Development and application of a new inversion algorithm for the time domain induced polarisation data in three dimensions

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The goal of this project is to use the information of the entire time series for the interpretation of the induced polarization in time domain. By default, only the area below the curve or the voltage during and directly after injection are used for interpretation.The aim is to develop an algorithm which inverts entire time series into a 3D model of the conductivity of the subsurface. The inversion is based on the Cole-Cole model or comparable models e.g. from Dias (2000).An approximation is used to calculate the step response fast and directly in the time domain (Hördt et al. (2006), Hönig and Tezkan (2007)). First, the transients are inverted independently for separate time channels into a subsurface conductivity model with a 3D DC resistivity code. Thus, a time-dependent resistivity for each cell of the model is obtained. The time-dependent resistivity can then be inverted into a Cole-Cole model which contains additional parameters for the characterization of the subsurface. The use of the entire time series requires a high standard of data quality and a large measuring effort. The data measured with the Terrameter LS during the first phase of the project satisfy these requirements and will be modeled with the above-described algorithm. .If frequency domain and time domain measurements are available for the same profiles, a comparison between them will also be made.