Estimation of van Genuchten-Mualem parameters from spectral induced polarization measurements

The application of spectral induced polarization (SIP) surveys to estimate hydrological properties of the subsurface is promising. For the interpretation of the SIP data, the knowledge of the relationships between soil hydraulic properties and parameters obtained from SIP measurements is essential. Therefore, we performed hydrological and SIP measurements in the laboratory on seven natural soils and a medium sand sample with a narrow grain size distribution. The SIP spectra were interpreted with the Debye decomposition, which yields integrating parameters for the resulting relaxation time distribution. To derive soil hydraulic parameters from the hydrological experiments, we fitted the van Genuchten-Mualem model, which is widespread in soil physics, to the measured hydrological data. In this study, we concentrate on the relationship between two parameters: the normalized chargeability from the Debye decomposition of SIP spectra and the parameter alpha from the van Genuchten-Mualem model. We present an approach to estimate the parameter alpha from the normalized chargeability.