State of the art of quantitative schlieren systems

The present paper details the recent advances in three schlieren visualization methods, considering only those applied to obtain values of gas-dynamic parameters of the phenomenon, namely SIV (schlieren image velocimetry), CCS (color-calibrated schlieren) and BOS (background-oriented schlieren). The above-mentioned advances refer to innovative optical configurations - introducing of new optical components or new optical alignments, state-of-the art or improved calibration methods, references to various post-processing algorithms, and present the possibility to improve system efficiency or validate the resulting schlieren data by coupling the schlieren systems with other optical methods.