Characterizing flow properties of unsaturated soils by geophysical measurements

  Graphic of Energy, CO2, and water fluxes Energy, CO2, and water fluxes between soil, vegetation and atmosphere govern weather evolution and climate. The representation of these exchange processes in coupled model systems will provide more reliable weather, flooding and climate predictions

This research project is part of the interdisciplinary Transregional Collaborative Research Centre 32 (TR32). In TR32, the soil-vegetation-atmosphere system is studied by research groups at the Universities of Aachen, Bonn, and Cologne and the Research Centre Jülich in the fields of soil and plant science, remote sensing, hydrology, geophysics, meteorology, and mathematics. The soil, vegetation and the lower atmosphere are key compartments of the earth, where almost all activities of mankind take place. This region is characterized by extremely complex patterns, structures and processes acting at different scales in time and space (Fig. 1). The quantitative prediction of the system behavior, the research aim in TR32, constitutes a major challenge to scientists and policy-makers, especially in view of the global climate change (see for more information). TR32 was formed in 2007 to integrate monitoring with modeling and data assimilation in order to develop a holistic view of the terrestrial system. It is now in the 3rd period (from Jan. 2015 until Dec. 2018), funded by the German science foundation, DFG.

  NMR slim-line logging tool The NMR slim-line logging tool will be applied to the field for characterizing the storage and flow properties of soils.

Process formulations, e.g. for describing water transport in the partially water saturated zone of the subsurface, often rely on so-called parameterizations that replace complex small-scale processes with macroscopic simplified descriptions. These descriptions typically contain additional quantities that we refer to as parameters, which need to be determined empirically. Our project aims at characterizing flow properties of partially water saturated soils without empirically determined parameters but by establishing direct relations between structural soil parameters (e.g., pore size distribution) and geophysical measurements. In particular, the geophysical methods NMR (nuclear magnetic resonance) relaxometry and IP (induced polarization) are considered in our project because they provide complementary information about size and connectivity of the water filled pores.

  Field measurement concept with all sensors Copyright: © GGE Ochs Field measurement concept with all sensors. The IP arrays will be used to determine zones of equal electrical conductivity where the transport properties of the soil are assumed to be equal. In these zones NMR will be measured at different water saturati

In the current project phase we estimate flow properties in the field for parameterizing hydrological models used for simulating water and gas flow in the vadose zone at larger scales by other TR32 projects. For that purpose, an NMR slim-line logging tool (Fig. 2), developed by another subproject, together with an IP borehole tool and surface electrodes as well as soil water tension sensors are applied in the field (Fig. 3). The measurements will be repeated at different saturation states. We will extend the joint inversion approach developed in the previous project phase and adapt it to field measurements.

This research project is part of the interdisciplinary Transregional Collaborative Research Centre 32 (TR32) and funded by the German science foundation, DFG.

Johanna Ochs, M. Sc. (GGE)

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