Image analysis approaches provide an accurate and efficient way to generate detailed concentration distributions from photographic data of flow-tank experiments where the tracer can be observed through a glass or Plexiglas(R) wall. The technique is non-intrusive, does not disturb plume dynamics, and provides an essentially continuous distribution of sampling points over the whole plume, as observed at the tank wall. Computer processing of the scanned image is required to correct for spatial and temporal lighting nonuniformity, and for heterogeneous media, to account for different grain sizes, and thus differing dye thicknesses along tank walls. In our model study, utilizing a Plexiglas(R) flow tank (107 cm long, 71 cm high, 5 cm wide), individual concentrations are estimated for square areas approximately 1.3 by 1.3 mm in size over the entire area of a side wall of the tank. The negatives were scanned on an Eikonix(R) 78/99 digital scanning system at a resolution of 1024 by 1024 by 12 bits. The image analysis system is comprised of a Digital Equipment Corporation Microvax II(R) computer and a Gould(R) IP9527 image processor. It transforms the scanned images, whose pixels represent dye intensity, into images whose pixels represent solute concentration.
