  Non-intrusive quantitative fluid density measurements methods are essential
in stratified flow experiments. Digital imaging leads to synthetic Schlieren
methods in which the variations of the index of refraction are reconstructed
computationally. In this study, an important extension to one of these methods,
called Background Oriented Schlieren (BOS), is proposed. The extension enables
an accurate reconstruction of the density field in stratified liquid
experiments. Typically, the experiments are performed by the light source,
background pattern, and the camera positioned on the opposite sides of a
transparent vessel. The multi-media imaging through air-glass-water-glass-air
leads to an additional aberration that destroys the reconstruction. A two-step
calibration and image remapping transform are the key components that correct
the images through the stratified media and provide non-intrusive full-field
density measurements of transparent liquids.
