HR: 0800h
AN: B41B-06    [Abstracts]
TI: A Novel Finite-Element Based Algorithm for Impedance Tomography of Arbitrarily Shaped Trees
AU: * Guenther, T
EM: Thomas.Guenther@gga-hannover.de
AF: Leibniz Institute for Applied Geosciences, Hannover, Stilleweg 2, Hannover, 30655, Germany
AU: Ruecker, C
EM: cruecker@uni-leipzig.de
AF: Institute of Geophysics and Geology, University of Leipzig, Talstra.35, Leipzig, 04103, Germany
AB: The electrical conductivity provides valuable information about trees due to its strong dependance on water content and pore fillings. Hence the impedance tomography is a cheap and non-destructive method for investigating the interior structure and for monitoring ongoing processes by means of current injection and voltage measurements. There are different algorithms for reconstructing the conductivity structure, most of them based on circle geometry. However, the tree shape strongly influences the electric field and may yield misinterpretations. We present a novel technique that is able to incorporate arbitrary shapes using unstructured triangular meshes. The field simulation is carried out via the finite element method on two different meshes in order to improve the efficiency: The pure geometric effect is calculated once on a highly refined mesh, whereas the simulations in every iteration are carried out very fast on a quite coarse mesh. We apply a Gauss-Newton method with smoothness constraints regularization to solve the inverse problem on a resolution-dependent mesh. Different examples for impedance tomography are regarded. For example we are able to detect a hollow core or regions of different stages of foulness. We show the effect of tree shapes and how a wrong assumption leads to artifacts. However there might be different reasons for conductive or resistive anomalies. An additional information can be obtained by using additional data as from seismic velocity derived from acoustic travel time tomography. A structural joint inversion enforces structural similarities in both images such that the results are more significant. Impedance data can also be measured at different time steps revealing information on the processes. A so-called reference technique is applied in order to focus on the temporal changes. We present a 24-hour sequence of data obtained from a lime tree showing how fluid flow changes in the course of daylight.
UR: http:www.resistivity.net/
DE: 0400 BIOGEOSCIENCES
DE: 0430 Computational methods and data processing
DE: 0499 New fields (not classifiable under other headings)
SC: Biogeosciences [B]
MN: 2007 Joint Assembly