Multi-frequency EIT monitoring at the field scale -- Challenges and experiences from the first year

Poster presented at the 5th International Workshop on Induced Polarization, 3.-5. October 2018, Rutgers University-Newark, USA

Multi-frequency electrical impedance tomography (EIT) is increasingly used to capture spatial variations in the spectral IP properties of the subsurface, thereby providing important additional information for an improved subsurface characterization. Compared to electrical resistivity tomography (ERT), a much more refined and controlled measurement setup is required to minimize measurement errors, especially for frequencies above 100 Hz. These requirements make long-term monitoring applications with high-temporal and spatial resolution challenging. In our work, we report on early findings in setting up and operating a multi-year EIT monitoring system on an agricultural test plot. Preliminary analysis suggests that reliable measurements up to 1 kHz are possible with this setup. Measurements using 40 electrodes with 25 cm spacing were performed up to 12 times per day (2 hour cycle) with measurement frequencies between 0.1 Hz and 45 kHz. A high temporal spacing potentially enables us to differentiate between various processes taking place in the subsurface (water flow, root-soil interactions, etc.). However, at the same time the amount of generated data requires automation of all processing steps and the need to establish new data management schemes. This was addressed using a distributed analysis system centered around a relational database. Preliminary analysis of the data focussed on recording and processing of telemetry data, which allowed us to detect anomalous states of the measurement system with only a few hours time delay. We further report on implications associated with long-term installation of electrodes and electromagnetic coupling issues that need to be addressed for accurate EIT measurements.