Background-oriented schlieren (BOS) techniques

This article gives an overview of the background-oriented schlieren (BOS) technique, typical applications and literature in the field. BOS is an optical density visualization technique, belonging to the same family as schlieren photography, shadowgraphy or interferometry. In contrast to these older techniques, BOS uses correlation techniques on a background dot pattern to quantitatively characterize compressible and thermal flows with good spatial and temporal resolution. The main advantages of this technique, the experimental simplicity and the robustness of correlation-based digital analysis, mean that it is widely used, and variant versions are reviewed in the article. The advantages of each variant are reviewed, and further literature is provided for the reader.