Calibration of near‐surface multi‐frequency electromagnetic induction data

Abstract

AbstractThe frequency‐domain electromagnetic induction method is a very efficient and convenient method to investigate a site of interest and for a large range of applications including hydrogeology and archaeology. Besides an easy infield acquisition, the data can be used to estimate the electrical, magnetic and, in certain cases, dielectric properties of the ground. It does, however, require calibration to get reliable quantitative values of these properties. We propose here an original and reliable self‐calibration method, specific to multi‐frequency measurements in the range of (5–100 kHz)‐based only on the consistency between the data at different acquisition frequencies. Contrary to other existing cross‐calibration procedures, no additional measurements with other methods are necessary. This self‐calibration (quadrature and in‐phase components of the electromagnetic induction signal) procedure is tested at a test site located at the centre for studies on risks, the environment, mobility and urban planning Normandie‐Centre facilities (Rouen, France). The developed quadrature self‐calibration has been successfully compared with the usual electrical resistivity tomography – electromagnetic induction cross‐calibration procedure. The main results reveal the potential of systematic assessment of all electromagnetic parameters from multi‐frequency and multi‐configuration electromagnetic induction data: The electrical resistivity and the magnetic susceptibility are estimated from the low‐frequency range, whereas the highest part of the frequency range is used for the dielectric permittivity.