Complex resistivity tomography (CRT) for fungus detection on standing oak trees

Abstract Complex resistivity tomography is presented as an extension of electrical impedance tomography for non-destructive structural tree investigation. Results of laboratory measurements with different frequencies suggest measuring the resistivity and in addition the phase shift at about 0.1 Hz. The measured data are processed using a finite-element-based inversion algorithm, which uses triangular meshes and is thus able to consider any tree shape. We apply the technique to three different oak trees with the aim of fungi detection. Measurements of a healthy tree both in summer and in winter show a ring-shaped structure and indicate a strong seasonal dependence, particularly for the resistivity magnitude. Tomograms on fungi-infected trees clearly show disturbances at the infections at different heights compared with healthy trees. A comparison with tree section photographs shows promising agreement. Moreover, a comparison with measurements at oak-wood samples in the laboratory shows at least partly quantitative coincidence. To conclude, the phase image provides additional information and helps to differentiate disturbances in the cell structure from pure moisture changes. Therefore, the method has the potential to deliver useful additional information, when carried out during routine tree assessment.

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