Adaptive synthetic Schlieren imaging

Abstract

Traditional schlieren photography has several important disadvantages when designing a system to image refractive index gradients including the relatively high cost of parabolic mirrors and the fact that the technique does not easily yield quantitative data. Both these issues are resolved by using synthetic Schileren photography, but this technique produces images with a lower resolution than traditional schlieren imaging. Synthetic schlieren imaging measures a refractive index gradient by comparing the distortion of two or more images with high frequency backgrounds. This method can either yield low-resolution quantitative data in two dimensions or high-resolution quantitative data in one dimension, but cannot give high-resolution data in two dimensions simultaneously. In order to yield high resolution imaging in two dimensions, a technique is described that based upon previously measured fields, adaptively modifies the high resolution background in order to maximize the resolution for a given flow field.