Electrical Tomography
ELETOM is a software that performs the complete
2D inversion (and not the simple iterative deconvolution of the pseudosections)
of surface electrical surveys with any measurement array
(Wenner, dipoledipole, poledipole, polepole, user defined arrays, mixed
arrays) with a maximum of 64 electrode positions that can be added as needed.
ELETOM uses the finite elements method (FEM) in
two dimensions to model the subsurface’s electrical response.
The elements that define the grid are
trapezoidal in form to enable to compensate any height difference between the
electrode’s positions. The current dispersion in the third spatial dimension (perpendicular
to section of interest) is considered by using Wannamaker’s correction.
With
ELETOM it is not necessary to specify any parameter to construct the grid. One
needs only to enter the positions and numbering of the electrodes used in the
survey’s measurements.
The iterative algorithm used to perform the
inversion is based on the minimisation of the mean square error between field
data and the data simulated by the FEM, with the method proposed by Sasaki
(1994).
The algorithm’s convergence is obtained by
estimating a stabilisation (performed with the generalised reciprocal
coefficients method) repeated during every iteration.
The reduction of the noise effect present in the
data, is obtained with an iterative linear regression calculation (Ward, 1990)
that enables to compensate for the fact that it is impossible to know the
statistical variance of each measurement.
The result is given by a real resistivity
section reconstructed with precision (in two dimensions) equal to the smallest
halved interelectrode distance, with the possibility to select a set of colour
shadings in order to enhance the anomalies present in the subsurface in the best
way possible. The results can be rendered as isoresistivity curves as well.
