Experimental challenge of observing the dynamics of water movement in unsaturated porous media

Water movement in unsaturated porous media is a key process for groundwater recharge and infiltration of solutes into the groundwater. In general, this water movement has its specific dynamics caused by temporal variation of the inflow boundary condition and by non-linear hydraulic properties of the porous media itself. Under laboratory conditions water movement can be visualized by dye tracer experiment in transparent experimental set-ups such as glass columns. However, quantitative analyses are only possible for the surface of the porous media by applying image processing techniques in such cases.