Qualitative and quantitative measurements using flow visualization techniques in supersonic flow are made by using Schlieren and shadow graph techniques. These are optical methods based on the variations of index of refraction due to variations in density in the supersonic flow.

Sunshine measurements Pvt Ltd manufactures Schlieren system to support flow visualization in supersonic tunnels which they manufacture and supply to educational institutions. It is a low cost system, versatile and suitable for research work also. Since the system contains delicate mirrors the system must be handled carefully by competent personal. It also requires a certain expertise to setup the system. This method can also be used to visualize transparent fields where ever refractive index varies like that in heated flows, flames etc.