Subsurface electrical impedance imaging using orthogonal linear electrode arrays

The main limitation of electrical impedance tomography as an imaging modality is its inherently poor spatial resolution. Although more information about the impedance distribution within an object can be retrieved by the use of larger numbers of surface electrodes, the additional information tends to relate to regions of the object close to the electrodes rather than at depth. The paper describes the application of an image reconstruction approach originally developed for medical electrical impedance tomography to the alternative problem of mapping electrical impedance distributions in a subsurface volume. The use of this geometry allows the chosen imaged plane to be approximately uniformly sensed by a surface grid of electrodes leading to uniform resolution in the image and the possibility of exploiting the relatively high resolution information available at shallow depths. The advantage of the use of an electrode grid, treated as two orthogonal sets of parallel linear arrays, is demonstrated and the behaviour of the point-spread function in planes parallel to the surface plane examined. The application of a spatial frequency filter to parallel to counteract reconstruction blur is described. Simulated reconstructions of subsurface structures and an example biomedical image are presented