Application of tomographic techniques to Schlieren imaging

纹影成像和摄影被用作跨音速流动的流动可视化技术已有近150年的历史，当时奥古斯特·托普勒发现，他可以通过将平行光束照射到感兴趣的区域来观察空气密度的变化。如果在成像透镜的焦点处使用刀口，则由折射率变化引起的偏转呈现明暗两种图案。然而，在这段时间的大部分时间里，它更多地用于定性测量，而不是定量测量。这张图像是所有流动现象的二维图，就像X光显示全身一样。

Schlieren imaging and photography have been used as a flow visualization technique in transonic flows for almost 150 years when August Toepler discovered that he could see variations in air density by shining parallel beams of light through the region of interest. The deflection caused by the variation of the indices of refraction appear as light and dark patterns if a knife-edge is used at the focal point of the imaging lens. However during most of this time, it has since been used more for qualitative rather than quantitative measurements. This image is a 2 dimensional view of the all the flow phenomena much like an X-ray shows all of the body.