Home > Publications database > Development of Electromagnetic Induction Measurement and Inversion Methods for Soil Electrical Conductivity Investigations |
Book/Dissertation / PhD Thesis | FZJ-2020-02823 |
2020
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Jülich
ISBN: 978-3-95806-490-4
Please use a persistent id in citations: http://hdl.handle.net/2128/25933 urn:nbn:de:0001-2020102027
Abstract: Electromagnetic induction (EMI) is a promising contact-free technique for non-invasive nearsurface geophysical investigations. Frequency-domain rigid-boom EMI systems with fixed distances between transmitter (Tx) and receivers (Rx) have been increasingly used for characterizing the upper meters (up to depths of approximately 1.5 times the maximum coil separation) of the subsurface. Such EMI systems enable the estimation of subsurface electrical conductivity distributions by inverting the apparent electrical conductivity (ECa) values measured from multiple different Tx-Rx configurations. However, calibration issues due to the thermal effects of the internal electronics as well as external electromagnetic influences hinder a reliable quantitative EMI data analysis. For a custom-made EMI system, a transfer function analyzer (TFA) circuit is developed to monitor thermal drift effects of the electrical parameters of the receiver circuit. In addition, ambient temperature sensors (ATS) were included into the setup. Here, three correction methods were compared based on data from ATS, TFA, and a combination of both TFA and ATS. The presented work tested these three methods in three different experimental studies where the transmitter unit temperature is kept constant while the receiver unit is heated and cooled (1) manually, (2) by cloudy ambient conditions and (3) by partly sunny weather conditions. The results demonstrate that the TFA in the receiver circuit provides suitable data for correcting the phase drift originated within the receiver coil but not for correcting the drift caused by electrical components in the read-out circuit. The latter drifts need to be corrected using ATS data. Consequently, the combination of TFA and ATS data returned the best correction results achieving a worst-case accuracy of 2.3mS/m compared to 10.2mS/m (ATS-only) and 24.9mS/m (TFA-only). The experimental results indicate that the drift of the transmitter unit is not negligible and needs to be corrected by a similar TFA circuit that should be investigated in future studies. In addition to the thermal effects, the external electromagnetic influences also shift the measured ECa data which are caused by the presence of the operator, cables or metallic objects included in the field setup. The presented work introduces a novel multi-elevation [...]
The record appears in these collections: |