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VLF Electromagnetic Data Inversion Starting from Current Density Pseudo-sections Obtained by Linear Filtering
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, Near Surface Geoscience 2015 - 21st European Meeting of Environmental and Engineering Geophysics, Sep 2015, Volume 2015, p.1 - 5
Abstract
We used current density pseudo-sections obtained by linear filtering of VLF data to create a starting model for an inversion procedure using the Polak-Ribiere variant of the conjugate gradient method. The inversion procedure looks for the minimum error between the observed data and forward modelling data, obtained by a finite-difference algorithm, of the initial subsurface model, where the model parameters are changed iteratively. The inputs for the procedure are the host medium resistivity within a range given by the user, the number of cells that should be used as an approximation of the real medium and the desired accuracy. The lateral positions of the cells, forming the initial model, are obtained automatically by looking for zeros in the second derivative in descending parts of the observed data curves. The depths of the cells, as well as their resistivities, are obtained from the maximum values of the current density pseudo sections within a given range of cells centred in the previously obtained lateral positions. Results for two simple synthetic models are shown.