Estimation of water saturation fields in a heterogeneous sand tank

Water flow in heterogeneous porous media is very complex. If preferential flow occurs, water saturations may vary largely even between adjacent regions. A laboratory technique is presented to estimate water saturations in a heterogeneous sand tank at a high spatial and temporal resolution. Images of reflected light of an infiltration experiment were analyzed with three slightly different calibration procedures. The results show that it is possible to detect paths of infiltrating water at a high resolution and estimate, for instance, the location of the infiltration front reliably. The different calibration procedures led, however, to rather different absolute water saturations. This large uncertainty originated partly from the use of a single calibration curve for all sands, but mainly from the fact that for two of the calibration procedures assumptions about the reference images were not met in the experiment. The calibration procedure based on a reference image of the fully saturated tank seemed to be the most reliable one.