Thermography
Thermographic phosphors can be used to determine the local temperatures in gas flows, by exciting the phosphors in the near-UV (355 nm), and collecting the output at two different temperatures. The spectral response of phosphors changes with temperature, so the ratio of spectral responses can be related to temperature.
By using small particles, it is possible to simultaneously obtain temperatures and velocities in a flow, as shown below for a heated jet.
Single-shot temperature-vorticity maps for a heated jet in air.
Further details in :
Fan, L., Gao, Y., Hayakawa, A. et al. Exp Fluids (2017) 58: 34. https://doi.org/10.1007/s00348-017-2313-2