Caglar, 2000;Routh and Oldenburg, 2001); most are complicated to implement, or are not well described. One approach that is relatively simple to implement is suggested by Pelton et al (1978).…”

Induced Polarization With Electromagnetic Coupling: 3d Spectral Imaging Theory: Emsp Project No. 73836

“…Possible sources of noise include random or correlated errors in the equipment, and ambient current sources within the ground, such as telluric currents or self potentials. Electromagnetic inductive or capacitive coupling, both of which scale with frequency, can also give spurious results, but this is considered to be a distortion of the data rather than noise (Wait, 1959;Dey and Morrison, 1973;. Because many of the measurements are made at the millivolt level, it is important to reduce noise levels at the site to a minimum and to filter out any spurious data points in the data set before performing an inversion.…”