Comparison of light transmission and reflection techniques to determine concentrations in flow tank experiments

Transmissive and reflective intensity measurements for visual concentration determinations in 2D flow tank experiments were compared and evaluated for their applicability in the study of flow and transport phenomena. A density-dependent heterogeneous flow experiment was conducted and transmission and reflection images of the dyed saltwater plume were analyzed. A single light source and dark curtains forced the light to pass through the porous media only, thus facilitating the transmission measurements. The reflection images delivered a more homogeneous spatial illumination than the transmission images. Major perturbations of the transmission images were lens flare effects and light dispersion within the bead-water-Plexiglas system which smear the front of the plume. Based on the conducted evaluation of transmissive and reflective intensity measurements, the reflection data delivered more reliable intensity values to derive solute concentrations in intermediate scale flow tank experiments.