Ratiometric Infrared Thermography for an Emissivity-Free Analysis in High-Enthalpy Test Facilities

Although infrared thermography has proven effective in ground testing facilities, it requires well-characterized radiative properties of the target. When high temperature gradients, complex chemical changes, particle ablation, et cetera are present, like during a thermal protection system evaluation, predicting radiative properties is futile; most notable of the properties is the surface emissivity. To counter this limitation, investigators implemented and tested several dual-wave, ratiometric thermography approaches, which are in principle independent of radiative properties. The details of this study involve a comparison of approaches (tested with a blackbody radiator) and the application of the most effective technique in high-enthalpy facilities. Overall, the capabilities of dual-wave, ratiometric thermography vastly improve the confidence of spatially resolved temperature measurements in complex environments (within 2% of optical pyrometers), providing a noteworthy tool for thermal protection system evaluators.