Laser induced incandescence-particle image velocimetry is a technique created by tracking incandescent particles seeded into a flow and illuminated by a laser sheet. Tracer particles of tungsten carbide (WC) of 0.1 micrometers are used to absorb 532 nm light from a PIV laser. The light collected from a filter around 450 nm is the incandescent light from the suspended particles in the air. Droplet velocities are obtained from Mie scatter at 532 nm. In this manner, droplet and gas velocities can be spectrally separated.
Experiments are currently underway to provide a simultaneous measurement of droplets and gas velocities.
Note the difference in velocities between the heavier droplets and the gas in the figures below.
Further details in : Fan, L., McGrath, D., Chong, C.T. et al. Exp Fluids (2018) 59: 156. https://doi.org/10.1007/s00348-018-2610-4