Design and operation of a long-term monitoring system for spectral electrical impedance tomography (sEIT)

[摘要] Spectral electrical impedance tomography (sEIT) is increasingly used tocharacterise the structure of subsurface systems using measurements in the megahertz to kilohertz range.Additionally, hydrogeophysical and biogeophysical processes are characterised andmonitored using sEIT.The method combines multiple, spatially distributed, spectroscopic measurementswith tomographic inversion algorithms to obtain images of the complexelectrical resistivity distribution in the subsurface at various frequencies.Spectral polarisation measurements provide additional information about thesystems under investigation and can be used to reduce ambiguities that occurif only the in-phase resistivity values are analysed.However, spectral impedance measurements are very sensitiveto details of the measurement setup as well as to external noise and errorcomponents.Despite promising technical progress in improving measurement quality as wellas progress in the characterisation and understanding of staticpolarisation signatures of the subsurface, long-term (i.e. multi-month tomulti-year) monitoring attempts with fixed setups are still rare.Yet, measurement targets often show inherent non-stationarity that wouldrequire monitoring for a proper system characterisation.With the aim of improving operating foundations for similar endeavours, we herereport on the design and field deployment of a permanently installed monitoringsystem for sEIT data.The specific aim of this monitoring installation is the characterisation ofcrop root evolution over a full growing season, requiring multiple measurementsper day over multiple months to capture relevant system dynamics.In this contribution, we discuss the general layout and design of themonitoring setup, including the data acquisition system, additional on-siteequipment, required corrections to improve data quality for high frequencies,data management and remote-processing facilities used to analyse the measureddata.The choice and installation of electrodes, cables and measurementconfigurations are discussed and quality parameters are used for thecontinuous assessment of system functioning and data quality.Exemplary analysis results of the first season of operation highlight theimportance of continuous quality control.It is also found that proper cable elevation decreased capacitive leakage currentsand in combination with the correction of inductive effects led toconsistent tomographic results up to 1 kHz measurement frequency.Overall, the successful operation of an sEIT monitoring system over multiplemonths with multiple daily tomographic measurements was achieved.

[学科分类] 再生能源与代替技术