Optical visualization of internal gravity waves in stratified fluid

The refractive index changes associated with flows in salt water systems allow such flows to be visualized by means of optical methods, e.g. schlieren and interferometry. Experiments that have been conducted by our group with internal gravity waves in stratified brine are reviewed. The experiments encompass visualization and quantitative measurement of internal gravity waves generated by a body oscillating around a fixed position and a test body moving with constant speed vertically through the stratified brine. It is also shown that the velocity field of an internal gravity wave can be measured by means of particle image velocimetry. References to respective wave theories are made.